U.S. patent application number 14/267798 was filed with the patent office on 2015-11-05 for configuration data.
This patent application is currently assigned to Metaswitch Networks Ltd. The applicant listed for this patent is Metaswitch Networks Ltd. Invention is credited to Robert BROCKBANK, Shaun CRAMPTON.
Application Number | 20150319044 14/267798 |
Document ID | / |
Family ID | 54290492 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150319044 |
Kind Code |
A1 |
BROCKBANK; Robert ; et
al. |
November 5, 2015 |
CONFIGURATION DATA
Abstract
Measures for use in generating path configuration data for an
optical network. A least cost path calculation process is performed
on a network graph representation of the optical network to
generate path configuration data for the optical network.
Performing the least cost path calculation process comprises
performing a network graph expansion process on the network graph
representation of the optical network to obtain an expanded network
graph representation of the optical network. Performing the network
graph expansion process comprises determining data identifying the
possible expansion paths to each optical node, the cost of each
path and the available wavelengths for each path, grouping together
wavelength and path data for paths of equal cost, and at one or
more nodes, identifying a subset of one or more wavelengths and
performing a wavelength pruning operation.
Inventors: |
BROCKBANK; Robert; (San
Francisco, CA) ; CRAMPTON; Shaun; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Metaswitch Networks Ltd |
Enfield |
|
GB |
|
|
Assignee: |
Metaswitch Networks Ltd
Enfield
GB
|
Family ID: |
54290492 |
Appl. No.: |
14/267798 |
Filed: |
May 1, 2014 |
Current U.S.
Class: |
398/79 |
Current CPC
Class: |
H04J 14/0267 20130101;
H04L 41/12 20130101; H04L 45/02 20130101; H04J 14/0227 20130101;
H04L 45/62 20130101; H04B 10/27 20130101; H04L 45/50 20130101 |
International
Class: |
H04L 12/24 20060101
H04L012/24; H04J 14/02 20060101 H04J014/02; H04L 12/723 20060101
H04L012/723; H04B 10/27 20060101 H04B010/27; H04L 12/751 20060101
H04L012/751 |
Claims
1. A method of generating path configuration data for an optical
network, the method comprising: performing a least cost path
calculation process on a network graph representation of the
optical network to generate path configuration data for the optical
network; wherein the optical network comprises a plurality of
optical nodes connected by optical links, each node in the
plurality being configured to transmit incoming data on an ingress
optical link at a first wavelength as outgoing data on an egress
optical link at the first wavelength or one or more wavelengths
different to the first wavelength; wherein performing the least
cost path calculation process comprises performing a network graph
expansion process on the network graph representation of the
optical network to obtain an expanded network graph representation
of the optical network; and wherein performing the network graph
expansion process comprises: determining data identifying possible
expansion paths to each optical node in the plurality, a cost of
each possible expansion path, and an available wavelengths for each
possible expansion path; grouping together wavelength and path data
for paths of equal cost; and at one or more nodes in the plurality:
identifying a subset of one or more wavelengths that have been
selected on an ingress link of the one or more nodes which cannot
be used on an egress link of the one or more nodes; and performing
a wavelength pruning operation comprising pruning the subset of one
or more identified wavelengths from the selected wavelengths of the
egress link of the one or more nodes in the expanded network graph
representation of the optical network.
2. A method according to claim 1, wherein the plurality of nodes
comprises at least one wavelength pass-through optical node
configured to transmit incoming data on an ingress optical link at
the first wavelength as outgoing data on an egress optical link at
the first wavelength only, wherein the one or more nodes comprise
the at least one wavelength pass-through optical node.
3. A method according to claim 1, wherein the plurality of nodes
comprises at least one wavelength conversion optical node
configured to transmit incoming data on an ingress optical link at
a second wavelength as outgoing data on an egress optical link at
one or more wavelengths different to the second wavelength, wherein
the one or more nodes comprise the at least one wavelength
conversion optical node.
