U.S. patent application number 11/166680 was filed with the patent office on 2005-12-01 for data driven remote device control model with general programming interface-to-network messaging adaptor.
This patent application is currently assigned to Microsoft Corporation. Invention is credited to Gandhi, Amar S., Layman, Andrew J..
Application Number | 20050267935 11/166680 |
Document ID | / |
Family ID | 27385293 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050267935 |
Kind Code |
A1 |
Gandhi, Amar S. ; et
al. |
December 1, 2005 |
Data driven remote device control model with general programming
interface-to-network messaging adaptor
Abstract
A general programmatic interface-to-network messaging adapter
exposes a suitable object integration interface or application
programming interface to applications on a controller device and
sends network data messages to invoke services or query status of a
controlled device. The adapter maps application calls to the
interface into network data messages according to service protocols
of the controlled device. The general adapter provides the
interface suitable to any specific service of a controlled device
based on a data description of the interface, and converts the
application calls to network data messages based on a data
description of a protocol and format for network data messages to
interact with the specific service. Once the interface/messaging
description is obtained, applications on the controller device can
programmatically interact with the adapter, and the adapter then
handles appropriate message exchanges with the service of the
controlled device. The general adapter allows controller device
applications to be written using object-oriented programming, while
avoiding code download.
Inventors: |
Gandhi, Amar S.; (Redmond,
WA) ; Layman, Andrew J.; (Bellevue, WA) |
Correspondence
Address: |
KLARQUIST SPARKMAN LLP
121 S.W. SALMON STREET
SUITE 1600
PORTLAND
OR
97204
US
|
Assignee: |
Microsoft Corporation
Redmond
WA
|
Family ID: |
27385293 |
Appl. No.: |
11/166680 |
Filed: |
June 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11166680 |
Jun 23, 2005 |
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09432854 |
Nov 2, 1999 |
|
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60139137 |
Jun 11, 1999 |
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60160235 |
Oct 18, 1999 |
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Current U.S.
Class: |
709/203 |
Current CPC
Class: |
H04L 12/281 20130101;
H04L 67/16 20130101; H04L 29/0602 20130101; H04L 29/12594 20130101;
H04L 47/2408 20130101; H04L 29/06 20130101; H04L 67/02 20130101;
H04L 69/329 20130101; H04L 67/14 20130101; H04L 61/2023 20130101;
H04L 67/125 20130101; H04L 12/4633 20130101; H04L 2012/2849
20130101; H04L 61/2092 20130101; H04L 29/12235 20130101; H04L
29/1232 20130101; H04L 61/3065 20130101; H04L 67/025 20130101; H04L
12/282 20130101 |
Class at
Publication: |
709/203 |
International
Class: |
G06F 015/16 |
Claims
1. (canceled)
2. (canceled)
3. A computing device providing a user control point with
connectivity to at least one controlled device via a networking
medium, the computing device comprising: memory having stored
thereon a controlled device description artifact having a service
control definition and a contract for configuring communications
involved with at least one service provided by the at least one
controlled device, wherein the contract comprises one or more of a
definition of network packets, request-response patterns and
specification of an endpoint to which the communications comprising
networking messages are sent; a general programming
interface-to-network messaging adapter operable as follows: based
on the service control definition in the controlled device
description artifact, to dynamically produce a service specific
programming interface to application programs running on the
computing device, to convert calls from the application programs to
the service specific programming interface into the networking
messages to the controlled device according to the contract
specified in the controlled device description artifact; and to
issue the networking messages via the networking medium to the
controlled device to invoke service specific operations of the at
least one service.
4. The device of claim 3, wherein the networking messages are in a
mark-up language and exchanged via a hypertext transport
protocol.
5. The device of claim 3, wherein the programmatic interface is an
object integration interface of an object-oriented programming
model.
6. The device of claim 3, wherein the service-specific operations
include invoking commands of the at least one service.
7. The device of claim 6, wherein invoking commands of the at least
one service comprises calling an invoke method member of the
service specific programming interface operable for accepting a
string argument specifying a service action associated with the at
least one service.
8. The device of claim 3, wherein the service-specific operations
include querying a state of the at least one service.
9. The device of claim 3, wherein the service-specific operations
include receiving and responding to events of the at least one
service.
10. A method for a client program on a first computing device to
programmatically control a service of a logical device realized on
a remote computing device on a data communications network via
peer-to-peer networking connectivity from the first computing
device on the data communications network, the method comprising:
obtaining a device description module having a textual description
of the logical device service via peer-to-peer networking from the
remote computing device, the device description module defining the
logical device service in text and a contract also in text for an
exchange of data messages via peer-to-peer networking connectivity
with the remote computing device for controlling the logical device
service on the remote computing device; based on the textual
description of the logical device service in the device description
module, dynamically generating code of a programmatic interface for
invocation by the client program to initiate service-specific
operations for remote control of the logical device service; and on
invocation of method members of the generated programmatic
interface by the client program, converting the client program's
programmatic interface invocation into the exchange of data
messages via peer-to-peer networking connectivity in accordance
with the contract defined in the device description entity for
effecting control of the logical device service.
11. The method of claim 10, wherein the contract defined in the
device description module for effecting control of the logical
device service specifies a type of protocol for the exchange of
data messages and a network endpoint to which the data messages are
sent.
12. The method of claim 10, wherein the data messages are in a
mark-up language and exchanged via a hypertext transport
protocol.
13. The method of claim 10, wherein the generated programmatic
interface comprises a invoke method member operable for accepting
at least one string argument specifying a command of the service
associated with the logical device.
14. The method of claim 10, wherein the programmatic interface is
an object integration interface of an object-oriented programming
model.
15. The method of claim 10, wherein the service-specific operations
include invoking commands of the service, querying a state of the
service, and receiving and responding to events of the service.
16. The method of claim 10, wherein the service has a set of
properties defining a state of the service, and the
service-specific operations include querying and setting values of
the set of properties.
17. A method for a client program on a first computing device to
programmatically control a service of a logical device realized on
a remote computing device over a data communications network via
peer-to-peer networking connectivity from the first computing
device on the data communications network, the method comprising:
obtaining device description data via peer-to-peer networking from
the remote computing device, the device description data comprising
a service-specific service control definition and a
service-specific contract for an exchange of data messages via
peer-to-peer networking connectivity with the remote computing
device for controlling the logical device service on the remote
computing device; based on the service-specific service control
definition in the device description data, dynamically producing an
instance of a programmatic interface for invocation by the client
program to initiate service-specific operations for remote control
of the logical device service, the programmatic interface
comprising an invoke method member operable for accepting a string
argument specifying a service action associated with the logical
device service; and upon a calling of the invoke method member of
the programmatic interface by the client program, translating the
invoke method call from the client program into the exchange of
data messages via peer-to-peer networking connectivity in
accordance with the contract defined in the description document
for effecting control of the logical device service.
18. The method of claim 17, wherein the contract defined in the
device description data for effecting control of the logical device
service comprises a definition of network packets, request-response
patterns and a specification of an endpoint to which the data
messages are sent.
19. The method of claim 17, wherein the service-specific operations
include invoking commands of the logical device service, querying a
state of the logical device service, and receiving and responding
to events of the logical device service.
20. The method of claim 17, wherein the data messages are in a
mark-up language and exchanged via a hypertext transport
protocol.
21. The method of claim 17, wherein the service-specific service
control definition is in text and the programmatic interface is
produced by executing code generated based at least in part on the
service-specific service control definition.
22. The method of claim 17, wherein the programmatic interface is
an object integration interface of an object-oriented programming
model.
Description
RELATED APPLICATION DATA
[0001] This application is based on provisional application No.
60/139,137 filed and Jun. 11, 1999, and provisional application
number [to be determined] filed Oct. 18, 1999.
TECHNICAL FIELD
[0002] This invention relates generally to dynamic configuration of
interconnectivity among distributed devices and services, and more
particularly relates to providing a capability to access device- or
service-specific operational information and perform remote
automation and control of embedded computing devices using a
data-driven remote programming model, such as in a pervasive
computing environment
BACKGROUND AND SUMMARY
[0003] The cost of computing and networking technologies have
fallen to the point where computing and networking capabilities can
be built into the design of many electronic devices in the home,
the office and public places. The combination of inexpensive and
reliable shared networking media with a new class of small
computing devices has created an opportunity for new functionality
based mainly on the connectivity among these devices. This
connectivity can be used to remotely control devices, to move
digital data in the form of audio, video and still images between
devices, to share information among devices and with the
unconstrained World Wide Web of the Internet (hereafter "Web") and
to exchange structured and secure digital data to support things
like electronic commerce. The connectivity also enables many new
applications for computing devices, such as proximity-based usage
scenarios where devices interact based at least in part on
geographical or other notions of proximity. A prevalent feature of
these connectivity scenarios is to provide remote access and
control of connected devices and services from another device with
user interface capabilities (e.g., a universal remote controller,
handheld computer or digital assistant, cell phones, and the like).
These developments are occurring at the same time as more people
are becoming connected to the Internet and as connectivity
solutions are falling in price and increasing in speed. These
trends are leading towards a world of ubiquitous and pervasive
networked computing, where all types of devices are able to
effortlessly and seamlessly interconnect and interact.
[0004] In accordance with a new device connectivity architecture
known as Universal Plug and Play, devices and services are
controlled by exchanging well-defined XML-format data messages. At
the programmatic level, on the other hand, it is useful and
productive to work in an object-oriented framework.
[0005] Prior connectivity models are not adequate to bridge between
object interfaces and the data messages exchanged with the
controlled device over a network. Some prior connectivity models
require a controlling device to download the program code (such as
a device driver, Jini code, etc.) for interacting with the
controlled device or service from a networked source. Such a code
download requirement is unsuitable to the Web and other ubiquitous
computing scenarios. Other connectivity models require use of a
custom-written object for specific classes of services. This
approach leads to deployment hassles (e.g., user setup and
configuration) and also is unsuitable to ubiquitous computing.
[0006] In accordance with a technology described herein, a general
programmatic interface-to-network messaging adapter (called a
"rehydrator") is a module that exposes a suitable object
integration interface or application programming interface to
applications on a controller device and sends network data messages
to invoke services or query status of a controlled device. The
adapter maps application calls to the interface into network data
messages according to service protocols of the controlled device.
The described adapter preferably is generic to all devices and
services compatible with the connectivity model, and adapts itself
to specific of the devices based on an interface and message
format/protocol description. In other words, this adapter operates
as a universal module through which network data message-driven
services on other networked computing devices can remote
programmatic application programming interfaces, including object
integration interfaces according to an object model such as
Microsoft's COM, CORBA, JAVA, and the like.
[0007] More specifically, this general adapter provides the
interface suitable to any specific service of a controlled device
based on a data description of the interface, and converts the
application calls to network data messages based on a data
description of a protocol and format for network data messages to
interact with the specific service. Once the interface/messaging
description is obtained, applications on the controller device can
programmatically interact with the adapter, and the adapter then
handles appropriate message exchanges with the service of the
controlled device. With the described adapter, no code download is
required, only the interface/messaging description is needed. The
description can be obtained from the controlled device, a network
server computer, or by pre-loading or caching on the controller
device. The technology allows controller device applications to be
written using object-oriented programming, while avoiding code
download.
[0008] Additional features and advantages will be made apparent
from the following detailed description of the illustrated
embodiment which proceeds with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1 and 2 are block diagrams of a device architecture
per Universal Plug and Play using user control points, controlled
devices and bridges for connectivity between devices.
[0010] FIG. 3 is a block diagram of a device model per Universal
Plug and Play.
[0011] FIG. 4 is a block diagram illustrating example devices
conforming to the device model of FIG. 3.
[0012] FIG. 5 is a block diagram illustrating device state
synchronization using a state table and eventing.
[0013] FIG. 6 is a block diagram illustrating device
addressing.
[0014] FIG. 7 is a block diagram of a programmatic
interface-to-network messaging adapter or Rehydrator in the device
control model of FIG. 3.
[0015] FIG. 8 is a general data flow diagram of the Rehydrator of
FIG. 7 in the device control model of FIG. 3.
[0016] FIG. 9 is a block diagram of an implementation design of the
Rehydrator of FIG. 7.
[0017] FIGS. 10 and 11 are block diagrams illustrating an internal
software architecture of the user control point and controlled
device in the device control model of FIG. 3.
[0018] FIG. 12 is a block diagram illustrating an internal software
architecture of a combined bridge and user control point in the
device control model of FIG. 3.
[0019] FIG. 13 is a data flow diagram illustrating a typical
browsing protocol sequence in the device control model of FIG.
3.
[0020] FIG. 14 is a listing showing a layout of a description
document in the device control model of FIG. 3.
[0021] FIG. 15 is a listing of an exemplary icon list of a
Description Document in the device control model of FIG. 3.
[0022] FIG. 16 is a listing of an exemplary service control
protocol declaration in a Description Document in the device
control model of FIG. 3.
[0023] FIGS. 17, 18, and 19 are a listing of an exemplary contract
in the device control model of FIG. 3.
[0024] FIGS. 20 and 21 are a listing of an XML schema for a Service
Control Protocol Declaration Language used in the device control
model of FIG. 3.
[0025] FIG. 22 is a block diagram of an eventing model used in the
device control model of FIG. 3.
[0026] FIG. 23 is a data flow diagram illustrating subscription,
notification and unsubscription in the eventing model of FIG.
22.
[0027] FIG. 24 is a block diagram of a computer system that may be
used in the device control model of FIG. 3.
[0028] FIG. 25 is a block diagram of a device having embedded
computing and networking capability per universal-plug-and-play
(UPNP) standards that may be used in combination with the computer
system of FIG. 24 in the device control model of FIG. 3.
[0029] FIG. 26 is a block diagram of a software architecture per
UPNP standards in the embedded computing device of FIG. 25
[0030] FIG. 27 is a data flow diagram of a process for automatic
network introduction of the embedded computing device of FIG. 25
into an ad hoc computer network environment per the UPNP
protocol.
[0031] FIG. 28 is a data flow diagram of a process for automatic
network introduction of the embedded computing device of FIG. 25
into a configured computer network environment per the UPNP
protocol.
[0032] FIG. 29 is a block diagram of a software architecture of a
client device per UPNP standards having embedded computing and
networking capability that may be used in the device control model
of FIG. 3.
[0033] FIG. 30 is a block diagram of an exemplary home or office
pervasive computing environment having a variety of computers as
per FIG. 24 and embedded computing devices as per FIG. 25
interconnected per UPNP standards that may be used in the device
control model of FIG. 3.
[0034] FIGS. 31 through 43 are program listings of interfaces used
in the Rehydrator implementation design of FIG. 9.
[0035] FIGS. 44-46 are an XML format listing that depicts an
exemplary contract for interacting with a stock quote Service.
[0036] FIGS. 47-50 are an XML format listing that depicts an XML
schema for defining Contracts.
DETAILED DESCRIPTION
[0037] The following detailed description is directed toward a
general programmatic interface-to-network messaging adapter (also
known as a "rehydrator") in a device control model. In one
described implementation, the rehydrator is used in a device
architecture 100 (FIG. 1), connectivity model, and device control
protocol proposed by Microsoft Corporation, called Universal Plug
and Play ("UPnP"). Although described in the context of a device
control model, and specifically UPnP, the general programmatic
interface-to-network messaging adapter of the invention also is
more generally applicable in other distributed networking
environments to provide an object-oriented or like application
programming interface to applications for interacting remotely
using network data messages.
[0038] Universal Plug and Play
[0039] Universal Plug and Play (UPnP) is an open network
architecture that is designed to enable simple, ad hoc
communication among distributed devices and services from many
vendors. UPnP leverages Internet technology and can be thought of
as an extension of the Web model of mobile web browsers talking to
fixed web servers to the world of peer-to-peer connectivity among
mobile and fixed devices. UPnP embraces the zero configuration
mantra of Plug and Play (PnP) but is not a simple extension of the
PnP host/peripheral model.
[0040] The cost, size and battery consumption of computing
technology--including processing, storage and displays--continues
to fall. This trend is enabling the evolution of stand-alone,
single or limited function computing devices such as digital
cameras, audio playback devices, smart mobile phones and handheld
computers. Concurrent with this, the economical storage and
transmission of digital audio, video and still images is enabling
highly flexible models for managing entertainment content.
[0041] While many of these devices are capable of useful
stand-alone operation, seamless connectivity with the PC can
enhance the value to the customer of both stand-alone devices and
the PC. Good examples of this synergy are digital image capture
combined with PC image manipulation, storage and email transfer/web
publishing and information synchronization between a PC and a
handheld computer or smart mobile phone.
[0042] Since many of these devices, and the PC itself, are mobile,
a suitable communication architecture must enable a highly dynamic
connectivity model and must enable peer-to-peer operating among
arbitrary combinations of devices.
[0043] The Internet has created a widespread awareness of the value
of simple, universal communication that is independent of the
underlying transmission technology and independent of technology
from any single vendor.
[0044] UPnP makes it possible to initiate and control the transfer
of bulk data (e.g. files) or A/V data streams from any device on
the network, to any device on the network, under the control of any
device on the network. UPnP enables the ad hoc addition or removal
of devices on the network, and it enables multiple controlling
devices to remain in sync with each other.
[0045] UPnP reuses existing protocols and technology whenever
possible. The transition to this highly connected (and connectable)
world will not occur overnight. UPnP builds on existing Internet
protocols, but accommodates devices that cannot run the complete
UPnP protocol suite. UPnP provides an architecture that enables
legacy devices to communicate with UPnP devices.
[0046] IP internetworking has been chosen as a UPnP baseline due to
its proven ability to span different physical media, to enable real
world multiple vendor interoperation and to achieve synergy with
the Internet and home and office intranets. Internet synergy
enables applications such as IP telephony, multiple player games,
remote control of home automation and security, Internet based
electronic commerce, in addition to simple email and web browsing.
UPnP's scope includes remote control of devices and bulk data
transfer. But, it does not specify A/V streaming formats or
protocols.
[0047] UPnP's media independence enables a great deal of
flexibility in the packaging of products. UPnP enables an A/V
system to be controlled through an A/C power communications
technology, while the transmission of A/V streams among the
components is analog or digital. One of the controllers of this
system could be on the television, while another is on a PC, and
yet another connected via radio or infrared.
[0048] Unlike Plug and Play, Universal Plug and Play is built on
top of networking and enables ad hoc peer-to-peer connectivity.
Networking, in this context, describes a style of connectivity that
enables any networked device to initiate a communication with any
other networked device, without having established a prior
relationship or maintaining a persistent relationship between the
devices. Networking also allows multiple devices to establish one
or more connections with a single device, and it allows for a
device to be capable of both initiating and accepting connections
to/from other devices. The PnP, or host/peripheral, model is
suitable whenever there is a natural persistent relationship
between two devices (e.g. a keyboard, mouse and display maintain
and a persistent relationship with a host computer). Even though
networking does not mandate low level persistent relationships, it
provides the needed anchors (addresses) for applications to choose
to maintain associations as a convenience for the customer (e.g.
remembering commonly used networked printers).
