U.S. patent application number 14/139145 was filed with the patent office on 2014-07-03 for optical switch and protocols for use therewith.
This patent application is currently assigned to Rockstar Consortium US LP. The applicant listed for this patent is Rockstar Consortium US LP. Invention is credited to Guo-Qiang Wang.
Application Number | 20140186036 14/139145 |
Document ID | / |
Family ID | 23427901 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140186036 |
Kind Code |
A1 |
Wang; Guo-Qiang |
July 3, 2014 |
OPTICAL SWITCH AND PROTOCOLS FOR USE THEREWITH
Abstract
A method of establishing a data connection between terminal
switching nodes in a network and switching nodes for implementing
the method. The method involves switching nodes participating in a
network layer wavelength routing (WR) protocol to determine the
next hop switching node for every possible combination of terminal
nodes based on the network topology. The method also involves the
switching nodes participating in a network layer wavelength
distribution (WD) once the data connection is to be established.
The WR protocol determines the path used through the network, while
the WD protocol assigns wavelengths on each link between switching
nodes. The wavelengths may be different on different optical links.
The switching nodes include wavelength converters with an optical
switch or optoelectronic converters with a digital electronic
switch. A digital electronic switch can also provide signal
reformatting. Advantages of using potentially different wavelengths
along various segments of a single end-to-end connection yields
increased wavelength efficiency.
Inventors: |
Wang; Guo-Qiang; (Nepean,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rockstar Consortium US LP |
Plano |
TX |
US |
|
|
Assignee: |
Rockstar Consortium US LP
Plano
TX
|
Family ID: |
23427901 |
Appl. No.: |
14/139145 |
Filed: |
December 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13797226 |
Mar 12, 2013 |
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14139145 |
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10360680 |
Feb 10, 2003 |
8463123 |
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13797226 |
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09362886 |
Jul 29, 1999 |
6529301 |
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10360680 |
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Current U.S.
Class: |
398/48 ;
398/45 |
Current CPC
Class: |
H04Q 11/0001 20130101;
H04Q 2011/0086 20130101; H04Q 2011/0039 20130101; H04B 10/27
20130101; H04Q 2011/0073 20130101; H04Q 2011/0011 20130101; H04Q
2011/009 20130101; H04Q 2011/0016 20130101; H04J 14/02 20130101;
H04Q 11/0005 20130101; H04Q 11/0003 20130101; H04Q 2011/0069
20130101; H04Q 11/0062 20130101 |
Class at
Publication: |
398/48 ;
398/45 |
International
Class: |
H04B 10/27 20060101
H04B010/27; H04Q 11/00 20060101 H04Q011/00 |
Claims
1-29. (canceled)
30. A method of establishing an optical connection between a first
terminal switching node and a second terminal switching node along
a path in an optical network, the path including at least one
intermediate switching node, the method comprising: sending a
connection request communication from the first terminal switching
node along the path; at each intermediate switching node along the
path from the first terminal switching node to the second terminal
switching node: receiving the connection request communication
request from a previous switching node along the path, responsive
to the connection request communication, identifying an optical
channel that is available on a link between the previous switching
node and the intermediate switching node, and sending a connection
request communication to a next switching node along the path; at
the second terminal switching node: receiving the connection
request communication request from a previous switching node along
the path, responsive to the connection request, identifying an
optical channel that is available on a link between the previous
switching node and the second terminal switching node, establishing
a connection to the previous switching node along the path using
the previously identified available optical channel, and sending a
connection confirm communication to the previous switching node
along the path; at each intermediate switching node along the path
from the second terminal switching node to the first terminal
switching node: receiving the connection confirm communication from
the next switching node along the path, responsive to the
connection confirm in communication, establishing a connection to
the previous switching node along the path using the previously
identified available optical channel, and sending a connection
confirm communication to the previous switching node along the
path; at the first terminal switching node: receiving the
connection confirm communication from the next switching node along
the path; and completing, establishment of the optical
connection.
31. The method of claim 30, wherein each connection request
communication comprises a connection request message.
32. The method of claim 30, wherein each connection confirm
communication comprises a connection confirm message.
33. The method of claim 30, further comprising: storing at the
first terminal switching node and at each intermediate switching
node along the path the following: a routing table identifying a
next hop switching node for the path, and an optical channel
availability table identifying any communication channels not yet
allocated to connections.
34. The method of claim 33, wherein each routing table identifies a
respective next hop switching node for a respective path between
each possible pair of first and second terminal switching
nodes.
35. The method of claim 34, wherein each optical channel
availability table identifies for each port of the switching node:
an adjacent switching node connected to that port; optical channels
provided on that port; and whether each optical channel provided on
that port is currently occupied or currently available.
36. The method of claim 30, wherein at least some of the optical
channels are wavelength channels.
37. The method of claim 36, wherein at least some of the optical
wavelength channels are optical wavelength channels on a wavelength
division multiplexed link.
38. The method of claim 30 further comprising: at a switching node
on the path, sending a connection deny communication to the
previous switching node on the path when the switching node cannot
identify an optical channel that is available on a link between the
switching node and the previous switching node on the path.
39. The method of claim 30 comprising, at a switching node on the
path: receiving a connection deny communication from the next
switching node on the path; and sending the connection deny
communication to the previous switching node on the path.
40. The method of claim 30, further comprising: receiving a
connection initiation communication at the first terminal switching
node, wherein the first terminal switching node sends the
connection request communication along the path responsive to the
connection initiation communication.
41. The method of claim 40 further comprising: sending a connection
deny communication from the first terminal switching node to a
source of the connection initiation communication.
42. The method of claim 41, further comprising: receiving a
connection deny communication at the first terminal switching node
from the next switching node along the path, wherein the first ten
final switching node sends the connection deny communication to the
source of the connection initiation communication responsive to the
connection deny communication.
43. The method of claim 40, wherein the source of the connection
initiation request is customer premises equipment.
44. The method of claim 30, further comprising: receiving a
connection initiation communication from a source at the first
terminal switching node, the connection initiation identifying at
least one signal format acceptable to the source; and sending a
connection deny communication from the first terminal switching
node to the source of the connection initiation communication when
the first terminal switching node cannot confirm that an optical
channel having a signal format matching a signal format of the at
least one signal format acceptable to the source is available.