4. A method according to claim 1, wherein the plurality of nodes
comprises: at least one wavelength pass-through optical node
configured to transmit incoming data on an ingress optical link at
the first wavelength as outgoing data on an egress optical link at
the first wavelength only; and at least one wavelength conversion
optical node configured to transmit incoming data on an ingress
optical link at a second wavelength as outgoing data on an egress
optical link at one or more wavelengths different to the second
wavelength, wherein performing the network graph expansion process
comprises, for at least one physical egress link of at least one
wavelength conversion optical node, expanding the at least one
physical egress link into at least one of: a virtual wavelength
pass-through egress link, wherein a predetermined pass-through cost
is assigned to an operation of the respective wavelength conversion
optical node passing through data on an ingress link to the virtual
wavelength pass-through egress link at the same wavelength; and a
virtual wavelength conversion egress link, wherein a predetermined
wavelength conversion cost assigned to an operation of the
respective wavelength conversion optical node converting data on an
ingress link to one or more different wavelengths on the virtual
wavelength conversion egress link; wherein the least cost path
calculation process is carried out based on the expanded network
graph representation of the network comprising virtual wavelength
pass-through and virtual wavelength conversion egress links.
5. The method of claim 4, wherein performing the network graph
expansion process comprises, at the least one wavelength conversion
optical node, selecting wavelengths on the virtual wavelength
pass-through egress link and virtual wavelength conversion egress
link of the at least one wavelength conversion optical node based
on the wavelengths selected on the ingress link, the available
wavelengths on the physical egress link and whether the egress link
is a virtual wavelength pass-through egress link or a virtual
wavelength conversion egress link.
6. The method of claim 1, wherein identifying the subset of one or
more wavelengths for a given node in the one or more nodes
comprises determining an intersection between the selected
wavelengths on the ingress link of the given node and the available
wavelengths on the physical egress link of the given node, and
wherein the pruned subset of one or more identified wavelengths
comprises the wavelengths which are determined not to be in the
intersection.
7. The method of claim 4, wherein performing the network graph
expansion process comprises, at the least one wavelength conversion
optical node, selecting wavelengths on the virtual wavelength
conversion egress link of the at least one wavelength conversion
optical node to be all of the available wavelengths on the physical
egress link of the at least one wavelength conversion optical
node.
8. The method according to claim 4, wherein, prior to performing
the wavelength pruning operation, the available wavelengths on each
of the first virtual wavelength pass-through egress link and the
second virtual wavelength conversion egress link of the at the
least one wavelength conversion optical node comprise the available
wavelengths on the physical egress link for the at least one
wavelength conversion optical node.
9. The method according to claim 1, comprising, for each path
produced by the least cost path calculation process, performing a
wavelength assignment operation to select wavelengths for
navigating each of the links comprised in the respective path in a
reverse direction to the least cost path calculation process,
wherein the output of the wavelength assignment operation comprises
path configuration data for the optical network.
10. The method according to claim 9, wherein performing the
wavelength assignment operation for a given path comprises: for a
given egress link of a given node, if the given node comprises a
wavelength pass-through optical node configured to transmit
incoming data on an ingress optical link at the first wavelength as
outgoing data on an egress optical link at the first wavelength
only, then the wavelength assigned for the ingress link to the
given node is the same as the selected wavelength on the ingress
link.
11. The method according to claim 9, wherein performing the
wavelength assignment operation for a given path comprises: for a
given egress link of a given node, if the given node comprises a
wavelength conversion optical node configured to transmit incoming
data on an ingress optical link at a second wavelength as outgoing
data on an egress optical link at one or more wavelengths different
to the second wavelength, then the wavelength assigned for the
ingress link to the given node is chosen arbitrarily from the list
of selected wavelengths on the ingress link.
12. The method according to claim 9, wherein the least cost path
calculation process is performed on the expanded network graph
representation of the network in a forward direction from a first
node in the network to a second node in the network and the
wavelength assignment operation is performed on the expanded
network graph representation of the network in a reverse direction
from the second node in the network to the first node in the
network.
13. The method according to claim 12, wherein performing the
wavelength assignment operation for a given path comprises for the
ingress link of the second node, arbitrarily assigning a wavelength
from a list of selected wavelengths on the ingress link of the
second node.
14. The method according to claim 1, comprising, prior to
performing the network graph expansion process: identifying at
least one wavelength available on at least one optical link which
has an associated available bandwidth which falls below a
predetermined minimum bandwidth threshold; and pruning the
identified at least one available wavelength from the available
wavelengths on at least one optical link from the network graph
representation of the optical network.