[0049] In order to achieve multiple vendor peer-to-peer
interoperation among devices, vendors desirably agree on common
technology and standards up to the highest level of desired
functional interoperation.
[0050] UPnP leverages formal protocol contracts to enable
peer-to-peer interoperation. Protocols contracts enable real-world
multiple-vendor interoperation.
[0051] UPnP enables devices to expose a user interface by
leveraging browser technology. In this context, the browser can be
considered to be a very rich remote terminal. Current browser
technology does not maintain a separation of presentation from
data, or in the case of devices, control. It is possible to hunt
through a page of HTML to extract data values, but it is not
convenient or robust. UPnP leverages the separation of presentation
and data enabled by the use of XML, and it extends this technology
to the device control domain.
[0052] UPnP provides a device-driven auto-configuration capability
that preserves the experience that customers have on the web.
Today, it is possible to navigate around the web without loading
programs beyond the browser itself. Since UPnP enables the browser
to be extended to control devices, and because UPnP devices are
controlled with explicit protocols, the browser must somehow learn
how to talk to UPnP devices. This learning process is driven
entirely from the device itself and is accomplishing entirely by
uploading an XML document that describes the capabilities of the
device. The architectural component that enables device-driven
auto-configuration is called the Rehydrator. The job of the
Rehydrator is to convert between APIs and protocols.
[0053] Since the auto-configuration process itself is driven only
by the exchange of formatted data, there is very little opportunity
for a malicious attack from a hostile piece of code.
[0054] There are some scenarios where the web UI model is not
sufficient for a rich customer experience. It would not be
convenient to have to a web for each light switch in a house. To
support a rich user interface and to enable the aggregation of
devices into a single UI, UPnP enables application control in
addition to browser control of devices. This is achieved simply by
enabling applications to call the same Rehydrator APIs that the
browser does. Applications can also directly generate and consume
the raw UPnP control protocols, provided they are not interested in
the device-driven auto-configuration enabled by the Rehydrator.
[0055] UPnP assumes that there will be more than one device with UI
that wants to control other devices in any given network, and it
provides a simple mechanism that enables these control points to
remain in sync. This mechanism can easily support device front
panels and wireless remotes that do not run UPnP protocols. The
UPnP control model is third-party control; any device can transfer
bulk data (e.g. files) or A/V data streams from any device on the
network, to any device on the network, under the control of any
device on the network.
[0056] Terminology
[0057] The detailed description that follows uses the terminology
defined below.
[0058] Module. A component of a device, software program, or system
that implements some "functionality", which can be embodied as
software, hardware, firmware, electronic circuitry, or etc.
[0059] User Control Point. The set of modules that enable
communication with a UPnP Controlled Device. User Control Points
initiate discovery and communication with Controlled Devices, and
receive Events from Controlled Devices. User Control Points are
typically implemented on devices that have a user interface. This
user interface is used to interact with Controlled Devices over the
network. The modules minimally include a Discovery Client, a
Description Client and a Rehydrator. User Control Points may also
include Visual Navigation, an Event Subscription Client, Event
Sink, a web browser and an application execution environment. User
Control Points can add value to the network by aggregating the
control of multiple Controlled Devices (the universal remote) or
they can implement a function as simple as initiating the transfer
of data to or from a Controlled Device. Examples of devices that
could be User Control Points are the personal computer (PC),
digital television (DTV), set-top box (STB), handheld computer and
smart mobile phone, and the like. Nothing prevents a single device
from implementing the functionality of a User Control Point and one
or more Controlled Devices at the same time.
[0060] Controlled Device. The set of modules that enable
communication with a User Control Point. Controlled Devices respond
to discovery requests, accept incoming communications from User
Control Points and may send Events to User Control Points. Devices
that support Controlled Device functionality may also support local
user interfaces such as front panel displays or wireless remotes.
The modules minimally include a Discovery Server, a Description
Server and a Control Server. Controlled Devices may also include a
Presentation (web) Server, Event Subscription Server and Event
Source. Examples of devices that could be Controlled Devices are
the VCR, DVD player or recorder, heating/ventilation/air-cond-
itioning equipment (HVAC), lighting controller, audio/video/imaging
playback device, handheld computer, smart mobile phone and the PC,
and the like. Nothing prevents a single device from implementing
the functionality of a User Control Point and one or more
Controlled Devices at the same time.
[0061] Bridge. A set of modules that enables Bridged and Legacy
Devices to interact with native UPnP devices. The bridge itself
exposes a collection of UPnP Controlled Devices to User Control
Points. The Bridge maps between native UPnP Device Control
Protocols and the underlying protocols exposed by the Bridged and
Legacy Devices. Optionally, such a device could expose UPnP
Controlled Devices to Legacy Devices in the manner required by the
Legacy Devices. Nothing prevents a single device from implementing
the functionality of a User Control Point, one or more Controlled
Devices and a Bridge at the same time.
[0062] Service Provider. A module used by a UPnP Bridge that
translates between UPnP protocols and the protocols used by Bridged
and Legacy Devices. No Service Providers are required for
communication among native UPnP devices.
[0063] Bridged Device. A device that cannot participate in UPnP at
the native protocol level, either because the device does not have
sufficient resources or because the underlying media is unsuitable
to run TCP and HTTP. Examples of devices that could be Bridged
Devices are power line-controlled A/V equipment, light switches,
thermostats, wristwatches and inexpensive toys. Bridged Devices are
UPnP complaint and are exposed to other UPnP devices through a UPnP
Bridge.
[0064] Legacy Device. Any non-UPnP compliant device that must be
exposed to other UPnP devices through a UPnP Bridge.
[0065] Device Model. The UPnP model of Controlled Devices. The
Device Model includes the addressing scheme, Description Document,
Devices and Services hierarchy and the functional description of
modules.
[0066] Device Control Protocol (DCP). A complete set of UPnP
protocols and schemas used to interact with a UPnP Controlled
Device.
[0067] Device Definition. The formal definition of a Device Type. A
Device Definition includes a Device Type Identifier, the fixed
elements in the Description Document, the required set of Service
Definitions in the Root Device, and the hierarchy of required
Devices and Service Definitions.
[0068] Service Definition. The formal definition of a Service Type.
A Service Definition includes a Service Type Identifier, definition
of the Service State Table (SST), definition of the Service Command
Set, the Service Control Protocol (SCP) and Service Control
Protocol Declaration (SCPD).
[0069] Device. In the context of the Device Model, a container for
Services. A Device generally models a physical entity such as a
VCR, but can also represent a logical entity. A PC emulating the
traditional functions of a VCR would be an example of a logical
device. Devices can contain other Devices. An example would be a
TV/VCR packaged into a single physical unit. UPnP enables the
association of user interface (display icon and root web page) with
every Device, including Root Device.
[0070] Root Device. The topmost Device in a hierarchy of nested
Devices. A Device with no nested Devices is always a Root
Device.
[0071] Device Type. A relatively high level classification of
Devices with common functionality. Device Type is intended to
enable Devices to be simply and automatically grouped for
presentation. An example of a Device Type is "VCR". Device Types
are formally defined in terms of a required set of Service
Definitions of minimum version that a compliant Device must
support. UPnP supports searches for all Devices of a specified
Device Type.
[0072] Device Type Identifier. A unique identifier that identifies
a Device Definition. This identifier adheres to the format of a
Uniform Resource Identifier (URI). See, T. Berners-Lee, R.
Fielding, L. Masinter, "Uniform Resource Identifiers (URI): Generic
Syntax", which can be found at
http://www.ietf.org/rfc/rfc2396.txt.
[0073] Device Friendly Name. A human readable string that is
initialized by vendors at the time of manufacturer of a Device.
Every Device, including Root Devices, has a Device Friendly Name. A
typical Device Friendly Name will contain manufacturer and model
information, and is used to enable a more precise identification of
a UPnP Device from the set of discovered Devices. Once identified,
the Unique Device Name (UDN) can be used to unambiguously identify
the same Device in the future. UPnP enables Device Friendly Names
to be changed by User Control Points. The Device Friendly Name
should not be used as device identifier.
[0074] Unique Device Name (UDN). The fundamental identifier of a
Device. Every Device, including Root Devices, has exactly one UDN.
The UDN is globally unique and permanent, even across power cycles
and physical location changes. The UDN is the only UPnP device
identifier guaranteed never to change. UPnP enables searches for
devices by UDN.
[0075] Description Document. A structured unit of data that is used
by a User Control Point or UPnP Bridge to learn the capabilities of
a Controlled Device. Description Documents are retrieved from the
Description Server on a UPnP Controlled Device. There is one
Description Document for every Root Device that describes the Root
Device and all non-Root Devices. Description Documents adhere to
XML grammar. To support localization, multiple Description
Documents can exist. A User Control Point requests the preferred
localized Description Document by using the standard HTTP
"accept-language" header.
[0076] Service. The fundamental UPnP controllable entity (but not
the finest level of control). An example of a Service is "Clock".
Services are defined with a mandatory common base set of
functionality. Vendors can extend the base set with proprietary
extensions provided the base functionality is implemented. Service
Definitions are versioned and later versions are constrained to be
supersets of previous versions. UPnP enables searches for all
Devices that contain a specified Service of a minimum version. This
search would find all clocks, regardless of their packaging. A
search for Device Type "Clock" would be used to find only
stand-alone clocks.
[0077] Service Type. A classification of Services by their
function.
[0078] Service Type Identifier. A unique identifier that identifies
a Service Definition. This identifier adheres to the format of a
Uniform Resource Identifier (URI). See, T. Berners-Lee, R.
Fielding, L. Masinter, "Uniform Resource Identifiers (URI): Generic
Syntax", which can be found at
http://www.ietf.org/rfc/rfc2396.txt.
[0079] Service State Table (SST). A logical table consisting of
rows of [Variable, Type, Legal Values, Default Value, Current
Value] that represents the current electrical, mechanical and/or
logical state of a Service. SST instances are stored on the
Controlled Device itself and are the ultimate authority of the
state of the Service. All local user interface, such as front
panels or wireless remotes are required to update the SST on UPnP
compliant devices.
[0080] SST Definition:
[0081] Service Command Set. A set of Commands that can be invoked
on a Service. Commands generally result in changes in the Current
Value field of one or more rows of a SST. Commands are logically
represented in the format Command (Variable=New Value, Variable=New
Value, . . . ). Services must accept or reject the complete set of
changes to a SST. There is a mandatory standard Query Command that
is used to retrieve the Current Value of any row of a SST.
[0082] Service Command Set Definition:
[0083] Service Control Protocol (SCP). The protocol used to invoke
Commands against a Service and to return results. There is exactly
one SCP per Service Definition. SCPs adhere to the grammar of SCP
XML schema. SCPs can be generated by an automated tool that accepts
a SST Definition and a Command Set Definition as input.
[0084] Service Control Protocol Declaration (SCPD). A formal
representation of the schema of a Service. The SCPD declares the
rows of a Service's SST and the associated Command Set. SCPDs are
uploaded from Controlling Devices in their Description Documents
and enable User Control Points or Bridges to invoke Commands on the
Service without any prior or persistent knowledge of the
capabilities (or schema) of the Service. There is exactly one SCPD
per Service Definition. SCPDs adhere to XML grammar. SCPDs can be
generated by an automated tool that accepts a SST Definition and a
Command Set Definition as input.
[0085] Event. An unsolicited message generated by a Controlled
Device and delivered to one or more User Control Points. Events are
used to maintain a consistent view of the state of Service across
all interested User Control Points. UPnP leverages the GENA event
architecture (see "Generic Event Notification") to transport event
messages. All events are delivered using TCP/IP for
reliability.
[0086] Generic Event Notification (GENA). An event transport
protocol. GENA leverages TCP/HTTP as a transport. GENA has been
submitted as an Internet Draft to the IETF. See, J. Cohen, S.
Aggarwal, Y. Goland, "General Event Notification Architecture Base:
Client to Arbiter", which can be found at
http://www.ietf.org/internet-drafts/draft-cohen-gena-clie-
nt-00.txt.
[0087] Simple Service Discovery Protocol (SSDP). A simple network
device discovery protocol. UPnP uses SSDP to allow User Control
Points to find Controlled Devices and Services. SSDP operates in a
default, completely automatic multicast UDP/IP based mode in
addition to a server-based mode that uses TCP/IP for registrations
and query. Transitions between the default dynamic mode and
server-based mode are automatic and transparent. SSDP enables every
Controlled Device to control the lifetime that its Description URL
is cached in all User Control Points. This enables a Controlled
Device to remain visible to User Control Points for a relatively
long time (through power cycles), in addition to enabling a
Controlled Device to appear and disappear very quickly, all under
the control of the Controlled Device. SSDP and related Multicast
and Unicast UDP HTTP Messages specifications have been submitted as
Internet Drafts to the IETF. See, Y. Goland, "Multicast and Unicast
UDP HTTP Messages", which can be found at
http://www.ietf.org/internet-drafts/draft-goland-ht- tp-udp-00.txt;
and Y. Goland, T. Cai, P. Leach., Y. Gu, S. Albright, "Simple
Service Discovery Protocol/1.0", which can be found at
http://www.ietf.org/internet-drafts/draft-cai-ssdp-v1-02.txt.
[0088] Client. In the context of UPnP, Client refers to a module
that initiates a TCP/HTTP connection to a peer HTTP server.
[0089] Server. In the context of UPnP, Server refers to an HTTP
server. This is a module that accepts incoming TCP/HTTP connections
and either returns a web page or forwards the payload data to
another module. Client and Server describe only the direction of
initiation of TCP/HTTP connections. There is no relationship
between the low level concepts of Client and Server and the high
level concepts of User Control Point and Controlled Devices.
Logically, User Control Points always discover and initiate
communication with Controlled Devices, but this communication
requires Client and Server functionality on both sides.
[0090] Hostname. A Hostname is the Domain Name System (DNS) or
NetBIOS Name Service (NBNS) that, when resolved to an IP address,
represents a network interface that can be used to establish TCP/IP
level connectivity to User Control Points, Controlled Devices or
Bridges. Hostnames can be used to provide persistent network level
addressing on a network where IP addresses are dynamically assigned
and of unknown lifespan or to integrate with an existing managed
network. UPnP provides an algorithm for seeding a device's hostname
from its UDN at manufacturing time.
[0091] Uniform Resource Locator (URL). A format for expressing web
addresses. URLs minimally contain an identification of the protocol
family that the URL is valid for, a Hostname, and a path. UPnP uses
URLs as addresses whenever the module accepting the incoming
connection is an HTTP server.
[0092] Description URL. The URL returned from a Controlled Device
or Bridge in response to any UPnP SSDP query. This URL always
points to a Description Server on the Controlled Device. An HTTP
GET can be issued on this URL to retrieve the Description Document.
This URL is valid as an address for the lifetime of the Hostname
embedded in the URL.
[0093] Discovery Server. The module that runs in a Controlled
Device or Bridge that responds to SSDP queries. This Server is
unique in that it must support UDP/HTTP rather than just
TCP/HTTP.
[0094] Discovery Client. The module that runs in a User Control
Point that initiates SSDP queries.
[0095] Description Server. The module that runs in a Controlled
Device or Bridge that responds to HTTP GETs and returns Description
Documents. This service consists of a TCP/HTTP server than can
retrieve and return a Description Document from persistent storage
(like a filesystem).
[0096] Visual Navigation. User Control Point functionality that
displays the icons of discovered Devices and enables the transfer
of control to a browser or application to interact with the
Controlled Device. In Windows, Visual Navigation could be
implemented as a folder of icons.
[0097] Presentation URL. A URL that can be used by a User Control
Point to navigate to the Presentation Server of a Controlled
Device. This URL is returned in the Description Document and is
valid as an address for the lifetime of the Hostname embedded in
the URL. All Devices, including non-Root Devices, can have an
associated Presentation URL.
[0098] Presentation Server. A web server. The module that runs in a
Controlled Device that responds to HTTP GETs or Presentation URLs
and returns user interface using web technologies (JavaScript,
Jscript.RTM., ECMAScript, VBScript, ActiveX.RTM., Java Applet,
etc.).
[0099] Browser. The Presentation Client. A web browser extended
with a Rehydrator.
[0100] Control URL. A URL that can be used by a User Control Point
to navigate to the Control Server of a Controlled Device or Bridge.
This URL is returned in the Description Document and is valid as an
address for the lifetime of the Hostname embedded in the URL. All
Services have an associated Control URL.
[0101] Control Server. The module that runs in a Controlled Device
or Bridge that responds to Commands invoked on a Service by a User
Control Point. Commands are encoded using the SCP specified in the
Service Definition. This service consists of a TCP/HTTP server than
passes control to the native control logic of a Service, updates
the SST and generates an event if the SST changes.
[0102] Rehydrator. In UPnP, the Control Client. A User Control
Point module that translates between native operating system APIs
and SCPs and events. The Rehydrator uploads SCPDs from Controlled
Devices and Bridges and generates appropriate SCPs in response to
application API requests to invoke Commands.
[0103] Event Subscription URL. A URL that can be used by a User
Control Point to navigate to the Event Subscription Server of a
Controlled Device or Bridge. This URL is returned in the
Description Document and is valid as an address for the lifetime of
the Hostname embedded in the URL. All Services have an associated
Event Subscription URL.
[0104] Event Subscription Server. The module that runs in a
Controlled Device or Bridge that responds to GENA SUBSCRIBE
requests from User Control Points. A SUBSCRIBE informs the
Controlled Device or Bridge of the User Control Point's desire to
receive future events. This service consists of a TCP/HTTP server
that adds the User Control Point's Event Sink URL to the list of
destinations to be NOTIFY'd whenever the SST associated with the
Service changes.
[0105] Event Subscription Client. The module that runs in a User
Control Point that sends GENA SUBSCIBE messages to the Event
Subscription Server.
[0106] Event Sink URL. A URL, supplied by a User Control Point,
that is used as an address to send event NOTIFYs to. This URL is
valid as an address for the lifetime of the Hostname embedded in
the URL. There is no explicit relationship between Event Sink URLs
and Subscription Identifiers.
[0107] Subscription Identifier (SID). A header in the GENA NOTIFY
message that identifies the source of an event. In UPnP, the SID
can be considered as an alias for the Event Source instance.
[0108] Event Sink. The module that runs in a User Control Point
that accepts incoming GENA event NOTIFYs. This service consists of
a TCP/HTTP server that passes the event information to interested
applications running on the User Control Point.
[0109] Event Source. The module that runs in a Controlled Device or
Bridge that sends GENA NOTIFYs to the Event Sink Servers of
SUBSCRIBES User Control Points.
[0110] Domain Name System (DNS). A distributed system of servers
that locates the IP addresses of other computers on a network based
on their hierarchical names.
[0111] NetBIOS Name Server (NBNS). A server that locates the IP
addresses of other computers on a network based on their flat
NetBIOS computer names.
[0112] Multicast DNS (MDNS). A peer-to-peer translation scheme that
does not require involvement of DNS servers.
[0113] UPnP Technologies Overview
[0114] An overview of technologies utilized in UPnP follows.
[0115] Device Discovery: Simple Service Discovery Protocol
(SSDP)
[0116] TCP/IP provides the ability to initiate a connection with a
specified application running on a specific device, provided both
the network address of the device (IP address) and the application
address (port) are known. Generally, application addresses (ports)
are standardized and widely known, but the problem of learning the
IP address of a device remains.