45. An optical communication system comprising a plurality of
switching nodes interconnected by optical links, at least two of
the switching nodes being adapted to operate as first and second
terminal switching nodes and at least one other switching node on a
path between the first and second terminal switching nodes being
adapted to operate as an intermediate switching node, the terminal
switching nodes and the intermediate switching nodes being adapted
to cooperate to establish an optical connection between the first
terminal switching node and the second terminal switching node
along a path comprising the at least one intermediate switching
node by: sending a connection request communication from the first
terminal switching node along the path; at each intermediate
switching node along the path from the first terminal switching
node to the second switching node: receiving the connection request
communication request from a previous switching node along the
path, responsive to the connection request communication,
identifying an optical channel that is available on a link between
the previous switching node and the intermediate switching node,
and sending a connection request communication to a next switching
node along the path; at the second terminal switching node:
receiving the connection request communication request from a
previous switching node along the path, responsive to the
connection request, identifying an optical channel that is
available on a link between the previous switching node and the
second terminal switching node, establishing a connection to the
previous switching node along the path using the previously
identified available optical channel, and sending a connection
confirm communication to the previous switching node along the
path; at each intermediate switching node along the path from the
second switching node to the first switching node: receiving the
connection confirm communication from the next switching node along
the path, responsive to the connection confirm communication,
establishing a connection to the previous switching node along the
path using the previously identified available optical channel, and
sending a connection confirm communication to the previous
switching node along the path; at the first terminal switching
node: receiving the connection confirm communication from the next
switching node along the path; and completing establishment of the
optical connection.
46. The system of claim 45, wherein each connection request
communication comprises a connection request message.
47. The system of claim 45, wherein each connection confirm
communication comprises a connection confirm message.
48. The system of claim 45, wherein the first terminal switching
node and each intermediate switching node along the path is adapted
to store: a routing table identifying a next hop switching node for
the path; and an optical channel availability table identifying any
communication channels not yet allocated to connections.
49. The system of claim 48, wherein each routing table identifies a
respective next hop switching node for a respective path between
each possible pair of first and second terminal switching
nodes.
50. The system of claim 49, wherein each optical channel
availability table identifies for each port of the switching node:
an adjacent switching node connected to that port; optical channels
provided on that port; and whether each optical channel provided on
that port is currently occupied or currently available.
51. The system of claim 45, wherein at least some of the optical
channels are wavelength channels.
52. The system of claim 51, wherein at least some of the optical
wavelength channels are optical wavelength channels on a wavelength
division multiplexed link.
53. The system of claim 45, wherein each inter mediate switching
node on the path is adapted to send a connection deny communication
to the previous switching node on the path when the switching node
cannot identify an optical channel that is available on a link
between the switching node and the previous switching node on the
path.
54. The system of claim 45 wherein each intermediate switching node
on the path is adapted to: receive a connection deny communication
from the next switching node on the path; and send the connection
deny communication to the previous switching node on the path.
55. The system of claim 45, wherein the first terminal switching
node is adapted to receive a connection initiation communication
and to send the connection request communication along the path
responsive to the connection initiation communication.
56. The system of claim 55 wherein the first terminal switching
node is adapted to send a connection deny communication to a source
of the connection initiation communication.
57. The system of claim 56, wherein the first terminal switching
node is adapted to receive a connection deny communication from the
next switching node along the path and to send the connection deny
communication to the source of the connection initiation
communication responsive to the connection deny communication.
58. The system of claim 55, wherein the source of the connection
initiation request is customer premises equipment.
59. The system of claim 45, wherein the first terminal switching
node is adapted to: receive a connection initiation communication
from a source, the connection initiation identifying at least one
signal format acceptable to the source; and send a connection deny
communication to the source of the connection initiation
communication when the first terminal switching node cannot confirm
that an optical channel having a signal format matching a signal
format of the at least one signal format acceptable to the source
is available.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of optical
switching in general and, more particularly, to optical switching
nodes for use in an optical network. The invention also pertains to
protocols governing the behaviour of the switching nodes.
BACKGROUND OF THE INVENTION
[0002] The development of high-capacity networks has been driven by
the need to establish high-bandwidth data connections among remote
sites, for instance, between clients and servers. Most often, the
communications infrastructure for such a network is provided by one
or more long-distance carriers serving the geographic region that
encompasses the various remote sites. A carrier may lease fiber
optic lines to customers wishing to establish high-capacity
connections. Within the carrier's network, optical switching nodes
are then configured to support the desired connections.
[0003] Usually, a carrier leases its fiber optic lines with a view
to long-term usage thereof. Thus, switch configurations established
at the time of provisioning the high-capacity connections are
expected to remain in place for a period of months or years.
Therefore, the switches in the network can be configured manually
with virtually no impact on cost or quality of service
provided.
[0004] However, it is not feasible to manually configure a large
number of switches when dealing with a network whose size and/or
topology are in constant evolution. Furthermore, the manual
configuration of switches cannot accommodate situations in which
the bandwidth or quality of service requirements of the traffic to
be transported through the network is time-varying or if there is
urgency in establishing new high-capacity connections through the
network. Although it is desirable to provide switches which are
automatically reconfigurable as a function of changes to the
topology and traffic load of the network, such a capability is
currently not available.
[0005] Moreover, the most common approach to establishing
end-to-end data connections in current optical networks relies on
the utilization of the same wavelength, say .lamda..sub.X, along a
manually configured path throughout the network. This prevents the
establishment of other data connections using .lamda..sub.X as an
end-to-end wavelength if part of the path corresponding to the new
connection intersects part of the path corresponding to the
original connection. This places a severe constraint on wavelength
usage in a current optical network, with the effect of drastically
reducing the overall bandwidth efficiency in the network.
[0006] Thus, it is apparent that there is a need in the industry to
provide an optical switching node which overcomes the above stated
disadvantages.
SUMMARY OF THE INVENTION
[0007] The invention can be described broadly as a switching node
that includes an optical switch fabric, a wavelength conversion
unit and a control unit. The optical switch fabric is connected to
the control unit and is used for switching optical signals arriving
on a set of input optical fiber segments over to a set of output
optical fiber segments in accordance with mapping instructions
received from the control unit. The wavelength conversion unit is
connected to the optical switch fabric and is used for modifying
the wavelengths occupied by incoming or switched optical signals in
accordance with conversion commands received from the control
unit.
[0008] The control unit is used for exchanging control information
with other switching nodes using a network layer protocol and
generating the mapping instructions and the conversion commands
based on this control information. This switching node allows the
input and output wavelengths of an optical data signal to occupy
different wavelengths, which provides many benefits, among which is
included the benefit of increased wavelength efficiency in an
optical network.
[0009] Preferably, the control information is exchanged using a
out-of-band control channel such as an optical supervisory
channel.
[0010] Preferably, the control unit includes a processor and a
memory element accessible by the processor. The memory element
preferably stores a routing table and a wavelength availability
table. The routing table contains a next hop switching node field
associated with every possible pair of terminal switching nodes.
The wavelength availability table contains the identity of the
switching nodes connected to any of the ports by a respective
multi-wavelength fiber optic link and, for each wavelength, an
indication of whether that wavelength is occupied or available.
[0011] The switching node is most often connected to a previous
switching node in a path identified by a first terminal switching
node and a second terminal switching node. In such a scenario, the
control unit is preferably operable to receive messages from the
previous switching node.
[0012] If the message is a so-called CONNECTION_REQUEST message,
then the control unit will preferably access the wavelength
availability table to identify an available wavelength on the link
between the current and previous switching nodes, the available
wavelength being associated with one of the input optical fiber
segments.