15. The method according to claim 14, comprising, in response to
the available bandwidth pruning operation leaving the at least one
optical link with no further available wavelengths, pruning the at
least one optical link from the network graph representation of the
optical network.
16. The method according to claim 1, wherein the network graph
expansion process and the subset identification and pruning
processes are carried out at least in part in parallel by separate
processing threads.
17. The method according to claim 9, wherein the network graph
expansion process and the wavelength assignment process are carried
out at least in part in parallel by separate processing
threads.
18. The method according to claim 9, wherein the subset
identification and bandwidth pruning operation and the wavelength
assignment process are carried out at least in part in parallel by
separate processing threads.
19. The method according to claim 1, comprising performing the
network graph expansion process such that at least one wavelength
conversion optical node configured to transmit incoming data on an
ingress optical link at a second wavelength as outgoing data on an
egress optical link at one or more wavelengths different to the
second wavelength and at least one ingress optical link thereto and
at least one egress optical link therefrom form the tip of a
hairpin in the network graph representation of the optical network
in order to provide wavelength conversion capabilities in at least
one part of the optical network where it would otherwise not be
possible to provide wavelength conversion capabilities due to a
lack of available wavelengths in the at least one part of the
optical network.
20. The method according to claim 1, wherein the least cost path
calculation process is performed as a bi-directional least cost
path calculation process on a network graph representation of the
optical network, the bidirectional least cost path calculation
process comprising a forward direction network graph expansion
process starting at a first node in the network and a reverse
direction network graph expansion process starting from a second,
different node in the network, wherein the forward and reverse
direction network graph expansion processes continue until they
meet at a common optical link between two optical nodes in the
network.
21. The method according to claim 4, wherein the predetermined
wavelength conversion cost is higher than the predetermined
wavelength pass-through cost.
22. The method according to claim 1, comprising configuring one or
more nodes in the plurality of optical nodes to route data
according to the path configuration data generated for the optical
network.
23. A system for use in generating path configuration data for an
optical network, the system comprising: at least one memory
including computer program code; and at least one processor in data
communication with the memory, the processor configured to: perform
a least cost path calculation process on a network graph
representation of the optical network to generate path
configuration data for the optical network, wherein the optical
network comprises a plurality of optical nodes connected by optical
links, each node in the plurality being configured to transmit
incoming data on an ingress optical link at a first wavelength as
outgoing data on an egress optical link at the first wavelength or
one or more wavelengths different to the first wavelength, wherein
performing the least cost path calculation process comprises
performing a network graph expansion process on the network graph
representation of the optical network to obtain an expanded network
graph representation of the optical network, wherein performing the
network graph expansion process comprises: determining data
identifying possible expansion paths to each optical node in the
plurality, a cost of each path, and an available wavelengths for
each path; grouping together wavelength and path data for paths of
equal cost; and at one or more nodes in the plurality: identifying
a subset of one or more wavelengths that have been selected on an
ingress link of the one or more nodes which cannot be used on an
egress link of the one or more nodes; and performing a wavelength
pruning operation comprising pruning the subset of one or more
identified wavelengths from the selected wavelengths of the egress
link of the one or more nodes in the expanded network graph
representation of the optical network.
24. A non-transitory computer-readable storage medium comprising
computer-executable instructions which, when executed by a
processor, cause a computerized device to perform a method for
generating path configuration data for an optical network, the
method comprising: performing a least cost path calculation process
on a network graph representation of the optical network to
generate path configuration data for the optical network, wherein
the optical network comprises a plurality of optical nodes
connected by optical links, each node in the plurality being
configured to transmit incoming data on an ingress optical link at
a first wavelength as outgoing data on an egress optical link at
the first wavelength or one or more wavelengths different to the
first wavelength, wherein performing the least cost path
calculation process comprises performing a network graph expansion
process on the network graph representation of the optical network
to obtain an expanded network graph representation of the optical
network, wherein performing the network graph expansion process
comprises: determining data identifying possible expansion paths to
each optical node in the plurality, a cost of each path, and an
available wavelengths for each path; grouping together wavelength
and path data for paths of equal cost; and at one or more nodes in
the plurality: identifying a subset of one or more wavelengths that
have been selected on an ingress link of the one or more nodes
which cannot be used on an egress link of the one or more nodes;
and performing a wavelength pruning operation comprising pruning
the subset of one or more identified wavelengths from the selected
wavelengths of the egress link of the one or more nodes in the
expanded network graph representation of the optical network.
