U.S. patent application number 08/948687 was filed with the patent office on 2001-08-09 for virtual gateway system and method.
Invention is credited to FOLEY, PETER F..
Application Number | 20010012319 08/948687 |
Document ID | / |
Family ID | 25488147 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012319 |
Kind Code |
A1 |
FOLEY, PETER F. |
August 9, 2001 |
VIRTUAL GATEWAY SYSTEM AND METHOD
Abstract
Existing (already installed) plain old telephone service (POTS)
wiring at a customer premises is used as the wiring infrastructure
for a local area network and additionally continues to provide
ordinary POTS services at the customer premises. The network
signals associated with the local area network and the POTS signals
delivering POTS services coexist on the POTS wiring at the customer
premises using frequency division multiplexing. In additional to
POTS service, the subscriber loop also provides access to xDSL
(digital subscriber line) signals associated with a wide area
network (WAN). Thus three distinct networks (the PSTN associated
with POTS, xDSL and the LAN)) coexist on a single wiring
infrastructure. A virtual gateway provides for communication
between each of the distinct networks without breaking the
electrical continuity of the POTS wiring at the customer premises
and thus maintaining lifeline POTS services, without the
installation of a new dedicated active (needing AC current) Gateway
device, and without the need to pull new cable to implement the
premises LAN.
Inventors: |
FOLEY, PETER F.; (LOS ALTOS
HILLS, CA) |
Correspondence
Address: |
CHRISTIE PARKER & HALE, LLP
P.O. BOX 7068
PASADENA
CA
911097068
|
Family ID: |
25488147 |
Appl. No.: |
08/948687 |
Filed: |
October 10, 1997 |
Current U.S.
Class: |
375/222 ;
348/E7.05; 348/E7.051 |
Current CPC
Class: |
H04M 7/0069 20130101;
H04N 7/108 20130101; H04M 11/062 20130101; H04N 7/106 20130101 |
Class at
Publication: |
375/222 |
International
Class: |
H04B 001/38; H04L
005/16; H04L 012/28; H04L 012/56 |
Claims
What is claimed is:
1. A virtual gateway system for providing bidirectional
communication between a first device network and a second device
network, comprising: a shared electrically contiguous communication
channel coupled to each of the device networks, the shared
electrically contiguous communication channel having first and
second separate spectral bands associated with the first and second
device networks respectively; and a gateway server operatively
coupled to the shared electrically contiguous communication
channel, the gateway server including; a first modem associated
with the first device network, having: a receive portion having an
input coupled to the shared communication channel, the receive
portion for converting information in the spectral band associated
with the first device network to baseband; and a transmit portion
having an output coupled to the shared communication channel, the
transmit portion for converting baseband information to the
spectral band associated with the first device network; a second
modem associated with the second device network, having: a receive
portion having an input coupled to the shared communication channel
for converting information in the spectral band associated with the
second device network to baseband; and a transmit portion having an
output coupled to the shared communication channel, the transmit
portion for converting baseband information to the spectral band
associated with the second device network; and a baseband
communication channel coupled to the first and second modems for
communicating baseband signals between the first and second
modems.
2. The system of claim 1 further comprising: a network protocol
translator coupled to the baseband communication channel for
translating baseband information from a first protocol associated
with the first device network to a second protocol associated with
the second device network.
3. The system of claim 1 wherein the shared communication channel
is unshielded twisted pair wiring coupled to a telephone central
office by a subscriber loop.
4. The system of claim 3 wherein the first device network is a
local area network having a plurality of network clients and access
to the second device network is provided by a digital subscriber
line (xDSL).
5. The system of claim 4 wherein the xDSL is an asymmetrical
digital subscriber line (ADSL).
6. The system of claim 3 wherein both the first and second modems
of the gateway are located at a single server device.
7. The system of claim 1 wherein the first device network is a
local area network having a plurality of network clients and the
second device network is a integrated services digital network
(ISDN) wide area network.
8. The system of claim 1 wherein the first device network is a
local area network having a plurality of network clients and the
second device network is a wide area network.
9. The system of claim 1 wherein the first device network is a
first local area network and the second device network is a second
local area network.
10. The system of claim 3 wherein the first device network is a
first local area network and the second device network is a second
local area network.
11. A virtual gateway system for providing bidirectional
communication between a first device network and a second device
network, comprising: a shared communication channel coupled to each
of the device networks, the shared communication channel having
first and second separate spectral bands associated with the first
and second device networks respectively; and a plurality of client
devices each including: a first modem associated with the first
device network, having: a receive portion having an input coupled
to the shared communication channel, the receive portion for
converting information in the spectral band associated with the
first device network to baseband; and a transmit portion having an
output coupled to the shared communication channel, the transmit
portion for converting baseband information to the spectral band
associated with the first device network; and a second modem
associated with the second device network, each having: a receive
portion having an input coupled to the shared communication channel
for converting information in the spectral band associated with the
second device network to baseband; and a transmit portion having an
output coupled to the shared communication channel for converting
baseband information to the spectral band associated with the
second device network; and a baseband communication channel coupled
to the first and second modems for communicating baseband signals
between the first and second modems.
12. The system of claim 11 further comprising: a network protocol
translator coupled to the baseband communication channel for
translating baseband information from a first protocol associated
with the first device network to a second protocol associated with
the second device network.
13. The system of claim 11 wherein the shared communication channel
is unshielded twisted pair wiring coupled to a telephone central
office by a subscriber loop.
14. The system of claim 13 wherein the first device network is a
local area network having a plurality of network clients and access
to the second device network is provided by a digital subscriber
line (xDSL).
15. The system of claim 14 wherein the xDSL is an asymmetrical
digital subscriber line (ADSL).
16. The system of claim 13 wherein both the first and second modems
of the gateway are located at a single server device.
17. The system of claim 11 wherein the first device network is a
local area network having a plurality of network clients and the
second device network is a integrated services digital network
(ISDN) wide area network.
18. The system of claim 11 wherein the first device network is a
local area network having a plurality of network clients and the
second device network is a wide area network.
19. The system of claim 11 wherein the first device network is a
first local area network and the second device network is a second
local area network.
20. The system of claim 13 wherein the first device network is a
first local area network and the second device network is a second
local area network.
21. A virtual gateway system for providing bi-directional
communication between a first device network and a second device
network, comprising: a shared communication channel coupled to each
of the device networks, the shared communication channel having
first and second separate spectral bands associated with the first
and second device networks respectively; and a plurality of client
devices each including: a first modem associated with the first
device network, having: a receive portion having an input coupled
to the shared communication channel, said receive portion for
converting information in the spectral band associated with the
first device network to baseband; and a transmit portion having an
output coupled to the shared communication channel, said transmit
portion for converting baseband information to the spectral band
associated with the first device network; and a gateway server
having a second modem having: a receive portion having an input
coupled to the shared communication channel, the receive portion
for converting information in the spectral band associated with the
second device network to baseband; and a transmit portion having an
input coupled to the shared communication channel, said transmit
portion for converting baseband information to the spectral band
associated with the second network.
22. The system of claim 21 further comprising: a network protocol
translator coupled to the baseband communication channel for
translating baseband information from a first protocol associated
with the first device network to a second protocol associated with
the second device network.
23. The system of claim 21 wherein the shared communication channel
is unshielded twisted pair wiring coupled to a telephone central
office by a subscriber loop.
24. The system of claim 23 wherein the first device network is a
local area network having a plurality of network clients and access
to the second device network is provided by a digital subscriber
line (xDSL).
25. The system of claim 24 wherein the xDSL is an asymmetrical
digital subscriber line (ADSL).
26. The system of claim 23 wherein both the first and second modems
of the gateway are located at a single server device.
27. The system of claim 21 wherein the first device network is a
local area network having a plurality of network clients and the
second device network is a integrated services digital network
(ISDN) wide area network.
28. The system of claim 21 wherein the first device network is a
local area network having a plurality of network clients and the
second device network is a wide area network.
29. The system of claim 11 wherein the first device network is a
first local area network and the second device network is a second
local area network.
30. The system of claim 23 wherein the first device network is a
first local area network and the second device network is a second
local area network.
31. A method of providing communication between a first and second
device network, comprising: coupling a first and a second device
network to a shared communication channel; communicating among
devices in the first device network using communication signals in
a first spectral band on the shared communication channel;
communicating among the devices in the second device network using
communication signals in a second spectral band distinct from the
first spectral band on the shared communication channel; and
converting information in the first spectral band to the second
spectral band to transfer information from the first device network
to the second device network.
32. The method of claim 31 further comprising coupling
telecommunications circuit connections to the shared communication
channel.
