U.S. patent application number 10/509276 was filed with the patent office on 2006-01-19 for suprvisory channel in an optical network system.
Invention is credited to Niraj Agrawal, Elke Jahn.
Application Number | 20060013149 10/509276 |
Document ID | / |
Family ID | 28051740 |
Filed Date | 2006-01-19 |
United States Patent
Application |
20060013149 |
Kind Code |
A1 |
Jahn; Elke ; et al. |
January 19, 2006 |
Suprvisory channel in an optical network system
Abstract
There is provided an optical network element for use in a node
of an optical network including a plurality of nodes which are
interconnected so as to be capable of carrying traffic between
selected nodes, comprising a local network management system
including means for building up a supervisory connection between
the network element and at least a network element of a further
node of the optical network. The local network management system is
installed to support an arbitrary network topology and to build up
a survivable supervisory connection to at least one predetermined
other node of the network so as the network element could be
integrated in an optical network with arbitrary topology. An
optical network and a method of providing a supervisory network are
also provided.
Inventors: |
Jahn; Elke; (Hochberg,
DE) ; Agrawal; Niraj; (Hochberg, DE) |
Correspondence
Address: |
OHLANDT, GREELEY, RUGGIERO & PERLE, LLP
ONE LANDMARK SQUARE, 10TH FLOOR
STAMFORD
CT
06901
US
|
Family ID: |
28051740 |
Appl. No.: |
10/509276 |
Filed: |
March 14, 2003 |
PCT Filed: |
March 14, 2003 |
PCT NO: |
PCT/EP03/02704 |
371 Date: |
August 4, 2005 |
Current U.S.
Class: |
370/254 |
Current CPC
Class: |
H04J 14/0284 20130101;
H04J 14/0283 20130101; H04Q 2011/0081 20130101; H04J 14/02
20130101; H04L 41/042 20130101; H04Q 2011/0077 20130101; H04Q
11/0062 20130101; H04Q 2011/0088 20130101; H04L 41/044 20130101;
H04J 14/0297 20130101 |
Class at
Publication: |
370/254 |
International
Class: |
H04L 12/28 20060101
H04L012/28 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2002 |
EP |
020007008.2 |
Claims
1. An optical network element for use in a node of an optical
network that includes a plurality of nodes that are interconnected
so as to be capable of carrying traffic between selected nodes, the
optical network element comprising: a local network management
system having means for building up a supervisory connection
between the optical network element of a first node of said
plurality of nodes and at least a network element of a second node
of said plurality of nodes of the optical network; wherein the
local network management system is supports an arbitrary network
topology and builds up the supervisory connection to at least one
predetermined other node of the plurality of nodes of the network
so that the network element can be integrated in an optical network
with arbitrary topology, wherein the supervisory connection is a
redundant connection through two or more paths, and wherein the
local network management system monitors the status of all paths of
the redundant supervisory connection, and establishes an
alternative route for a specific supervisory connection in the
event of an impairment of the specific supervisory connection.
2. The optical network element according to claim 1, wherein the
local network management system provides self healing of the
supervisory connection for an impairment of the supervisory
connection.
3. The optical network element according to claim 1, further
comprising a software module associated with the network management
system, that acts as a node manager and includes a software agents
selected from the group consisting of: a start-up manager, a
process, thread and session manager, a supervisory channel manager,
a hardware devices manager, a status, fault, and events monitor, a
database system manager, at least one user interfaces, and a system
resources and functions manager, and any combinations thereof.
4. The optical network element according to claim 1 wherein the
local network management system can be configured by standard
software protocols.
5. The optical network element according to claim 1, wherein the
local network management system automatically discovers network
elements of adjacent network nodes of said plurality of nodes and
to exchanges Link State Advertisement with the adjacent network
elements of the adjacent network nodes of said plurality of
nodes.
6. The optical network element according to claim 1, further
comprising: at least one back-plane including a plurality of
electrical transmission lines running across the back-plane and a
plurality of electrical terminals connected to the plurality of
electrical transmission lines; a plurality of line-card slices
having line-card slice electrical terminals, wherein each line-card
slice is attached to the back-plane, so that the line-card slice
electrical terminals are electrically connected to the electrical
terminals of the plurality of electrical terminals of the
back-plane; at least one optical receiver associated with at least
one of the plurality of line-card slices for receiving optical
signals from the network; at least one opto-electrical converter
integrated in or optically connected to the optical receiver with
electrical terminals of the at least one opto-electrical converter
and; at least one optical transmitter associated with at least one
of the plurality of line-card slices for transmitting optical
signals to the network; at least one electro-optical converter
integrated in or optically connected to the optical transmitter
with electrical terminals of the at least one opto-electrical
converter; and at least one supervisory card plugged to the
back-plane capable of functions selected from the group consisting
of transmitting supervisory signals, processing supervisory
signals, and a combination thereof, wherein at least one of the
electrical terminals of said plurality of electrical terminals are
switch terminals that provide selected and reconfigurable
electrical interconnections among components of at the least one
line-card slice selected from the group consisting of the receiver,
the transmitter, the converter, and any combination thereof,
wherein the interconnections are accomplished by devices selected
from the group consisting of an electrical switches and at least
one electrical cross-connect, and wherein the supervisory card is
electrically connected via the electrical transmission lines of the
back-plane to a one of said plurality of line-card slices by a
connection selected from the group consisting of directly
connection and a cross-connect.