[0013] If the current switching node is the second terminal
switching node, then the control unit will preferably generate
mapping commands for establishing a connection, using the available
wavelength, between the input optical fiber segment associated with
the available wavelength and one of the output optical fiber
segments; and send a CONNECTION_CONFIRM message to the previous
switching node.
[0014] Otherwise, if the current switching node is not the second
terminal switching node, the control unit will preferably access
the routing table to determine the contents of the next hop
switching node field associated with the first and second terminal
switching nodes; and forward the CONNECTION_REQUEST message to the
switching node identified by the next hop switching node field.
[0015] If, on the other hand, the message is a so-called
CONNECTION_CONFIRM message, then the control unit will preferably
generate mapping commands for establishing a connection using the
available wavelength between the input optical fiber segment
associated with the available wavelength and one of the output
optical fiber segments; and send a CONNECTION_CONFIRM message to
the previous switching node.
[0016] In order to accommodate a packet-based architecture, in
which incoming optical signals are formed of packets having a
header and a payload, the switching node may include an additional
conversion unit connected to the input optical fiber segments and
to the control unit, for extracting the header of each packet. In
this case, the mapping instructions and the conversion commands
generated by the controller will further be dependent on the
information contained in the header of each packet.
[0017] In another embodiment, the switching node includes a first
set of optoelectronic converters and a second set of optoelectronic
converters. The first set of converters is used for converting
input optical signals occupying respective wavelengths into
electronic signals, while the second set of converters is used for
converting output electronic signals into output optical signals
occupying respective wavelengths.
[0018] The switching node also includes a digital switch fabric
connected to the optoelectronic converters, for switching the input
electronic signals over to the output electronic signals in
accordance with switching instructions. Finally, the switching node
includes a control unit connected to the digital switch fabric and
to the optoelectronic converters. The control unit exchanges
control information with other switching nodes using a network
layer protocol and generates the switching instructions based on
the control information.
[0019] In this embodiment, the switching node provides grooming
functionality in the sense that the input electronic signals can be
reformatted so that when these reformatted signals are switched and
then converted into an optical format by the second set of
converters, the resulting optical signal can be in a desired
format. This improves compatibility among end user equipment in a
network.
[0020] The invention may be summarized at the network level as a
method of establishing a data connection between first and second
terminal switching nodes. The network is understood to include the
terminal switching nodes as well as a group of other switching
nodes interconnected by multi-wavelength optical links.
[0021] The method includes a first step of identifying a path
comprising a set of links and wavelengths for transporting data
between the first and second terminal switching nodes via zero or
more intermediate switching nodes.
[0022] The method also includes the step of, at each intermediate
switching node connected to a respective ingress link and a
respective egress link in the identified path, switching the
optical signals arriving on the respective ingress link over to the
respective egress link and performing wavelength conversion if the
wavelengths occupied on the respective ingress and egress links are
different. Advantageously, this allows a data connection to be
established using different wavelengths along the way.
[0023] The invention can also be summarized as a wavelength
distribution protocol for enabling a data connection to be
established between a first terminal switching node and a second
terminal switching node via zero or more intermediate switching
nodes along a path in a network. The protocol is executed at the
various switching nodes in the network.
[0024] At each current switching node connected in the path between
a previous switching node and/or a next switching node by
respective optical links, the protocol includes the capability to
receive messages from the previous or next switching node.
[0025] If the message is a CONNECTION_REQUEST message, then if the
current switching node is not the first terminal switching node,
the protocol includes identifying and storing an available
wavelength on the link between the current and previous switching
nodes.
[0026] Also, if the message is a CONNECTION_REQUEST message and if
the current switching node is indeed the second terminal switching
node, the protocol includes establishing a connection using the
available wavelength and sending a CONNECTION_CONFIRM message to
the previous switching node, otherwise forwarding the
CONNECTION_REQUEST message to the next switching node.
[0027] If, however, the message is a CONNECTION_CONFIRM message,
then the protocol includes establishing a connection using the
previously stored available wavelength and if the current switching
node is not the first terminal switching node, sending a
CONNECTION_CONFIRM message to the previous switching node.
[0028] For the protocol to operate as intended, an initial
CONNECTION_REQUEST message is assumed to be sent to the first
terminal switching node upon initially requesting the data
connection.
[0029] By participating in this protocol, switching nodes
automatically participate in the end-to-end establishment of data
connections using dynamically assigned wavelengths, which improves
overall bandwidth efficiency of the optical network and provides
more flexible protection switching, which no longer requires the
input and output wavelengths to be identical.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] These and other aspects and features of the present
invention will become apparent to persons skilled in the art upon
review of the following description of specific embodiments of the
invention in conjunction with the accompanying drawings, in
which:
[0031] FIG. 1 illustrates in schematic form a switching node in
accordance with the preferred embodiment of the present
invention;
[0032] FIG. 2A shows a possible structure of a wavelength
availability table created by the controller in the switching node
of FIG. 1;
[0033] FIG. 2B shows a possible structure of a routing table
created by the controller in the switching node of FIG. 1;
[0034] FIG. 3 illustrates in schematic form an optical network and
a route linking two switching nodes in the network;
[0035] FIG. 4 illustrates in schematic form a switching node in
accordance with an alternative embodiment of the present
invention;
[0036] FIG. 5 shows a flowchart illustrating an inventive
wavelength routing protocol;
[0037] FIG. 6 shows a flowchart illustrating an inventive
wavelength distribution protocol; and
[0038] FIGS. 7A and 7B illustrate routing table entries for two
switching nodes along the route in FIG. 3.
DETAILED DESCRIPTION PREFERRED EMBODIMENT
[0039] FIG. 1 shows an optical switching node 400 for connection to
other switching nodes in an optical network. According to the
preferred embodiment of the present invention, the switching node
400 comprises a plurality of ports 402, 404, 406, 408 connected
externally to a respective plurality of multi-wavelength optical
fiber segments 412, 414, 416, 418.
[0040] Optical fiber segments 412, 414, 416, 418 are bidirectional
and serve both as ingress and egress links to neighbouring
switching nodes (not shown). Alternatively, multiple optical fiber
segments (e.g., one for ingress and one for egress) could connect
the switching node 400 to each of its neighbours.
[0041] Optical fiber segments 412, 414, 416, 418 preferably carry
data to and from the neighbouring switching nodes. Optical fiber
segments 412, 414, 416, 418 also preferably serve as control links
between the neighbouring switching nodes by using dedicated
supervisory wavelengths (known as an optical supervisory channel).
Other ways of establishing control links to the switching node
include the use of dedicated electronic control lines.
[0042] Although depicted as having four ports, the switching node
400 can have any number of ports greater than or equal to two.
Also, while optical fiber segments 412, 414, 416, 418 are intended
to be connected between ports of neighbouring switching nodes, it
should be understood that one or more of the optical fiber segments
412, 414, 416, 418 can be used for transporting individual or
multiplexed optical channels to or from customer premises
equipment. In this case, the switching node 400 would be referred
to as an add/drop node.
[0043] Within the switching node 400, ports 402, 404, 406, 408 are
connected to respective directional couplers 432, 434, 436, 438 by
respective intermediate optical fiber segments 422, 424, 426, 428.