[0117] Simple Service Discovery Protocol (SSDP) is a protocol that
enables devices to learn of the existence of potential peer devices
and the required information (an IP address) needed to establish
TCP/IP connections to them. The successful result of an SSDP search
is a Uniform Resource Locator (URL). The Hostname embedded in the
URL can be resolved to an IP address that can be used to make a
connection to the discovered device. The name to address resolution
is outside of the functionality of SSDP.
[0118] SSDP specifies a default, completely automatic, best-effort
multicast UDP-based operating mode, in addition to a server mode
that uses TCP for registration and query. Fall-forward to server
mode and fallback to the default dynamic mode can occur
automatically and transparently as a server is added or removed
from a network. Server mode can be used to reduce network traffic,
to implement searches based on location or policy and to integrate
with a directory system.
[0119] SSDP requires that all devices specify a maximum lifetime
that SSDP level knowledge of the device will remain cached in other
network devices. If a device does not refresh the cache of other
network devices before this interval expires, the device will
disappear from the network. This interval can be chosen to be
larger than a typical power down cycle to enable device visibility
to persist for a relatively long time, or a smaller interval can be
chosen to enable more dynamic visibility control. In all cases,
devices that are abruptly removed from the network will eventually
disappear from all networked devices.
[0120] In response to an SSDP search, UPnP devices return a
Description URL in the SSDP Location and optionally the Alternate
Location (AL) SSDP headers. An example location header is a
follows:
[0121] Location:
http://device.local/description/path/description.xml
[0122] In this example, the device.local is the Hostname of the
Controlled Device, and the "description/path/description.xml"
element of the URL is the path and name of the Description Document
on the device.
[0123] Eventing: Generic Eventing Notification (GENA)
[0124] Eventing, in the context of UPnP, is the ability for a
device to initiate a connection at any time to one or more devices
that have expressed a desire to receive events from the source
device. Events are used to enable synchronization among multiple
devices organized into a many to one relationship. UPnP events are
mainly used for asynchronous notifications of state changes.
[0125] TCP/IP provides the fundamental support for the connections
that carry event information. Generic Event Notification (GENA)
adds conventions for establishing relationships between interested
devices and an addressing scheme to enable the unambiguous delivery
of events. GENA leverages HTTP addressing and encapsulation.
[0126] User Control Points, Controlled Devices and Bridges
[0127] With reference now to FIGS. 1 and 2, UPnP is an
application-level distributed network architecture where the
logical nodes on the network are User Control Points 104-105,
Controlled Devices 106-107 and Bridges 120. These classifications
refer to functionality rather than physical entities. The
functionality of UPnP User Control Points 104-105, Controlled
Devices 106-107 and Bridges 120 can be packaged into physical
entities (e.g., multiple function devices 102-103) in any
combination.
[0128] The primary distinction between a User Control Point 104-105
and a Controlled Device 106-107 is that the User Control Point is
always the communication initiator. After the initial
communication, User Control Points can receive events from
Controlled Devices.
[0129] Controlled Devices 106-107 are responsible for storing the
state of Services. User Control Points are required to synchronize
to the state on Controlled Devices and to share state directly
among themselves.
[0130] User Control Points typically have user interface that is
used to access one or more Controlled Devices on the network.
Controlled Devices only have local user interfaces.
[0131] Bridges 120 (FIG. 2) expose devices that do not expose
native UPnP protocols as native UPnP Controlled Devices. The Bridge
itself looks to other UPnP User Control Points like a set of
Controlled Devices.
[0132] The following table lists the modules in the User Control
Points 104-105 and Controlled Devices 106-107, along with their
functions.
1 User Control Point Controlled Device Function Module Function
Module Initiate discovery Discovery Client Respond to Discovery of
Controlled discovery Server Devices. requests. Retrieve Description
Client Provide Description Description Description Server
Documents. Documents. Display a folder Visual Navigation of icons
per discovered Device and allow transfer of control to a selected
device. View user Web Browser Provide user Presentation interface
exposed inteface for (Web) Server by a Controlled remote User
Device. Control Points. Execute Application applications. Execution
Environment Invoke Rehydrator Accept incoming Control Server
Commands on a Commands in plus native Controlled Device SCPs and
control logic by sending execute them. Service Control Protocols in
response to local API calls. Inform a Event Accept requests Event
Controlled Device Subscription for Events and Subscription of a
desire to Client remember them. Server receive Events. Receive an
Event. Event Sink Send an Event. Event Source
[0133] Device Model
[0134] The UPnP Device Model 200 shown in FIG. 3 is the model of a
UPnP Controlled Device or Bridge that is emulating native
Controlled Devices. The Device Model includes the addressing
scheme, eventing scheme, Description Document schema, Devices and
Services schema and hierarchy, and the functional description of
modules. The UPnP Device Model extends beyond simple API or a
command and control protocol definitions to enable multiple User
Control Points to have a consistent view of Controlled Devices.
This requires that the state of running services be formally
modeled and that all state changes be visible to User Control
Points. Central to the distributed UPnP architecture is the rule
that Controlled Devices are the ultimate authority for the state of
Services running on them.
[0135] Service
[0136] The fundamental controllable entity in UPnP is a Service
210-217. Every running instance of a Service includes:
[0137] A Service State Table (SST) 230, which represents the
current state of the Service.
[0138] The SST 230 can be used to represent the operational mode of
device or to act as an information source or sink for structured
data or simple files. The SST of a VCR 254 (FIG. 4) could represent
the current transport mode, tuner channel selection, input and
output switch selections, audio and video decoding format and
current timer program. The SST of clock 251 (FIG. 4) would likely
represent the current time. The SST of an image rendering device
could implement a video frame-buffer that can accept raw pixel
information or formatted JPG files. The SST of an audio or video
playback device could implement a transfer buffer or queue of
material to be played. The SST of PDA could implement a collection
of formatted data that has changed and needed to be synchronized
with another device, in addition to a transfer buffer for accepting
incoming formatted data.
[0139] The logical structure of a SST published in the Service
Definition, but the actual storage format of an instance of a SST
is entirely up the device. The only interaction with a SST is
through a formal application level network protocol.
[0140] A Control Server 232, which accepts incoming Commands
expressed in the Service's Service Control Protocol (SCP). The
Control Server passes the command to the Service's native command
processing logic and waits for command completion. When the command
is completed successfully, the SST is updated, an event is
generated, and a successful response is returned to the User
Control Point. In the event of an illegal command or unsuccessful
command, no changes are made to the SST and a failure response is
returned. The Command and response sequence is payload to a
TCP/HTTP request/response.
[0141] An Event Subscription Server and Event Source 234. The Event
Subscription Server accepts incoming GENA SUBSCRIBE messages from
User Control Points and adds them to a list of User Control Points
interested in SST change events from the Service. The Event Source
initiates a TCP/HTTP connection to each interested User Control
Point and sends a GENA NOTIFY each time the Service's DST changes.
The NOTIFY payload includes the changed contents of the DST.
[0142] A Control URL that identifies the Control Server.
[0143] An Event URL that identifies the Event Subscription
Server.
[0144] The formal definition of a Service (Service Definition)
includes:
[0145] The definition of the SST. SST layouts are logically
specified in terms of rows of [Variable, Type, Legal Values,
Default Value]. The actual instance of a SST would also include a
Current Value field in every row.
[0146] The definition of the Service Command Set that can be
invoked against the Service's SST. Commands are logically specified
in terms of Command (Variable=New Value, Variable=New Value, . . .
). If a Command results in more than a single Variable change, the
updates are atomic and the Command will fail if it is illegal to
make the specified change to any one Variable.
[0147] The definition of a structured unit of data called a Service
Control Protocol Declaration (SCPD). SCPD is used to advertise the
layout (schema) of the SST and Command Set of the Service to a User
Control Point or Bridge. The SCPD enables the User Control Point to
invoke Commands (through the Rehydrator) on the Controlled Device
without any prior or persistent knowledge of the capabilities of
the device. The SCPD is uploaded from the Controlling Device as
part of the Description Document. An automated tool that accepts
the SST definition and Command Set definition as inputs can
generate the SCPD for a Service.
[0148] The definition of a network protocol used to invoke Commands
against the SST associated with a Service and to return results. An
automated tool that accepts the SST definition and Command Set
definition as inputs can generate the SCP for a Service. The SCP
can also be generated from the SCPD. The Rehydrator's job is to
convert SCPDs into SCPs. The reason for a formal SCP specification
is to enable the implementation of the Control Server itself and to
enable simple peer-to-peer device interoperation using only
published protocols.
[0149] An identifier, called the Service Type Identifier, that
identifies a unique Service Definition. Service Definitions are
versioned in controlled manner. Every later version of a Service
must be proper superset of the previous version.
[0150] Device
[0151] According to the device model 200 shown in FIG. 3, a UPnP
Device 202-205 (e.g., multiple function devices 102-103 of FIG. 1
and bridged devices 122-123 of FIG. 2) is a logical container of
one or more Services 210-217. Generally a Device represents a
physical entity such as a VCR. Typical Services in the VCR Device
example might be "TRANSPORT", "TUNER", "TIMER" and "CLOCK". While
Devices are often physical entities, a PC emulating the traditional
functions of a VCR could also be modeled in the same way as the
stand-alone VCR. Devices can contain other Devices. An example
would be a TV/VCR 250 (FIG. 4) packaged into a single physical
unit. A Device (e.g., devices 202-203) may also be a logical
container of other Devices. The top-most Device in a hierarchy of
nested Devices 203-205 is called the Root Device 202. A Device with
no nested Devices is always a Root Device.
[0152] The UPnP Device Model was designed to be general and
flexible. It should be possible to model an entire Nuclear Power
Plant as a single Service or as a deeply nested hierarchy of
Devices and Services. In general, a Service 210-217 is cohesive set
of functions that enables flexible packaging into a variety of
Devices. Services can be versioned independently of Devices.
[0153] All Devices, including Root Devices belong to one or more
Device Types. Device Types are intended to enable instances of
Devices to be simply and automatically grouped for presentation. An
example of a Device Type is "VCR" 254 (FIG. 4). Device Types are
formally defined in terms of a minimal set of versioned Services
that a Device of Device Type must support. Device Types are not
formally versioned. Device Type is a relatively high level
grouping. A Device of Device Type only ensures that minimal set of
Services of a minimal version is present. There can be other
Services, higher versioned Services and Services with vendor
extensions present on such a Device.
[0154] UPnP enables SSDP level searches for a unique instance of a
Device (by UDN), all Devices of type Device Type and all Devices
that contain at least one Service Type of minimum version. The
result of an SSDP search is always a URL that points to the
Description Document contained in the Root Device. In the event
that matching Device is not the Root Device, the Description
Document has a tree of nested Devices that can be traversed to find
the matching Device.
[0155] Every Device includes:
[0156] One or more Device Types.
[0157] One or more Services.
[0158] Optionally, one or more Devices.
[0159] Optionally, a Presentation (web) Server 220-223 that can be
used to expose Device user interface. Every Presentation Server has
an associated Presentation URL.
[0160] A globally unique identifier called the Unique Device Name
(UDN). The UDN is the fundamental identifier of an instance of a
Device. Every Device, including Root Devices, has exactly one
UDN.
[0161] Every Root Device 202 also includes the Description Document
226 and Description Server 228 for all Devices under and including
itself.
[0162] The formal definition of a Device (Device Definition 226)
includes:
[0163] The fixed elements of the Description Document that describe
the Device.
[0164] The required hierarchy of Devices and Service
Definitions.
[0165] There can be many Device Definitions that belong to a single
Device Type.
[0166] Device Types
[0167] The formal definition of a Device Type includes:
[0168] A Device Type Identifier.
[0169] The required hierarchy of Devices and Service Definitions of
minimum versions.
[0170] Service State Table
[0171] A Service State Table (SST) logically consists of rows
of:
[0172] Variable, Type, Legal Values, Default Value, Current Value
Although entries of the Service State Table in UPnP consist of
these five items, the state table alternatively can contain fewer
or additional items. Generally, each entry will minimally consist
of a Variable name or identifier, and its current value.
[0173] The following table lists various Types available in
UPnP.
2 Type Description Example String A sequence of UNICODE characters.
Number A number, with no limit on digits; 15, 3.14, -123.456E+10
may potentially have a leading sign, fractional digits, and
optionally an exponent. Punctuation as in US English. Boolean TRUE
or FALSE. DateTime A date in ISO8601 format, with 19941105T08:15:5
+ 03 optional time and optional zone. Fractional seconds may be as
precise as nanoseconds. See, "Data elements and interchange formats
- Information interchange - Representation of dates and times",
which can be found at http://www.iso.ch/marke- te/ 8601.pdf.
ByteBlock An unstructured sequence of bytes.
[0174] The ByteBlock is essentially a data buffer. In one use, a
variable of this type can be used to effect transfer of a file from
the Controlled Device to the User Control Point. The file to be
transferred is kept in the Service State Table as the current value
of this variable. On a change in the file, the file is transferred
to any subscribing User Control Point in an event notification.
[0175] The reason for representing Services this way is to ensure
that the state of a Service is easily available in a common way to
multiple User Control Points.
[0176] An SST can be used to represent to current operational mode
of device, act as an information source or sink and/or simply be a
repository for commands. The SST of a VCR Service could represent
the current transport mode, tuner channel selection, input and
output switch selections, audio and video decoding format and
current timer program. Alternatively, the VCR 254 could be
represented as a Transport Service 260, Tuner Service, I/O Switch
Service, A/V Decoding Configuration Service and Programmable Timer
Service 261.
[0177] The SST of a clock 251 would likely represent the current
time. Additionally an alarm clock could include Service Variables
to configure the clock.
[0178] The SST of an image rendering device could implement a video
frame-buffer that can accept raw pixel information or formatted JPG
files. The SST of an audio or video playback device could implement
a transfer buffer or queue of material to be played. The SST of PDA
could implement a collection of formatted data that has changed and
needed to be synchronized with another device, in addition to a
transfer buffer for accepting incoming formatted data.
[0179] User Control Point Synchronization
[0180] In accordance with an device state and eventing model
illustrated in FIG. 5, UPnP rules require that every change to an
SST generate a corresponding event to announce the change to the
all interested User Control Points.
[0181] Device Addressing
[0182] With reference now to FIG. 6, UPnP is built on top of HTTP
and leverages the native address format of the web, Uniform
Resource Locators (URLs). URLs minimally contain an identification
of the application protocol family ("http") that the URL is valid
for, a Hostname and a path. In the context of UPnP, the path part
of a URL can represent either a filesystem path or simply an
identifier of the local system module and context that can process
incoming messages.
[0183] While UPnP modules are described as HTTP servers, there is
no requirement that implementations be based on actual web servers.
In most cases, the job of the HTTP server is simply to accept the
incoming connection, look at the local destination part of the
address (the path) and forward the payload to another module. UPnP
enables, but does not require, that all HTTP Servers be based on a
common software implementation or runtime instance. Controlled
Devices and Bridges can include a TCP port specification as part of
a URL to override the default value of 80.
[0184] The successful result of a UPnP SSDP level search is always
one or more Description URLs. These URLs can be used to navigate to
the Description Document of a Controlled Device or Bridge. A User
Control Point uploads the Description Document and extracts the
URLs of the Servers running on the Controlled Device or Bridge.
[0185] All URLs returned in the Description Document have a
lifetime equal to the lifetime of the Hostname embedded in them.
User Control Points can store these URLs as addresses without going
through a search sequence first. Once they have been advertised in
a Description Document, Controlled Device and Bridges cannot
arbitrarily change Server URLs.
[0186] Whenever a Hostname changes, all URLs associated with all
Devices addressed by that Hostname are invalidated. The UDN is the
only UPnP identifier guaranteed never to change. Any persistent
associations maintained by applications should at least store the
UDN to able to unambiguously identify the target Device.
[0187] The lifetime of a Description URL is determined by
Controlled Device or Bridge that advertises it. If a Controlled
Device or Bridge allows an SSDP advertisement of a Description URL
to expire, the URL is invalidated.
[0188] User Control Points use the Event Subscription URL returned
by the Controlled Device or Bridge to connect to the Event
Subscription Server. This server does the housekeeping of
remembering all User Control Points that are interested in
receiving Events on a Service. The Event Subscription Server needs
an address to send the events back to. This address is called the
Event Sink URL, and is supplied to the Controlled Device or Bridge
in the GENA SUBSCRIBE message. The lifetime of an event
subscription, and the Event Sink URL, is determined by the timeout
on the SUBSCRIBE message.
[0189] Further details of UPnP addressing are listed in the
following table.
3 UPnP Addresses URL Function Description Points to the Description
Server and Document path on a URL Root Device. This URL is returned
by the Description Server as part of the discovery process.
Presentation Points to a Presentation (web) Server on a Controlled
URL Device. There is one Presentation URL per Device, including
Root Devices. This URL can be entered into the address bar of a web
browser to navigate to the root web page of a Device. This URL is
returned in the Description Document. Control URL Points to the
Control Server implementing a Service on a Controlled Device. There
is one Control URL per instance of a Service. This URL is returned
in the Description Document. Event Points to an Event Subscription
Server on a Controlled Subscription Device. This URL is returned in
the Description Document. URL Event Sink Points to an Event Sink
(an HTTP Server) on a User URL Control Point. This URL is specified
by the User Control Point in the GENA SUBSCIBE message.
[0190] Device Discovery and Identification
[0191] UPnP enables SSDP searches for a unique Root or non-Root
Device by UDN, devices of a specified Device Type and devices
containing a Service of a specified Service Type.
4 UPnP SSDP Level Searches and Results Search for Returns A unique
Root A single Description URL pointing to the Description Device
(by Server and Document path on the Root Device. UDN) A unique non-
A single Description URL pointing to the Description Root Device
Server and Document path on the Root Device that (by UDN) contains
the non-Root Device. Type of Device A set of Description URLs
pointing to the Description Servers/Document paths of all Root
Devices that match the Device Type, or contain a non-Root Device
that matches the Device Type. Type of A set of Description URLs
pointing to the Description Service Servers/Document paths of all
Root Devices that contain a matching Service, or contain a non-Root
Device that contains a matching Service.
[0192] SSDP specifies Service Type (ST), Notification type (NT),
and Unique Service Name (USN) header fields for queries and for
announcements. UPnP uses the ST or NT header to carry one of the
UPnP defined identifiers. A unique USN is required for each unique
SSDP announcement.
[0193] Multiple instances of the same Service Type within a
Controlled Device 106-107 or Bridge 120 are not independently
announced.
[0194] UPnP search identifiers are used during the discovery
process. The result of a successful discovery is one or more
Description URLs. The format for search identifiers is:
5 upnp:searchtype:[ allformat .vertline. UDNformat .vertline.
srvformat .vertline. devformat ] searchtype = [ UDN .vertline.
SrvType .vertline. DevType .vertline. all ] allformat = all
UDNformat = UDN:namespace:uniqueid namespace = [ GUID .vertline.