33. The method of claim 31 further comprising: coupling the
communication channel to a subscriber loop coupled to a central
telephone office; and coupling a plain old telephone service (POTS)
compatible device to the shared communication channel to connect
the POTS compatible device to the central telephone office.
34. The method of claim 31 further comprising centralizing the
conversion of information in the first spectral band to the second
spectral band at a single gateway server.
35. The method of claim 31 further comprising distributing the
conversion of information in the first spectral band to the second
spectral band at across a plurality of client devices.
36. The method of claim 31 further comprising converting
information in the second spectral band to the first spectral band
to transfer information from the second device network to the first
device network.
37. The method of claim 36 further comprising centralizing the
conversion of information in the first spectral band to the second
spectral and the conversion of information in the second spectral
band to the first spectral band at a single gateway server.
38. The method of claim 36 further comprising distributing the
conversion of information in the first spectral band to the second
spectral band across a plurality of client devices and distributing
the conversion of information in the second spectral band to the
first spectral band across a plurality of client devices.
39. The method of claim 36 further comprising centralizing the
conversion of information in the first spectral band to the second
spectral at a single gateway server and distributing the conversion
of information in the second spectral band to the first spectral
band across a plurality of client devices.
40. A method for interconnecting a plurality of distinct device
networks, comprising: generating first network signals associated
with a first device network having a first network protocol, said
first network signals being in a first spectral band; generating
second network signals associated with a second device network
having a second network protocol, said second network signals being
in a second spectral band; coupling the first and second network
signals generated by the first and second device networks to a
shared communication channel; detecting network signals coupled to
the shared communication channel in the first spectral band that
are addressed to a device associated with the second device
network; and converting detected signals to a network signal
compatible with the second network protocol and in the second
spectral band.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation in part of application
Ser. No. attorney docket number 2959 entitled "Home Area Network
System and Method" filed on Aug. 28, 1997, by Peter F. Foley; which
application is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to computer network
gateways and more particularly to computer network gateways that
connect a local area network to one or more distinct networks
sharing the same electrically contiguous communication channel.
[0004] 2. Description of the Related Art
[0005] The expansion of the Internet and the world wide web, the
prevalence of telecommuting, and the anticipation of video on
demand has generated a demand for the delivery of digital
information to customer premises at bandwidths higher than can be
delivered using traditional voice-grade modem technology.
[0006] Various solutions to the high bandwidth delivery problem are
under development. Unfortunately, many of these solutions require
the installation of a new wiring or cabling infrastructure to
deliver information to a customer premises. One class of technology
that does not have this drawback is digital subscriber line (xDSL)
technology. Digital subscriber line technology has the advantage
that it uses the existing subscriber line (local loop)
infrastructure to deliver a higher bandwidth signal to a customer
premises. This means that it uses the existing unshielded twisted
pair (UTP) copper wiring that connects to a customer premises
(subscriber premises).
[0007] The preferred xDSL technology, Asymmetric Digital Subscriber
Line (ADSL), achieves the delivery of higher bandwidth by
installing ADSL modems at both ends of the subscriber loop (e.g.,
at the telephone central office and at the customer premises). ADSL
signals are then transmitted between the ADSL modem at the central
office (ATU-C), and premises ADSL modem (ATU-R) over the existing
UTP subscriber loop wiring.
[0008] FIG. 1 illustrates the spectral allocation 100 on an
asymmetrical digital subscriber line (ADSL). The baseband portion
of the spectrum is allocated for POTS connections 101 and the
portion from 25 KHz to 1.2 Mhz is allocated for ADSL signals 102.
ADSL signals 102 provide access to wide area computer networks and
the POTS connections provide access to the public switched
telephone network (PSTN).
[0009] Many customer premises provide xDSL access to more than one
computer at a premises. Conventionally, this multiple access is
provided using a 10baseT LAN to connect multiple computers to an
xDSL modem/hub. The xDSL modem/hub performs xDSL modem functions
and additionally may perform gateway (networking bridging)
functions to facilitate communication between the premises LAN and
the WAN made accessible via xDSL technology.
[0010] FIG. 2 illustrates a conventional xDSL system that provides
multiple computers 201 with access to a wide area network (WAN) 202
via xDSL. The exemplary xDSL system uses asymmetrical digital
subscriber loop (ADSL) technology. The system includes a
conventional ADSL modem/hub 203 that operates as a network hub
(e.g., a 10/100baseT Ethernet hub) for local area network 205. LAN
205, also known as the Premises Distribution Network is a point to
point LAN having a star configuration centered around the hub
portion of ADSL modem/hub 203. Installing LAN 105 involves the
installation of a wiring network that supports 10/100baseT
Ethernet. This means that new wiring or cabling must be "pulled"
for each computer 201 to be included in LAN 205
[0011] ADSL modem/hub 203 is coupled to a telephone central office
207 via a subscriber loop. ADSL modem/hub 203 includes a POTS
splitter 213 that may couple plain old telephone service signals to
the exiting (installed) plain old telephone service (POTS) UTP
wiring (POTS wiring) 206 at the customer premises 204.
[0012] In operation, a conventional ADSL modem 208 (ATU-C) located
at central office 207 receives digital signals from a wide area
network 202, modulates the received signals and then places them on
the UTP subscriber loop using a POTS splitter at the central
office. This POTS splitter combines ADSL signals and POTS signals
for transmission to the premises and conversely splits POTS and
ADSL signals upon reception from the premises.
[0013] Preferably, ADSL modem/hub 203 is located at the telephone
Network Interface (TNI) 110 at the demarcation point between the
subscriber loop and the customer premises so that the output of the
POTS splitter 213 is coupled to the premises UTP wiring before any
branching occurs and before the installation of any RJ-11 jacks.
The subscriber loop is thus terminated at the ADSL modem/hub, which
is an active device requiring AC power. Locating POTS splitter 213
elsewhere at a customer premises requires knowledge of the customer
premises wiring topology and the willingness to electrically
"break" the wiring at the splitter insertion point in order to
insert the active device (e.g., the ADSL modem/hub 203). Without a
clear understanding of the customer premises wiring topology, it is
difficult to know which part of the premises wiring will carry both
ADSL and POTS signals as opposed to only POTS signals. Most
typically, the POTS splitter is integral with the ADSL modem/hub
(as shown in FIG. 1) therefor, it is preferred to install the ADSL
modem/hub 203 at or near the TNI 110. Placing on ADSL modem/hub 203
at the TNI 110, however, has certain drawbacks such as the need for
an AC power source/outlet near the TNI and the risk of exposure to
harsh environmental elements (e.g., temperature extremes, rain,
etc.). Further, when the hub and the modem are combined, new wiring
must be "pulled" to the TNI from computers 201 to complete network
connections.
[0014] The above described system known in the art provides for
communication between multiple device networks: a WAN, a LAN at a
customer premises and the PSTN. This communication is enabled using
an active device (e.g., an ADSL modem/hub) that breaks the
electrical continuity between the subscriber loop and the premises
LAN (Premises Distribution Network) with the installation of an
active device, typically a hub, in order to provide hub/gateway
functionality between the LAN and the WAN.
[0015] The above described system has several drawbacks. The system
requires the installation of a new active device (the hub 203) that
adds considerable cost and installation complexity. Further,
installing new wiring for a LAN at the customer premises is complex
and costly, and the LAN and the subscriber loop do not share the
same electrically contiguous communications medium. The LAN wiring
does not support DC current flow from the subscriber loop, which
means POTS, and more particularly, POTS lifeline service, is not
supported on the LAN wiring.
[0016] Thus, there is a need for an improved system and method for
interconnecting distinct premises LAN and subscriber loop WAN
device networks without the need for insertion of an active
hub/gateway device between the premises POTS wiring and the
subscriber loop, without the pulling of new cable to implement the
premises LAN, and without breaking the electrical continuity (DC
current capability) of the wiring--which would preclude POTS
lifeline service.
SUMMARY OF THE INVENTION
[0017] In accordance with the present invention, there is provided
a system and method for providing bidirectional communication
between a first device network and a second device network using a
shared electrically contiguous communication channel such as an
existing (already installed) customer premises plain old telephone
(POTS) wiring. Each device network is coupled to the shared
electrically contiguous communication channel and each are further
allocated separate spectral bands for use on the shared
communication channel. Thus, two distinct device networks coexist
on a single shared communication channel using frequency division
multiplexing. Communication between the distinct device networks is
perfected by converting signals from the spectral band associated
with the source network to the spectral band(s) associated with the
destination network.
[0018] The gateway server of the present invention is
advantageously operatively coupled to the shared communication
channel without breaking the electrical continuity of the shared
communication channel. Because electrical continuity is not broken,
DC current may pass; and the customer premises wiring is capable of
maintaining POTS lifeline services and POTS signaling
protocols.