7. The optical network element according to claim 6, further
comprising a node PC, that is plugged to the back-plane, that
provides and/or receives an electrical supervisory signal, that is
transmitted to or from the supervisory card.
8. The optical network element according to claim 7, wherein the
node PC is connected to the network as a standalone computer
sub-system.
9. The optical network element according to claim 1, wherein the
supervisory connection provides at least a part of an in-band
supervisory data by using electrical multiplexing and
demultiplexing of the supervisory data with client's data, carried
by the optical network.
10. The optical network element according to claim 1, wherein the
supervisory connection provides at least a part of an out-of-band
supervisory data multiplexed onto or demultiplexed from one or more
optical fiber links of the optical network by a device selected
from the group consisting of a WDM coupler and a filter.
11. An optical network that includes a plurality of nodes that are
interconnected so as to be capable of carrying traffic between
selected nodes, comprising: a plurality of network elements
according to claim 1; a network management system carried out by at
least one of the local network management systems of the network
elements; and supervisory connections between predetermined network
elements.
12. The optical network according to claim 11, wherein the network
management system provides establishment of a direct logical
supervisory connection between any desired pair of nodes of said
plurality of nodes interconnected by the supervisory
connection.
13. The optical network according to claim 12, wherein at least one
of the direct logical supervisory connections are carried at least
in part by a technique selected from the group consisting of time
division multiplexing, statistical multiplexing, and a combination
thereof, over a single physical supervisory connection between a
pair of nodes.
14. The optical network according to claim 11, wherein the network
management system provides a function selected from the group
consisting of: hardware fault detection on all of the supervisory
connections, software error detection on all of the supervisory
connections, auto-recovery of the supervisory connections,
fault-tolerant supervisory connections, redundant supervisory
connections, automatic discovery of nodes of the optical network,
and any combinations thereof.
15. A method of providing a supervisory network in an optical
network having an arbitrary network topology that includes a
plurality of nodes that are interconnected so as to be capable of
carrying traffic between selected nodes, the method comprising:
automatically discovering the network topology; and establishing of
redundant supervisory connections between predetermined nodes of
said plurality of nodes of the network; monitoring the status of
all paths of the redundant supervisory connection; and establishing
an alternative route for a specific supervisory connection in the
event of an impairment of the specific supervisory connection.
16. The method according to claim 15, wherein each node of the
plurality of nodes of the network includes a local network
management system, wherein the local network management system of
each of said plurality of nodes communicates with the local network
management system of adjacent nodes of said plurality of nodes and
exchanges Link State Advertisements, so that each node of said
plurality of nodes discovers all of the adjacent nodes of said
plurality of nodes and by utilizing the exchanged Link State
Advertisements a routing table is generated that is stored in at
least one of the plurality of nodes.
17. The method according to claim 16, wherein the node manager of
each node of said plurality of nodes executes a single OSPF,
wherein the OSPF in each node of said plurality of nodes
communicates with the node manager of the adjacent nodes of said
plurality of nodes so that the OSPF converges on the topology of
the network.
18. The method according to claim 15, further comprising monitoring
the status of the supervisory connections and configuring
alternative routes in the event of link failure.
19. The method according to claim 15, further comprising: sending
supervisory data that is carried by the optical network for use in
a supervisory management layer of the network in the form of
messages through at least one available redundant connections from
a sending end to a receiving end of the network; giving each
message a sequence number; and 19.3 discarding duplicate messages
on the receiving end and passing only one of several arriving
messages on to the supervisory management layer.
20. The method according to claims 16, wherein the network
management is carried out by the node manager present in the local
management systems in at least one node of the network.
21. The method according to claim 15, further comprising carrying
out a function on all supervisory connections, wherein the function
is selected from the group consisting of hardware fault detection,
software error detection, and a combination thereof.
22. The method according to claim 15, further comprising carrying
out a function on all supervisory connections, wherein the function
is selected from the group consisting of auto-recovery and
self-healing.
23. The method according to claim 15, further comprising the steps
of: monitoring a status of each supervisory connection by sending
keep-alive messages at predetermined intervals of time between the
predetermined nodes and by resending reply-messages on receiving of
a keep-alive message; and closing down the supervisory connection
between the predetermined nodes in the event that the reply-message
in response to the keep-alive message is not received within a
predetermined time period.
24. The method according to claim 23, further comprising the step
of automatically re-establishing a new connection between the
predetermined nodes via an alternative connection path.