25. A network of optical nodes configured to route data based on
path configuration data generated according to the method of claim
1.
26. A method of generating path configuration data for an optical
network, the method comprising: performing a least cost path
calculation process on a network graph representation of the
optical network to generate path configuration data for the optical
network, wherein the optical network comprises a plurality of
optical nodes connected by optical links including: at least one
wavelength pass-through optical node configured to transmit
incoming data on an ingress optical link at a first wavelength as
outgoing data on an egress optical link at the first wavelength
only; and at least one wavelength conversion optical node
configured to transmit incoming data on an ingress optical link at
a second wavelength as outgoing data on an egress optical link at
one or more wavelengths different to the second wavelength, wherein
performing the least cost path calculation process comprises
performing a network graph expansion process on the network graph
representation of the optical network to obtain an expanded network
graph representation of the optical network, wherein performing the
network graph expansion process comprises, for at least one
physical egress link of at least one wavelength conversion optical
node, expanding the at least one physical egress link into: a
virtual wavelength pass-through egress link, wherein a
predetermined pass-through cost is assigned to the operation of the
respective wavelength conversion optical node passing through data
on an ingress link to the virtual wavelength pass-through egress
link at the same wavelength; and a virtual wavelength conversion
egress link, wherein a predetermined wavelength conversion cost
assigned to the operation of the respective wavelength conversion
optical node converting data on an ingress link to one or more
different wavelengths on the virtual wavelength conversion egress
link, wherein the least cost path calculation process is carried
out based on the expanded network graph representation of the
network comprising virtual wavelength pass-through and virtual
wavelength conversion egress links.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present disclosure relates to optical networks. In
particular, but not exclusively, the present disclosure relates to
generating path configuration data for optical networks.
[0003] 2. Description of the Related Technology
[0004] Core optical networks for large Internet service providers
may consist of very large numbers of network elements (optical
routers, switches, etc.) with complex inter-connectivity. Managing
these networks to set up dedicated Multiprotocol Label Switching
(MPLS) routes between two nodes is a complex task. As the network
size increases, the complexity of calculating these routes becomes
a Non-deterministic Polynomial-time hard (NP-hard) problem and
finding an exact solution computationally becomes unfeasible. Quite
often, a network engineer will plan routes by pen-and-paper.
[0005] Simplifications in the network representation may be used to
calculate computationally near-optimal routes in these complex
networks. New ways to simplify the calculation allow computational
path calculations that can yield better results than pen-and-paper
optimization.
[0006] The well-known Dijsktra algorithm can be used to solve least
cost paths through simple networks consisting of a set of nodes and
weighted links joining the nodes. Optical networks, whilst
consisting of a set of nodes (optical switches, amplifiers, etc.)
and links (optical links) there-between, are more difficult to
handle because they have added degrees of freedom, for example the
use of different wavelengths to transmit data along the same link
and the ability of the node to either pass-through the wavelength,
retransmit the data over a different wavelength or re-pack the data
into a new or existing wavelength.
[0007] In one scenario, a wavelength is either passed through an
optical node directly, i.e. the ingress wavelength is the same as
the egress wavelength. In another scenario, an ingress wavelength
is converted to a different wavelength at the egress (which may or
may not require repacking/reframing of the data). The former
scenario is referred to herein as wavelength pass-through and the
latter scenario is referred to herein as wavelength conversion.
[0008] One known mechanism for generating path configuration data
with least cost routing is to represent the network as a graph,
where the network graph is expanded to have separate edges for each
available wavelength between two nodes. With a large number of
available wavelengths on a single fiber, such an expanded graph
representation may become excessively large increasing dramatically
the network complexity. In some cases, the added complexity may
render least cost routing incalculable within a reasonable
timeframe.