[0019] In a centralized architecture, the virtual gateway of the
present invention includes first and second modems, each associated
with one of the device networks. It should be understood that as
used herein, "modem" means a modulator-demodulator device or a
transceiver and the like. Further, as used herein "modem" includes
modems that effect direct current (DC) baseband signaling as well
as bandpass and highpass signaling and the like. The modem
associated with the first device network has a receive portion and
a transmit portion for converting signals from the spectral band
associated with the first network to baseband and for converting
baseband signals to the spectral band associated with the first
network, respectively. Similarly, the modem associated with the
second device network has a receive portion and a transmit portion
for converting signals from the spectral band associated with the
second network to baseband and for converting baseband signals to
the spectral band associated with the second network, respectively.
The virtual gateway server additionally provides for communication
of baseband data between the first and second modems using means
conventionally found within a personal computer or similar
computing device (such as a PCI bus, etc.). It should be understood
that as used herein "baseband" includes data not modulated by a
carrier frequency, such as data processed by a microprocessor of
transferred over a personal computer bus such as a PCI bus.
[0020] Information is sent from a sending network to a receiving
network by first demodulating the information in accordance with
the protocol and modulation scheme associated with the sending
network to generate baseband data. The baseband data is then
processed to generate a band pass signal in accordance with the
modulation scheme and protocol associated with the receiving
network. The baseband processing includes any required protocol
conversion to translate the data from the protocol associated with
the sending network to the protocol associated with the receiving
network.
[0021] In accordance with another aspect of the invention, rather
than locating the first and second modems centrally on a gateway
server, the gateway functionality is distributed across a plurality
of network clients. Thus, first and second modems, each associated
with the first and second networks, respectively, are located at a
plurality of network clients. Advantageously, this distribution of
the gateway functionality reduces network traffic and improves
overall system performance because the same data need not be
transmitted on multiple spectral bands in order to be received by
clients of either device network.
[0022] In accordance with another aspect of the invention, the
virtual gateway functionality is partially distributed such that
the modems located at the clients provide both transmit and receive
capability in the spectral band associated with the first network
but provide only receive capability in the spectral band associated
with the second network. The transmit capability associated with
the second network is not distributed but instead is centrally
located at a server. This partially distributed architecture is
particularly advantageous when the second network is characterized
by asymmetrical data traffic patterns. For example, in cases where
the second network is a wide area network supplying video on
demand, the data traffic is highly asymmetrical. Advantageously,
this partial distribution of the gateway functionality reduces
network traffic and improves overall system performance because
data transmitted on the second network need not be retransmitted in
the spectral band of the first network to be received by clients of
the first network.
[0023] The features and advantages described in the specification
are not all-inclusive, and particularly, many additional features
and advantages will be apparent to one of ordinary skill in the art
in view of the drawings, specification, and claims hereof.
Moreover, it should be noted that the language used in the
specification has been principally selected for readability and
instructional purposes, and may not have been selected to delineate
or circumscribe the inventive subject matter, resort to the claims
being necessary to determine such inventive subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates spectral allocation on a digital
subscriber line.
[0025] FIG. 2 illustrates a conventional local area network
installed at a customer premises.
[0026] FIG. 3 illustrates a home area network (HAN) using installed
POTS wiring.
[0027] FIG. 4A is an illustration of spectrum utilization on the
POTS wiring shown in FIG. 3.
[0028] FIG. 4B is an illustration of alternative spectrum
utilization on the POTS wiring shown in FIG. 3.
[0029] FIG. 5A is a functional block diagram of a network interface
card (NIC) included in a computer installed in the HAN shown in
FIG. 3.
[0030] FIG. 5B is a functional block diagram of an external network
peripheral interface used to connect a computer to the HAN shown in
FIG. 3.
[0031] FIG. 6 is a flow diagram of the receive-side processing
steps performed by the NICs shown in FIGS. 5A and 5B.
[0032] FIG. 7 is a flow diagram of the transmit-side processing
steps performed by the NICs shown in FIGS. 5A and 5B.
[0033] FIG. 8 shows a lowpass filter shown in the HAN illustrated
in FIG. 3.
[0034] FIG. 9 shows diplexer filter which is alternatively used in
place of the lowpass filter shown in the HAN illustrated in FIG.
3.
[0035] FIG. 10 shows an alternative embodiment of a HAN using
filters at customer premises equipment in accordance with the
present invention.
[0036] FIG. 11 is a block diagram of the diplexer filters used to
connect the legacy POTS customer premises equipment to the HAN as
shown in FIG. 10.
[0037] FIG. 12 is a frequency response graph illustrating the group
delay associated with a filter in accordance with the
invention.
[0038] FIG. 13 is a frequency response graph illustrating the group
delay associated with a filter in accordance with the
invention.
[0039] FIG. 14A is a functional block diagram of a customer
premises having a centralized virtual gateway in accordance with
the present invention.
[0040] FIG. 14B is a functional block diagram of a network
interface card used in the virtual gateway shown in FIG. 14A.
[0041] FIG. 15 is flow diagram of the virtual gateway method
implemented by the centralized virtual gateway shown in FIG.
14.
[0042] FIG. 16 is a functional block diagram of a customer premises
having a fully distributed virtual gateway in accordance with the
present invention.
[0043] FIG. 17 is a functional block diagram of a customer premises
having a partially distributed virtual gateway in accordance with
the present invention.
[0044] FIG. 18 is a functional block diagram of a customer premises
having two separate HANs operating on customer premises POTS
wiring.
[0045] FIG. 19 is an illustration of the spectral allocation of the
customer premises wiring shown in FIG. 18.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0046] FIGS. 3-19 depict a preferred embodiment of the present
invention for purposes of illustration only. One skilled in the art
will readily recognize from the following discussion that
alternative embodiments of the structures and methods illustrated
herein may be employed without departing from the principles of the
invention described herein.
[0047] The virtual gateway of the present invention provides an
interconnection between two or more device networks that are each
coupled to a shared communication channel. In a preferred
embodiment, the virtual gateway interconnects a home local area
network (a HAN) to a POTS-accessed WAN and to an ADSL-accessed WAN.
Further, in the preferred embodiment, the HAN wiring infrastructure
leverages the existing (installed) customer premises wiring which
is a shared communication channel common among the HAN, POTS
service and ADSL service at a customer premises. To further
understand the virtual gateway of the present invention, a HAN is
first described.
[0048] FIG. 3 illustrates a home area network (HAN) 300 in
accordance with the present invention. HAN 300 includes existing
(installed) plain old telephone service (POTS) wiring 301, network
clients 302, the computer port side of modem 303 and fax 304. POTS
wiring 301 provides wiring infrastructure used to network multiple
network clients 302 at a customer premises 307.
[0049] POTS wiring 301 is conventional unshielded twisted pair
(UTP) wiring that is generally routed internally in the walls of
the customer premises 307 (e.g., a house) to various locations
(e.g., rooms) within customer premises 307.
[0050] Subscriber loop 306 (also called a "local loop") is a
physical wiring link that directly connects an individual customer
premises 307 to the central office. Subscriber loop 306 is
unshielded twisted pair (UTP) wire. UTP wire causes signal
attenuation over extended distances. This attenuation is greater
for higher frequency signals. To accommodate the constraints
imposed by the electrical properties of subscriber loop 306,
subscriber loop 306 line lengths are generally confined to a length
no greater than 18 kilometers, although longer line lengths are
sometimes used. Nonetheless, subscriber loop 306 is not well suited
to transmit signals greater than 1.1 MHz.
[0051] Customer premises 307 is a subscriber premises that has
arranged (generally for a monthly telephone service fee or for a
per calling minute fee) with a local provider (such as a local
telephone company) for a connection to a central office. A central
office is a central telephone office (also called a local exchange)
that provides local switching and non-local switching (via the
Public Switched Telephone Network (PSTN)).
[0052] Network client 302 is personal computer equipped with a
network interface card (shown in FIG. 5A). It should be understood,
however, that the principles of the present invention apply to HANs
including other types of network clients such as specific purpose
computers, computer appliances, computer-enabled devices or other
types of network devices.
[0053] In addition to providing connectivity among (e.g.,
networking) network clients 302, POTS wiring 301 connects to
conventional POTS-compatible POTS on telecommunications devices
(such as telephones 305, modem 303 and facsimile machine 304). POTS
wiring 301 thus additionally couples telephone 305 and modem 303 to
a central office via subscriber loop 306. The central office, in
turn, connects the POTS-compatible devices to another
POTS-compatible device located off premises.