25. The method according to claims 15, further comprising storing
information concerning the network status in the local network
management system of at least one predetermined node, wherein the
information is selected from a group consisting of predetermined
information, real time information, and a combination thereof.
26. The optical network element according to claim 3, wherein the
at least one user interface is selected from the group consisting
of GUI, console and TL1.
27. The optical network element according to claim 4, wherein the
standard software protocol is selected from the group consisting of
OSPF, MPLS, and a combination thereof.
28. The optical network element according to claim 6, wherein each
line-card slice is connected to the back-plane by an attachment
selected from the group consisting of direct attachment and a
plug-in module.
29. The method according to claim 16, wherein the local network
management system includes at least one node manager.
30. The method according to claim 18, wherein monitoring the status
of the supervisory connections is accomplished by OSPF.
Description
[0001] The present invention belongs to the field of optical
communication systems and, more particularly, to dense wavelength
division multiplexed optical networks with arbitrary topology,
e.g., point-to-point, ring, mesh, etc.
[0002] The soaring demand for virtual private networks, storage
area networking, and other new high speed services are driving
bandwidth requirements that test the limits of today's optical
communications systems. In an optical network, a node is physically
linked to another using one or more optical fibres (cf. FIG. 1).
Each of the fibres can carry as many as one hundred or more
communication channels, i.e., wavelengths in WDM (Wavelength
Division Multiplex) or Dense WDM (DWDM) systems. Thus, for example,
for a node with three neighbours as many as three hundred or more
wavelength signals originate or terminate or pass through a given
node. Each of the wavelengths may carry signals with data rates up
to 10 Gbit/s or even higher. Thus each fibre is carrying several
terabits of information. This is a tremendous amount of bandwidth
and information that must be managed automatically, reliably,
rapidly, and efficiently. It is evident that large amount of
bandwidth needs to be provisioned. Fast and automatic provisioning
enables network bandwidth to be managed on demand in a flexible,
dynamic, and efficient manner. Another very important feature of
such DWDM networks is reliability or survivability in presence of a
failure such as an inadvertent fibre-cut, various types of hardware
and software faults, etc. In such networks, in case of a failure,
the user data is automatically rerouted to its destination via an
alternate or restoration path. For example, for the mesh network
shown in FIG. 1, the primary and restoration paths are as follows:
TABLE-US-00001 TABLE 1 Demand ID End Nodes Protocol Primary Path
Restoration Path D1 [#1,#5] A #1 <-> #2 <-> #5 #1
<-> #4 <-> #5 D2 [#1,#3] C #1 <-> #2 <-> #3
#1 <-> #4 <-> #3
[0003] Note that if the primary paths of demands D1 or D2 fail due
to the failure of link #2-#5 or link #2-#3, a single wavelength
channel over link #1-#4 could be used to restore both demand-ids D1
and D2. This is due to the fact that under single point of failure
assumption, either link #2-#5 or link #2-#3 fails but not both at
the same time. Thus as opposed to 1+1 where a 100% overcapacity is
required for survivability, the same extra capacity can be shared
between different demands for restoration. This results in
significant savings in overall extra capacity required to realize
survivable DWDM systems.
[0004] There have been proposals to create such mesh networks using
cross-connects, which in case of core networks with several
neighbours and large wavelength count, require gigantic switch
matrices or cross-connects and several O/E and E/O conversions
making the cost of such a system prohibitively expensive. While a
handful of the national and international carriers are able to
afford such expensive systems, such systems are outside the budget
of small and local carriers and enterprises, which operate the
so-called metro, or enterprise networks. Such networks require
relatively smaller number of wavelengths but tend to be more
"meshy" than core networks. Thus it follows that there is a
tremendous need for DWDM systems, which are highly modular and
low-cost and which can be scaled both upwards and downwards in
capacity and cost for smaller customers. The situation is analogous
to the case of the personal computer and mainframes, where the
customer wants and needs some of the key features of a complex and
large system but needs and can afford to pay for only a small (in
terms of hardware) system. Automatic provisioning and restoration
is highly desirable but at present is unaffordable for metro or
enterprise networks. In such a network a complete
protection/restoration of the network under single point of failure
is provided.
[0005] Up to now, to increase capacity, carriers implement protocol
dependent architectures and switches/cross-connects, e.g.
SONET(Synchronous Optical Network)/SDH (Synchronous Digital
Hierarchy) multiplexing with its ring architecture, ATM
(Asynchronous Transfer Mode) and fibre-channel switches, etc. Such
networks, which provide protection against multiple types of
failures including the fibre cut, are expensive and work only for
ring architecture and specific protocols.
[0006] It is an object of the present invention to overcome the
disadvantages of the state of the art and especially to provide a
network element for use in an optical network to create
intelligent, transparent, any-protocol-at-any-time, high speed
systems comprising multiple nodes in an arbitrary topology, e.g.,
point to point, ring, mesh, etc. Moreover, an optical network with
a network management system built up from such network elements
should be provided. In particular, a supervisory network should be
provided for information exchange between various nodes in an
optical network with arbitrary topology.