IEEEMAC .vertline. 1394] srvformat = SrvType:servicetype:version
devformat = DevType:devicetype
[0195]
6 UPnP Search Identifiers Format Example all upnp:all upnp:all
Unique Device upnp:UDN:namespace: upnp:UDN:IEEEMAC: Name (UDN)
uniqueid 0C0099123456 Device Type upnp:DevType:devicetype
upnp:DevType:vcr Service Type upnp:SrvType:servicetype:ver
upnp:SrvType:clock:1
[0196] SSDP specifies that SSDP announcements must be made for all
SSDP searchable values. The SSDP announcements with "all" as the
notification header value must carry the Root Device UDN as the USN
header value. SSDP announcements for Device Types must carry the
UDN of the Root Device concatenated with the Device Type URI as the
USN header value. SSDP announcements for a Service Type will carry
the UDN of the Root Device concatenated with the Service Type URI
value as the USN header value. SSDP announcements of UDNs will
repeat the UDN value as the USN header.
7 UPnP SSDP Announcements UPnP Notification Announcement Type SSDP
USN "all" Root Device UDN Unique Root Root Device UDN Root Device
UDN Device Unique non- Non-Root Device Non-Root Device UDN Root
Device UDN Device Type Device Type Root Device UDN + Device Type
Identifier Identifier Service Type Service Type Root Device UDN +
Service Type Identifier Identifier
[0197] UPnP Bridges 120 (FIG. 2) announce Bridged Devices 122-123
and associated Services using SSDP. The identifiers associated with
the Bridged Devices are unique for the device, and they do not
duplicate identifiers for Controlled Devices and Services directly
available on the Bridge itself. This means that a Bridge that is
also a Controlled Device must announce Bridged Devices and local
Controlled Devices independently, with appropriate unique
identifiers, Description Documents and associated URLs.
[0198] Description
[0199] The UPnP Description Document 226 (FIG. 3) provides the
information necessary to identify, describe, connect and control a
UPnP Controlled Device 106-107 or Bridge 120 from a User Control
Point 104-105.
[0200] The Description Document is an XML document. UPnP defines
the use of HTTP and XML for the Description Document and wire
protocols. UPnP adheres to the schema declaration rules of XML-Data
and Y. Goland, "Flexible XML Processing Profile."
[0201] The top level XML elements are separated into three
categories: per Device, per Service and shared.
[0202] Rehydrator
[0203] With reference now to FIG. 7, all (UPnP) Controlled Devices
106-107 (FIG. 1) or Bridges 120 (FIG. 2) expose one or more
Services 210-217 (FIG. 3) that can be controlled remotely.
Controlling such Services involves a message exchange between a
User Control Point 104 and the device 106. This message exchange
happens according to a specific Service Control Protocol (SCP) 402,
which specifies the content and sequence of the messages
exchanged.
[0204] User Control Points 104 are not required to have any prior
knowledge of the SCPs 402 required to control the Services on the
various devices. Therefore, a Controlled Device or Bridge must be
able to describe to a User Control Point the protocols required to
control its Services, such that the User Control Point will be able
to implement these protocols dynamically. This requires a standard
way of declaring Service Control Protocols in a concise and
unambiguous fashion. UPnP introduces a technique for declaring
Service Control Protocols using a series of XML documents.
[0205] A Rehydrator 410 is a module that exposes a suitable API to
applications and either invokes Commands on a Service or queries
the state of that Service, or receives and responds to events. The
primary job of the Rehydrator is to map between API calls and the
Service Control Protocol sequence that invokes the Command.
[0206] As part of the Service Definition 406, a Service State Table
230 and Command Set 408 are defined. These things can be combined
in a deterministic way defined by UPnP to produce a Service Control
Protocol Definition (SCPD) 406, which includes a Service Control
Declaration 404 and a Service Control Protocol 402. The SCPD 406 is
a representation of the schema of a Service. It is possible to
reconstruct the SST, Command Set and SCP from the SCPD.
[0207] The SCPD is directly embedded into the Description Document
226 of a Controlled Device. When the Description Document is
uploaded into the User Control Point 104, the Rehydrator 410 can
extract the SCPD from it. At this point, the Rehydrator has enough
information to issue Service specific SCPs 402.
[0208] General Operation of the Rehydrator
[0209] More generally with reference to FIG. 8, the Rehydrator 410
operates as a universal adapter to provide a programmatic interface
to any service-specific protocol of a remote computing device. The
Rehydrator 410 simply obtains a data description or declaration of
the methods, properties and events of the remote service, as well
as a definition of the protocol of network data messages through
which the Rehydrator invokes the methods, queries or sets the
properties, and receives event notifications. In UPnP, this data
description takes the form of the Description Document 226, which
contains a Contract 412. The Contract defines network data packets
413 (e.g., XML data), request/response patterns, and protocol
(e.g., GENA, HTTP, SSDP) via which the packets are exchanged. This
information is sufficient for the Rehydrator to exchange the
appropriate network data packets to interact with the Controlled
Device Service, including to invoke commands, query and set
properties, and receive and respond to events, without download of
any executable code to the User Control Point 104 device and with a
zero installation or configuration experience.
[0210] The Description Document 226 also includes a declaration of
the methods, properties and events for the Service. Based on this
declaration, the Rehydrator produces a corresponding programmatic
interface for use by applications at the User Control Point. The
programmatic interface is an application programming interface that
can be in the form of an object integration interface of an
object-oriented programming model, such as Microsoft COM, CORBA,
Java classes, and scripting engine name extensions. In the example
illustrated in FIG. 8, the Rehydrator 410 exposes a COM object
integration interface ("IClock" interface 414), with methods
getTime( ) and setTime( ), for a Controlled Device having a "Clock"
Service with GetTime and SetTime commands. The Rehydrator 410
converts calls of an application program 416 to the IClock
interface 414 into the network data messages specified in the
Contract to invoke the corresponding commands of the Clock Service.
The Rehydrator 410 likewise creates suitable further programmatic
interfaces for other Services (e.g., Services 210-217 of FIG. 3)
based on the Description Document of their respective Controlled
Devices.
[0211] Accordingly, the Rehydrator operates as a universal proxy
object with data-driven conversion of programmatic interfaces to
network data messages. Further, the Rehydrator produces the
programmatic interface at the User Control Point based solely on an
XML data description. This operation allows the Rehydrator to
produce just-in-time transient interfaces to remote device Services
without the complexity of code downloads and installation or
configuration. Upon a later release of the interface by the
application, the Rehydrator destroys the interface without need to
de-install or clean up persistent configuration data in a registry
or configuration file of the operating system or object execution
run-time.
[0212] Rehydrator Implementation
[0213] Summary. With reference to FIG. 9, a preferred
implementation 440 of the Rehydrator 410 is as an internal
Microsoft Windows component that routes service control requests
from the UPnP API to devices. Applications wishing to control a
service on a UPnP device obtain a Service object through the UPnP
API and use the methods of this object to query the state variables
of the service and invoke its actions. Those methods use the
private Rehydrator API to turn the service control requests into
network messages that travel to the UPnP device. In this sense, the
Rehydrator performs a mapping between API calls and network
protocols.
[0214] Basic Functionality. The preferred implementation of the
Rehydrator is able to translate a service control call to the UPnP
API into the appropriate network messages defined by the Service
Control Protocol.
[0215] Asynchronous Event Notification. The preferred
implementation of the Rehydrator is able to notify UPnP API clients
of any asynchronous events generated by the devices they are
controlling. Event notification is done by means of the event
interfaces defined below.
[0216] Error Reporting. For a variety of reasons, state variable
queries and action invocations may fail. The preferred
implementation of the Rehydrator is able to provide a way to
communicate the success or failure status of such operations to the
parties initiating them.
[0217] Rehydrator Implementation Design. As illustrated in FIG. 9,
the preferred implementation of the Rehydrator is used in two ways.
First, the Device Finder 450 uses it to create Service objects 460.
Then, these Service objects use it to carry out service control
operations (querying state variables and invoking actions).
[0218] Creating Service Objects. When the Device Finder 450 creates
a Device object, it invokes the Rehydrator 410 to create Service
objects 460 for each of the service instances on that device. Each
service instance supports a particular Service Control Protocol and
the Rehydrator needs a description of this protocol in order to
create a properly hydrated Service object.
[0219] The Service Control Protocol is declared in two separate XML
documents: the DCPD and the Contract. The Rehydrator needs the
information in both documents. These two documents are passed to
the Rehydrator as IXMLDOMDocument interface pointers in the
RehydratorCreateServiceObject( ) API call.
8 HRESULT RehydratorCreateServiceObject( IN IXMLDOMDocument *pDCPD,
IN IXMLDOMDocument *pContractDocument, OUT IUPnPService
**pNewServiceObject);
[0220] This API returns a pointer to an IUPnPService interface on a
newly created Service object. In addition to the creating the
Service object, the Rehydrator sets up its internal data structures
so that it can properly handle requests to control the service.
Specifically, it creates a list of the properties and actions
exported by the service. Since all service instances of the same
service type export the same properties and the same actions, this
information is kept only once for each service type and is indexed
by Service Type Identifier.
[0221] The Rehydrator stores the information that is specific to a
particular service instance as private data within the Service
object itself. This includes the control URL and information about
the control server 232 (such as the HTTP verbs it supports). The
Service Type Identifier is the link between the Service object that
represents one instance of a service type and the Rehydrator
internal data structures that contain information common to all
instances of that service type. The Service Type Identifier is
stored as a private data member in the Service object.
[0222] Querying Service Properties. Applications can query the
values of service properties by invoking the
IUPnPService::GetProperty( ) method on a Service object.
Internally, this method makes a call to the RehydratorQueryState
Variable( ) function.
9 HRESULT RehydratorQueryStateVariable( IN LPCTSTR lpcszVerb, IN
LPCTSTR lpcszControlURL, IN LPCTSTR lpcszSTI, IN LPCTSTR
lpcszVarName, OUT VARIANT *pValue);
[0223] The first two in parameters to this function supply the
service instance specific information: the HTTP verb to use and the
control URL to which the network messages will be targeted. The
third parameter is the Service Type Identifier that will be used to
locate the Service Control Protocol information in the Rehydrator's
internal data structures. The fourth parameter is the name of the
variable that is being queried (the Rehydrator will validate this
against is internal list of state variables exported by the
service) and the final parameter is the address of a VARIANT
structure in which the Rehydrator will place the variable's
value.
[0224] This function will generate an HTTP request to the control
server on the device. The body of this request will be an XML
fragment containing a XOAP-encoded request for the variable's
value. The following is an example of such a request (the exact
header and payload format of this message is defined in the service
contract):
10 M-POST /clockService HTTP/1.1 Host: spather-xeon:8586
Content-Type: text/xml Man:
"http://www.microsoft.com/protocols/ext/XOAP"; ns=01 01-MethodName:
queryStateVariable 01-MessageType: Call Accept-Language: en-gb,
en;q=0.8 Referer: http://myhouse/VCR1Pres- entation Content-Length:
84 User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
Connection: Keep-Alive <queryStateVariable>
<variableName>currentTime</variableName>
</queryStateVariable>
[0225] The control server will respond to this message with another
XML fragment: the XOAP-encoded method response. The following is an
example of such a response:
11 HTTP/1.1 200 OK Connection: Close Cache-Control: private Date:
Mon Oct 11 12:13:38 PDT 1999 Expires: Mon Oct 11 12:13:38 PDT 1999
Content-Type: text/xml Content-Length: 62 Man:
"http://www.microsoft.com/protocols/ex- t/XOAP"; ns=01
01-MessageType: CallResponse <queryStateVariableResponse>
<_return>12:13:28</- _return>
</queryStateVariableResponse>
[0226] The rehydrator will extract the return value from this XML
fragment, place it in the VARIANT structure whose address was
passed as the last parameter to RehydratorGetServiceProperty( ) and
then return.
[0227] Invoking Service Actions. The process of invoking a service
action is very similar to querying a state variable. An application
calls IUPnPService::InvokeAction( ) on a Service object, passing it
the name of an action to invoke, and an array of arguments to the
action. Internally, IUPnPService::InvokeAction( ) calls
RehydratorlnvokeServiceAction( ), declared as shown below.
12 HRESULT RehydratorInvokeServiceAction( IN LPCTSTR lpcszVerb, IN
LPCTSTR lpcszControlURL, IN LPCTSTR lpcszSTI, IN LPCTSTR
lpcszActionName, IN SAFEARRAY saActionArgs, OUT LONG *pStatus);
[0228] As was the case for querying state variables, the service
instance specific information is passed in the first two
parameters, followed by the Service Type Identifier in the third.
The action name and an array of arguments are passed as the next
two parameters, and the final parameter is the address of a
variable in which to store the status of the operation.
[0229] RehydratorInvokeServiceAction( ) will send an HTTP request
to the control server identified by the second parameter. As
before, the body of this message will be an XML fragment containing
a XOAP-encoded method call. An example HTTP request to invoke an
action is shown below.
13 M-POST /clockService HTTP/1.1 Host: spather-xeon:8586
Content-Type: text/xml Man:
"http://www.microsoft.com/protocols/ext/XOAP"; ns=01 01-MethodName:
invokeAction 01-MessageType: Call Accept-Language: en-gb, en;q=0.8
Referer: http://myhouse/VCR1Pres- entation Content-Length: 119
User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
Connection: Keep-Alive <SerializedStream main="invokeAction">
<invokeAction id="invokeAction">
<actionName>setCurrentTime</actionName>
<actionArg>15:41:29</actionArg> </invokeAction>
</SerializedStream>
[0230] The encoding of the body of this message is again specified
in the service contract. The Rehydrator will wait for the HTTP
response to this request, which would look something like the
example below.
14 HTTP/1.1 200 OK Connection: Close Cache-Control: private Date:
Mon Oct 11 15:22:38 PDT 1999 Expires: Mon Oct 11 15:22:38 PDT 1999
Content-Type: text/xml Content-Length: 50 Man:
"http://www.microsoft.com/protocols/ex- t/XOAP"; ns=01
01-MessageType: CallResponse <invokeActionResponse>
<_return>0</_return> </invokeActionResponse>
[0231] After receiving a response such as this, the Rehydrator will
extract the return value, place it in the out parameter it was
passed, and then return.
[0232] FIGS. 31 through 43 are program listings defining various
interfaces used in the preferred implementation of the Rehydrator,
including an IUPNPDevice Interface, an IUPNPPropertyBag Interface,
an IUPNPService Interface, an lUPNPDevices Interface, and an
IUPNPServices Interface.
[0233] Description Document
[0234] With reference to FIG. 13, User Control Points 104 can
retrieve a Description Document 226 by issuing an HTTP GET on a
Description URL. This URL is returned in the location header of
either an SSDP announcement or an SSDP query response.
[0235] The HTTP GET must include an accept-language header that is
used to request the preferred language of the response. If the
requested language is not supported, a Description Document in the
default language supported by the Controlled Device or Bridge may
be returned.
[0236] An HTTP GET is used to retrieve sub elements of a
Description Document that are expressed as URLs.
[0237] URL Handling
[0238] URLs embedded in Description Documents 226 take one of 3
forms: a fully qualified URL or a relative URL.
[0239] Fully qualified URLs take the form:
[0240] http://devicename/pathname
[0241] The devicename part of the URL is a Hostname or IP address
and the pathname is a filesystem path or equivalent. A fully
qualified URL is used "as is" to establish an HTTP connection to a
device.
[0242] A relative URL does not contain the ":" character and is of
the form:
[0243] pathname
[0244] /pathname
[0245] Relative URLS are a compact representation of the location
of a resource relative to an absolute base URL. All relative URLs
in a Description Document are appended to the value of the
Description Document element <URLbase> to form fully
qualified URLs.
[0246] Binary Data
[0247] Some elements of a Description Document are binary. XML does
not directly support the embedding of binary data. In order to
include binary data directly in a Description Document, one must
convert the data to text using the Base 64 encoding scheme. This
tends to increase the size of the data by 25% on the average. Much
of this overhead can be eliminated if the binary data is passed by
reference instead of by value. To reference binary data, a URL to
the data is provided in a Description Document. The binary data can
be retrieved by doing a HTTP GET with that URL.
[0248] As an example, consider the <image> element in the
following Description Document:
15 <iconList> <icon> <size>16</size>
<imageType>PNG</imageTyp- e>
<color>1</color> <depth>8</depth>
<image> "http://device.local/iconpath/icon.png" / >
</icon> </iconList>
[0249] The icon would be retrieved with an HTTP GET of the
following format:
[0250] GET iconpath/icon.png HTTP 1.1
[0251] Host: device.local
[0252] The HTTP response would look like:
[0253] HTTP/1.1 200 OK
[0254] Content-Type: image/png
[0255] Content-length: ###
[0256] <binary color icon data in the PNG format>
[0257] Description Document Layout
[0258] The basic layout of the Description Document 226 is shown in
FIG. 14.
[0259] The following table lists Description Document elements that
are sub-elements to the root element.
16 Root The XML root element of a UPnP Description Document.
specVersionMajor The major version of the UPnP Architectural
Reference that this Description Document was created against. This
value must be 1. specVersionMajor The minor version of the UPnP
Architectural Reference that this Description Document was created
against. This value must be 0. URLBase An optional element used to
construct fully qualified URLs. Relative URLS are appended to the
value of <URLBase> to create fully qualified URLs. If this
element is present, it must agree with the HTTP Base header.
manufacturer A required element that contains a textual
manufacturer name. manufacturer An optional element containing a
URL that points to the web page of the URL manufacturer. modelName
A required element containing a textual product name.
modelDescription A required element containing a textual product
description. modelNumber An optional element containing a textual
product model number. modelURL An optional element containing a URL
that points to the web page of the product. UPC An optional element
containing the product Universal Product Code (UPC). serialNumber
An optional element containing a textual item serial number.
[0260] The Description Document elements listed in the following
table are associated with devices.
17 rootDevice A required sub element of the root. This element is a
container for one or more service elements and the elements that
describe the rootDevice. device An optional sub element of the root
or another device element. This element contains the same kinds of
elements as a rootDevice element. UDN A required sub element of
every rootDevice or device element containing the Unique Device
Name. friendlyName A required sub element of every rootDevice or
device element containing a textual friendly name. This element can
be updated remotely. deviceType A required sub element of every
rootDevice or device element containing a standardized Device Type
Identifier. presentation An optional sub element of a rootDevice or
device element URL containing a Presentation URL. iconList A
required sub element of every rootDevice or device element. This
element is a container for one or more icon elements. UPnP requires
a base set of six icons that must exist in the iconList. All
devices must support PNG icon image formats of three sizes, 16 by
16, 32 by 32 and 48 by 48 pixels in both color and black and white
at 8 bit depth. Additional formats and sizes, including JPEG, GIF,
BMP, ICON and VML, may be supported by adding them to the list.
icon A required sub element of every iconList element. This element
is a container for the elements that define an icon. size A
required sub element of every icon element. There must be icon
elements with associated size elements with the values 16, 32 and
48. Other icons may specify other sizes. color A required sub
element of every icon element with value 0 or 1. Each icon of size
16, 32 or 48 must exist in color and black and white. depth A
required sub element of every icon element. All required icons must
exist with a value of 8. imageType A required sub element of every
icon element that identifies the format of the binary icon: png,
jpeg, vml, gif, bmp, or ico. image A required sub element of every
icon element that references a binary icon.