SUMMARY
[0009] According to a first embodiment, there is a method of
generating path configuration data for an optical network, the
method comprising: performing a least cost path calculation process
on a network graph representation of the optical network to
generate path configuration data for the optical network, wherein
the optical network comprises a plurality of optical nodes
connected by optical links, each node in the plurality being
configured to transmit incoming data on an ingress optical link at
a first wavelength as outgoing data on an egress optical link at
the first wavelength or one or more wavelengths different to the
first wavelength, wherein performing the least cost path
calculation process comprises performing a network graph expansion
process on the network graph representation of the optical network
to obtain an expanded network graph representation of the optical
network, wherein performing the network graph expansion process
comprises: determining data identifying the possible expansion
paths to each optical node in the plurality, the cost of each path
and the available wavelengths for each path; grouping together
wavelength and path data for paths of equal cost; and at one or
more nodes in the plurality: identifying a subset of one or more
wavelengths that have been selected on an ingress link of the one
or more nodes which cannot be used on an egress link of the one or
more nodes; and performing a wavelength pruning operation
comprising pruning the subset of one or more identified wavelengths
from the selected wavelengths of the egress link of the one or more
nodes in the expanded network graph representation of the optical
network.
[0010] According to a second embodiment, there is a system for use
in generating path configuration data for an optical network, the
system comprising at least one processor, and at least one memory
including computer program code, the at least one memory and the
computer program code being configured to, with the at least one
processor, cause the system at least to: perform a least cost path
calculation process on a network graph representation of the
optical network to generate path configuration data for the optical
network, wherein the optical network comprises a plurality of
optical nodes connected by optical links, each node in the
plurality being configured to transmit incoming data on an ingress
optical link at a first wavelength as outgoing data on an egress
optical link at the first wavelength or one or more wavelengths
different to the first wavelength, wherein performing the least
cost path calculation process comprises performing a network graph
expansion process on the network graph representation of the
optical network to obtain an expanded network graph representation
of the optical network, wherein performing the network graph
expansion process comprises: determining data identifying the
possible expansion paths to each optical node in the plurality, the
cost of each path and the available wavelengths for each path;
grouping together wavelength and path data for paths of equal cost;
and at one or more nodes in the plurality: identifying a subset of
one or more wavelengths that have been selected on an ingress link
of the one or more nodes which cannot be used on an egress link of
the one or more nodes; and performing a wavelength pruning
operation comprising pruning the subset of one or more identified
wavelengths from the selected wavelengths of the egress link of the
one or more nodes in the expanded network graph representation of
the optical network.
[0011] According to a third embodiment, there is a computer program
product comprising a non-transitory computer-readable storage
medium having computer readable instructions stored thereon, the
computer readable instructions being executable by a computerized
device to cause the computerized device to perform a method for
generating path configuration data for an optical network, the
method comprising: performing a least cost path calculation process
on a network graph representation of the optical network to
generate path configuration data for the optical network, wherein
the optical network comprises a plurality of optical nodes
connected by optical links, each node in the plurality being
configured to transmit incoming data on an ingress optical link at
a first wavelength as outgoing data on an egress optical link at
the first wavelength or one or more wavelengths different to the
first wavelength, wherein performing the least cost path
calculation process comprises performing a network graph expansion
process on the network graph representation of the optical network
to obtain an expanded network graph representation of the optical
network, wherein performing the network graph expansion process
comprises: determining data identifying the possible expansion
paths to each optical node in the plurality, the cost of each path
and the available wavelengths for each path; grouping together
wavelength and path data for paths of equal cost; and at one or
more nodes in the plurality: identifying a subset of one or more
wavelengths that have been selected on an ingress link of the one
or more nodes which cannot be used on an egress link of the one or
more nodes; and performing a wavelength pruning operation
comprising pruning the subset of one or more identified wavelengths
from the selected wavelengths of the egress link of the one or more
nodes in the expanded network graph representation of the optical
network.