[0054] Advantageously, HAN 300 connects (networks) network clients
302 without disrupting ordinary telephone and telecommunications
services (including digital subscriber line (xDSL)) services
conventionally provided on POTS wiring 301. HAN 301 and
conventional POTS services simultaneously utilize POTS wiring 301
by frequency division multiplexing network related signals (HAN
signals) and POTS signals to achieve spectral avoidance.
[0055] FIG. 4A is an illustration of the utilization of spectrum
400 on POTS wiring 301 at a customer premises in accordance with
the present invention. Spectrum 400 shows four separate frequency
bands in which information is communicated: a POTS band 401, an
ADSL upstream band 402, an ADSL downstream band 403 and HAN band
404. POTS band 401 is baseband up to approximately 4 KHz.
Conventional POTS signals such as voice signals, modem signals and
facsimile signals occupy the baseband region of the spectrum with a
maximum bandwidth of 4 KHz. ADSL upstream band 402 and ADSL
downstream band 403 both carry signals in accordance with
asymmetrical digital subscriber line (ADSL) protocol. ADSL upstream
band 402 occupies a band ranging from 25 KHz to 1.1 MHz and carries
ADSL signals from a customer premises to a central office. ADSL
downstream band 403 occupies a band ranging from 140 KHz up to 1.1
MHz and carries ADSL signal from a central office to a customer
premises. Instead of employing FDM to separate the upstream and
downstream bands, the ADSL protocol allows upstream band 402 and
downstream band 403 to overlap and share spectrum from 25 KHz to
140 KHz using echo cancellation. ADSL supports full-duplex
communication. In accordance with ADSL protocol, the bandwidth
allocated to downstream signals (downstream band 403) is greater
than the bandwidth allocated to the upstream channel (upstream band
402) band in order to better accommodate models of information flow
that anticipate a greater amount of data flowing into a customer
premises rather than out of a customer premises.
[0056] HAN band 404 occupies the portion of the spectrum above 1.1
MHz. Due to line lengths associated with subscriber loops and the
resulting signal attenuation at frequencies above 1.1 MHz, it is
not practical to use this portion (the portion above 1.1 MHz) of
the spectrum for communications between a central office and a
customer premises. Line distances within a customer premises,
however, are sufficiently short that signals above the 1.1 MHz
range are successfully transmitted and received within a customer
premises. HAN 300 therefore, utilizes the portion of spectrum above
1.1 MHz thereby avoiding that portion of the spectrum utilized at
the central office to send signals to a customer premises.
[0057] FIG. 4B is an illustration of an alternative utilization of
spectrum 410 on POTS wiring 301 in accordance with the invention.
Spectrum 410 includes POTS band 401, ADSL upstream band 402, ADSL
downstream band 403 and HAN band 411. HAN band 411 occupies the
portion of the spectrum above 4 MHz. Spectrum 410 thus includes
spacing band 412. Spacing band 412 is a "dead band" that is not
occupied by signal, other than any signal due to frequency bleeding
from adjacent bands (e.g., from ADSL downstream band 403 or HAN
band 411). Use of spacing band 412 eases filter implementation by:
(i) eliminating the need for strict filter characteristics; (ii)
reducing the impact of group delay by allowing the placement of the
filter cutoff frequency further up into the dead band; and (iii)
providing a frequency band to transition between the highpass and
lowpass sections of the diplex filters discussed below.
[0058] HAN 300 is a symmetric network. This means that data rates
in the transmit and receive directions can be the same. Further,
HAN 300 provides a half duplex channel meaning that a single
network client transmits at a time. Thus HAN bands 404,411
accommodate both transmit and receive signals in a half duplex mode
of operation.
[0059] Referring back again to FIG. 3, each network client 302 is
equipped with an internally mounted HAN network interface card
(NIC). FIG. 5A is a functional block diagram of a preferred network
interface card (NIC) 500 in accordance with the present invention.
NIC 500 includes RJ-11 jacks 501, analog front end (AFE) block 502,
HAN modem ASIC 503, PCI connector 504 and digital video connector
505. RJ-11 jacks 501 are conventional POTS-compatible telephone
jacks. Thus, NIC 500 (and hence network client 302) are coupled to
HAN 300 in the same manner that conventional telephones are coupled
to the central office, by simply plugging into an existing RJ-11
wall jack. AFE block 502 is an interface circuit that performs
analog signal conditioning and provides electrical isolation and
surge protection in compliance with the Code of Federal Regulations
(C.F.R.) Part-68 for connection to the PSTN. In order to facilitate
HAN connectivity to multiple POTS lines (e.g., multiple networks of
POTS wiring 301) as is the case with a customer premises 306
equipped with two phone lines, AFE block 502 is equipped with two
RJ-11 jacks 501. In the two-phone-line-architecture a single
network is created by bridging the separate phone lines in the HAN
spectral domain.
[0060] HAN modem ASIC 503 is an application specific integrated
circuit (ASIC) including circuit modules for performing signal
processing including signal modulation and demodulation. HAN modem
ASIC 503 additionally includes an AFE interface 508, a PCI
interface 506 and a video interface 507. PCI interface 506 provides
the interface formatting and hand shake signals used to communicate
with the CPU on network client 302 over a PCI bus. In an
alternative embodiment, communication with the network client CPU
is over an ISA bus. Video interface 507 couples a digital video
stream, such as received from a satellite (DSS/DVB) receiver to the
HAN modem ASIC 503. Advantageously, video connector 505 and video
interface 507 together allow any NIC 500 to directly forward a
digital video stream from a source (such as a digital cable TV
receiver, or a satellite receiver) onto HAN 300 without requiring
the host CPU (the network client CPU) to receive the video and
without routing the video over the PCI bus. This direct interface
improves system performance and makes each NIC 500 "video
ready".
[0061] In another preferred embodiment, network client 302 is not
connected to HAN 300 via NIC 500 but instead is connected via a HAN
peripheral device external to network client 302. FIG. 5B shows a
HAN peripheral device 510 in accordance with the invention. HAN
peripheral device 510 includes RJ-11 jacks 511, AFE block 512, HAN
modem ASIC 513, digital video connector 514 and external interface
bus 515. Interface bus 515 is a conventional interface bus such as
USB or IEEE 1394 (FireWire). HAN modem ASIC 513 includes signal
processing functionality (e.g., modulation and demodulation), an
AFE interface, a digital video interface and an external bus
interface. HAN peripheral device 510 allows any network client 302
with a USB or IEEE 1394 (FireWire) interface to connect to HAN
300.
[0062] In alternative embodiments, HAN modem ASICs 503 and 513
additionally include POTS modem functionality (e.g., V.34 or V.56)
thereby providing access to both HAN network signals and to
conventional POTS signals. Further in accordance with this
embodiment, AFE blocks 502 and 512 additionally include a
conventional PSTN Data Access Arrangement (DAA) to provide POTS
modem capability. This added POTS modem capability advantageously
provides a user with connectivity to both the HAN and conventional
telecommunications services on a single NIC 500 (or HAN peripheral
device 510).
[0063] NIC 500 provides processing circuitry to demodulate and
decode HAN signals on the receive side and to encode and modulate
HAN signals on the transmit side. In a preferred embodiment, HAN
signals are modulated using quadrature phase shift keying (QPSK).
QPSK modulation is a relatively simple and thus a low cost
modulation scheme, though not noted for spectral efficiency.
Advantageously, the system is not constrained to a narrow spectral
band due to the relatively short lengths of UTP installed at a
customer premises. As discussed previously, as the length of UTP
increases, signal attenuation becomes a limiting factor,
particularly at higher signal frequencies. Therefore, bit rates are
maintained by using spectrum up to 40 MHz. In an alternative
embodiment, HAN signals are modulated using quadrature amplitude
modulation having either 4 states (QAM-4) or 16 states
(QAM-16).
[0064] FIG. 6 is a functional block diagram of the receive-side
processing 600 performed by HAN modem ASIC 503, 513. The processing
blocks include gain control amplifier 601, AGC loop filter 602, ADC
603, interpolator/DDC 604, Nyquist filter 605, clock recovery 606,
AGC 607, adaptive equalizer 608, demap and differential decoder
609, carrier recovery module 615 and forward error correction logic
610. Forward error correction logic 610 includes viterbi decoder
611, convolutional de-interleaver 612, Reed-Solomon decoder 613 and
descrambler 614. The receive side processing blocks process,
demodulate and decode a differentially encoded analog signal
received from the HAN.
[0065] The received analog signal is coupled to gain control
amplifier 601. The voltage of the received signal is first adjusted
by gain control amplifier 601 to bring the signal into a preferred
range for linear sampling by analog to digital converter (ADC) 603.