[0007] The object of the invention is realized by an optical
network element according to claim 1, a corresponding optical
network according to claim 7 and a method of providing a
supervisory network in an optical network according to claim 11.
The subclaims describe preferred embodiments of the invention.
[0008] With one or more of the network elements according to the
invention an intelligent optical network could be build up or an
existing network could be adapted or scaled up to an intelligent
system. Intelligence refers to, among other things, how information
related to various aspects of network configuration, operation, and
management is stored in the network. Information refers to any
details related to the state of network elements, the state of the
network, various primary and redundant paths through the network,
configuration data, and any other data which is pertinent to the
optical network management system, etc. All information can be a)
stored at a single node, b) duplicated over several or all network
nodes, or c) distributed over several or all network nodes. The
distributed approach c) scales well as the number of nodes
increases because any single node needs to deal with a reduced
amount of information. But a software overhead penalty must be paid
because the various pieces of information must be obtained from
various nodes and inconsistencies between any duplicated
information must be resolved. An alternative is to store all the
information at a single node (approach a), which can be accessed by
any user at any of the network nodes, or a user located elsewhere
such as one or more management offices. However, if this node fails
all the valuable data is lost. In order to solve this problem, the
same data can be stored at several or all network nodes (approach
b). In case one of the network nodes fails, the data can then be
retrieved from one of the several other nodes which carry a copy of
the original data. Another aspect of intelligence involves who
takes the required management actions and how. A management action
involves performing a set of tasks and can be carried out in a
centralized, distributed, or hybrid manner. The various tasks can
in turn also be performed in a centralized or distributed manner.
In the centralized approach a single task is carried out for
example by one or more software agents residing at various nodes. A
software agent is a software process or an execution thread which
is used to implement a certain software functionality.
[0009] The optical network element according to the present
invention for use in a node of an optical network including a
plurality of nodes which are interconnected so as to be capable of
carrying traffic between selected nodes comprises a local network
management system. The local network management system includes
means for building up a supervisory connection between the
respective network element and at least a further network element
of a further node of the optical network. The local network
management system, that means the network management system of a
specific network element in the network, is able to support an
arbitrary network topology so as to build up a supervisory
connection to at least one other node of the network with the
arbitrary topology. Therefore, the optical network element
according to the present invention could be integrated in an
optical network with arbitrary topology, for example either in an
existing network or a new network comprised of a plurality of
network elements according to the invention.
[0010] In a preferred embodiment the network element is provided
with a local network management system that provides self healing
of the supervisory connection between the respective network
element and a predetermined further network element of the network.
Thereby, self healing means, that in the event of an impairment of
a specific supervisory connection the local network management
system re-establishes the respective supervisory connection or
establishes an alternative supervisory connection between these
nodes which were interconnected by the now disrupted supervisory
connection.
[0011] Preferably, the local network management system comprises of
a software module which acts as a node manager. This node manager
preferably includes one or more software agents, which are
described in further detail in the following with reference to the
figures.
[0012] In a preferred embodiment, the local network management
system has the flexibility to be configured by standard software
protocols, for example by OSPF (Open Shortest Path First) which is
a routing protocol used in general within larger autonomous system
networks in preference to the RIP (Routing Information Protocol).
However, of course the network management system according to the
present invention could be configured by RIP. A further protocol by
which the local network management system could be preferably
configured is the MPLS (Multiprotocol Label Switching).
Multiprotocol Label Switching is a versatile solution to address
the problems faced by present-day networks, for example speed,
scalability, quality-of-service management, and traffic
engineering.
[0013] In a preferable embodiment the local network management
system is provided with a functionality that provides an automatic
discovery of network elements of adjacent network nodes and an
automatic exchange of Link State Advertisement with the discovered
network element.
[0014] A very preferable embodiment of the network element
according to the invention is an intelligent network element which
comprises of at least one back-plane with a plurality of electrical
transmission lines, which run across the back-plane. Furthermore,
the back-plane contains a plurality of electrical terminals, which
are connected to the transmission lines for attaching of electrical
devices such as various cards and/or circuit packs with determined
circuitry that should be interconnected by the back-plane.
[0015] The hardware structure of the network element according to
these very preferable embodiment is described in the application
02007008.2 from the same applicant, filed with the EPO on
27.03.2002, the disclosure of which is incorporated into the
present application by reference. As described, these network
element further comprises at least one of a first line-card slice
with at least one receiver for receiving of optical signals from a
predetermined path of the optical network in which the network
element is integrated. The network element furthermore comprises of
at least one of a second linecard slice with at least one
transmitter for transmitting of optical signals to a predetermined
path of the optical network. The line-card slices can be local
line-card slices or remote line-card slices, for example the said
first line-card slice could be a local line-card slice and the said
second line-card slice could be a remote line-card slice. However,
it is also possible to provide to local or remote line-card slices,
one for receiving and one for transmitting of optical signals from
respective to the optical network, or both for receiving and
transmitting of optical signals. The terms "local" and "remote" are
used herein to distinguish between two line-card slices, which
provide transmit/receive interfaces to local user equipment in a
central office or data centre and the user equipment located at a
remote node.