[0261] The following elements of the Description Document are
associated with Services.
18 service An optional sub element of the rootDevice or another
device element. This element is a container for the Service
Definition. serviceType A required sub element of every service
element containing a standardized Service Type Identifier.
controlURL A required sub element of every service containing a
Control URL. eventSubURL A required sub element of every service
containing an Event Subscription URL. SCPD A required sub element
of every service. The SCPD is a container for the standardized
Service Control Protocol Declaration associated the Service.
[0262] FIG. 15 shows an exemplary icon list in a Description
Document 226.
[0263] Service Control Protocol and SCP Declaration
[0264] As part of the Service Definition 406 shown in FIG. 7, a
Service State Table 230 and Command Set 408 are defined. The SCPD
406 is a representation of the schema of a Service. It is possible
to reconstruct the SST 230, Command Set 408 and SCP 402 from the
SCPD.
[0265] The declaration of such a protocol must specify the list of
Variables that can be queried, the set of Commands that can be
invoked, as well as the wire protocol (the content and sequence of
network messages) required to carry out these operations. SCPD is
specified in two XML documents. The first or Service Control
Definition document 404, written in a language called Service
Control Protocol Declaration Language (SCPDL), declares the list of
state Variables and Commands associated with the Service Type to be
controlled by the protocol. The second or Service Control Protocol
document 402 is written in Contract Definition Language (CDL) and
declares the wire protocol that will be used to query the values of
the state variables and invoke the actions associated with the
service.
[0266] Declaring the Service State Table and Command Set
[0267] A SCPDL document 404 is used to specify the list of state
Variables that a SCP can query and the set of Commands that it can
invoke. SCPDL is an XML schema, a set of rules for writing XML
documents (Service Control Protocol Declarations).
[0268] FIG. 16 shows an exemplary SCPDL document. This XML document
consists of a root <scpd> element containing two
sub-elements, <serviceStateTable> and <actionList>.
Within the <serviceStateTable> element is a
<stateVariable> element for each state variable associated
with the service. The Service in this example is a TV tuner with
has only one state variable, currentChannel. The elements within
the <stateVariable> element specify the name, data type and
allowed values for the state variable. Had the Service more state
variables, they would be represented by additional
<stateVariable> elements within the <deviceStateTable>
element.
[0269] The <actionList> element contains an <action>
element for every action associated with the Service. The elements
within an <action> element specify the name of the action and
any arguments the action may take. In this case, the service
supports two actions that do not take arguments, ChannelUp and
ChannelDown, and another, SetChannel, that takes a new channel
number as an argument. The <argument> element and the
elements nested within it define the argument. The
<relatedStateVariable> element within <argument>
specifies the name of one of the state variables to which the
argument is related. In the UPnP Device Model, all arguments to
actions must correspond directly to some state variable.
[0270] Declaring the Contract
[0271] The Contract is a specification of the wire protocol that
will be used to query state Variables, invoke Commands and carry
notifications or events. This contract specifies the type of
protocol used, the network endpoint to which messages are sent, the
contents of those messages, the contents of the expected responses
and the contents of events. Contracts are written in Contract
Definition Language (CDL).
[0272] All UPnP SCPs will use essentially the same contract. A
specific contract applies to a single Service instance (since it
specifies the network endpoint to which messages are sent and
network endpoints are specific to service instances). However,
other than the network endpoint definition, all contracts for all
Service instances should be the same.
[0273] FIGS. 17-19 show an exemplary Contract. This Contract
defines two methods: queryStateVariable and invokeAction. These
methods are invoked by exchanging XML messages with a Control
Server on a UPnP Controlled Device or Bridge. The Contract
completely defines the header and payload of each message. By
passing the appropriate arguments to these methods, any of the
state Variables declared in the SCPDL declaration can be queried
and any of the actions invoked.
[0274] FIGS. 20 and 21 show an XML schema for the SCPDL.
[0275] Basic UPnP Eventing Architecture
[0276] With reference to FIG. 22, the UPnP architecture 200 (FIG.
3) requires that clients of the UPnP API be enabled to receive
notifications reliably from UPnP services 210-217 as their states
change. Since state changes are relatively common, the eventing
subsystem is efficiency and performance is a major consideration in
this design. FIG. 22 and the following discussion describe the
Basic UPnP Eventing Architecture 600, which encompasses both the
controlled device (CD) 106 and user control point (UCP) 104 sides
of the eventing service. It also includes the support APIs for both
a low-level service interaction and a higher level COM-based
wrapper of those APIs. The latter enables automation controllers
like Visual Basic and JScript 602 to receive event
notifications.
[0277] What is an Event?
[0278] Property change events are defined as any change in the
value of a row of the Device State Table (DST) 230 (FIG. 3) for a
service 210-217. This change will be reflected as a property change
notification. For example, if a "VCR" device has a "VCR Transport"
service, one row in that service's DST may be TapeState and the
value could be TapePresent. If the tape is ejected, the new value
would be TapeAbsent. This state change would be reflected as a
notification sent to all subscribers.
[0279] What is a Notification?
[0280] A UPnP event notification is an XML message sent over
HTTP/TCP to each and every subscriber to a particular UPnP service.
The content of the XML is defined below. The important contents of
this message are the unique identifier for the subscription, the
property name, new value, and property type.
[0281] Notification Processing
[0282] In UPnP, the listener to Notifications is the SSDP service
itself. SSDP already listens on another multicast address for
"alive" and "byebye" messages sent by UPnP devices. The same
listener will listen on a TCP port for notifications sent. All
subscriptions sent from that UCP contain the same callback URL and
so all notifications will be directed to that URL. When a
notification arrives the SSDP service will examine the NT header of
the message and determine if it is an event notification. If so,
the message is parsed further to determine if it should be
forwarded on to subscribers (which must exist). GENA defines the
format of the HTTP message, what headers can be used, and what they
can be used for.
[0283] GENA
[0284] GENA is the protocol of communication that, in a preferred
embodiment, UPnP devices use to send event notifications.
Therefore, UPnP devices that wish to notify UCPs of state changes
are recommended to use GENA. Notification subscribers will never be
required to interact with a UPnP device directly and so they are
not required to use GENA. The eventing API will encapsulate this
complexity. Other appropriate event transport protocols may be
used, such as publish/subscribe systems.
[0285] Receiving Notifications
[0286] Applications written in C (C Application 604) will be able
to utilize the SSDP C API 610 to receive callbacks when
notifications are processed by the SSDP service. This is analogous
to SSDP clients registering for notifications that services have
become available. When a UCP registers for a notification, it
passes as a parameter the URL of the service for which it is
interested in receiving notifications. This URL is obtained from
the description document for that service. (When a service is
registered on a UPnP device, it uses this same URL to listen for
subscription requests).
[0287] When a notification message is received by the SSDP service
listener, the SID header is checked against the list of subscribers
it maintains. If a subscriber is found, the callback function for
that subscriber is invoked, with one of the parameters being the
contents of the notification message. The notification client that
implements the callback function can process this message in any
appropriate way.
[0288] Notifications in the UPnP API
[0289] The UPnP API 410 is a consumer of the basic C interface
provided by the SSDP C API 610 component. In order to integrate
seamlessly, the registration of notifications is handled by the
Service Object 612 inside the UPnP Object Model. Service objects
will register for notifications when they are created. This ensures
that the DST is maintained by the UPnP API and is kept up to date.
They will implement the callback function required by the
registration function. If this callback function is invoked, it
will pass on that notification to UCPs. The UCPs can be written in
C, C++, VB, or script code, so the mechanism for passing on
notifications can be different.
[0290] Script Support
[0291] A feature of the illustrated eventing system is that it
supports script languages such as VBScript and JavaScript 602. For
VBScript, this is made possible by providing a property on the
Service object that, when set, contains the IDispatch pointer for a
VBScript function or subroutine that will be the event handler.
When the Service object's notification callback is invoked, it
checks to see if this IDispatch pointer was set, and if so, it
calls IDispatch::Invoke on DISPID 0 of that interface to call the
VBScript subroutine. An equivalent mechanism is implemented for
JScript.
[0292] Eventing Subsystem Terminology
[0293] UCP--User control point. Any piece of software that searches
for devices and controls them.
[0294] CD--controlled device. A hardware or software device that
announces its availability thru SSDP and allows control by
UCPs.
[0295] Subscriber--A UCP who wishes to be notified of event
changes.
[0296] Notifying Resource (or simply "Resource")--For the purposes
of this document, this will always be a service contained within a
UPnP CD 106.
[0297] Event Source--a service that provides events. UPnP services
are event sources. All notifying resources are event sources and
vice versa.
[0298] Event--message generated when a change in a resource's state
occurs.
[0299] Property--a single entry in the service's state table whose
DefaultValue can change. Properties and events always have a one to
one correspondence.
[0300] Subscribing to Resources
[0301] Integrating with the UPnP API
[0302] The UPnP API 410 exposes several interfaces with which a
consumer can find and enumerate devices, control services, and get
properties on devices and services. To allow the integration of
events into this model, we add a new property to the IUPnPService
interface called EventHandler. When this property is set, it tells
the Service object 612 that its client is interested in receiving
notifications for that service. The SSDP API RegisterNotification(
) API is called when the Service object is created so that it can
maintain a local copy of the DST for that service. The Service
object knows the URL of the service and therefore it can provide
this as a parameter to RegisterNotification( ).
RegisterNotification( ) is also provided a callback function which
is a static member of the Service object class. This function will
be invoked for each and every notification sent by that particular
UPnP service.
[0303] The Notification Callback
[0304] The Service object 612 includes a static member function
called EventNotifyCallback( ) which is invoked for each
notification sent by the UPnP service. The callback is passed the
entire HTTP message contents in a structure which is a parameter to
the function. The prototype looks like this:
19 static VOID CUPnPService::EventNotifyCallback-
(SSDP_CALLBACK_TYPE ssdpType, SSDP_MESSAGE *pssdpMsg, LPVOID
pcontext);
[0305] The ssdpType parameter should always be SSDP_PROPCHANGE. The
pssdpMsg parameter contains the relevant information about the
event. The key piece of information is the body of the XML message.
The body contains information about what property changed, what its
new value is and what type it is, among other information. The
pContext parameter will always be the this pointer of the Service
object. This allows the code to call a method to fire the event to
the UCP. The callback will parse the XML body using the XML DOM
services. Property changes are iterated and the local DST is
updated to reflect these changes. After this processing is done, an
event notification may be fired for each property that was changed
to the owner of the subscription if one exists. Depending on what
environment the owner is written in (C++ or script, etc . . . ), a
different mechanism for firing the event may be employed.
[0306] A special case for this process is the very first
notification received after a subscription is established. This
notification contains the entire set of properties and their values
and is used to locally sync up the DST. Events will not be fired to
clients of the UPnP API in this case.
[0307] Firing Notifications
[0308] When the EventNotifyCallback( ) function is called, the
local copy of the DST for the service is updated. After this, an
event needs to be fired if a subscriber exists. A subscriber exists
if the put_EventHandler( ) method was called, either from VBScript,
C++ code, or another source. To abstract away this complexity, a
new interface called IUPnPEvents is needed.
[0309] This interface currently has one method called NotifyEvent(
) which takes several parameters (TBS). When put_EventHandler( )
function is called, its argument is an IUnknown. This pointer is
Queryinterface'd( ) for IDispatch first, and if it succeeds, then
IDispatch::Invoke( ) is called with DISPID 0 to invoke the default
method. This allows VBScript 602 to be called. If that fails,
however, it is Queried for IUPnPEvents, and if that succeeds, the
NotifyEvent( ) method is called with the same parameters as for
Invoke( ). The handles C++ UCPs effectively.
[0310] Subscribing with C++
[0311] To subscribe to a UPnP service from C++, a UCP instantiates
a UPnP service object, issues Queryinterface( ) to it for
IUPnPEvents, and calls the IUPnPEvents::SetEventCallback( )
function. This function takes 2 parameters, a callback function
pointer and a context pointer.
[0312] Subscribing with VBScript
[0313] To subscribe to a UPnP service's events, all that needs to
be done by a script 602 is to create a function or subroutine as a
handler function and set the pointer of that function to the
EventHandler property of the Service object. Now, anytime an event
is fired, this VBScript function or subroutine will be called. In
VBScript, this is written as the following:
20 Dim UPnPAPI Set UPnPAPI = CreateObject("UPnPAPI.1") Devices =
UPnPAPI.FindDevices( . . . ) For each device in Devices For each
service In devices.services If service.dcpi = "clock.v1"
Service.EventHandler = GetRef ("clock_PropertyChanged") End if Next
service Next device Sub clock_PropertyChanged(prop, value) MsgBox
"The time has changed. It is now " & value & "." End
Sub
[0314] In this example, the script enumerates all devices, looking
for any device that supports the "Clock" interface. When it finds a
device that supports that interface, it enumerates that device's
services looking for the one that has the "clock.v1" interface.
Once it finds that service, it sets that service's EventHandler
property to the VBScript subroutine called "clock_PropertyChanged".
This name is arbitrary.
[0315] Sending and Receiving Notifications
[0316] GENA Client API
[0317] GENA clients are actually UPnP services. A GENA client
creates a new event source when it is initialized. The GENA client
API 620 facilitates this. It also provides a way for GENA clients
to send their notification messages. It is also important to note
that the HTTP server that lives on the UPnP device is also a client
of this API. The GENA client API consists of the following
functions:
[0318] RegisterUpnpEventSource( )
[0319] The RegisterUpnpEventSource( ) API gives a GENA client the
ability to register itself as an event source. The prototype is as
follows:
21 BOOL RegisterUpnpEventSource( LPTSTR szRequestUri, DWORD cProps,
UPNP_PROPERTY *rgProps );
[0320] Parameters: szRequestUri [in] an arbitrary Request-Uri that
SUBSCRIBE requests will be sent to. When a SUBSCRIBE request
arrives at the given URI, it is acknowledged and the subscriber is
added to the list of notification recipients. Note that this URI
should match the URI provided in the description for this service.
CProps [in] the number of properties that this event source
provides. RgProps [in] Array of UPNP_PROPERTY structures which
contain information about each property. The property information
is derived from the DST for the event source.
[0321] Return Value: The function returns a TRUE if successful. If
the given URL has already been registered as an event source, the
return value is FALSE and GetLastError( ) returns
ERROR_ALREADY_EXISTS.
[0322] Notes: The initial state of the event source needs to be
given to the API so that it can effectively maintain the up-to-date
state of the event source.
[0323] DeRegisterUpnpEventSource( )
[0324] The DeRegisterUpnpEventSource( ) API gives a GENA client the
ability to deregister itself as an event source. The prototype is
as follows:
22 VOID DeRegisterUpnpEventSource( LPCTSTR szRequestUri );
[0325] Parameters: szRequestUri [in] an arbitrary Request-Uri that
SUBSCRIBE requests will be sent to. When a SUBSCRIBE request
arrives at the given URI, it is acknowledged and the subscriber is
added to the list of notification recipients. Note that this URI
should match the URI provided in the description for this
service.
[0326] UPnP Property
23 typedef struct _UPNP_PROPERTY { LPTSTR szName; LPTSTR szValue;
LPTSTR szType; } UPNP_PROPERTY;
[0327] Where szname is the name of the property, szValue is the
current value of property, and szType is the type of property
(string, integer, etc . . . ).
[0328] SubmitUpnpPropertyEvent( )
[0329] The SubmitUpnpPropertyEvent( ) API allows the GENA client to
submit a UPnP property change event to be sent to subscribers as a
notification. The prototype is as follows:
24 BOOL SubmitUpnpPropertyEvent( LPCTSTR szRequestUri, DWORD
dwFlags, DWORD cProps, UPNP_PROPERTY *rgProps );
[0330] Parameters: "szRequestUri [in]" identifies the event source
to which this event belongs. This is the same Request-Uri passed to
RegisterUpnpEventSource( ). "DwFlags [in]" is unused. "CProps [in]"
is the number of events that are being submitted. "RgProps [in]" is
an array of UPNP_PROPERTY structures which contain information
about each event.
[0331] Return Value: If the function fails, the return value is
FALSE. The get extended error information, call the GetLastErroro
function.
[0332] Notes: When a series of properties is submitted for event
notification, the local version of the property state for the given
event source is updated with the list of properties passed in.
SubmitUpnpPropertyEvent( ) calls SubmitEvent( ) after it has
generated an XML body.
[0333] SubmitEvent( )
[0334] The SubmitEventO API allows the GENA client to submit an
unstructured event to be sent to subscribers as a notification. The
prototype is as follows:
25 BOOL SubmitEvent( LPCTSTR szRequestUri, DWORD dwFlags, LPCTSTR
szHeaders, LPCTSTR szEventBody );
[0335] Parameters: SzRequestUri [in] identifies the event source to
which this event belongs. This is the same Request-Uri passed to
RegisterUpnpEventSource( ). DwFlags [in] Unused. SzHeaders [in]
null-terminated text string containing the headers for the event,
each separated by CRLF. SzEventBody [in] null-terminated text
string containing the body of the event message
[0336] Return Value: If the function fails, the return value is
FALSE. The get extended error information, call the GetLastError( )
function.
[0337] Notes: If no subscribers exist, the function does nothing.
If one or more subscribers exist, a message is sent to each
subscriber. SubmitEvent( ) will always send to all subscribers.
[0338] UPnP Controlled Device Architecture
[0339] In UPnP, every UPnP service 210-211 that supports property
change event notifications is to be a GENA client. Therefore, when
the service is initialized, it must register itself as a GENA event
source. It will do this with the RegisterUpnpEventSource( ) API.
This returns a handle which can be used in subsequent APIs.
[0340] RegisterUpnpEventSource( ) takes a URL and an array of
properties as parameters. Inside the API, an entry in an array of
structures is initialized and the index is returned as the handle.
The structure contains the source URL as one of the members. A
second member of the structure, an array of destination URLs, is
left uninitialized. This is filled in each time as subscriber is
added for that event source. Another member of the structure is the
list of properties that this event source provides. This is
effectively a cached copy of the DST for the event source. As
events are submitted, the local properties are updated.
[0341] When SubmitUpnpPropertyEvent( ) is called, each property
submitted replaces the corresponding property already maintained by
the API. If no subscribers exist, the request to submit an event is
ignored. If one or more subscribers exist, their callback URLs are
looked up in the list of subscribers for the given event source and
a NOTIFY message is constructed and sent to each URL, one at a
time, in order of subscription.
[0342] If an event is submitted and no response is received (or a
CD-side error occurs), the CD continues to attempt to send to the
UCP. If the subscription timeout expires, then the subscription is
removed. If the UCP becomes available again, it will re-subscribe
because it will notice the sequence numbers are not contiguous.