The sampled received signal is then fed to an interpolator/digital
down converter (DDC) 604. Interpolator/DDC 604 downconverts the
passband input signal to baseband. Interpolator/DDC 604 is driven
by clock recovery circuit 606 and carrier recovery module 615 to
generate four samples per symbol. Clock recovery circuit 606
recovers the symbol clock. Carrier recover module 615 recovers the
carrier frequency. In some implementations, in order to decrease
the clock rate of the subsequent downstream processing, the
incoming data is split into inphase and quadrature streams (not
shown), typically with two samples per symbol. The data are then
passed through matching Nyquist filter 605 for optimal signal
detection. After filtering, the signal is coupled to adaptive
equalizer 608 which removes the intersymbol interference caused
principally by the hostile reflection/multipath environment of
customer premises wiring (POTS wiring). Equalization is carried out
prior to any processing which is not linear time invariant such as
the decision circuitry in demap and differential decode 609. Demap
and differential decoder 609 includes a demapper and a differential
decoder. The demapper decodes the output symbol into a serial bit
stream according to the constellation transmitted (2 bits for QPSK
or QAM-4, 4 bits for QAM-16), and then the result is passed through
the differential decoder. The received analog data stream is
differentially encoded on the transmit side to allow simple
coherent detection and prevent phase ambiguities in the recovered
carrier from resulting in inaccurate data recovery.
[0066] The receive side processing blocks also include circuit
blocks for clock recovery (clock recovery 606), carrier recovery
module 615, and automatic gain control (AGC 607). The clock and
carrier recovery circuits 606, 615 utilize phase lock techniques to
maintain lock in the presence of noise. They also include sweep
generators for initial signal acquisition. When, in an alternative
embodiment, the gain control amplifier 601 is located externally to
HAN modem ASIC 503,513, either as a separate amplifier, or within a
tuner, AGC 607 generates a PWM signal that is low pass filtered
using an external LC filter (not shown).
[0067] The differentially decoded serial bit stream then enters
forward error correction (FEC) logic 610. Preferably, data is
encoded using a block outer code, such as Reed-Solomon, followed by
a convolutional inner code. Viterbi decoder 611 recovers the
convolutionally encoded data. Convolutional de-interleaver 612 then
de-interleaves the data. Next, a Reed-Solomon decoder 613 verifies
and error corrects the data using the check data added to the
bitstream. Depending on the propensity of the channel to burst
noise, the data may have been interleaved to effectively spread the
burst errors over time where they can be effectively corrected by
the convolutional and/or block coding. Although shown as part of
the FEC block, the function of descrambler 614 is to recover the
bit stream that was randomized in order to spread the transmit
signal energy and prevent any prominent spectral lines that might
arise due to periodic data patterns in the bit stream.
[0068] The result of processing in accordance with the functional
blocks shown in FIG. 6 is a received digital bit stream that is
coupled to the network client CPU using the appropriate interface
protocol (e.g., PCI, ISA, USB, IEEE 1394).
[0069] FIG. 7 is a functional block diagram of the transmit-side
processing blocks 700 of HAN modem ASIC 503, 513. The transmit-side
processing blocks include forward error correction encoder 701
(including Reed-Solomon encoder 703, convolutional interleaver 704,
viterbi encoder 705), scrambler 702, mapper and differential
encoder 706, Nyquist filter 707, interpolator 708, digital mixer
709, digital-to-analog converter (DAC) 710. Digital mixer 709
includes number controlled oscillator (NCO) 711, multipliers 712
and adder 713.
[0070] In operation, HAN modem ASIC 503, 513 receives a digital bit
stream for transmission over HAN 300. The incoming bit stream is
first randomized by scrambler 702. Scrambler 702 uses a linear
feedback shift register implementing a fifteenth order generator
polynomial. This scrambling disperses the transmit energy
throughout the available band and prevents the emergence of strong
spectral lines corresponding to periodic data in the input stream.
The randomized output is then fed into the FEC 701, which includes
an outer code implemented using a Reed-Solomon block, followed by a
Viterbi convolutional inner code. Depending on the propensity of
the channel to burst noise, the data is also interleaved using
convolutional interleaver 704 to effectively spread the burst
errors over time where they can be corrected by the convolutional
and/or block encoding.
[0071] Mapper and differential encoder 706 next receives the serial
bit stream for processing. The serial bit stream is mapped into
symbol space according to the constellation in use (2 bits for QPSK
or QAM-4, 4 bits for QAM-16), and differentially encoded to
facilitate coherent detection and unambiguous carrier/phase
recovery at the receiver. This processing generates symbol
data.
[0072] The symbol data is then Nyquist filtered using Nyquist
filter 707 to bandlimit the signal to the minimum required for
symbol recovery, and minimize intersymbol interference. Nyquist
filter 707 is preferably realized using a transversal finite
impulse response (FIR) structure.
[0073] The filtered symbol data is then interpolated by
interpolator 708 before being mixed (by digital mixer 709) into the
in-phase and quadrature phase components of the PSK signal. A
numerically controlled oscillator 711 (preferably implemented using
a table lookup) provides the sine and cosine coefficient data. The
quadrature components are then summed using summer 713 (preferably
resistively) prior to being fed to DAC 710.
[0074] Now referring again to FIGS. 5A, 5B, the analog transmission
signal generated by HAN modem ASIC 503,513 is next coupled to POTS
wiring 301 via AFE 502, 512. The resulting analog transmission
signal is a bandpass signal that occupies a region of the spectrum
above the portion occupied by conventional POTS services. Thus, the
analog transmission signals (the HAN network signals) are
transmitted using the POTS wiring 301 at a customer premises 306
without interfering with conventional POTS signals. Advantageously,
HAN network signals and conventional POTS services signals (e.g.,
conventional call connections and xDSL signals) simultaneously use
the same wiring infrastructure at a customer premises. The
installation of a separate client network infrastructure is avoided
and instead existing POTS wiring is leveraged for a second,
additional use.
[0075] In a preferred embodiment, network clients 302 share the HAN
bandwidth in accordance with a time division multiple access (TDMA)
protocol. In the preferred HAN embodiment where only one spectral
band is utilized, only one receiver/transmitter pair of network
clients 302 communicates at a time and each receiver/transmitter
pair are allocated a time slot for communication. Network usage
thus transitions from one receiver/transmitter pair to the next. In
this approach, overall network performance is significantly
affected by the speed at which receiver/transmitter network client
302 pairs effectively transition into network usage. To effect this
transition efficiently, selected signal processing control and
configuration parameters used in the receive and transmit
processing 600, 700 shown in FIGS. 6 and 7 are predetermined during
an initialization process and than stored locally on the HAN modem
ASIC 503. The stored parameters are then used to initialize both
the receive-side and transmit-side processing 600 and 700,
respectively each time a receiver/transmitter pair initiates
communication.
[0076] In particular, during the HAN system initialization process,
training is conducted to determine and store processing parameters
associated with each receiver-transmitter network client pair
(e.g., each communication channel). During network operation, HAN
signals (the modulated information signals) are modified in
accordance with the stored processing parameters for the associated
receiver/transmitter pair. Keeping local copies of processing
parameters at each network client avoids retraining each time a
receiver is to receive data from a new transmitter and allows rapid
switching of receivers and transmitters.
[0077] In one embodiment, the stored processing parameters (modem
parameters) include are a set of adaptive equalization coefficients
associated with adaptive equalizer 608 and the HAN signals are
modified by applying an equalization filter using the adaptive
filter coefficients. In accordance with this embodiment, the
initialization process includes a training session for each
communication channel to generate a set of adaptive filter
coefficients that match the characteristics of the channel. By
determining and storing the coefficients for each channel during an
initialization process, network throughput and performance is
improved.
[0078] Other modem parameters which are preferably predetermined
and stored include control parameters for AGC 607, for clock
recovery 606, carrier recovery 615, and NCO 711 and filter
coefficients for Nyquist filter 605, Nyquist filter 707, and
interpolator 708.
[0079] In accordance with another embodiment of the present
invention, the system and method monitors the channel
characteristics associated with a plurality of communication
channels to detect any change in the channel characteristics. After
detecting a change, the system and method can either update the
current modem parameters from the stored set of pre-trained
parameters, or request that the system retrain. This embodiment of
the invention is particularly advantageous during network operation
when the network experiences a change in configuration such as when
a telephone "ring" signal is received or when a telephone receiver
is picked up or when the network is physically modified by the
addition of a stub such as occurs when an additional telephone is
plugged in.
[0080] In accordance with still yet another embodiment of the
invention, the system and method implements an adaptive error
correction scheme. The system and method determines the type of the
data being communicated. For example, the system and method
determines whether the data is voice data, text data, graphic,
video and so forth. After determining the data type, the system and
method selects and applies one of a plurality of error correction
methods responsive to the determined data type. Further in
accordance with this embodiment of the invention, the system and
method additionally or alternatively determines the channel
characteristics associated with the receiver-transmitter pair and
selects one of the plurality of error correction methods responsive
to the channel characteristics. Advantageously, such an adaptive
error correction method provides for the selection of a preferred
error correction method (e.g., one better suited for video as
opposed to graphics or text etc.) based on data type as well as on
the particular characteristics associated with the channel to
improve channel throughput or to reduce channel latency.