[0016] Each line-card slice with a receiver comprises an
opto-electrical converter for converting the received optical
signals to electrical signals. The opto-electrical converter could
be integrated in the receiver (so-called opto-electrical receiver)
or attached as an independent device to the receiver. The at least
one electrical terminal of the opto-electrical converter is
attached to one or more electrical terminals of the at least one of
the electrical terminals of the line-card slice.
[0017] Each line-card slice, which comprises a transmitter, is
provided with an electro-optical converter, which could be
integrated in the transmitter (so-called electro-optical
transmitter) or attached as an independent device to the
transmitter. The electrical terminal of the electro-optical
converter is connected to one or more of the at least one of the
electrical terminals of the line-card slice.
[0018] The line-card slices are plugged--directly or indirectly,
with the latter preferably by means of a chassis--into the
back-plane such that the electrical terminals of the line-card
slices are connected to the electrical terminals of the back-plane
and thereby the electrical terminals of various line-card slices
are interconnected, thus allowing them to communicate with each
other, via the electrical transmission lines in the back-plane.
[0019] The network element according to the preferable embodiment
comprises a plurality of switch terminals, which are provided
between the converters of various line-card slices and/or between
various converters on a single line-card slice. The switch
terminals allow providing predetermined but reconfigurable
electrical interconnections between various optical receivers and
transmitters in the network element. The switch terminals may be
provided on the back-plane, however, it is preferred to provide
them on the line-card slices such that one or more of the
electrical terminals of a converter on a line-card slice could be
electrically connected to a predetermined electrical terminal or
set of terminals of the line-card slice or to one or more of the
electrical terminals of one or more further converters on the same
line-card slice. Preferably, the switch terminals allow
reconfigurable interconnections among various electrical terminals
by using software or software commands, this means intelligence
offered by software can be used to determine in real-time as to
which terminals are interconnected in order to react dynamically to
the various possible network states. To provide the reconfigurable
electrical interconnections are preferably used electrical switches
or--as described in the following--electrical cross-connects.
[0020] For switching of signals from a first path to a second
path--for example primary path to restoration path--the network
element preferably comprises at least one electrical cross-connect
having first electrical terminals for receiving and/or input of
electrical signals and second electrical terminals for transmitting
and/or output of electrical signals. The electrical cross-connect
directs electrical signals from selected first to selected second
electrical terminals, thereby determining the way of the signals
through the network. The electrical cross-connect is plugged into
the back-plane--directly or indirectly--whereby the electrical
terminals of the cross-connect are connected to the electrical
terminals of the back-plane so that the first electrical terminals
are interconnected via the electrical transmission lines of the
back-plane to electrical terminals of selected first line-card
slices (with at least one receiver) and the second electrical
terminals of the cross-connect are interconnected via the
electrical transmission lines to electrical terminals of selected
second line-card slices (with at least one transmitter).
[0021] To keep the electrical connections between the line-card
slices and the cross-connect short in order to achieve low signal
attenuation the line-card slices and the at least one cross-connect
are preferably distributed on the back-plane in such a way that
each cross-connect is electrically sandwiched between a
predetermined number of line-card slices with at least one receiver
and line-card slices with at least one transmitter. By this
arrangement the electrical signals from a first line-card slice,
e.g. a local line-card slice, are transmitted over very short
transmission lines to the cross connect and then further from the
cross-connect over very short transmission lines to the second
line-card slice e.g. a remote line-card slice. The various
line-card slices and electrical cross-connects can be attached to
the back-plane for example either directly or as plug in
modules.
[0022] Especially in bi-directional network architectures each
line-card slice comprises preferably both of one optical
transmitter and one optical receiver together with the
corresponding converters. In bi-directional network architectures
each node is connected to another node by at least two separate
lines for signal traffic with signals travelling in opposite
directions. The signals reaching one node are received and
converted by the receiver and the signals leaving the node are
preferably converted and transmitted by the optical transmitter of
each line-card slice, respectively.
[0023] For use of the network element in a DWDM network system the
network element comprises preferably at least one filter-unit for
transforming of the optical multi-wavelength signals into
individual wavelength channel signals. The filter-unit is arranged
in an optical path before (with respect to the flow of optical
signals) an optical receiver of a line-card slice or behind an
optical transmitter of a line-card slice. The filter-unit is
preferably implemented in one or more filter-cards, which are
pluggable--directly, or indirectly, the latter preferably by means
of a chassis into the back-plane. By use of the transmission lines
running across the back-plane and the corresponding electrical
terminals the filter-units or cards could be electrically managed
and controlled via the back-plane or by means of electrical devices
attached to the back-plane.