[0343] When an HTTP server 626 receives a SUBSCRIBE message, it
passes it along to a function which parses the message for the
necessary information. The Request-URI identifies the service that
is to be subscribed to. The callback URL is obtained from the
"Callback" header. Since the Callback header can contain multiple
URLs, it picks the first "http://" URL it finds. It then adds the
subscriber to the list of subscribers for this event source. A
unique subscription identifier is constructed which it will send
back to the subscriber in the HTTP response to the SUBSCRIBE
request.
[0344] If no event source matches the Request-URI from the
subscription message, the HTTP server should return "404 Not
Found".
[0345] When a subscription is added, the local copy of the DST is
sent as a NOTIFY message. This special NOTIFY message contains
sequence number 0 which informs the UCP that this is an initial
state population event and not a notification where every event has
changed.
[0346] When a CD receives an UNSUBSCRIBE message, it checks the
"SID" header to obtain the subscription identifier. It looks up the
subscriber ID in the list of subscribers for that event source and
removes the destination URL entry associated with it.
[0347] GENA Server API
[0348] GENA servers 630 are generally going to be UPnP UCPs. A GENA
server is anything that receives and processes NOTIFY messages to
handle notifications from resources and sends SUBSCRIBE and
UNSUBSCRIBE messages to receive notifications from resources. These
APIs leverage the already existing SSDP APIs. The following are the
changes to the APIs:
[0349] RegisterNotification( )
[0350] The RegisterNotification( ) allows a UPnP UCP to request
notification when an event occurs for a given UPnP service. The
prototype is as follows:
26 HANDLE RegisterNotification( NOTIFY_TYPE nt, // SSDP_ALIVE
.vertline. SSDP_PROPCHANGE .vertline. ?? LPTSTR szResourceType, //
based on NOTIFY_TYPE, unused if // SSDP_PROPCHANGE is used. LPTSTR
szEventUrl, ServiceCallbackFunc fnCallback, void *pContext );
[0351] Parameters: Nt [in] An enumeration that determines the type
of notification requested. The values are: SSDP_ALIVE--a service
has become available, and SSDP_PROPCHANGE--a property has changed
on the service. SzResourceType [in] A null-terminated string
specifying the resource type desired. For SSDP_ALIVE, this is the
service type, for SSDP_PROPCHANGE this is unused. SzEventUrl [in] A
null-terminated string specifying the URL that a subscription
request should be sent to. FnCallback [in] A pointer to a function
that will be called each time a notification is received. The
function pointer is defined in the SSDP spec. PContext [in] This
parameter is included as a parameter when invoking the
client-supplied callback function.
[0352] Return Value: If the function succeeds, the return value is
a handle used in a subsequent call to the
DeregisterEventNotification( ) function. If the function fails, the
return value is INVALID_HANDLE_VALUE error code. To get extended
error information, call GetLastError.
[0353] ServiceCallbackFunc
27 typedef enum _SSDP_CALLBACK_TYPE { SSDP_FOUND = 0, SSDP_ALIVE =
1, SSDP_BYEBYE = 2, SSDP_DONE = 3, SSDP_PROPCHANGE = 4, }
SSDP_CALLBACK_TYPE, * PSSDP_CALLBACK_TYPE;
[0354] UPnP UCP Architecture
[0355] When a UPnP UCP wishes to subscribe to notifications for a
particular UPnP service, it calls the RegisterNotification( ) API.
It passes to this API a notification type that identifies the type
of notification being requested, a URL to which a subscription
should be sent, and a callback function and context for use when
the notification is received.
[0356] RegisterNotification( ) will compose a SUBSCRIBE message,
using the data passed in, and send that to the URL specified by the
caller. The Callback header of the SUBSCRIBE message will be
composed on the fly, as an arbitrary URL for notifications to be
sent to for this subscription. This callback URL will likely be a
constant since the server API will always know how to handle
requests sent to this URL. It will then send the SUBSCRIBE message
and await a response.
[0357] RegisterNotification( ) in the SSDP API does not currently
send HTTP requests, but it can be modified to do so. It also needs
to await a response which it will also be modified to do so.
[0358] When the response is received, the Subscription-ID header
contains a SID which is associated with the callback function
specified by the caller.
[0359] Immediately after the response is received, the UCP should
expect an initial NOTIFY message that contains the complete set of
properties maintained by the CD. This becomes the local cached DST
on the UCP side. From this point on, all modifications to the table
are made via NOTIFY messages. This initial NOTIFY message will have
sequence number 0 that indicates it is an initial property set and
not an update. The UCP can use this information in any way it sees
fit. This ensures the UCP's state table is always in sync with the
one on the CD.
[0360] When a message is received by the HTTP server on the UPnP
UCP, it is passed to a function which determines the method name
and Request-URI. If this is a NOTIFY message, the headers are
parsed and packaged up into a structure. The callback function that
was specified to RegisterNotification( ) is called with that
structure as one of the parameters. UCPs who implement the callback
function can find the headers and body of the NOTIFY message and do
additional processing based on the notification type.
[0361] This all requires that the SSDP HTTP server listen on a TCP
socket in addition to the UDP multicast port it already listens to.
However, once a NOTIFY message is received, it is processed in the
same way regardless of from which connection it originated.
[0362] Handling Failures
[0363] The following are subscription/notification failures that
can occur and their solutions:
[0364] Leaked Subscriptions
[0365] To protect against subscriptions that exist on the
controlled device, but no longer on the UCP, we institute the
timeout feature of GENA subscriptions. The scenario is this: A UCP
subscribes to a CD, then the UCP reboots. Meanwhile, the CD is
still trying to send notifications to that UCP. If the UCP never
comes back, the subscription would be leaked because the UCP never
told the CD that it was going away. So to correct this, each
subscription request includes an arbitrary timeout value which
indicates to the CD that the UCP will be re-subscribing every n
seconds indicated in the timeout header of the subscription
request. If the timeout expires on the CD, the subscription is
removed. The UCP is required to re-subscribe before the timeout
period has elapsed. If it fails to do so, the subscription will be
terminated by the CD.
[0366] Some time before the timeout expires on the UCP, a
re-subscribe message should be sent. The re-subscribe message is
similar to the subscribe message, but it does not contain an NT or
Callback header. If the UCP is unable to re-subscribe within the
timeout period, the subscription will be terminated by the CD. If
the UCP sends a re-subscribe after the CD has terminated the
subscription, the CD will return "412 Precondition Failed".
[0367] Reboot of a Controlled Device
[0368] If a controlled device reboots, information about all of its
subscribers would be lost. To prevent this, the subscriber
information will be persisted across reboots of the device. Because
the subscription info contains a timeout member, the absolute
expiration time will be used when the subscription information is
persisted. That way, when the device comes back up, it can check
the timeout for each subscriber and if that time has passed, the
subscription will be removed.
[0369] Network Error Sending Event Notifications
[0370] If a controlled device receives an error sending an event
notification to a subscriber, it will NOT cease to send
notifications. It will continue to send notifications and receive
errors until the subscription expires. The problem for the UCP is
that it will have missed a number of event notifications and so its
state table will be out of sync. To correct this, each event
notification message will contain a 32-bit sequence number that
starts at 0 and increments for each message sent to a subscriber.
If a subscriber receives a notification with a sequence number that
is not exactly one more than the previous notification, it will
know that it has lost events and will ignore all future
notifications until it receives one with sequence number 0 again.
Events with sequence number 0 indicate that the event is an
"initial state" event.
[0371] Once it realizes that is has lost one or more events, the
UCP will send an UNSUBSCRIBE message, followed by a SUBSCRIBE
message. This is not the same as a re-subscription because
re-subscriptions do not cause the CD to start the sequence over at
0. In this case, the active unsubscribe/subscribe will cause the CD
to restart the sequence at 0 and send the entire state table with
the first notification message.
[0372] The SUBSCRIBE Message
[0373] When a UPnP UCP wishes to subscribe to event notifications
for a UPnP service 210-211, it will form a SUBSCRIBE message of the
following format:
[0374] SUBSCRIBE service1 HTTP/1.1
[0375] Host: vcr.local:200
[0376] NT: upnp:event
[0377] Callback: <http://danielwe/upnp:923>
[0378] Timeout: Second-600
[0379] The response is as follows::
[0380] HTTP/1.1 200 O.K.
[0381] SID: uuid:kj9d4fae-7dec-11d0-a765-00a0c91e6bf6
[0382] Timeout: Second-600
[0383] This example of a GENA SUBSCRIBE request and response
demonstrates a subscription to event notifications for "service1."
The host is "vcr.local." All notifications for this service will be
sent to the callback URL http://danielwe/upnp:923. In the response,
the "Subscription-ID" header provides the subscriber with an
identifier to use when it wants to unsubscribe to this resource.
The "Timeout" header indicates that the subscriber will send a
re-subscription request before 10 minutes have elapsed. If the
device does not receive this request within that period of time, it
will remove the subscription.
[0384] The Re-SUBSCRIBE Message
[0385] When a UPnP UCP wishes to re-subscribe to event
notifications for a UPnP service, it will form a SUBSCRIBE message
of the following format:
[0386] SUBSCRIBE service1 HTTP/1.1
[0387] Host: vcr.local:200
[0388] SID: uuid:kj9d4fae-7dec-11d0-a765-00a0c91e6bf6
[0389] Timeout: Second-600
[0390] The response would be as follows::
[0391] HTTP/1.1 200 O.K.
[0392] SID: uuid:kj9d4fae-7dec-11d0-a765-00a0c91e6bf6
[0393] Timeout: Second-600
[0394] Note that the NT and Callback headers are absent, but the
SID header exists. This tells the CD 106 which subscription is
being renewed and restarts the timeout. When the CD receives this
message, it will persist the subscriptions to disk (or other
persistent data storage medium), updating the absolute timeout
based on the current time and a new timeout sent by the UCP (if it
was different).
[0395] The NOTIFY Message
[0396] When a resource wishes to send an event notification, it
will form a NOTIFY message of the following format:
[0397] NOTIFY upnp HTTP/1.1
[0398] Host: danielwe:923
[0399] NT: upnp:event
[0400] NTS: upnp:propertychanged
[0401] SID: uuid:kj9d4fae-7dec-11d0-a765-00a0c91e6bf6
[0402] Seq: 123
[0403] Content-Length: xxx
[0404] Content-Type: text/xml
[0405] <event XML schema>
[0406] The response is as follows::
[0407] HTTP/1.1 200 O.K.
[0408] This example of a GENA NOTIFY request and response
demonstrates that a "upnp:propertychanged" event is being sent to
http://danielwe/upnp:923. The USN header identifies "vcr.service1"
as the event source. The XML contains the property name, value, and
type. The "Seq" header indicates the sequence number of the
notification. Sequence number 0 indicates the initial state update
for the subscriber.
[0409] Property Change Event XML Schema
[0410] A UPnP property change event will be of the following
form:
28 <U:propertyset xmlns:U="upnp">
<U:propcount>2</U:propcount> <U:property>
<U:foo> <U:type>string</U:type> goodbye
</U:foo> </U:property> <U:property> <U:bar>
<U:type>integer</U:type> 27 </U:bar>
</U:property> </U:propertyset>
[0411] Here, a property named "foo" is of type "string" and has a
value of "goodbye" and a property named "bar" has a type of
"integer" and has a value of 27. The XML will be contains a list of
multiple properties that have changed, along with a count to make
it easy to determine this.
[0412] The UNSUBSCRIBE Message
[0413] When a UPnP UCP wishes to unsubscribe to event notifications
for a UPnP service, it will form an UNSUBSCRIBE message of the
following format:
[0414] UNSUBSCRIBE service1 HTTP/1.1
[0415] Host: vcr.local:200
[0416] SID: uuid:kj9d4fae-7dec-11d0-a765-00a0c91e6bf6
[0417] The response would be as follows::
[0418] HTTP/1.1 200 O.k.
[0419] This example of a GENA UNSUBSCRIBE request and response
demonstrates that the UCP is no longer interested in receiving
event notifications from http://vcr.local/service1:200.
[0420] Step By Step: UCP to CD & Back
[0421] This section will take a step by step approach to what
happens on both sides (UCP & CD) of an event notification. The
description starts at the initialization of a UPnP device. FIG. 23
illustrates the subscription, notification, and unsubscription
process.
[0422] 1. A UPnP device called "vcr" initializes.
[0423] a. It sets itself up to be an HTTP server by doing the
following:
[0424] i. It binds to a TCP socket using its IP address and an
arbitrary port number. This address/port pair will be referenced by
all incoming URL requests.
[0425] ii. It listens for incoming connection requests on that
socket and sets itself up to accept any incoming connections.
[0426] b. It sets itself up to be an HTTP client by doing the
following:
[0427] i. Calls InternetOpeno to get a handle to the internet
session
[0428] c. For each service it exposes, it does the following:
[0429] i. It calls the SSDP API RegisterUpnpEventSource( ) to let
the SSDP server know that it will be accepting subscriptions and
sending event notifications. At this point, it has no subscribers.
Note that this is called before the service has announced itself so
that it can be ready to accept subscriptions immediately.
RegisterUpnpEventSource( ) sends no network traffic on the wire. It
is a local initialization only. RegisterUpnpEventSource( ) does the
following:
[0430] 1. Adds a structure to the list of event sources containing
the following:
[0431] a. A URL to which subscribers will send subscription
requests
[0432] b. A list of destination URLs. A notification message will
be sent to each destination URL.
[0433] c. The state table for the event source. This structure
contains the property name, value, and type for each property
supported by the service.
[0434] ii. It calls the SSDP API RegisterService( ) to let the
world know that it has become available. RegisterService( ) will
send out an SSDP "alive" message on the multicast channel that will
be heard by any device running the SSDP service.
[0435] d. It starts sending events immediately, even without
subscribers. Each event submission updates the local state table.
This submission needs to be atomic with regard to adding
subscribers, so between the time the SubmitEvent( ) API is called,
and the time the local state table is updated, no subscriptions can
be added or removed.
[0436] 2. Meanwhile, a UPnP UCP initializes.
[0437] a. It initializes its HTTP server, passively listening on a
TCP port.
[0438] b. If the UCP started up before the UPnP device initialized,
it won't see any services become available. When the device finally
starts, the UCP will be notified.
[0439] c. Once the UPnP services have been announced the UCP will
be able to access one or more of them.
[0440] d. The UCP drives the UPnP API to instantiate a UPnP Service
Object.
[0441] e. The UPnP Service Object does the following when it is
instantiated:
[0442] i. It obtains the event subscription URL from the
description for that service.
[0443] ii. It calls the SSDP API RegisterNotification( ) specifying
SSDP_PROPCHANGE as the event type, the event subscription URL, a
callback function pointer (which is a static member function of the
class), and a context pointer (which is the "this" pointer of the
class). RegisterNotificationo does the following:
[0444] 1. It makes an LRPC call to the SSDP service. The rest
happens on the service side.
[0445] 2. If this is the first time it is called for
SSDP_PROPCHANGE notifications, RegisterNotification( ) will call
InternetOpen( ) to get a handle to an internet session. This handle
is shared among all local UPnP UCPs.
[0446] 3. It calls InternetConnecto passing the server name given
in the URL it was passed.
[0447] 4. It calls HttpOpenRequest( ) passing in the rest of the
URL it was passed.
[0448] 5. The handles returned by these functions are saved with
the structure that maintains the subscription.
[0449] 6. It composes a SUBSCRIBE message, using the data passed
in, by calling HttpAddRequestHeaders( ). It adds the "NT",
"Callback", and "Timeout" headers. The Callback header of the
SUBSCRIBE message will be composed on the fly, as an arbitrary URL
for notifications to be sent to for this subscription. The server
name is the local IP address, and the port is the same one referred
to by step 2a above.
[0450] 7. It calls HttpSendRequest( ) to send the request to the
CD. This is a synchronous function that will return when the
request has been responded to by the CD.
[0451] 8. It calls HttpQueryInfo( . . . , HTTP_QUERY_CUSTOM, . . .
) to get the "Subscription-Id" header. The resulting SID will be
stored with the subscription structure.
[0452] 9. It calls HttpQueryInfo( . . . , HTTP_QUERY_CUSTOM, . . .
) to get the "Timeout" header. The resulting timeout value will be
stored with the subscription structure.
[0453] 10. A timer is started for re-subscription based on the
timeout value returned in the response. When the timer goes off,
the re-subscription will be sent.
[0454] 11. The SID, callback function pointer, and timeout values
are stored in a structure that maintains the list of local
subscriptions.
[0455] 3. Back on the UPnP CD, the subscription request is received
by the HTTP server. The following occurs:
[0456] a. The request is parsed into URI, NT, Callback, and Timeout
fields.
[0457] b. The NT field must match "upnp:event". If it doesn't, the
CD responds with "412 Precondition Failed."
[0458] c. The URI identifies the event source. The URI is converted
into a URL and matched with the list of event sources registered on
the CD. If no match is found, the CD responds with "404 Not
Found".
[0459] d. If a match is found, the following occurs:
[0460] i. The Callback URL is added to a list of subscriber
URLs.
[0461] ii. The Timeout value is processed and an absolute time is
stored with the event source data. If this time expires and a
re-subscribe message has not been received, the subscription is
removed.
[0462] iii. A new SID is created, and stored with the subscriber in
the event source.
[0463] iv. A sequence number is initialized to 0.
[0464] v. A subscription response is composed, including an echo of
the Timeout header and the SID just created.
[0465] vi. The response is sent.
[0466] vii. If the response is sent successfully, the list of event
sources is persisted to disk for recovery purposes.
[0467] viii. A timer is started using the same timeout value as the
header echoed to the UCP. When this timer elapses, the subscription
is removed. If the CD receives a re-subscribe request, this timer
will be reset. In an ideal world, the timer will never elapse.
[0468] ix. An initial event notification is sent to initialize the
UCP's state table. The following describes that process:
[0469] 1. InternetOpen( ) is called if an existing internet session
handle does not exist.
[0470] 2. InternetConnect( ) is called, passing the server name
specified in the callback URL for this subscription.
[0471] 3. HttpOpenRequest( ) is called, passing in the rest of the
callback URL.
[0472] 4. A NOTIFY message is composed, using the data passed in,
by calling HttpAddRequestHeaders( ). It adds the "NT", "NTS",
"SID", "Seq", "Content-Length", and "Content-Type" headers.
[0473] a. The NT header will always be "upnp:event". The NTS header
will always be "UPnP:propertychange".
[0474] b. The SID header contains the SID stored in the event
source structure
[0475] c. The Seq header will always be 0.
[0476] d. The Content-Length header will be the number of bytes in
the XML body.
[0477] e. The Content-Type header will always be "text/xml".
[0478] f. The body of the message is composed from the list of
properties stored within the event source structure:
[0479] i. Write the <propertyset> opening tag.
[0480] ii. Write the <propcount> n</propcount> tag.
Where n is the number of total properties.
[0481] iii. For each property:
[0482] 1. Write the <property> opening tag.
[0483] 2. Write the <prop> opening tag, where prop is the
name of the property.
[0484] 3. Write the <type> type </type> tag, where type
is the stringized type name of the property type.
[0485] 4. Write the property value.
[0486] 5. Write the <Iprop> closing tag.
[0487] 6. Write the </property> closing tag
[0488] iv. Write the </propertyset> closing tag
[0489] 5. It calls HttpSendRequestEx( ), then InternetWriteFile( ),
then HttpEndRequest( ) to send the request to the CD.