[0081] Referring back again to FIG. 3, HAN 300 performance is
improved using a symmetric passive lowpass filter (filter) 308 at
the telephone network interface (TNI). The telephone network
interface is the demarcation point between the customer premises
and the subscriber loop. Filter 308 prevents HAN signals from being
placed on subscriber loop 306 and prevents noise generated on
subscriber loop 306 in the HAN spectral range from intruding on HAN
300. FIG. 8 shows filter 308 coupled to TIP and RING lines on both
the subscriber loop side and the customer premises side at the TNI.
Filter 308 has a cutoff frequency above the frequency of the POTS
services signals (e.g., above 1.1 MHz for POTS services including
ADSL). Signals passing from the customer premises to the subscriber
loop are lowpass filtered and similarly, signals passing from the
subscriber loop to the customer premises are lowpass filtered. As
stated previously, one advantage of the spectral avoidance/FDM
technique of the present invention is the interoperability with
legacy communications standards such as POTS, ISDN, and xDSL. Two
further advantages are that the spectral allocation of the HAN can
be moved even higher up the spectrum (as shown in FIG. 4B) to: (i)
avoid noisy areas of the spectrum and improve the overall system
signal to noise ratio; and (ii) facilitate embodiments wherein
filters 308 are inexpensive passive filters having less stringent
design requirements.
[0082] To understand the impact of HAN spectral allocation on the
design criteria imposed on filter 308, the filter requirements
stemming from a HAN allocation just above ADSL (e.g., above 1.1
MHz) is discussed. Then, for comparison, the design criteria
imposed on filter 308 when HAN spectral allocation is several MHz
above ADSL (e.g., 3 or 4 MHz or higher) is discussed.
[0083] In the first example, the goal is to design a passive
lowpass filter to pass ADSL signals, but not signals in the HAN
spectral range, and to place the bottom of the HAN spectral range
close to the upper edge of the ADSL band (e.g., close to 1.1 MHz).
As ADSL signals generally have significantly reduced energy by the
time they reach the customer premises, any additional insertion
loss or modification of the ADSL signal would degrade reception.
Therefore, the HAN lowpass filters (and diplexers) are designed for
maximum transparency in the lowpass filter passband. The filter is
preferably designed with a cutoff frequency near the top of the
ADSL band with a steep rolloff to avoid interference in the HAN
spectral band. A passive 5th order Chebychev lowpass filter with
0.2 dB of ripple in the passband and a cutoff frequency of 1.2 MHz
meets this design criteria. Such a filter gives essentially flat
attenuation throughout the ADSL passband of 1.1 MHz, and provides
35 dB of attenuation by 2 MHz.
[0084] FIG. 12 shows the group delay associated with this filter.
As the group delay graph of this filter shows, there is a
significant increase in group delay (over 500 nanoseconds) near the
top of the ADSL passband. This rapid increase in group delay added
by the passive filter could impair the ability of ADSL modems to
equalize the line. This type of group response, where there is a
rapid increase in group delay near the cutoff frequency, is typical
of passive ladder filters of the Butterworth/Chebychev type. The
group delay peak increases rapidly as the filter order is
increased.
[0085] However, as the lower edge of the HAN spectral range is
moved up in frequency (e.g., move the HAN band up the spectrum),
the design criteria for filter 308 relaxes. The cutoff frequency of
the filter 308 also moves up. As a result, the area of poor group
delay characteristic also moves up and into the unused frequency
range between the top of the ADSL passband and the bottom of the
HAN spectral range. For example, consider the selection of design
criteria in a system using HAN band 411 having a lower frequency of
4 MHz. FIG. 13 graphs the group delay characteristics of a passive
5th order Chebychev lowpass filter with 0.2 dB of ripple in the
passband and a cutoff frequency of 2.5 MHz. The group delay
increases over 300 ns from 1.5 MHz to 2.5 MHz, and in particular
there is a rapid increase in group delay from 2.1 MHz to 2.3 MHz,
but this will not adversely affect either the HAN or ADSL signaling
because the increase occurs in the transition band. The filter
gives essentially flat attenuation and constant group delay
throughout the ADSL passband, yet provides 35 dB of attenuation by
4 MHz. Note that moving the cutoff frequency up to 2.5 MHz
substantially decreases the values of the inductive elements in the
filter--this is beneficial because smaller inductors cost less, and
have higher self resonance frequencies.
[0086] Further movement of the bottom of the HAN spectral range up
in frequency would allow the use of lower order filters with
shallower rolloff, thus saving cost.
[0087] Lowpass filter 308 reflects signal energy in the filter
stopband (e.g., in the HAN spectral range) back onto the POTS
wiring. This reflected energy degrades signal quality, and although
this can be compensated for using adaptive equalization at the
receiver, it is advantageous if lowpass filter 308 is replaced at
the TNI by a diplexer filter. FIG. 9 shows a passive diplexer
filter 900. Use of diplexer filter 900 at the TNI advantageously
provides a matched termination impedance to HAN 300 at HAN 300
operating frequencies starting in the 3-4 MHz range. Matching
termination impedance advantageously reduces signal reflections on
HAN 300 thereby improving signal quality. Diplexer filter 900
includes a 100 ohm resistor 901, highpass filter 902 (having a
passband starting in the 3-4 MHz range--corresponding to the HAN
operating frequency range) and lowpass filter 903 (having a cutoff
not below 1.2 MHz). Lowpass filter 903 is connected in-line with
the POTS wiring 301 at the telephone network interface. Termination
resistor 901 is coupled to HAN 300 via highpass filter 902. Thus,
the impedance matching effect of termination resistor 901 is
limited to frequencies in the passband of highpass filter 902. For
frequencies at which HAN 300 operates, and also the frequencies
that highpass filter 902 passes signals, the impedance (z) of POTS
wiring 301 has an almost purely resistive impedance that is closely
approximated by the 100 ohm resistor 901.
[0088] FIG. 10 shows HAN 1000, an alternative embodiment of a HAN
in accordance with the present invention. HAN 1000 includes passive
diplex filters 1001 at the interface of customer premises equipment
(e.g., POTS telephones 1002 and modem 1003). HAN 1000 additionally
includes POTS wiring 1004 and network clients 1005. HAN 1000
couples network clients 1005 to form a computer network using
existing customer premises wiring (POTS wiring 1004) by frequency
division multiplexing as discussed in reference to FIG. 3. Filters
1001 improve HAN 1000 performance by (i) preventing energy in the
HAN spectral range (e.g. starting at 3-4 MHz) from entering POTS
wiring 1004; (ii) preventing energy in the HAN spectral range from
being aliased down to the operating frequency range of the customer
premises equipment (POTS telephones 1002 and modem 1003); and (iii)
providing a matched termination to HAN 1000. Matching the
termination of HAN 1000 is particularly advantageous in the case of
POTS telephones which change impedance in the HAN spectral range
when switching from on hook to off hook (e.g., when the handset is
picked up).
[0089] FIG. 11 is a block diagram of the diplex filters 1001 used
at the interface of the POTS telephones 1002 and modem 1003 as
shown in FIG. 10. Filter 1001 includes a 100 ohm resistor 1101
coupled to a highpass filter 1102 (having a pass band starting
between 3 and 4 MHz) and a lowpass filter 1103 (having a cutoff not
below 1.2 MHz). Resistor 1101 provides a matched termination to HAN
1100 at its operating frequencies. Passive diplex filter 1001 also
prevents energy in the HAN spectral range from entering the
subscriber loop, and energy in the HAN spectral range on the
subscriber loop from entering premises POTS wiring 1004.
[0090] The filters shown in and described in reference to FIGS. 3
and 8-11 are preferably passive filters that support telephone
voltages and currents. These passive filters pass DC signals on the
subscriber loop to the Customer premises wiring, even in the event
of a power failure. Use of such passive filters in conjunction with
the frequency division multiplexing (FDM) spectral avoidance
technique of the present invention enable continued telephone
service in the event of a local AC power failure ("lifeline
services"). Ordinary telephone service continues, despite the power
failure, because conventional POTS telephones operate off of a DC
current supplied by the central office. Advantageously, there is
thus no need for a backup battery to ensure continued availability
of telephone service in the event of a power failure. In contrast,
conventional PBX systems located at a customer premises cannot
offer lifeline service unless they also provide battery backup.