[0012] According to a fourth embodiment, there is a method of
generating path configuration data for an optical network, the
method comprising: performing a least cost path calculation process
on a network graph representation of the optical network to
generate path configuration data for the optical network, wherein
the optical network comprises a plurality of optical nodes
connected by optical links including: at least one wavelength
pass-through optical node configured to transmit incoming data on
an ingress optical link at a first wavelength as outgoing data on
an egress optical link at the first wavelength only; and at least
one wavelength conversion optical node configured to transmit
incoming data on an ingress optical link at a second wavelength as
outgoing data on an egress optical link at one or more wavelengths
different to the second wavelength, wherein performing the least
cost path calculation process comprises performing a network graph
expansion process on the network graph representation of the
optical network to obtain an expanded network graph representation
of the optical network, wherein performing the network graph
expansion process comprises, for at least one physical egress link
of at least one wavelength conversion optical node, expanding the
at least one physical egress link into: a virtual wavelength
pass-through egress link, wherein a predetermined pass-through cost
is assigned to the operation of the respective wavelength
conversion optical node passing through data on an ingress link to
the virtual wavelength pass-through egress link at the same
wavelength; and a virtual wavelength conversion egress link,
wherein a predetermined wavelength conversion cost assigned to the
operation of the respective wavelength conversion optical node
converting data on an ingress link to one or more different
wavelengths on the virtual wavelength conversion egress link,
wherein the least cost path calculation process is carried out on
the basis of the expanded network graph representation of the
network comprising virtual wavelength pass-through and virtual
wavelength conversion egress links.
[0013] Further embodiments comprise system and/or computer program
products according to the fourth embodiments.
[0014] Further features of embodiments will become apparent from
the following description of preferred embodiments of the
disclosure, given by way of example only, which is made with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows an optical network according to one or more
disclosed embodiments;
[0016] FIG. 2 shows nodes in an optical network according to one or
more disclosed embodiments;
[0017] FIG. 3 shows nodes in an optical network according to one or
more disclosed embodiments;
[0018] FIG. 4 shows an optical network according to one or more
disclosed embodiments;
[0019] FIGS. 5A and 5B show nodes in an optical network according
to one or more disclosed embodiments;
[0020] FIG. 6 shows an optical network according to one or more
disclosed embodiments;
[0021] FIG. 7 shows an optical network according to one or more
disclosed embodiments;
[0022] FIGS. 8A and 8B show nodes in an optical network according
to one or more disclosed embodiments;
[0023] FIG. 9 shows nodes in an optical network according to one or
more disclosed embodiments;
[0024] FIG. 10 shows nodes in an optical network according to one
or more disclosed embodiments; and
[0025] FIG. 11 shows nodes in an optical network according to one
or more disclosed embodiments.
DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS
[0026] FIG. 1 shows an example optical network 100 according to
embodiments. Optical network 100 comprises six optical nodes, A, B,
C, D, E and F with various optical links there-between. Each of the
links has one or more available wavelengths at which data can be
passed along that link. For example, on the optical link between
optical node A and optical node B, the wavelengths L1, L2 and L5
are available for the transfer of data, whereas on the optical link
between optical node C and optical node D, the wavelengths L1, L2
and L3 are available for the transfer of data. The network topology
in FIG. 1 is given as an example only and embodiments may be
applied to other topologies comprising more (or fewer) than six
nodes with differing combinations of available wavelengths on any
of the optical links.
[0027] Embodiments comprise measures, including methods, systems
and computer program products for handling simultaneous least cost
routing and wavelength assignment using reduced expansion of a
network graph representation of an optical network.
[0028] Embodiments employ optical link cost metrics that are
average based, and therefore solutions obtained are approximations.
In embodiments, an iterative approach may be used to perform
multiple calculations to refine the least cost solution.
[0029] Embodiments group together wavelength information to reduce
the number of calculations, memory storage and/or expansion data
than would otherwise be required if expanding the network graph
with separate links for each wavelength. In embodiments, the
calculation process makes use of least cost path calculations, for
example using the Dijkstra algorithm, which deal with a single
minimum cost expansion edge. However, embodiments diverge from
standard Dijkstra in several ways, for example because different
minimum costs for each combination of node, ingress edge and
wavelength grouping are employed. Whilst this means that the cost
of expansion is greater than Dijkstra, the expanded network graph
representation undergoes wavelength pruning to ensure a reduced
number of expansions are required, whilst maintaining least-cost
groups of wavelengths on each link. In embodiments, some of the
calculation can be off-loaded to different threads/processors thus
parallelizing some of the calculation.