Intermediate optical fiber segments 422, 424, 426, 428 are
bidirectional and preferably carry both data and control signals to
and from the inside of the switching node 400. The directional
couplers 432, 434, 436, 438 are known components which couple two
unidirectional multi-wavelength signals travelling in opposite
directions to a single bidirectional multi-wavelength signal.
[0044] In one direction, each directional coupler 432, 434, 436,
438 retrieves incoming data and control signals carried on the
respective intermediate optical fiber segment 422, 424, 426, 428
and feeds the incoming signals so retrieved to a respective optical
demultiplexer 452, 454, 456, 458 along a respective intermediate
optical fiber segment 442, 444, 446, 448.
[0045] In the opposite direction, outgoing data and control signals
are fed to the directional couplers 432, 434, 436, 438 by a
respective optical multiplexer 552, 554, 556, 558 along a
respective intermediate optical fiber segment 542, 544, 546, 548.
Each directional coupler 432, 434, 436, 438 transfers the
respective outgoing data and control signals onto the respective
intermediate fiber optic segment 422, 424, 426, 428 connected to
the respective port 402, 404, 406, 408.
[0046] Each optical demultiplexer 452, 454, 456, 458 separates the
multi-wavelength optical signal arriving on the respective
intermediate optical fiber segment 442, 444, 446, 448 on the basis
of wavelength to produce a respective set of individual optical
signals appearing on a respective plurality of single-wavelength
optical fiber segments 462A-D, 464A-D, 466A-D, 468A-D.
[0047] Although FIG. 1 shows each of the optical demultiplexers
452, 454, 456, 458 as being associated with four single-wavelength
optical fiber segments, it is to be understood that the number of
segments emanating from an optical demultiplexer can correspond to
the number of wavelengths in each multi-wavelength optical signal
arriving at the respective optical demultiplexer along the
respective intermediate optical fiber segment 442, 444, 446,
448.
[0048] Among the plurality of single-wavelength optical fiber
segments emanating from each demultiplexer, at least one of these
will preferably be used for transporting control information and
the remaining ones will preferably be used for transporting data to
be switched. The transport of control information on a dedicated
wavelength between two switching nodes is known as establishing an
"out-of-band" control channel. Alternatively, an "in-band" control
channel can be established by embedding a control-laden header
within the data transported between two switching nodes, e.g., in a
header portion.
[0049] In the specific case of FIG. 1, single-wavelength optical
fiber segments 462A, 464A, 466A, 468A provide out-of-band control
channels for carrying incoming control information from
neighbouring switching nodes. Each single-wavelength optical fiber
segment 462A, 464A, 466A, 468A is connected to a respective
optoelectronic converter 472A, 474A, 476A, 478A. Each
optoelectronic converter 472A, 474A, 476A, 478A converts the
optical control signal on the respective single-wavelength optical
fiber segment 462A, 464A, 466A, 468A into an electronic control
signal on a respective input control line 482A, 484A, 486A, 488A.
Input control lines 482A, 484A, 486A, 488A are connected to a
controller 490.
[0050] The remaining sets single-wavelength optical fiber segments
462B-D, 464B-D, 466B-D, 468B-D carry incoming data and each set is
fed to a respective bank of controllable wavelength converters
472B-D, 474B-D, 476B-D, 478B-D. Each wavelength converter 472B-D,
474B-D, 476B-D, 478B-D is a device which translates the optical
signal on the respective single-wavelength optical fiber segment
462B-D, 464B-D, 466B-D, 468B-D from its present wavelength onto a
(possibly different) wavelength specified by a control signal sent
by the controller 490 along a respective control line (not
shown).
[0051] It should be appreciated that wavelength conversion as
performed by the wavelength converters 472B-D, 474B-D, 476B-D,
478B-D could be achieved via direct optical methods or by
conversion into the electronic domain, followed by conversion back
into the optical domain on another specified wavelength.
[0052] The signals converted by each bank of wavelength converters
472B-D, 474B-D, 476B-D, 478B-D appear on a respective set of
single-wavelength input optical fiber segments 462B'-D', 464B'-D',
466B'-D', 468B'-D' which are fed to respective input ports of an
optical switch fabric 492.
[0053] The optical switch fabric 492 also has a plurality of output
ports connected to a respective plurality of single-wavelength
output optical fiber segments 562B-D, 564B-D, 566B-D, 568B-D. The
optical switch fabric 492 comprises circuitry for controllably
establishing one-to-one optical connections between
single-wavelength input optical fiber segments 462B'-D', 464B'-D',
466B'-D', 468B'-D' and single-wavelength output optical fiber
segments 562B-D, 564B-D, 566B-D, 568B-D. The data connections are
established on the basis of mapping instructions received from the
controller 490 via a control line 494.
[0054] Those skilled in the art will appreciate that because the
various intermediate optical fiber segments 442, 444, 446, 448,
542, 544, 546, 548 may accommodate differing numbers of
wavelengths, the number of single-wavelength output optical fiber
segments connected to the optical switch fabric 492 may differ from
the number of single-wavelength input optical fiber segments
connected thereto.
[0055] It will also be understood that the banks of wavelength
converters could be connected to the single-wavelength output
optical fiber segments 562B-D, 564B-D, 566B-D, 568B-D at the output
of the optical switch fabric 492 rather than to the
single-wavelength input optical fiber segments 462B'-D', 464B'-D',
466B'-D', 468B'-D' at the input of the optical switch fabric
492.
[0056] A plurality of output control lines 582A, 584A, 586A, 588A
emanating from the controller 490 form part of the respective
out-of-band control channels linking the switching node 400 to
neighbouring switching nodes. The output control lines 582A, 584A,
586A, 588A are respectively connected to a plurality of
optoelectronic converters 572A, 574A, 576A, 578A. The
optoelectronic converters 572A, 574A, 576A, 578A convert electronic
control signals output by the controller 490 into optical signals
appearing on respective single-wavelength optical fiber segments
562A, 564A, 566A, 568A.
[0057] Each single-wavelength optical fiber segment 562A, 564A,
566A, 568A carrying outgoing control information from the
controller 490 is connected to a respective one of the optical
multiplexers 552, 554, 556, 558. Also leading to the optical
multiplexers 552, 554, 556, 558 are respective sets of
single-wavelength output optical fiber segments 562B-D, 564B-D,
566B-D, 568E-D carrying switched signals (i.e., outgoing data) from
the optical switch fabric 492. The optical multiplexers 552, 554,
556, 558 combine the individual optical signals carried by
respective groups of single-wavelength optical fiber segments
562A-D, 564A-D, 566A-D, 568A-D into respective multi-wavelength
optical signals carried to respective directional couplers 432,
434, 436, 438 by respective intermediate optical fiber segments
542, 544, 546, 548.
[0058] The controller 490 preferably comprises a processor 490A
connected to a memory element 490B. The processor 490A is
preferably a micro-processor running a software algorithm.