This is because they are installed between the subscriber loop and
the customer premises wiring and thus "break" the electrically
contiguous subscriber loop which ordinarily provides the DC
current.
[0091] It should be understood that in alternative embodiments, the
baseband signals occupying the POTS wiring are derived from sources
other than the subscriber loop. In other embodiments, the baseband
signals are derived from a wireless telecommunications link, a
coaxial cable-based source or other wide area networking means. For
example, alternative embodiments support delivery of broadband
digital data throughout the home from varied sources such as
satellite (DSS/DVB), terrestrial microwave (MMDS), digital
cable/CATV ("All TV"), digital or high definition television
(DTV/HDTV/ATV) and digital video disk (DVD) drive.
[0092] The above described HAN is an exemplary LAN that leverages
use of existing customer premises POTS wiring. Network signals
generated by the HAN coexist with POTS connection signals and with
xDSL signals on an already installed wiring network (POTS wiring)
at a customer premises. POTS signals are WAN signals in that they
can be associated with the PSTN, with a connection local to the
central office or another type of connection to a
telecommunications device located remote for the customer premises.
xDSL signals are associated with yet another WAN. Thus, signals
from three distinct networks (the PSTN, the xDSL WAN and the HAN)
coexist on a single electrically contiguous wiring infrastructure
at a customers premises. It is desirable to provide communication
among the three distinct networks. It is further desirable to
provide such communication without breaking the continuity of the
POTS wiring installed at the customer premises in order to maintain
lifeline POTS services. It should be understood that if the
existing POTS UTP wiring is to be used as the communications medium
for all three networks, maintaining lifeline POTS services
precludes breaking the line and the insertion of an active device
that prevents DC current flow upon loss of AC power. Such
internetwork communication and delivery of lifeline POTS service is
realized using a virtual gateway in accordance with the present
invention. Furthermore, the gateway functionality can be provided
by an existing PC coupled to the premises POTS wiring without the
addition of a new dedicated gateway hub device.
[0093] FIG. 14A illustrates a customer premises system 1400
providing access to, and interconnection among, three distinct
device networks: POTS-based WAN 1402, ADSL-based WAN 1403 and HAN
1404. It should be understood that, as used herein, POTS- and
ADSL-"based" WANs include WANs that are accessed via POTS and ADSL
services, respectively, over the subscriber loop. Thus, the
physical layer signaling protocol is either POTS or ADSL. WAN 1403
and WAN 1402, however, may both use the same higher layer
protocols. In fact the ADSL based WAN 1403 and the POTS based WAN
1402 may even be configured to access the same network (e.g. the
Internet). Through the POTS subscriber loop, using the POTS
physical layer protocol, one can access the PSTN or any number of
other networks. Through the POTS subscriber loop, using the ADSL
physical layer protocol one can access a number of, possibly
similar, networks.
[0094] Referring still to FIG. 14A, system 1400 includes a virtual
gateway (a gateway server) 1401 that facilitates the communication
among the distinct networks 1402-1404. The customer premises system
1400 also includes HAN network clients 1405 interconnected via HAN
1404 using installed POTS wiring 1407. System 1400 further includes
telephones 1406 coupled to POTS-based WAN 1402 via installed POTS
wiring 1407 and coupling devices 1408.
[0095] Virtual gateway 1401 is a gateway server that operates as a
gateway providing HAN 1404 with bidirectional communication with
WANs 1402 and 1403. Virtual gateway 1401 is a personal computer
having a plurality of network interface cards as described in
reference to FIG. 14B above. Virtual gateway 1401 additionally
includes a gateway software module that performs a virtual gateway
method to effect network protocol conversion and communication
among devices from the distinct networks 1402, 1403 and 1404. HAN
network clients 1405 are network clients associated with
(interconnected by) HAN 1404.
[0096] HAN network clients 1405 are personal computers each
equipped with a network interface card 500 described in reference
to FIG. 5A above. It should be understood, however, that the
principles of the present invention apply to virtual gateways 1401
serving other types of network clients such as specific purpose
computers, computer appliances, computer-enabled devices or other
types of network devices.
[0097] POTS wiring 1407 is conventional UTP wiring that is
generally routed internally in the walls of a customer premises
(e.g., a house) to various locations (e.g., rooms) within the
customer premises. POTS wiring 1407 is coupled to a telephone
central office via a subscriber loop.
[0098] HAN 1404 is a home local area network as described in
reference to FIGS. 3-11 above. HAN 1404 occupies a selected
spectral band on POTS wiring 1407. It should be understood that
although HAN 1404 is shown in FIG. 14A as a separate entity from
POTS wiring 1407, HAN network clients 1405 and virtual gateway 1401
HAN 1404 use (and thus includes) POTS wiring 1407 to interconnect
HAN network clients 1405 and virtual gateway 1401.
[0099] Coupling devices 1408 are combined HAN filter and POTS
splitter devices that perform passive filtering and impedance
matching discussed above. Coupling devices 1408 provides a matched
termination to the HAN in the HAN spectral range and includes a low
pass filter having a cutoff frequency at the low end of the ADSL
band (near 25 KHz).
[0100] Virtual gateway 1401 sends and receives signals in the
spectral ranges associated with each of the distinct networks
1402-1404 to effect bi-directional communication from HAN 1404 to
WANS 1402 and 1403. Each HAN network client 1405 associated with
HAN 1404 sends and receives signals limited to the HAN spectral
domain and virtual gateway 1401 "hops" network traffic between the
spectral domains of WANs 1402,1403 and HAN 1404 to effect a bridge
between the networks. Data received from a WAN (either 1402 or
1403) is first down converted to baseband, processed for network
protocol conversion then upconverted to the HAN spectral range and
then retransmitted on HAN 1404 so that it can be received by the
appropriate HAN network client 1405. Conversely, data received from
a HAN network client 1405 bound for either WAN 1402 or 1403 is
transmitted over the HAN to virtual gateway 1401 for conversion
down to baseband, network protocol conversion and followed by
modulation in accordance with the requirements of the destination
WAN and retransmission on the (to the) destination WAN. Other
implementations described below in reference to FIGS. 16 and 17
improve upon HAN bandwidth utilization. The implementation
described in reference to FIG. 14A, however, reduces the complexity
of the network interface card 500 installed in each HAN network
client 1405.
[0101] FIG. 14B is a functional block diagram of virtual gateway
server 1401. Virtual gateway server 1401 is a personal computer
1422 running virtual gateway software 1426 and equipped with a HAN
NIC 500, a POTS modem card 1420 and an ADSL modem card 1421.
Virtual gateway software 1426 executes on virtual gateway 1401 and
processes baseband data received from POTS modem card 1420 and ADSL
modem card 1421. The baseband processing performed by virtual
gateway software 1426 performs network protocol conversion to
convert data from the protocol associated with the sending network
to the protocol associated with the receiving network. HAN NIC 500
is the HAN NIC described above in reference to FIG. 5A. HAN NIC 500
is coupled to the customer premises wiring 1407 (shown in FIG. 14A)
via an RJ-11 jack 1423.
[0102] POTS modem card 1420 is a conventional POTS modem card that
provides modem (modulation-demodulation) functionality using the
POTS portion of the spectrum. POTS modem card 1420 is coupled to a
coupling device 1424 that includes an ADSL POTS splitter low pass
filter and HAN terminating matching impedence. POTS modem card 1420
is coupled to customer premises wiring 1407 via an RJ-11 jack 1423
and coupling device 1424.
[0103] ADSL modem card 1421 is a conventional ADSL modem card that
provides ADSL modem (modulation-demodulation) functionality. ADSL
modem card 1421 is coupled to coupling device 1425. Coupling device
1425 includes an ADSL POTS splitter high pass filter and a HAN
filter that has a stop band in the frequency range corresponding to
the HAN. ADSL modem card 1421 is coupled to customer premises
wiring 1407 via an RJ-11 jack 1423 and coupling device 1425.
[0104] FIG. 15 illustrates an example of the internetworking
functionality that can be provided by virtual gateway server 1401.
Specifically, virtual gateway server 1401 provides communication
between an asynchronous transfer mode (ATM) WAN and the TCP/IP
HAN.
[0105] In this embodiment, the ADSL-accessed WAN provides ATM
services directly to the premises through the ADSL modem, and the
HAN provides transmission control protocol/Internet protocol
(TCP/IP) services between the HAN clients on the premises
distribution network. In order to successfully internetwork these
dissimilar networks, the virtual gateway provides functionality on
a number of different levels according to the standard reference
models.
[0106] FIG. 15 shows the TCP/IP layers 1501 in the standard OSI
reference model and the ATM layers 1502 using the B-ISDN ATM
reference model. Rough functional equivalence between the models
layers can be seen by their horizontal adjacency in the diagram.