[0490] 6. The response is ignored except for debugging
purposes.
[0491] 4. The UPnP CD now is ready to send an event notification.
It does this by calling the SubmitUpnpPropertyEvent( ) API. The
following occurs inside that API:
[0492] a. The event source handle is converted to an event source
structure.
[0493] b. The properties that have changed as a result of the event
are passed into the function and updated in the local list of
properties stored with the event source.
[0494] c. For each subscriber, the following occurs:
[0495] i. lnternetConnecto is called, passing the server name
specified in the callback URL for this subscription.
[0496] ii. HttpOpenRequesto is called, passing in the rest of the
callback URL.
[0497] iii. A NOTIFY message is composed, using the data passed in,
by calling HttpAddRequestHeaders( ). It adds the "NT", "NTS",
"SID", "Seq", "Content-Length", and "Content-Type" headers.
[0498] 1. The NT header will always be "upnp:event". The NTS header
will always be "UPnP:propertychange".
[0499] 2. The SID header contains the SID stored in the event
source structure
[0500] 3. The sequence number for the event source is incremented
and the Seq header is created with this value.
[0501] 4. The Content-Length header will be the number of bytes in
the XML body.
[0502] 5. The Content-Type header will always be "text/xml".
[0503] 6. The body of the message is composed from the list of
properties stored within the event source structure:
[0504] a. Write the <propertyset> opening tag.
[0505] b. Write the <propcount> n</propcount> tag.
Where n is the number of total properties.
[0506] c. For each property that has been submitted:
[0507] i. Write the <property> opening tag.
[0508] ii. Write the <prop> opening tag, where prop is the
name of the property.
[0509] iii. Write the <type> type </type> tag, where
type is the stringized type name of the property type.
[0510] iv. Write the property value.
[0511] v. Write the </prop> closing tag.
[0512] vi. Write the </property> closing tag
[0513] d. Write the </propertyset> closing tag
[0514] iv. SubmitEvento is called, passing the event source handle,
the handle to the headers created by 4c(i) thru 4c(iii) above, and
the body created in step 4c(iii)6. SubmitEvent( ) does the
following:
[0515] 1. It calls HttpSendRequestEx( ), then InternetWriteFile( )
on the body, then HttpEndRequest( ) to send the request to the
CD.
[0516] 2. The response is ignored except for debugging
purposes.
[0517] 5. The UPnP UCP receives the notification message. The
message is processed as follows:
[0518] a. The HTTP server receives a NOTIFY message with a
Request-URI and several other headers.
[0519] b. The NOTIFY message is parsed, looking at the "NT" header
first. If this header contains "upnp:event", then the message is
further processed for event notifications as follows:
[0520] i. The message is parsed for the NTS header. If that
contains "upnp:propertychanged", then the message is parsed further
as follows:
[0521] 1. The message is parsed for the SID header. The SID
indicates to the UPnP control point which subscription this message
applies to.
[0522] 2. The message is parsed for the "Seq" header. If this
header contains a value of 0, the UCP knows this is an initial
state populate request. If the local sequence number is exactly one
less than the Seq header, the local sequence number is updated
(incremented), and the message is processed further.
[0523] 3. The Request-URI can be ignored, since the HTTP server
knows all NOTIFY messages with an NT header of "upnp:event" are
sent to the same Request-URI.
[0524] 4. If the Seq header contains a number that is not exactly
one more than the local sequence number, the UCP knows it has
missed an event. In this state, it needs to unsubscribe and
re-subscribe to the event source in order to re-sync its state.
[0525] 5. The SID is matched against the list of subscriptions
maintained on the UCP. When the SID is matched, its associated
callback function is invoked.
[0526] 6. The callback function is passed an SSDP_MESSAGE structure
which contains all the relevant headers and the body of the XML
message received.
[0527] 7. The callback function is implemented by the UPnP API, as
a static member of the Service object. When this function is
called, the following occurs:
[0528] a. The body of the message is parsed using the XML DOM
services.
[0529] b. As properties are enumerated, their values are stored in
the local state table for the service.
[0530] c. An event is fired to all high-level clients of the UPnP
API. This event contains the list of properties that have changed
and their new values.
[0531] 6. The re-subscription timer for one of the UCPs
subscriptions expires. The following occurs:
[0532] a. A re-subscribe message is composed. This message is very
similar to a subscribe message except in doesn't include an NT or
Callback header, but it does have a SID header.
[0533] b. The request is sent to the CD.
[0534] c. The response contains the new timeout value.
[0535] d. The timer is reset with this timeout.
[0536] UCP State Synchronization Models
[0537] CD-Initiated NeedsSync Method
[0538] This method begins with the CD sending its initial state to
the subscriber the first time an event is submitted by the service.
UCPs will subscribe to the service first, then receive
notifications for events as they occur. The first event will happen
to be the initial state of the service. The UCP state table will
always be in sync with this method.
[0539] When the CD sends a notification to a subscriber and
receives an error. In this case, it marks the subscriber as
"NeedsSync" and the next time an event is submitted, all events are
sent to the subscriber. The problem with this is that the API needs
to keep track of which subscribers need syncing and which ones
don't. The client of this API (the UPnP service) would need to send
separate messages to each subscriber and know which ones needed all
events and which ones just wanted the ones that changed.
[0540] UCP-Initiated sync
[0541] This method states that the UCP should subscribe to event
notifications, then call a function that obtained the state from
the service. This means that any events that were received in the
meantime would need to be matched against the incoming set of
events and replaced if they were older. This method leads to
synchronization issues where the UCP may receive events that are
newer but when it queries for the state, it gets an older view of
the table. This requires using sequence numbers to determine which
information is newer. If the view of the table received by the
query is too old, it has to be discarded. Alternatively, the
properties that were not received by event notification would not
be overwritten, but all other properties would be. Using sequence
numbers make this more complicated.
[0542] CD-Initiated sync
[0543] This preferred method takes a simpler approach. Any time the
UCP subscribes to a service, the service will immediately
afterwards, send the entire contents of the state table with the
first notification. This precludes the UCP from making a query for
the state table. Subsequent events update the local state table on
the UCP. If the connection is lost, the UCP will lose its
subscription. If the UCP realizes it has not received an event
after a certain amount of time has elapsed, it will re-subscribe.
At that point, the CD will re-send the entire state table again,
and the UCP is ensured to be up to date.
[0544] Exemplary Computer Hardware
[0545] FIG. 24 and the following discussion are intended to provide
a brief, general description of a suitable computer which may be
used in the above described UPnP device control model. This
conventional computer 820 (such as personal computers, laptops,
palmtops or handheld-PCs, set-tops, servers, mainframes, and other
variety computers) includes a processing unit 821, a system memory
822, and a system bus 823 that couples various system components
including the system memory to the processing unit 821. The
processing unit may be any of various commercially available
processors, including Intel x86, Pentium and compatible
microprocessors from Intel and others, including Cyrix, AMD and
Nexgen; Alpha from Digital; MIPS from MIPS Technology, NEC, IDT,
Siemens, and others; and the PowerPC from IBM and Motorola. Dual
microprocessors and other multi-processor architectures also can be
used as the processing unit 821.
[0546] The system bus may be any of several types of bus structure
including a memory bus or memory controller, a peripheral bus, and
a local bus using any of a variety of conventional bus
architectures such as PCI, VESA, AGP, Microchannel, ISA and EISA,
to name a few. The system memory includes read only memory (ROM)
824 and random access memory (RAM) 825. A basic input/output system
(BIOS), containing the basic routines that help to transfer
information between elements within the computer 820, such as
during start-up, is stored in ROM 824.
[0547] The computer 820 further includes a hard disk drive 827, a
magnetic disk drive 828, e.g., to read from or write to a removable
disk 829, and an optical disk drive 830, e.g., for reading a CD-ROM
disk 831 or to read from or write to other optical media. The hard
disk drive 827, magnetic disk drive 828, and optical disk drive 830
are connected to the system bus 823 by a hard disk drive interface
832, a magnetic disk drive interface 833, and an optical drive
interface 834, respectively. The drives and their associated
computer-readable media provide nonvolatile storage of data, data
structures, computer-executable instructions, etc. for the computer
820. Although the description of computer-readable media above
refers to a hard disk, a removable magnetic disk and a CD, it
should be appreciated by those skilled in the art that other types
of media which are readable by a computer, such as magnetic
cassettes, flash memory cards, digital video disks, Bernoulli
cartridges, and the like, may also be used in the exemplary
operating environment.
[0548] A number of program modules may be stored in the drives and
RAM 825, including an operating system 835, one or more application
programs 836, other program modules 837, and program data 838.
[0549] A user may enter commands and information into the computer
820 through a keyboard 840 and pointing device, such as a mouse
842. Other input devices (not shown) may include a microphone,
joystick, game pad, satellite dish, scanner, or the like. These and
other input devices are often connected to the processing unit 821
through a serial port interface 846 that is coupled to the system
bus, but may be connected by other interfaces, such as a parallel
port, game port or a universal serial bus (USB). A monitor 847 or
other type of display device is also connected to the system bus
823 via an interface, such as a video adapter 848. In addition to
the monitor, computers typically include other peripheral output
devices (not shown), such as speakers and printers.
[0550] The computer 820 operates in a networked environment using
logical connections to one or more remote computers, such as a
remote computer 849. The remote computer 849 may be a server, a
router, a peer device or other common network node, and typically
includes many or all of the elements described relative to the
computer 820, although only a memory storage device 850 has been
illustrated in FIG. 24. The logical connections depicted in FIG. 24
include a local area network (LAN) 851 and a wide area network
(WAN) 852. Such networking environments are commonplace in offices,
enterprise-wide computer networks, intranets and the Internet.
[0551] When used in a LAN networking environment, the computer 820
is connected to the local network 851 through a network interface
or adapter 853. When used in a WAN networking environment, the
computer 820 typically includes a modem 854 or other means for
establishing communications (e.g., via the LAN 851 and a gateway or
proxy server 855) over the wide area network 852, such as the
Internet. The modem 854, which may be internal or external, is
connected to the system bus 823 via the serial port interface 846.
In a networked environment, program modules depicted relative to
the computer 820, or portions thereof, may be stored in the remote
memory storage device. It will be appreciated that the network
connections shown are exemplary and other means of establishing a
communications link between the computers may be used.
[0552] In accordance with the practices of persons skilled in the
art of computer programming, the present invention is described
below with reference to acts and symbolic representations of
operations that are performed by the computer 820, unless indicated
otherwise. Such acts and operations are sometimes referred to as
being computer-executed. It will be appreciated that the acts and
symbolically represented operations include the manipulation by the
processing unit 821 of electrical signals representing data bits
which causes a resulting transformation or reduction of the
electrical signal representation, and the maintenance of data bits
at memory locations in the memory system (including the system
memory 822, hard drive 827, floppy disks 829, and CD-ROM 831) to
thereby reconfigure or otherwise alter the computer system's
operation, as well as other processing of signals. The memory
locations where data bits are maintained are physical locations
that have particular electrical, magnetic, or optical properties
corresponding to the data bits.
[0553] Exemplary Embedded Computing Device
[0554] FIGS. 25 and 26 are intended to provide a brief, general
description of a suitable embedded computing device 900 which may
be used in the illustrated implementation of the invention. The
embedded computing device 900 can be any variety of device
incorporating electronics to control operational functions
(operational circuitry 906), and in which computing and networking
capabilities are embedded. For example, devices in which computing
and networking functions can be embedded include communications
devices (e.g., telephones, cell phones, audio and video
conferencing systems, 2-way radios, etc.), office equipment
(printers, fax machines, copiers, dictation, etc.), audio-video
equipment (audio and video recorders and players, including
televisions, radio receivers, compact disk (CD), digital video disk
(DVD), camcorders, etc.), entertainment devices (set-top boxes,
game consoles, etc.), environment control equipment (thermostats,
heating/ventilation/air-condi- tioning equipment, light switches,
etc.), security systems, home appliances (coffee makers,
dishwashers, clothes washer/dryer), automobiles, public facilities
equipment (signs, traffic signals, etc.), manufacturing equipment,
and many others.
[0555] With reference to FIG. 25, the device 900 includes a
processing unit 902, and a memory 904 to provide embedded computing
capability. The processing unit 902 has hardware interfaces to the
operational circuitry 906 that operates devices functions. The
processing unit 902 can be a microprocessor or micro-controller,
such as are available from Intel, Motorola, IBM, and others. The
memory 904 preferably incorporates RAM and ROM to hold software and
data for basic operating code as well as for user applications.
[0556] The device 900 also includes a network adapter 908 for
connecting with a network media 910 that is interconnected with the
computer network in which the authoritative names registry
(described below) is implemented in accordance with the invention.
The network adapter 908 can be a network interface card (or chip
set integrated on a single board with the processing unit 902)
appropriate to the particular network media 910. The network media
can be any of various wired or wireless network media, including
Ethernet, IEEE 1394 (a.k.a. firewire), radio frequency (including
satellite, cell, pager, commercial signal sideband, etc.), power
line carrier (PLC), phone line, and television cable, among
others.
[0557] With reference now to FIG. 26, the embedded computing device
100 (FIG. 25) has a software architecture 120 that conforms to the
above described UPNP device control model. UPNP provides a
mechanism for the embedded computing device to operate in the
Internet, as well as networks that have no administrator and no
connection to the Internet, and hence no access to configuration
services like the Dynamic Host Configuration Protocol (DHCP). DHCP
is a mechanism for providing devices with configuration information
needed to access the Internet. The mechanism functions through the
use of a multicast request for configuration information that is
generally responded to with an IP address and DNS server location.
Additional information can only be returned in the response.
[0558] In non-configured (ad-hoc) networks, UPNP uses the AutoIP
protocol.
[0559] AutoIP is an enhancement to DHCP that allows devices to
claim IP addresses in the absence of a DHCP server or similar IP
configuration authority. IP addresses are claimed from a reserved
range that is not allowed to be transmitted on the open Internet;
thus they are only good for the local network. The embedded
computing device 100 claims an address by randomly generating an
address in the reserved range and then making an ARP request to see
if anyone else has already claimed that address. AutoIP systems
will continually check for the presence of a DHCP server so that if
one should ever come online, all the AutoIP devices will attempt to
switch their IP addresses to one provided by the DHCP server. This
allows a network to operate in isolation, be connected to the
Internet with DHCP support and then to be returned to isolation.
This type of scenario will be common in homes that use dial-up
access.
[0560] The UPNP protocol also uses Multicast DNS for addressing the
embedded computing device 900. The Internet Domain Name System
(DNS) is a mapping system that translates human readable domain
names, like microsoft.com, into their equivalent IP address. Most
corporate intranets implement an internal version of the same
technology to provide the same services. In small networks, such as
at home or in small business, DNS servers may not exist. Multicast
DNS allows DNS requests to be multicast. This allows a machine to
see requests for its own name and respond to them. Like AutoIP,
Multicast DNS is only used when a DNS server is not available. (For
more information, see B. Woodcock, Zocolo, and B. Manning,
"Multicast Discovery of DNS Services," which can be found at http:
search.ietf.org/internet-drafts/draft-manning-multicast-dns-01
txt.)
[0561] UPNP implements a peer discovery mechanism that uses the
Simple Service Discovery Protocol (SSDP) for discovery of devices
on IP networks. SSDP is based on profiles. A single identifier
specifies a profile that defines a contract between the client and
service (e.g., operational functions provided by the embedded
computing device). By identifying itself with the profile, the
service advertises compliance with the associated contract. Using a
single identifier makes it possible to implement an extremely
simple discovery system. Clients send out a User Datagram Protocol
(UDP) multicast packet containing the identifier of the desired
service on some standard channel. Services listen on the standard
channel, read the request, see whether they provide the service,
and respond if so.
[0562] UPNP also provides a Directories mechanism to allow
discovery to scale--to the entire Internet if needed. When present,
a directory will read all incoming service requests and respond to
them itself. This requires that all services (e.g., the embedded
computing device 900) register with the directory so that the
directory is able to properly answer on their behalf. The directory
is also responsible for communicating with other directories in
order to determine whether the service is available within the
local network, the WAN and potentially the Internet.
[0563] To simplify the discovery protocol, directories are treated
as proxies. A proxy is a service that accepts requests and takes
responsibility for finding the proper response. When a client comes
online, it will perform discovery for the proxy. If the proxy is
present, then the client will send all future discovery requests to
the proxy. If the proxy isn't present, then the client will send
all discovery requests to the reserved discovery multicast channel.
Regardless of the presence of a proxy, the client's request format
and procedures will always be the same. The only difference will be
the address to which the client sends its requests. For services,
the difference between a proxied and unproxied network is their
need to answer discovery requests. On a proxied network, services
need do nothing once they have registered with the proxy. On an
unproxied network, they answer discovery requests directly.
[0564] SSDP uses the UDP- and Transmission Control Protocol
(TCP)-based Hyptertext Transport Protocol (HTTP) to provide for
service discovery. SSDP uses a Uniform Resource Identifier (URI) to
represent the service and the OPTIONS method to provide for
discovery. SSDP also will provide support for proxies. These
proxies, which are really just fronts for directories, redirect
discovery requests to themselves. It is the proxy's job to collect
announce requests in order to determine what services are available
as well as to communicate with other proxies in order to provide
for scalable service discovery.
[0565] The discovery process returns only the basic information
needed to connect to the embedded computing device. Once a service
has discovered its peers, the service often needs to find out more
information in order to work best with them. The description
process returns a schema providing descriptive data about the
service.
[0566] A schema is a structured data definition that defines a set
of structured values that provide descriptive information about a
service. UPNP uses the Extensible Markup Language (XML) for schema,
because XML's self-describing structured data format provides the
level of expressiveness and extensibility needed by a universal
schema and data format.
[0567] Accordingly, UPNP supports automatic network introduction,
meaning that devices and their related services have the ability to
be self-describing and allow automatic configuration. When a device
is plugged into the computer network, the device automatically
configures itself and acquires a TCP/IP address. The device then
announces its presence to other devices already on the network
using a simple discovery protocol based on the Internet HTTP
protocol and is immediately ready to share its services with any
device that requests them.
[0568] With UPNP, device developers are not required to develop
specific device drivers to operate under UPNP. The task of
preparing a device for operation in this network environment thus
is fairly simple. Moreover, in configured networks, dynamic
detection allows an operating system to immediately begin using
added devices or stop using removed devices without rebooting.
[0569] UPNP Devices support automatic discovery, identification,
and configuration to achieve interoperability in the home
environment, but must also operate correctly in a managed corporate
network. Devices can be networked instead of being attached
directly to a PC, and devices are all autonomous citizens on the
network, able to talk with each other and exchange information.
UPNP provides a unified way of performing directory services with
automatic configuration. Capability for simple discovery mechanism
used in the home environment provides the ability for any device to
become a node on the global Internet. Additionally, directory
services can be leveraged if they are available in the corporate
environment.
[0570] UPNP provides a common set of interfaces for accessing
devices and services, enabling the operational unification of
diverse media types. Communications protocols for Universal Plug
and Play are based on industry standards, especially key Internet
standards such as TCP/IP, HTML, XML, HTTP, DNS, LDAP, and others.