Alternatively, the processor could be a digital signal processor or
other programmable logic device.
[0059] The memory element 490B stores wavelength availability
information in the form of a wavelength availability table. FIG. 2A
shows the structure of a wavelength availability table 700 in
accordance with the preferred embodiment of the present invention.
The wavelength availability table 700 comprises a PORT column 710,
a WAVELENGTH column 720 and an AVAILABILITY column 730. The PORT
column 710 contains one entry for each port in the switching node.
In the case of the switching node 400 in FIG. 1, the number of
ports, and therefore the number of entries in the PORT column 710
of the wavelength availability table 700, is equal to four. The
ports are identified by their reference numerals from FIG. 1,
namely 402, 404, 406 and 408.
[0060] For each row corresponding to a given port, there may be
multiple entries in the WAVELENGTH column 720, depending on the
number of wavelengths that can enter or exit the switching node
through that port. For example, in the case of the switching node
400 in FIG. 1, there are six entries in the WAVELENGTH column 720
corresponding to each of the ports 402, 404, 406, 408. For each
entry in the WAVELENGTH column 720, there is an entry in the
AVAILABILITY column 730 indicating whether or not the corresponding
wavelength is currently occupied on the corresponding port. A
binary value is adequate for representing each entry in the
AVAILABILITY column 730.
[0061] The memory element 490B also stores topological information
about the network. Specifically, the memory element 490B stores the
identity of those switching nodes which are directly connected to
switching node 400 via one of the optical fiber segments 412, 414,
416, 418. The memory element 490B also stores similar topological
information about the rest of the network, which is transmitted to
the switching node 400 by the neighbouring switching nodes. The
processor 490A in the switching node 400 uses topological
information stored in the memory element 490B to construct a
topological tree of the entire network with the switching node 400
as the root. This tree is then used by the processor 490A to
construct a routing table which is also stored in the memory
element 490B.
[0062] FIG. 2B illustrates the format of a routing table 600 in
accordance with the preferred embodiment of the invention. The
routing table 600 preferably contains four fields, namely a source
switching node (SSN) field 610, a destination switching node (DSN)
field 620, a traffic characteristic information (TCI) field 630 and
a next hop switching node (NHSN) field 640.
[0063] The entries in the SSN and DSN fields 610, 620 account for
every possible combination of end switching nodes in the network.
The TCI field 630 contains the traffic characteristic information
received from the switching node identified by the entry in the DSN
field 620 of the corresponding row in the routing table. In this
way, the TCI field 630 identifies the signalling formats acceptable
by the respective optical interface in each destination switching
node.
[0064] Typically, it will not be possible to send data from a
source switching node to a destination switching node without
passing through at least one intermediate switching node. Thus, the
switching node 400 will generally be one in a series of
intermediate switching nodes located between source and
destination. The next intermediate node along the route leading to
the destination switching node is known as the next hop switching
node and is identified in the NHSN field 640 of the routing table.
The next hop switching node is a function of the source switching
node, the destination switching node, the network topology and the
position of the current switching node within that topology. Thus,
the routing table is different for each switching node in the
network and is basically static, changing only when the network
undergoes a topological alteration.
[0065] In operation, the manner in which control information is
communicated and interpreted by the various switching nodes in the
network is governed by a network-layer wavelength routing (WE)
protocol. An end-to-end path for transferring data from a source
switching node to a destination switching node along a path in a
network can be established by having each switching node
participate in a network-layer wavelength distribution (ED)
protocol. Both protocols are now described.
[0066] The WR protocol is implemented by having the processor in
each switching node run an algorithm such as the one illustrated in
the flowchart of FIG. 5. Specifically, FIG. 5 depicts an
information propagation step 1010, an information storing step 1020
and an information processing step 1030.
[0067] Firstly, the propagation step 1010 consists of the
controller 490 sending topology information and traffic
characteristic information to neighbouring switching nodes via the
appropriate control channel (either out-of-band or in-band). The
topology information includes the identity of the switching node
400 and the identity of each switching node adjacent the switching
node 400 and connected to one of its ports. The traffic
characteristic information may consist of a listing of signalling
types that are acceptable to each port. The contents of this
listing may be governed by end user formatting requirements.
[0068] In addition, as another part of the propagation step 1010,
the switching node 400 relays control information received from any
neighbouring switching node to all other neighbouring switching
nodes. The control information sent by the switching node 400 can
be transmitted at regular intervals of, for instance, ten seconds
or, alternatively, only when there is a change in the received
control information.
[0069] It is noted that because each switching node forwards not
only its own control information but also that of its immediate
neighbours, every switching node is recursively made aware of the
topology of the entire network and of the acceptable signalling
types associated with each switching node in the network.
[0070] The storing step 1020 consists of the controller 490
storing, in the memory element 490B, its own topology and traffic
characteristic information as well as that received from
neighbouring switching nodes.
[0071] Finally, the processing step 1030 consists of the controller
490 in the switching node 400 generating the routing table stored
in the memory element 490B, either periodically or after a topology
change, as a function of the network topology information and
traffic characteristic information stored in the storing step 1020.
With reference to the routing table shown in FIG. 2B, in order to
fill the NHSN field 640 for a particular row in the routing table
600, the software in the processor of the switching node executes a
next hop routing algorithm, for example the well-known Dijkstra
algorithm. (See J. Moy, Network Working Group RFC 1583, pp.
142-160, hereby incorporated by reference herein). If the Dijkstra
algorithm produces no suitable next hop switching node for a given
row in the routing table 600, this fact can be signalled by leaving
blank the corresponding entry in the NHSN and TCI fields 630, 640,
respectively.
[0072] The WD protocol is implemented by the processor in each
switching node running an algorithm such as the one illustrated in
the flowchart of FIG. 6. The inventive wavelength distribution (WD)
protocol consists of the exchange and interpretation of several
types of messages, including an INITIAL_CONNECTION_REQUEST message,
a CONNECTION_REQUEST message, a CONNECTION_CONFIRM message and a
CONNECTION_DENY message.
[0073] Referring to the flowchart in FIG. 6 and, more specifically,
to step 1610, the processor in a given switching node waits to
receive a message. Upon receipt of a message the processor
verifies, at step 1620, whether it is an INITIAL_CONNECTION_REQUEST
message. An INITIAL_CONNECTION_REQUEST message is typically
generated by customer premises equipment connected to the source
switching node, for example.
[0074] If the received message is indeed an
INITIAL_CONNECTION_REQUEST message, then itwill specify the source
and destination switching nodes, as well as the signalling format
(say, TCI.sub.S) used by the interface connected to the source
switching node. At step 1630, the processor verifies whether
TCI.sub.S matches any one of the signalling formats accepted by the
interface connected to the destination switching node. If there is
no TCI match, then the source switching node customer is informed
that a connection cannot be established.