[0024] The filter-unit advantageously comprises a modular structure
with various stages, whereby each stage comprises of at least one
of a band-pass filter, an interleaver and a DWDM filter. By using a
modular structure a very high flexibility and low costs for
producing and integrating of the filter-units in the network
element could be reached.
[0025] For providing of very high data rates the network element
comprises preferably a single back-plane for providing of the
electrical connections between the different devices such as
line-card slices, electrical cross-connects, filter cards etc.
Furthermore, by combining of DWDM line-card slices, filters, and
optical cross-connect functionality in a single hardware unit of
the network element, highly flexible and reliable optical network
architectures can be realized that can support arbitrary data
protocols. The hardware in such networks combined with
sophisticated software intelligence can be used to support advanced
features such as dynamic provisioning/bandwidth trading, remote
performance monitoring, and fast automatic restoration, etc.
Intelligent optical switches and cross-connects can be used to
support virtually any network topology including point-to-point,
ring, and mesh architectures, allowing service providers, to evolve
their existing infrastructures while immediately cutting both
capital and operating costs. Whereas survivable ring architectures
mandate the reservation of 100% excess capacity, mesh architectures
leave the choice of protection to the service providers themselves,
reducing costs by as much as 70% with acceptable critical
restoration times. The present invention allows the operator to
achieve varying levels of flexibility and survivability in optical
networks and trade off costs with desired features and vice
versa.
[0026] The network element according to the preferable embodiment
of the present invention supports one or more uni-directional
optical fibre links between a pair of nodes without any restriction
to the total number of the nodes in the network or to the number of
nearest neighbours which a given node can have. Each
uni-directional or bi-directional optical fibre links supports
multi-wavelength signals. In one preferred embodiment the maximum
number of wavelengths in the aforementioned multi-wavelength
signals is seventy two.
[0027] The components of a given network element according to the
preferable embodiment of the invention are bit-rate and protocol
transparent. This implies that the network element is configurable
to various bit-rates and data networking protocols under the
intelligence provided by hardware and software programming under
static or dynamic/real-time operation conditions. The network
element could be used to built optical networks with arbitrary
topology to provide automatic or point-and-click provisioning,
fault protection/restoration, and other services such as band-width
trading, etc. with a centralized distributed, or hybrid form of
network management system, which comprises various software modules
as described later in this document.
[0028] The network element of the above described preferable
embodiment further comprises of a supervisory card plugged to the
back-plane for transmitting and/or processing of supervisory
signals. The supervisory card is preferably electrically connected
via the electrical transmission lines of the back-plane to a
predetermined line card slice directly or through a
cross-connect.
[0029] Further, the network element could contain a node PC,
especially also in form of a plug-in card, plugged to the
back-plane. The node PC provides an electrical supervisory signal
that is transmitted to the supervisory card.
[0030] Furthermore, the present invention provides an optical
network comprising a plurality of network elements according to the
invention. The network management system of the optical network
according to the invention, which could be called global network
management system in contrast to the local network management
systems of the single nodes, is carried out by one or more of the
local management systems of the network elements. The optical
network according to the present invention consists of among other
things supervisory connections between predetermined network
elements.
[0031] In a preferred embodiment the network management system
provides the establishment of a direct logical supervisory
connection between any desired pair of nodes interconnected by one
or several physical supervisory connections. This means, although
two specific nodes are connected by a sequence of several physical
supervisory connections, for example via several nodes of the
network, to provide one or several end-to-end supervisory
connections so that the said pair of nodes can exchange information
between each other. The logical supervisory connection allows a
unidirectional and/or bi-directional communication channel as
needed.
[0032] The network management system of the optical network
according to the invention preferably provides one or several of
the following functions, comprising of hardware fault detection
and/or software error detection especially on all of the
supervisory connections: auto-recovery from various faults and
errors, that is, self-healing of supervisory connections, fault
tolerant and/or redundant supervisory connections, and automatic
discovery of nodes of the network.
[0033] A method according to the invention allows an intelligent
management of an optical network by providing a supervisory network
in an optical network with arbitrary topology. The method according
to the invention comprises of the steps of automatic discovery of
the network topology and establishing of supervisory connections
between predetermined nodes of the network.
[0034] The automatic discovery of the network topology is
preferably done by one or more node managers of a local network
management system in a network element of a node by communicating
with the local network management system of an adjacent node and
exchanging Link State Advertisements. Each node, namely, the node
manager of each network element in each node discovers all of its
adjacent nodes and exchanges Link State Advertisements with the
same. Thereby a routing table is generated that could be stored in
one, several or in all of the nodes of the network.
[0035] Preferably, the node manager of each node executes a single
OSPF, whereby the OSPF in each node is configured to communicate
with the node manager of adjacent nodes so that the OSPF converges
on the topology of the network, that means on the whole
network.