For example, the physical layer 1501a of the HAN corresponds to
transmission convergence sublayer 1502b and physical medium
dependent sublayer 1502a. Similarly, application layer 1502e of the
HAN corresponds to application layer 1502f of the ADSL ATM
network.
[0107] Gateway server 1401 provides the HAN physical and data link
layer functionality primarily through the HAN NIC card 500,
although some of the data link layer may be implemented by virtual
gateway software 1426 on the gateway server 1407. The TCP/IP
functionality found in layers three (Network) and four (Transport)
of the OSI model (1501c, d) are conventionally provided as a
portion of the server PC operating system. The ADSL layers shown in
the diagram are provided by a conventional ADSL modem/NIC card (not
shown), although some of the ATM functionality, particularly the
AAL sublayers (1502d, e) and ATM layer 1502c may be provided by
software running on the gateway server PC.
[0108] The virtual gateway software 1426 running on the server PC
implements protocols between the various layers 1501 and 1502 in
the two reference model stacks. Virtual gateway software 1426
allows applications running on the ATM network (the ADSL-accessed
network) to communicate with applications running on the TCP/IP HAN
network. In order to accomplish this, virtual gateway software 1426
handles protocol issues at the various levels, including, but not
limited to, address resolution, routing, segmentation and
reassembly, flow control/traffic shaping, error management,
acknowledgments, synchronization, QoS issues, security issues,
accounting issues, and multicasting/broadcasting issues. ATM is a
connection oriented/virtual circuit, cell oriented technology with
strong focus on QoS, whereas TCP/IP is a connectionless datagram
oriented service, therefore the protocol differences between the
two networks are significant.
[0109] Virtual gateway software 1426 thus provides a baseband
channel (a communication means) between the HAN NIC 500 and the
ADSL modem card both installed in gateway server 1401.
[0110] It should be understood that the xDSL accessed WAN need not
be an ATM network, but rather it could be a TCP/IP network or any
number of different network types. The internetworking issues
surrounding communicating with any dissimilar network are similar
to those outlined above.
[0111] The system 1400 described in reference to FIG. 14A is a
centralized gateway system. Alternative embodiments of the
invention use either a partially distributed gateway or a fully
distributed gateway. Fully and partially distributed virtual
gateways described below in reference to FIGS. 16 and 17,
respectively, improve HAN bandwidth utilization as compared to use
of a central virtual gateway.
[0112] FIG. 16 illustrates a customer premises having a fully
distributed virtual gateway system 1600 that provides access to
distinct networks 1602,1603 and 1604.
[0113] WAN 1602 is a POTS-based network, WAN 1603 is an xDSL
accessed WAN and HAN 1604 is a home local area network as described
above in reference to FIGS. 3-11. Access to each network 1602-1604
is provided using installed POTS wiring 1607. Telephones 1606 are
coupled to POTS -based WAN 1602 via coupling devices 1609 and POTS
wiring 1607. HAN network clients 1605 are each coupled to HAN 1604
and to xDSL-based WAN 1603 using existing POTS wiring 1607 accessed
via an RJ-11 telephone jack 1611. In this fully distributed
implementation, the gateway/bridge functionality is not
centralized, and instead each HAN network client 1605 both sends
and receives information on either HAN 1602 or WAN 1603. This
distributed implementation results in improved system flexibility
and robustness but increases the complexity of each HAN network
client 1605. Overall throughput on all of the networks is optimized
because data does not need to be "hopped" or retransmitted on any
of the networks.
[0114] HAN network clients 1605 are conventional personal computers
or other network client devices equipped with a HAN NIC 500 as
described above in reference to FIG. 5. HAN network client 1605
additionally includes a conventional ADSL modem card 1610. ADSL
modem card 1610 performs both transmit and receive functions to
transmit and receive signals in accordance with ADSL format and
protocol. Both the HAN NIC 500 and ADSL modem 1610 are coupled to
POTS wiring 1607 via RJ-11 jack 1611. The ADSL modem 1610, however,
is coupled to RJ-11 jack 1611 via ADSL coupling device 1612. ADSL
coupling device 1612 has an ADSL POTS splitter portion that is a
high pass filter as well as a HAN filter (providing filtering in
the HAN spectral range).
[0115] FIG. 17 illustrates a customer premises system 1700 having a
partially distributed virtual gateway. System 1700 provides access
to distinct networks 1702, 1703, and 1704. Network access is
provided using installed POTS wiring 1707, a gateway server 1701
and a unidirectional gateway at each HAN client 1705. In this
implementation, HAN clients 1705 receive WAN (1702,1703) data
directly but send data to the destination WAN by going through
gateway server 1701. System 1700 thus provides distributed
"receive"-side access to ADSL-accessed WAN 1703. This partially
distributed implementation is preferred for broadcast type WAN data
such as video on-demand (VOD). System 1700 provides conventional
telephones 1706 with access to POTS-based WAN 1702 via passive
coupling device 1708.
[0116] HAN clients 1705 are conventional personal computers or
other network client devices equipped with a HAN NIC 500 as
described above in reference to FIG. 5. HAN network client 1705 is
additionally equipped with an ADSL modem card 1711. ADSL modem card
1711 is a "receive only" modem card that provides ADSL receiving
functionality. ADSL modem card 1711 is coupled to POTS wiring 1707
via RJ-11 jack 1712 and coupling device 1713. Gateway server 1701
is coupled to POTS wiring 1707 via RJ-11 jack 1712. Gateway server
1701 is a personal computer equipped with an ADSL modem card 1714
as well as a HAN NIC 500. ADSL modem card 1714 is a "transmit only"
ADSL modem card that provides ADSL transmit capability.
[0117] FIG. 18 shows another embodiment of a virtual gateway system
1800 in accordance with the present invention. This embodiment
provides two distinct home local area networks (HANs) using
installed customer premises wiring and further provides
interconnectivity between the district HANs as well as between each
HAN and various WANs accessed using the installed customer premises
wiring. The system 1800 includes POTS-based WAN 1801, ADSL-accessed
WAN 1804, first HAN (HAN1) 1803 and second HAN (HAN2) 1810
interconnected via POTS wiring 1811. FIG. 19 illustrates the
spectral allocation (the spectrum 1900) of the POTS wiring 1811.
POTS signals 1901 occupy baseband up to approximately 4 KHz. ADSL
upstream signals 1902 occupy spectrum from approximately 25 KHz to
1.1 MHz; ADSL downstream signals 1903 occupy from approximately 140
KHz to 1.1 MHz. The spectrum 1900 also includes a dead band 1904
separating HAN1 spectrum 1905 from the ADSL signals 1903. HAN1
spectrum 1905 occupies approximately from 4 MHz to 10 MHz and HAN2
spectrum 1907 occupies from approximately 14 MHz to 20 MHz with
HAN1 spectrum 1905 and HAN2 spectrum 1907 being separated by a dead
band 1906.
[0118] Referring now back to FIG. 18, system 1800 includes a
plurality of HAN1 clients 1805, a plurality of HAN2 clients 1806 as
well as conventional telephones 1808 coupled to customer premises
wiring (POTS wiring) 1811 via passive coupling devices 1807. System
1800 also includes a central virtual gateway 1809.
[0119] HAN1 1803 provides communication among HAN1 clients 1805
using information signals confined to the spectral band associated
with HAN1 1803 as shown in FIG. 19. Similarly, HAN2 1810 provides
communication among HAN2 clients 1806 using information signals
confined to the spectral band associated with HAN2 1810 as shown in
FIG. 19. Information is transferred between HAN1 1803 and HAN2 1810
using virtual gateway 1809.
[0120] Virtual gateway 1809 includes a HAN NIC (as described above
in reference to FIG. 5) for each of HANI 1803 and HAN2 1810.
Virtual gateway 1809 additionally includes an ADSL modem card
allowing bidirectional communication with WAN2 1804 and a POTS
modem card for communicating with networks accessed using
conventional POTS-compatible modems. Thus, two distinct local area
networks (HAN1 1803 and HAN2 1810) coexist on the same wiring
infrastructure (customer premises wiring) that also delivers
conventional POTS services.
[0121] It should be understood that although the above described
embodiments have modem cards (e.g., HAN NIC cards, ADSL modem cards
and POTS modem cards) that are separate circuit cards, other
embodiments of the invention combine one or more of the above
described modems into a single modem chip located on a single modem
card.
[0122] The foregoing discussion discloses and describes merely
exemplary methods and embodiments of the present invention. As will
be understood by those familiar with the art, the invention may be
embodied in other specific forms without departing from the spirit
or essential characteristics thereof. Accordingly, the disclosure
of the present invention is intended to be illustrative, but not
limiting, of the scope of the invention, which is set forth in the
following claims.
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