[0075] On the other hand, if there is a TCI match, then the
processor looks up the entry in the NHSN field of the row of the
routing table associated with the source and destination switching
nodes and subsequently sends a CONNECTION_REQUEST message to the
switching node identified by that entry. The CONNECTION_REQUEST
message preferably contains a SSN parameter for identifying the
source switching node and a DSN parameter for identifying the
destination switching node. The intended recipient of the
CONNECTION_REQUEST message is also known as the "next" switching
node along the route between the source and destination nodes.
[0076] The message found to be received at step 1620 might not be
an INITIAL_CONNECTION_REQUEST message, but may be a
CONNECTION_REQUEST message (such as the one sent by the source
switching node after an INITIAL_CONNECTION_REQUEST message). The
CONNECTION_REQUEST message is assumed to be received by the current
switching node from a "previous" switching node along the route
between the source and destination switching nodes.
[0077] In the event that a CONNECTION_REQUEST message was received,
step 1640 provides verification of whether there is a free
wavelength between the previous switching node and the current
switching node. If there is no such wavelength, then the processor
causes a CONNECTION_DENY message to be sent to the previous
switching node, as indicated at step 1650.
[0078] On the other hand, if there is a free wavelength, then step
1660 consists of storing this free wavelength in the memory element
connected to the processor in the current switching node. This is
followed by step 1670, at which it is verified whether the current
switching node is in fact the destination switching node. If not,
then, as indicated by step 1680, the CONNECTION_REQUEST message is
forwarded to the next switching node along the route.
[0079] If, however, the current switching node is indeed the
destination switching node, then step 1690 involves the
establishment of a data connection through the optical switch
fabric of the current switching node. This can be achieved by the
controller 490 providing an appropriate mapping instruction to the
optical switch fabric 492. This connection links the
single-wavelength optical fiber associated with the free wavelength
(as stored in the memory element after execution of step 1660) and
the optical fiber segment leading to the customer premises
equipment connected to the destination switching node.
[0080] If the wavelength occupied by the customer premises
equipment is different from the free wavelength stored in the
memory element, then appropriate instructions must also be sent to
the wavelength converter associated with the free wavelength.
Furthermore, the wavelength availability table is updated to
reflect that the "free" wavelength is no longer available on the
corresponding port linking the current switching node with the
previous switching node.
[0081] After a connection has been established, step 1700 indicates
that a CONNECTION_CONFIRM message is sent to the previous switching
node, which is now optically connected to the current switching
node by the free wavelength. The CONNECTION_CONFIRM message
specifies the free wavelength.
[0082] Returning now to step 1620, if the received message is a
CONNECTION_DENY message, then as indicated at step 1730, the action
to be taken depends on whether the current switching node is the
source switching node. If the current switching node is not the
source switching node, then the CONNECTION_DENY message is
backwarded to the previous switching node as indicated at step
1650. Thus, the CONNECTION_DENY message eventually reaches the
source switching node where, according to step 1740, the customer
is alerted to the fact that a connection cannot be established.
[0083] Finally, if the message found to be received at step 1620 is
a CONNECTION_CONFIRM message, then the action to be taken again
depends on whether the current switching node is the source
switching node as indicated at step 1710. If the current switching
node is indeed the source switching node, then a connection is
established (step 1720) between the optical fiber segment connected
to the customer premises equipment and the single-wavelength
optical fiber segment carrying data between the source switching
node and the next switching node.
[0084] Otherwise (step 1690), a connection is established which
joins the single-wavelength optical fiber segment carrying data
between the current switching node and the previous and next
switching nodes. In addition, the locally stored wavelength
availability table is also updated to reflect the new wavelength
occupancy on the optical fiber segment carrying data between the
current switching node and the previous and next switching nodes.
If necessary, wavelength conversion instructions are sent in either
case to the appropriate wavelength converter. As shown at step
1700, a CONNECTION_CONFIRM message is subsequently sent to the
previous switching node.
[0085] An example illustrating how an end-to-end connection is
prepared using the WD protocol is now described with reference to
FIG. 3, which shows an optical network 800 comprising a plurality
of switching nodes 802-824 connected in a meshed matrix pattern via
a plurality of optical fiber segments 826-858. Switching node 802
is connected to customer premises equipment (CPE) 860 via an
optical fiber segment 862 which uses a wavelength .lamda..sub.S.
The CPE 860 uses a signalling format which may be denoted
TCI.sub.S. Switching node 824 is connected to CPE 864 via an
optical fiber segment 866 which uses a wavelength .lamda..sub.F.
The CPE 864 accepts signalling formats which may be identified by
the set {TCI.sub.F}.
[0086] The switching nodes 802-824 participate in the inventive WR
protocol. Thus, a routing table will be generated at each switching
node. This routing table is different for each switching node but
is static until the topology of the network changes. For purposes
of illustration and without loss of generality, FIG. 7A shows part
of a routing table 900 generated at switching node 802
corresponding to the row in which the source switching node is
designated as switching node 802 and the destination switching node
is designated as switching node 824. Specifically, the entry in the
TCI column 630 indicates that the CPE 864 connected to switching
node 824 is capable of receiving data in the listed formats, namely
OC-4, OC-32, OC-192 and Gigabit Ethernet (GEE). The entry in the
NHSN column 640 indicates that the next hop switching node in the
route joining switching nodes 802 and 824 is switching node
808.
[0087] Similarly, FIG. 7B shows an example row from a routing table
950 stored in the memory element of switching node 808. This row
again corresponds to the source-destination combination involving
switching nodes 802 and 824, respectively. Of course, the routing
table 950 is generated from the perspective of switching node 808
and therefore the entries in the NHSN column 640 will be different
from those in the routing table 900 stored in switching node 802.
In the example of FIG. 7B, the entry in the NHSN column 640
specifies switching node 810. Similarly, the corresponding entry in
the NHSN column 640 in the routing tables stored in switching nodes
810, 816 and 818 can specify switching node 816, 818 and 824,
respectively.
[0088] Thus, a potential route exists between switching node 802
and 824, consisting of optical fiber segments 830, 836, 842, 848
and 854 as indicated by the thick solid line in FIG. 3. Similarly,
potential routes exist between all other combinations of source
switching node and destination switching node.
[0089] The messaging scheme of the WD protocol is now illustrated
with continued reference to the network of FIG. 3 and the flowchart
of FIG. 6. Firstly, the desire to establish an end-to-end data
connection between CPE 860 and CPE 864 is signalled to the source
switching node 802 in any suitable way. That is to say, an
INITIAL_CONNECTION_REQUEST message is received by switching node
802.
[0090] In accordance with the WD protocol (at step 1630), switching
node 802 compares the signalling format of CPE 860, namely
TCI.sub.S, to the set of acceptable signalling formats associated
with CPE 864, namely the set {TCI.sub.F}. If a TCI match is
detected, then the processor in the source switching node 802
consults its routing table (FIG. 7A) and extracts the identity of
the switching node in the NHSN field of the row corresponding to
the particular source-destination switching node combination. In
this case, the switching node so identified would be switching node
808. (It should be noted that if TCI.sub.S is not an element of the
set {TCI.sub.F}, then the connection request is denied. As
indicated in step 1740 of FIG. 6, the controller in the source
switching node 802 may take action to alert the end user that the
connection request has been denied.)