[0036] The status of the supervisory connections is preferably
monitored, preferably by OSPF, and in the event of a link failure
an alternative route for the respective supervisory connection is
configured.
[0037] In one embodiment of the invention any supervisory data for
use in the supervisory management layer of the network, which in
turn is carried by the optical network, is sent through one or
several or possibly all available redundant connections in form of
messages. Thereby, the supervisory data corresponding to the
messages is/are sent from one sending end of the network to one
receiving end of the network. Each message is given a sequence
number. On the receiving end the duplicate messages are discarded
and only one of the several, for example arriving messages is
passed on to the supervisory management layer.
[0038] In the following, preferred embodiments of the invention
should be described in more detail with reference to the
figures.
[0039] FIG. 1 shows examples of network topologies in which the
present invention could be used;
[0040] FIG. 2 shows software architecture for building up a
supervisory channel;
[0041] FIG. 3 shows examples of software agents contained in a node
manager;
[0042] FIG. 4 shows examples for an implementation of a supervisory
channel;
[0043] FIG. 5 shows the implementation of a supervisory channel in
a network by means of a plurality of physical supervisory channel
connections;
[0044] Referring to FIG. 2, `n` local network management systems 11
of `n` optical network elements in a network of arbitrary topology
are shown. The network elements with their local network management
systems 11 are interconnected by means of supervisory connections
10.1. The several supervisory connections 10.1 define together a
supervisory channel 10, which preferably interconnects all of the
nodes of the network by a respective plurality of supervisory
connections.
[0045] The local network management systems 11 comprise a software
module, a so called node manager 100. Every shown node manager 100
can be configured by a software protocol 116 and uses the shown
software modules 110, called NetProc to communicate with the node
manager of a further network element.
[0046] With reference to FIG. 3, software architecture for a node
manager is shown, which could preferably be implemented in a
network element in one embodiment of the present invention. Note
that this node manager in addition to the local hardware management
serves as a centralized network manager and/or as one of the
several distributed network managers for the entire optical
network. In particular, it unifies point-to-point, ring, and mesh
architectures and is also scalable, affordable, robust, and
reliable. Some of the examples of software agents as shown in the
FIG. 3 are start-up manager 101, process, thread, and sessions
manager 102, supervisory channel process manager 103, hardware
devices manager 104, status, fault, and events manager 105,
database system manager 106, user interfaces (e.g., GUI, console,
TL1, etc.) 107, System Resources and Functions Manager 108.
[0047] In the distributed management approach a single task is
carried out by one or more software agents residing at various
nodes. A management action is said to be carried out in a
centralized mode if all of the tasks it is comprised of are carried
out in a centralized manner. A management action is said to be
carried out in a distributed mode if all of the tasks it is
comprised of are carried out in a distributed manner. A management
action is to be carried out in a hybrid mode if one or more of the
tasks it is comprised of are carried out in a centralized manner
while others are carried out in a distributed manner. For example,
in case of a fault in the optical network the management action may
involve the following tasks: 1) fault detection/isolation, 2) fault
signalling to the network management system (which itself may be
centralized, distributed, or hybrid), 3) alternate path calculation
and allocation, 4) signalling for restoration activation, 5)
optical signal switching at various nodes (6) updating various
databases and reclaiming the system resources, 7) restoring the
failed hardware or software. Each of these tasks can be carried out
using a software agent located at a single node or several nodes.
Thus this management action can be completed using a centralized,
distributed, or hybrid approach.
[0048] The management system of an optical network with arbitrary
topology, see for example FIG. 1, especially the local management
system of a network element in a single node utilizes a supervisory
channel to provide the necessary intelligence by signalling with
other nodes to manage the network and also to resolve any problems
which may occur. In general, the realization of supervisory channel
requires both, hardware and software support. In a preferred
embodiment of the present invention, the software module which
implements the supervisory channel is termed NetProc, which enables
a supervisory communication link between any two nodes in the
supervisory network. In an optical network a network element
according to one embodiment of the present invention and a software
module called NetProc when combined together provides the following
supervisory network features: [0049] 1) Supervisory connection
establishment between two network nodes. Each node can have one or
more NetProcs. This architecture allows establishment of a direct
logical supervisory connection between any arbitrary pair of nodes
interconnected by the supervisory channel (cf. FIG. 2). [0050]
Fault-tolerant or redundant connections through two or more paths.
In a preferred embodiment these paths are node and link disjoint,
as will be described in more detail. The management system uses
NetProc's services to exchange messages with other nodes. Any
supervisory data is sent through one or several or all of the
available redundant connections. Each message is given a sequence
number. On the receiving end the duplicate messages are discarded
and only one, for example the first, of the arriving message is
passed on to the supervisory management layer. [0051] 2) Hardware
fault and software error detection on all paths of the supervisory
channel and the associated auto-recovery to re-establish the
supervisory channel. Error checking in the data transmission is
done by using sequence numbers on the messages. The status of each
connection is monitored by sending keep-alive messages at regular
intervals. In the event that a reply to keep-alive message is not
received within a specified time the connection is explicitly
closed and the two nodes try to re-establish connection between
themselves. The closing of connection(s) and attempts to
re-establish them are done automatically. [0052] 3) Relaying
information reliably to one or more network managers running on one
or more network nodes or other work stations. [0053] 4) The
management of the network is carried out by a node manager present
in each node or at one or more nodes or other centralized
locations. The various node managers communicate using the NetProc
(cf. FIG. 2).