Individual implementations for particular networks and buses are
built on established protocols.
[0571] As shown in FIG. 26, the software architecture 920 of the
embedded computing device 900 (FIG. 25) includes the following
software code modules that implement UPNP: device functions 922,
simple discovery 924, Hypertext Transport Protocol (HTTP) 925,
Transmission Control Protocol/Internet Protocol (TCP/IP) stack 926,
Autonet 928, Dynamic Host Configuration Protocol (DHCP) 930, and
physical media 910 (also shown in FIG. 25). The device functions
922 is a software code module to implement the device's
functionality. For example, where the embedded computing device is
a VCR, the device functions code can include code to implement
start, stop, pause, record and other functions that the VCR can
perform.
[0572] The simple discovery 924 is a software code module (about 4
Kbytes) that implements a simple discovery procedure (described
below) for automatic network introduction under the UPNP
protocol.
[0573] The simple discovery procedure additionally provides an
Extensible Markup Language (XML) format device description, which
is downloaded to clients that access the device to allow activation
of device functionality from the client. XML is a textual,
tag-based markup language. It was originally designed to be the
"webby" simplification of SGML (Standard Generalized Markup
Language), and is therefore intended to be used to create
"vocabularies" of tags that can be used to apply semantic markup to
documents, such as who the author was, what constitutes a paragraph
(semantically, not from a display point of view), when the author
last had breakfast, and so on. (For more information, see A.
Layman, E. Jung, E. Maler, H. Thompson, J. Paoli, J. Tigue, N. H.
Mikula, S. De Rose, "XML-Data", which can be found at
http://www.w3.org/TR/1998/NOTE-xml-data-0105; and MSDN Online, XML
Data Center at http://msdn.microsoft.com/xml/default.asp.) In the
context of UPNP, XML is used to provide the description of services
and capabilities of the embedded computing device. The embedded
computing device makes its features visible to clients by providing
its XML device description, which the client can use to activate
device functions 922. For example, if the device is a camera, the
client's browser can direct the camera to zoom in/out or adjust
contrast using the mechanism of XML.
[0574] The XML device description can provide links (via a uniform
resource locator or URL address) to an accompanying XSL format
style sheet. The XSL style sheets are used to present the data in
different ways, i.e., the style sheets are applied to present
different views of the same data. For example, if the device
contains a file system, one style sheet can show the file
selections; another shows the file sizes in some sort of diagram;
yet another style sheet could make thumbnails of these image
files.
[0575] The HTTP 925 is a software code modules (about 20 Kbytes)
that implements the standard HTTP protocol, which is an open
standard mechanism for client/server message-based communication.
HTTP provides for proxying, content negotiation and security. (For
more information, see R. Fielding, J. Gettys, J. Mogul, H. Frystyk,
T. Berners-Lee, "Hypertext Transfer Protocol--HTTP/1.1", which can
be found at http://www.ietf.org/rfc/rfc2068.txt.)
[0576] The TCP/IP stack 926 implements the standard TCP/IP
networking protocols for communication on the computer network. The
Internet Protocol (IP) is the foundation protocol of the Internet.
It defines how a single message is sent from a source through zero
or more routers to its final destination. It covers issues such as
message length, message fragmentation, addressing, and routing
concerns. The Transmission Control Protocol (TCP) is an IP-based
protocol that provides support for the reliable, ordered delivery
of messages over IP. Additionally, User Datagram Protocol (UDP) and
Internet Group Management Protocol (IGMP) multicast send/listen
capability are included in the implementation.
[0577] The Autonet 928 is a software code module also used for
automatic network introduction via AutoIP in the UPNP protocol.
Autonet uses a predefined set of IP addresses and, when a device is
connected to the network, it pings an address in this address
space. If it gets no replies, the device assumes that the address
is available and assigns it to itself. To make this functionality
even more useful it is combined with Multicast DNS, in which the
device itself holds its own name. Thus it is not even necessary to
determine what IP address the device assigned to itself, because
its name can always be used instead. An IP Multicast is a mechanism
for sending a single message to multiple recipients. IP
multicasting is especially useful for discovery operations where
one does not know exactly who has the information one seeks. In
such cases, one can send a request to a reserved IP multicast
address. Any services that can provide the requested information
will also subscribe to the multicast request and thus be able to
hear the information request and properly respond. Multicast DNS is
a proposal to the IETF on rules for making normal DNS requests
using multicast UDP. (For more information, see B. Woodcock, B.
Manning, "Multicast Discovery of DNS Services", which can be found
at http://www.ietf.org/internet-drafts/draft-manning-multica-
st-dns-01.txt.)
[0578] The DHCP 930 is a software code module that implements the
Dynamic Host Configuration Protocol (DHCP), which is a mechanism
for providing devices with configuration information needed to
access the Internet. The mechanism functions through the use of a
multicast request for configuration information that is generally
responded to with an IP address and DNS server location. Additional
information can only be returned in the response.
[0579] FIGS. 27 and 28 show processes 934, 940 per the UPNP
protocol for automatic network introduction of the embedded
computing device 900 (FIG. 25) into an ad hoc (where the device
does not have a configured IP address) and a configured computer
network environment, respectively. The automatic network
introduction process establishes an appropriate configuration
(e.g., with an IP address) of the embedded computing device upon
connection to a server computer on a computer network, so as to
enable access to the device from a client. The processes 934, 940
involve five phases: announce, discovery, response to discovery,
autonet, and device description.
[0580] At the announce phase, the embedded computing device 900
sends out a small multicast packet so that other devices can find
it on the network. The multicast message packet essentially says,
"I am here, I am, (say), a camera, and you can reach me at this IP
address or URL."
[0581] At the discovery phase, the embedded computing device 900
listens for a discovery packet coming from a simple discovery
client, i.e., the device announces itself, then listens for
discovery. The discovery packet also is sent out by multicast.
[0582] At response to discovery, the embedded computing device 900
listens to the multicast address and then parses the information
from a Simple Discovery request to decide if the request is for its
kind of device. If so, the device 100 then sends back a response
packet containing the following information: the IP address or URL
where it can be reached; identification of its own device type; and
the discovery packet ID so the requesting client knows which
request is being answered.
[0583] At the Autonet phase, the Autonet module 928 of the embedded
computing device 900 uses a predefined set of IP addresses and,
when the device is connected to the network, it pings an address in
this address space. If no reply is received, the device 900 assumes
that the address is available and assigns it to itself.
Alternatively, the device 900 may combine Autonet with Multicast
DNS, and itself hold its own name. In which case, it is not
necessary to determine what IP address the device assigned to
itself, because its name can always be used instead.
[0584] Both the Announce and Discovery packets also contain a link
or a URL to an XML file that is used by the embedded computing
device at the device description phase to describe itself (i.e.,
its functionality). This XML data contains all the facts about the
device. XML can also have URLs that point to appropriate style
sheets (XSL files) that are used for optimal presentation. The XSL
style sheets are used to present the data in different ways, i.e.,
the style sheets are applied to present different views of the same
data. For example, if the device contains a file system, one style
sheet can show the file selections; another shows the file sizes in
some sort of diagram; yet another style sheet could make thumbnails
of these image files.
[0585] Exemplary Client
[0586] With reference now to FIG. 29, a client that accesses and
uses the embedded computing device 900 over the computer network
has an exemplary client software architecture 950, which includes
software code modules for applications 952, simple discovery 954,
XML 955, LDAP 956, TCP/IP stack 958 and a network interface card
(NIC) 960 that provides a physical connection to the computer
network. The applications 952 is a software code module that
provides a user interface features for locating desired devices
(e.g., embedded computing device 900) and services on the computer
network, and also user interface features to interact with the
located device or service. The applications 952 can include an
Internet browser, such as the Microsoft Internet Explorer, that can
present the XML device description in accordance with an associated
XSL style sheet for interaction with the embedded computing device
and activation of its operational functionality.
[0587] The simple discovery 954 is a module that implements the
above-described simple discovery per the UPNP protocol. The XML 955
is a module that processes the XML device description and XSL style
sheets for presentation in the application's user interface. The
LDAP 956 implements the standard LDAP directory protocol for name
look-up. The TCP/IP stack 958 implements the TCP/IP protocol for
communications over the computer network.
[0588] Illustrative Pervasive Computing Environment
[0589] FIG. 30 illustrates a pervasive computing environment 1000,
such as may be installed in a home, office or public place, which
includes a large number of embedded computing devices, such as the
illustrated device 900 (FIG. 25). The pervasive computing
environment 1000 includes personal computers 1002, 1004 (e.g., of
the type shown in FIG. 24) connected via a local area network (LAN)
1006. The PC 1002 is connected via a universal serial bus 1016 to a
telephone modem 1010, XDSL interface 1011 or a cable modem 1012,
which in turn provide a connection with the computer network, e.g.,
the Internet.
[0590] Various embedded computing devices also connect to the
computer network via various network connections to the PCs 1002,
1004. These include an audio device 1014 (e.g., speakers, radio
tuner, microphone), and printer 1015 which connect to the PC 1004
through a USB 1017. Also, a digital camera 1020, a handheld PC
(H/PC) 1021 and another personal computing device 1022 connect via
an infrared port (IRDA) 1024, which also attaches to the PC 1004
through the USB 1017. Also, lighting switches 1030 and like home
appliances are connected via an A/C power line-based networking
1032 to the PC 1002. Further, a chain of IEEE 1394 cables 1048
connect a digital TV 1040, DVD player 1041, digital video camcorder
(DV/DVC) 1042, an audio device 1043 (e.g., CD player/recorder,
radio receiver, amplifier, and like audio system component), and a
game console 1044. Devices, such as a portable telephone 1050 and
remote control 1051, have a radio frequency network connection with
the PC 1004.
[0591] With their various inter-networked connections, the embedded
computing devices are "visible" and accessible from a client device
950 (FIG. 30) also connected to the computer network.
[0592] Contract Definition Language
[0593] Overview
[0594] Contracts describe the public behavior of UPnP devices, and
alternatively of other entities on the Web (reachable via HTTP,
mostly) or other computer network that react to and emit messages.
The Contract is written in a Contract Definition Language (CDL).
The messages for the most part are structured documents, e.g., in
XML. The messages may also be HTML pages, streaming media, images
or other datatypes appropriate to the WebObject.
[0595] The contract will describe the following attributes of a
WebObject:
[0596] end-point (well-defined name)
[0597] protocol
[0598] messaging patterns
[0599] delivery characteristics
[0600] payloads
[0601] All of these attributes may not be present in the contract
as some of them (the end-point, for instance) may not be available
at development time.
[0602] Protocol Description
[0603] WebObjects can be accessed using multiple protocols: HTTP,
GENA, SMTP, FTP, MSMQ, . . . This section discusses how to describe
the protocol bindings particular to a WebObject. The templates for
describing the protocol use the format:
29 <protocol> <HTTP> // HTTP specific settings go here
</HTTP> </protocol> <protocol> <HTTP> //
GENA specific settings go here </HTTP> </protocol>
[0604] The "protocol" element may have an "id" attribute. This is
useful when multiple messaging patterns will use the same protocol
definition. This will be covered in more detail below.
[0605] For the sake of convenience, we only cover HTTP-based
protocols here. Extending this model to cover the other protocols
is straightforward.
[0606] HTTP
[0607] GET
30 <protocol> <HTTP version="1.0"> <GET/>
<URL> http://172.30.184.20/fullsiz- e.jpg </URL>
</HTTP></protocol>
[0608] GET with query string
31 <protocol> <HTTP version="1.1"> <GET/>
<URL> http://search.yahoo.com/bin/- search </URL>
<QUERY name="pattern" required="yes" /> <QUERY
name="limit" value="50" required="no" /> <QUERY name="xml"
value="yes" required="yes" /> </HTTP>
</protocol>
[0609] This description indicates that the following are valid
URLs:
[0610]
http://search.yahoo.com/bin/search?pattern=Rio+player&limit=50&xml=-
yes
[0611]
http://search.yahoo.com/bin/search?xml=yes&pattern=Rio+player
[0612] The reason for not associating the query variables with the
GET verb is because it is valid to send a POST message to a URL
containing query variables.
[0613] The "value" attribute for the "QUERY" element implies that
the value is static--it is to be treated as a part of the URL.
Declaring it this way allows the appropriate construction of the
query string to be handled by the caller.
[0614] POST
32 <protocol> <HTTP version="1.1"> <URL>
http://www.amazon.com/exec/obidos/generic- quicksearch-query
</URL> <POST> <PARAM name="mode" default="blended"
required="yes" /> <PARAM name="keyword-query" required="yes"
/> <PARAM name="zipcode" value="98112" required="yes" />
</POST> </HTTP> </protocol>
[0615] The default attribute indicates that the parameter's value
can be changed.
[0616] M-POST
33 <protocol id="protocolDef"> <HTTP version="1.1">
<URL> http://investor.msn.com/stockquot- es.xsp </URL>
<QUERY name="symbol" required="yes" /> <M-POST>
<MAN> http://www.upnp.org/service-control/m- post
</MAN> </M-POST> <HEADER name="Content-Type"
value="text/xml" /> </HTTP> </protocol>
[0617] The M-POST and the enclosed MAN elements declare the
mandatory extension mechanism to be used. The optional extension
mechanism can also be handled in this way.
[0618] The "HEADER" element allows the declaration of HTTP headers
to be used.
[0619] GENA
[0620] Payload Description
[0621] Below is an example of an XML payload description.
34 <schema xmlns="urn:schema-microsoft-com:xml-data"
xmlns:dt="urn:schema-microsoft- com:datatypes"> // // symbol: a
ticker symbol // <ElementType name="symbol" dt:type="string"
/> // // symbols: array of "symbol" elements // <ElementType
name="symbols"> <element type="symbol" maxOccurs="*" />
</ElementType> // // stockQuote: quote details //
<ElementType name="stockQuote"> <element type="company"
/> <element type="ticker" /> <element
type="previousClose" /> <element type="openingTrade" />
<element type="lastTrade" /> <element type="volume" />
</ElementType> <ElementType dt:type="string"
name="company" /> <ElementType dt:type="string" name="ticker"
/> <ElementType dt:type="string" name="previousClose" />
<ElementType dt:type="string" name="openingTrade" />
<ElementType dt:type="string" name="lastTrade" />
<ElementType dt:type="string" name="volume" /> // //
stockQuotes: array of "stockQuote" elements // <ElementType
name="stockQuotes"> <element name="stockQuote" maxOccurs="*"
/> </Element> // // error: error info // <ElementType
name="error"> <element type="reason" />
</ElementType> <ElementType dt:type="string" name="reason"
/> </schema>
[0622] Using this declaration, the below are valid XML
fragments:
35 <symbol> MSFT </symbol> <symbols>
<symbol> MSFT </symbol> <symbol> IBM
</symbol> <symbol> AOL </symbol> <symbol>
YHOO </symbol> <symbol> AMZN </symbol>
</symbols> <stockQuote>
<company>Microsoft%20Corporation</co- mpany>
<ticker>MSFT</ticker>
<previousClose>84%2011/16</previousClose>
<openingTrade>85%201/16</openingTrade>
<lastTrade>84%205/16</lastTrade>
<volume>28.66%20Mil</volume> </stockQuote>
[0623] Messaging Patterns
[0624] The messaging pattern declaration acts as an anchor for
pulling together the protocol, delivery characteristics and the
payload information. The messaging pattern declarations can include
these types.
[0625] Request/response
[0626] Solicit/response
[0627] One way
[0628] Request/response (RR). The RR pattern is named. The two
samples below are equivalent mechanisms for declaring the protocol
to be used for the RR messaging pattern. The linking mechanism is
useful when multiple RR pairs use the same protocol data. This is
the case for UPnP. Also, a service may employ multiple protocols
for achieving the same "method"-call. The "is" attribute accepts a
list of ID-Refs--implying that either of the protocols are equally
suitable for accessing the functionality.
36 <RequestResponse name="getImage"> <protocol>
<HTTP version="1.0"> <GET/> <URL>
http://172.30.184.20/fullsize.jpg </URL> </HTTP>
</protocol> ... </RequestResponse> <protocol
id="protocolDef1"> <HTTP version="1.0"> <GET/>
<URL> http://172.30.184.20/fullsize.jpg </URL>
</HTTP> </protocol> <RequestResponse
name="getImage"> <protocol is="protocolDef1" /> ...
</RequestResponse>
[0629] The payloads for request, response and error, in case of XML
data, are identified by the names of the elements referenced by the
"is" attribute. The schema information is assumed to be in the same
document. Below are examples using the two schemes:
37 <RequestResponse name="getQuote"> // protocol declaration
goes here <in is="symbol" /> <out is="stockQuote" />
<error is="error" /> </RequestResponse>
<RequestResponse name="getQuote"
xmlns:f="http://electrocommerce.org/finance.xml"
xmlns:c="http://electrocommerce.org/common.xml" > // protocol
declaration goes here <in is="f:symbol" /> <out
is="f:stockQuote" /> <error is="c:error" />
</RequestResponse>
[0630] The CDL described herein keeps the element declarations in
the "schema" block rather than sprinkle them in with the messaging
pattern definitions. The reasons for this are:
[0631] Re-use of element declarations is easy.
[0632] We can re-use fragment validation support as is.
[0633] Keeping schemas in one place is consistent with the use of
in-line schemas in SQLI2 and ADO.
[0634] In case the request or response are not XML documents but
HTML documents, or binary files, the following syntax will be used.
The contained element defines the nature of the data. The use of
MIME is not in the HTTP-specific sense but in the "nature of the
payload" sense. The presence of the "is" attributes indicates that
the MIME type is "text/xml."
38 <RequestResponse name="getImage"> ... <out> <mime
type="image/jpeg"/> </out> ...
</RequestResponse>
[0635] Delivery Characteristics
[0636] The contract may specify the delivery characteristics
(sometimes also referred to as quality of service) required or
supported by the server. Examples are:
[0637] Ordered, best-effort
[0638] Guaranteed delivery
[0639] Fire-and-forget
[0640] Exactly once
[0641] At least once
[0642] Transactional
EXAMPLE
[0643] FIGS. 44-46 depict an exemplary contract for interacting
with a stock quote Service.
[0644] FIGS. 47-50 depict an XML schema for defining Contracts.
[0645] Having described and illustrated the principles of our
invention with reference to an illustrated embodiment, it will be
recognized that the illustrated embodiment can be modified in
arrangement and detail without departing from such principles. It
should be understood that the programs, processes, or methods
described herein are not related or limited to any particular type
of computer apparatus, unless indicated otherwise. Various types of
general purpose or specialized computer apparatus may be used with
or perform operations in accordance with the teachings described
herein. Elements of the illustrated embodiment shown in software
may be implemented in hardware and vice versa.
[0646] In view of the many possible embodiments to which the
principles of our invention may be applied, it should be recognized
that the detailed embodiments are illustrative only and should not
be taken as limiting the scope of our invention. Rather, we claim
as our invention all such embodiments as may come within the scope
and spirit of the following claims and equivalents thereto.
* * * * *
References