[0091] The processor in the source switching node 802 then
formulates a CONNECTION_REQUEST message for transmission to
switching node 808 (step 1680). The CONNECTION_REQUEST message
identified switching node 802 as the source switching node and
switching node 824 as the destination switching node. The
CONNECTION_REQUEST message is transmitted by the source switching
node 802 to switching node 808 via the appropriate out-of-band or
in-band control channel.
[0092] In accordance with step 1640 of FIG. 6, switching node 808
consults its wavelength availability table to determine whether
there is a free wavelength on the fiber optic segment 830 linking
ii, to the previous switching node, in this case source switching
node 802. Consequently, either a wavelength is found, in which case
the wavelength request is further propagated along the route by
forwarding a copy of the CONNECTION_REQUEST message to switching
node 810 (step 1680), or a wavelength is not found, in which case
the connection request is denied and a CONNECTION_DENY message is
sent back to the source switching node 802 (step 1650). In this
case, since switching node 808 is not the destination switching
node 824, a connection is not yet established.
[0093] If sent, the CONNECTION_DENY message is of a suitable format
indicating that the connection request has been denied and the
reasons therefor, in this case, an inability to find an available
wavelength on fiber optic segment 830. According to steps 1730 and
1740 of FIG. 6, upon receipt of a CONNECTION_DENY message, the
controller in the source switching node 802 may take action to
alert the end user of CPE 860 that the connection request has been
denied.
[0094] Each of the switching nodes 810, 816, 818 runs the same
algorithm and therefore performs essentially the same tasks as
switching node 808. Hence, if wavelengths are available on each of
fiber optic segments 836, 842 and 848, the CONNECTION_REQUEST
message dill eventually be received at the destination switching
node 824. Similarly, a CONNECTION_DENY message returned to an one
of the switching nodes 810, 816, 818 is relayed back to the source
switching node 802, where action can be taken to alert the end user
that a connection request has been denied.
[0095] Assuming that TCI.sub.S belongs to the set {TCI.sub.F} and
that a suitable wavelength path is available, the
CONNECTION_REQUEST message transmitted by the source switching node
802 will eventually reach the destination switching node 824 via
"intermediate" switching nodes 808, 810, 816 and 818. Since it is
identified by the DSN parameter in the CONNECTION_REQUEST message,
the destination switching node 824 knows that it is the last
switching node on the potential route leading from the source
switching node 802. In the example scenario of FIG. 3, the final
destination is CPE 864 which is connected to the destination
switching node 824 via optical fiber segment 866 adapted to carry
optical signals on wavelength .lamda..sub.F. In response to the
CONNECTION_REQUEST message, the processor in the destination
switching node 824 attempts to find a free wavelength on optical
fiber segment 854 connecting the destination switching node 824
with intermediate switching node 818.
[0096] If such a wavelength is found, say .lamda..sub.I, then a
data connection is established (step 1720). Specifically, the
controller sends mapping instructions to its optical switch fabric
for switching the optical signal on the single-wavelength input
optical fiber segment associated with .lamda..sub.I over to the
optical fiber segment 866 leading to the customer premises
equipment 864. In addition, the controller sends the value of the
wavelength .lamda..sub.F to the wavelength converter associated
with the single-wavelength input optical fiber segment carrying the
optical signal on wavelength .lamda..sub.I. If .lamda..sub.I is
different from .lamda..sub.F, that wavelength converter will be
required to perform wavelength conversion. Furthermore, the
destination switching node 824 updates its wavelength availability
table with information about the newly established data connection.
That is to say, the entry in the AVAILABILITY field 730 of the
appropriate row is given a value indicating the fact that
wavelength .lamda..sub.I on optical fiber segment 854 is taken,
i.e., unavailable.
[0097] After instructing its optical switch fabric to set up a data
connection, the WD protocol as described at step 1700 in FIG. 7
requires that the destination switching node 824 send a
CONNECTION_CONFIRM message to the intermediate switching node 818.
The CONNECTION_CONFIRM message specifies the wavelength
.lamda..sub.I, which is the wavelength (prior to wavelength
conversion) associated with the single-wavelength input optical
fiber segment connected through the optical switch fabric in the
destination switching node 824.
[0098] Upon receipt of the CONNECTION_CONFIRM message sent by the
destination switching node 824, intermediate switching node 818
itself establishes a connection between the single-wavelength
output optical fiber whose signal at wavelength .lamda..sub.I is
carried on optical fiber segment 854 and the single-wavelength
input optical fiber 848 whose signal at the previously stored free
wavelength (say, .lamda..sub.J) is carried on optical fiber segment
848. If .lamda..sub.I does not equal .lamda..sub.J then the
corresponding wavelength converter is instructed to perform the
appropriate wavelength conversion. The controller in intermediate
switching node 818 then updates its wavelength availability table
and subsequently sends a CONNECTION_CONFIRM message to intermediate
switching node 816. This message will specify .lamda..sub.J (rather
than .lamda..sub.I or .lamda..sub.F).
[0099] Backtracking of the CONNECTION_CONFIRM message continues
until this message is received at the source switching node 802.
According to step 1720 of the algorithm described with reference to
FIG. 7, the controller in the source switching node 802 sends
mapping instructions to its optical switch fabric with the aim of
establishing a connection between the optical fiber segment 862
occupying wavelength .lamda..sub.S connected to CPE 860 and the
single-wavelength optical fiber segment whose signal is carried on
a wavelength .lamda..sub.K by optical fiber segment 830. If
.lamda..sub.K differs from .lamda..sub.S, wavelength conversion
commands are sent to the wavelength converter associated with
optical fiber segment 862.
[0100] From the above, it is seen that the route between the source
and destination switching nodes 802, 824 consisting of optical
fiber segments 830, 836, 842, 848, 854 may occupy different
wavelengths. As a result of topology and traffic characteristic
information exchanged automatically by virtue of the various
switching nodes participating in the WR protocol, the just
described wavelength distribution (WD) protocol allows wavelengths
to be assigned to specific optical fiber segments in a dynamic
fashion each time a new connection is requested. Consequently, the
available network bandwidth is used more efficiently and the time,
effort and cost involved in configuring the switching nodes in the
network are dramatically reduced.
[0101] While the above description of the WD protocol has dealt
with the case in which a source switching node wishes to
unilaterally send data to a destination switching node, the present
invention also applies to the case in which one switching node
wishes to extract data from another. In this reverse unidirectional
situation, it is more appropriate to call the two end switching
nodes "client" (wishing to receive data) and "server" (transmitting
the data to the client) switching nodes.
[0102] Considering the example network and proposed route shown in
FIG. 3, it can be assumed that the client is connected to switching
node 802 and that the server is connected to switching node 824.