[0054] A preferred supervisory network according to the invention
has the flexibility to be configured by standard protocols like
OSPF, MPLS or by using NetProc. Following features apply: [0055]
The supervisory network topology is automatically discovered with
the help of OSPF. Each Node Manager executes a single OSPF and the
OSPF in each node is configured to talk with neighbouring nodes.
[0056] The nodes discover their neighbours and exchange Link State
Advertisements. Once the Link State adjacencies are formed and the
OSPF converges on the topology, each node possesses the routing
table and is able to reach other nodes over the supervisory
channel. [0057] The status of the supervisory channel is monitored
by OSPF and in the event of link failure the alternate routes are
configured. Fault-tolerant connections are set up using two or more
Label Switched Paths over two or more disjoint paths to each
destination. Thus a signalling message sent to a node travels
through multiple Label Switched Paths and reaches its appropriate
destination.
[0058] With respect to the FIGS. 4 and 5 the hardware architecture
for the supervisory channel in a preferred embodiment of the
optical network according to the present invention is shown and
furthermore the communication of supervisory messages.
[0059] An out-of-band supervisory channel is implemented either by
using one of the wavelengths on each fibre link between a pair of
nodes or a 1510 nm signal (outside the EDFA amplifier range) is
used (cf. FIG. 4a). Alternatively, an in-band supervisory channel
can be implemented using electrical (de)multiplexer (cf. FIG. 4b)
which can be done using special purpose chips implementing bit or
byte processors. As an example, in the special case of SONET/SDH
protocol, an in-band supervisory channel could be implemented by
(de)multiplexing data from/into the DCC channel. In preferred
network systems, the node PC (through an appropriate plug-in card)
provides an electrical out-of-band supervisory signal which is
connected to the supervisory card (SC). The supervisory signals
terminated at SC cards are connected to suitable default remote
line card slices using back-plane connections of the chassis.
However, in case of fault the supervisory signal can be switched to
alternate line-card slices using one or more cross-connects. The
supervisory card provides interfaces for multiple supervisory
signals from/to various nodes to the node controller PC of the said
node.
[0060] As shown in FIG. 5, the same physical supervisory channel
over the link XY using whether in-band or out-of band signalling or
any other arrangement could be used to establish a logical
supervisory connection using paths S1:Z1XYZ2 and S2: UZ1XY, where
S1 and S2 are the supervisory channels and the corresponding
supervisory connections between nodes (Z1, Z2) and (U, Y),
respectively. In order to achieve this the supervisory signals for
different logical channels are multiplexed, demultiplexed, and
routed through a particular node.
[0061] The multiplexing and demultiplexing of supervisory messages
is done, e.g., in time domain using either time division
multiplexing and/or statistical multiplexing techniques. Thus each
node acts like a multiplexer, demultiplexer,
router/switch/cross-connect, sender, and receiver for arbitrary
number of supervisory messages which may pass-through it or
originate/terminate at it. The messages arriving via the
supervisory channel at a node are sent to the Node Manager. The
Node Manager decides where to route the message and chooses the
appropriate outgoing port/interface. The message is then carried
over the fiber to the next node as explained above.
[0062] A supervisory channel could be preferably used to manage the
entire optical network. Thereby, the supervisory channel can be
used to manage the network using existing standards such as SNMP or
proprietary protocols. The supervisory channel enables preferably a
uni-directional or bi-directional logical connection between any
pair of nodes over redundant paths. This ensures that the logical
communication between any pair of nodes will survive under the
single failure assumption involving failure of any single link or a
single node except for the two communicating nodes themselves. Let
(Z1, Z2) represent a node pair. The logical connection between Z1
and Z2 is established through two or more node-link-disjoint paths,
e.g., Z1Z2, Z1VZ2 and Z1XYZ2, etc. The number of
node-link-disjoint-paths available depends on the actual topology
of the optical network. If more than two node-link-disjoint paths
are used between the communicating nodes, survivability of the
supervisory channel against multiple failures can be achieved. A
redundant (additional) supervisory card is preferable provided in
every main card chassis, that means for example in every the
back-plane receiving chassis of a single network element, to
protect against the failure of the first supervisory card.
TABLE-US-00002 Reference Numerals 1 . . . 9, A . . . F, Nodes U, V,
X, Y, Z 10 Supervisory channels 10.1 Supervisory connection 11
Local network management system 100 Node manager 101 . . . 108
Software agent 110 Software module
* * * * *