The client 802 is connected to CPE 860 via an optical fiber segment
862, while the server 824 is connected to a data base 864 via an
optical fiber segment 866. The above-described WR protocol remains
the mechanism by which the various switching nodes in the network
exchange and process control information. However, to accommodate
the transfer of data from server 824 to client 802 (which is in the
opposite direction to the data flow in the previously described
source-destination example), the WD protocol is slightly
modified.
[0103] Specifically, step 1630 in FIG. 6 (in which a TCI comparison
is to be performed) may not be executable at the client switching
node since the signalling type transmitted by the server may not be
known. Therefore, this step must be postponed until a
CONNECTION_REQUEST message is received at the server switching
node, whereupon this step is performed by the server switching
node.
[0104] It should also be understood that although route selection
is achieved by the switching nodes executing a routing control
algorithm, it is possible for the source switching node or client
to preselect the desired route through the network for particular
combinations of end points. In other words, the NSHN entries in the
routing table in each switching node can be pre-computed. Manual
route pre-selection is also acceptable as there are advantages to
be gained by having the wavelengths dynamically assigned along each
segment in the route in accordance with the WD protocol. Thus, the
WR protocol could simply be used for distributing and gathering
traffic characteristic information, while omitting the processing
step.
[0105] It is also within the scope of the invention to provide a
bidirectional data connection between two end switching nodes.
Wavelength allocation for one direction of communication can follow
the algorithm in the above source-destination scenario, while
wavelength allocation for the reverse direction can follow the
algorithm in the above-described client-server scenario.
[0106] Moreover, the invention extends to certain cases in which
the signalling types at the end points do not match but are
"compatible". For example, if the destination switching node
accepts OC-48 signals but the source switching node transmits OC-12
signals, then either the end switching nodes or one of the
intermediate switching nodes along the route between the two end
switching nodes can be assigned the task of grooming the OC-12
signals so that they become OC-48 signals. In this case, OC-48 and
OC-12 signalling types are said to be compatible.
[0107] Accordingly, the WD protocol can be modified so that a
CONNECTION_DENY message is sent if all wavelengths are unavailable
or if TCI.sub.S is incompatible with every element of the set
{TCI.sub.F}. Within each switching node, compatibility may be
determined by consulting a table of compatible pairs of signalling
types which can be stored in the respective memory element.
[0108] In order to provide the desired grooming functionality, it
is necessary to modify the design of the switching node. FIG. 4
shows a switching node 900 in accordance with an alternative
embodiment of the present invention. Switching node 900 is
identical to switching node 400, except for certain differences
which are now explained.
[0109] Switching node 900 comprises groups of optoelectronic
converters 902B-D, 904B-D, 906B-D, 908B-D connected between
respective demultiplexers 452, 454, 456, 458 and a grooming
processor and switch 992. Converters 902B-D, 904B-D, 906B-D, 908B-D
are used for converting received optical data signals on respective
single-wavelength input optical fibers 462B-D, 464B-D, 466B-D,
468B-D into electrical signals fed to the grooming processor 992.
Analog-to-digital converters (not shown) are preferably provided
between the optoelectronic converters 902B-D, 904B-D, 906B-D,
908B-D and the grooming processor and switch 992.
[0110] The grooming processor and switch 992 is preferably a
high-speed digital signal processor which is programmed to convert
digital electronic signals from one signalling type to another. The
grooming processor and switch 992 also provides a digital
cross-connect facility for connecting each groomed electronic
signal to any one of a plurality of electronic signal lines 962B-D,
964B-D, 966B-D, 968B-D.
[0111] Groups of electronic signal lines 962B-D, 964B-D, 966B-D,
968B-D are connected to respective optical multiplexers 552, 554,
556, 558 via respective, groups of optoelectronic converters
972B-D, 974B-D, 976B-D, 978B-D. The optoelectronic converters
convert the respective electronic signals into optical signals at a
wavelength controllable from the controller 490 via respective
control lines (not shown). For this reason, wavelength converters
are not explicitly required in the design of the switching node in
FIG. 4, since their functionality is implicit in the optoelectronic
converters 972B-D, 974B-D, 976B-D, 978B-D.
[0112] In accordance with another embodiment of the present
invention, the switching nodes in FIGS. 1 and 4 and the WR and WD
protocols governing their behaviour can be used to implement a
reliable protection facility in a meshed network. More
specifically, if a data connection is established over a particular
fiber optic link and if that link fails, then a new data connection
request can be initiated by the source switching node. Since each
switching node participates in the WR protocol, the change in the
topology of the network resulting from the broken link will
automatically result in different values for the NHSN column in the
respective routing tables.
[0113] Those skilled in the art will appreciate that a new
connection request can be programmed to occur after a failure is
detected, which request is handled by the WD protocol of the
present invention, resulting in a new and reliable route for the
originally disrupted data connection. Further advantages of relying
on the WR and WD protocols described herein include wavelength
efficiency, since protection wavelengths need not be dedicated in
advance, as well as independent re-routing for different
wavelengths occupied by a single optical fiber segment. This latter
feature is advantageous because it allows the protection of
individual wavelengths wherever there is capacity in the
network.
[0114] According to yet another alternative embodiment of the
invention, there may be provided an all-optical switching fabric
similar to the switch fabric 492 in FIG. 1. However, instead of
mapping each single-wavelength input optical fiber segment to one
single-wavelength output optical fiber segment for the duration of
a data connection, the switch fabric can be made responsive to
switching instructions for a particular input optical signal that
vary as a function of time.
[0115] This functionality can be useful in situations where the
nature of the input optical signal is packet-based, with each
packet having a header portion and a payload portion. The header
may identify the source and destination switching nodes. Although
different packets share the same wavelength and the same
single-wavelength optical fiber segment, their associated headers
may indicate an entirely different source and/or destination.
[0116] In this alternative embodiment of the invention, the
switching node could thus comprise a bank of optical taps (e.g.,
PIN diodes) connected to the single-wavelength input optical fiber
segments. These taps would be connected to optoelectronic
converters, which would all be connected to the controller. The
header of each incoming packet could thus be read and processed by
the controller.
[0117] In operation, the wavelength routing (WR) protocol functions
as previously described. Furthermore, once a data connection
request is made, in which a respective source-destination pair is
identified, a specific set of mapping instructions and wavelength
conversion commands are generated using the wavelength distribution
(WD) protocol, based on the network topology.
[0118] In this case, however, an additional step is performed
before mapping the single-wavelength input optical fiber segment to
the single-wavelength output optical fiber segment in order to
establish a particular data connection. Specifically, the header of
each packet on the input optical fiber segment is examined. It is
only if the source and destination specified in the header match
the source-destination pair for which a connection has been
prepared using the WD protocol that the previously derived mapping
instructions and wavelength conversion commands are used.
[0119] Of course, it is also within the scope of the invention to
allow multiple mappings to be associated with each
single-wavelength input optical fiber segment, with a single
mapping being applied for each packet, depending on the source and
destination switching nodes specified in the header.
[0120] While preferred and alternative embodiments of the present
invention have been described and illustrated, it will be
understood by those skilled in the art that further variations and
modifications are possible while remaining within the scope of the
invention as defined in the appended claims.
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