[0030] Embodiments involve performing a bandwidth pruning operation
on a network representation of the network to remove links and
wavelengths that do not meet one or more bandwidth
requirements.
[0031] Embodiments involve network graph expansion to add virtual
links for handling wavelength pass-through (where wavelengths are
equivalent on ingress and egress links), or wavelength conversion
optical-electrical-optical (where wavelengths may vary on ingress
and egress links).
[0032] Embodiments involve applying a routing algorithm to find the
least cost path through the network which provides a set of
available links and wavelengths on each link.
[0033] Embodiments involve assigning the set of wavelengths within
the least cost path.
[0034] In embodiments, the optical network is represented as a
network graph comprising a set of optical nodes (for example
optical switches) with links between each node.
[0035] In embodiments, the optical network comprises at least one
wavelength pass-through optical node configured to transmit
incoming data on an ingress optical link at a first wavelength as
outgoing data on an egress optical link at the first wavelength
only. A wavelength pass-through node is thus a node which supports
wavelength pass-through only, i.e. the output wavelength is always
("passed-through") the same as the input wavelength.
[0036] In embodiments, the optical network comprises at least one
wavelength conversion optical node configured to transmit incoming
data on an ingress optical link at a second wavelength as outgoing
data on an egress optical link at one or more wavelengths different
to the second wavelength or the second wavelength. A wavelength
pass-through node is thus a node which supports wavelength
pass-through and also wavelength conversion, i.e. the output
wavelength may be the same as the input wavelength or the output
wavelength may be different from the input wavelength.
[0037] In embodiments, the data associated with each link is
initialized with an average cost metric for hopping between links
where no wavelength conversion is required (optical
pass-through).
[0038] In embodiments, the data associated with each link is
initialized with an average cost metric for hopping between links
where wavelength conversion is required. This represents an average
cost of a node to convert between wavelengths.
[0039] In embodiments, the data associated with each link is
initialized with a list of wavelengths and the available bandwidth
for each wavelength on that link.
[0040] In embodiments, the data associated with each link is
initialized with a connectivity matrix describing how ingress and
egress links on the node may be connected.
[0041] Embodiments comprise measures including methods, systems and
computer program products for generating path configuration data
for an optical network. A least cost path calculation process is
performed on a network graph representation of the optical network
to generate path configuration data for the optical network. The
optical network comprises a plurality of optical nodes connected by
optical links and each node in the plurality is configured to
transmit incoming data on an ingress optical link at a first
wavelength as outgoing data on an egress optical link at the first
wavelength or one or more wavelengths different to the first
wavelength. In such embodiments, performing the least cost path
calculation process comprises performing a network graph expansion
process on the network graph representation of the optical network
to obtain an expanded network graph representation of the optical
network. In such embodiments, performing the network graph
expansion process comprises determining data identifying the
possible expansion paths to each optical node in the plurality, the
cost of each path and the available wavelengths for each path,
grouping together wavelength and path data for paths of equal cost,
and at one or more nodes in the plurality identifying a subset of
one or more wavelengths that have been selected on an ingress link
of the one or more nodes which cannot be used on an egress link of
the one or more nodes, and performing a wavelength pruning
operation comprising pruning the subset of one or more identified
wavelengths from the selected wavelengths of the egress link of the
one or more nodes in the expanded network graph representation of
the optical network.
[0042] The wavelength pruning operation leads to a less complex
network graph representation of the network.
[0043] In some embodiments, the plurality of nodes comprises at
least one wavelength pass-through optical node configured to
transmit incoming data on an ingress optical link at the first
wavelength as outgoing data on an egress optical link at the first
wavelength only, and the one or more nodes comprise the at least
one wavelength pass-through optical node. In some embodiments, the
plurality of nodes comprises at least one wavelength conversion
optical node configured to transmit incoming data on an ingress
optical link at a second wavelength as outgoing data on an egress
optical link at one or more wavelengths different to the second
wavelength, and the one or more nodes comprise the at least one
wavelength conversion optical node. Embodiments do not involve
naively expanding the network graph to have separate edges for each
available wavelength between two nodes as in known systems.
[0044] In embodiments, the network graph representation of the
network is expanded to double up each link into two virtual links,
where the available wavelengths on each virtual link are identical,
but one link is marked as a "wavelength pass-through" link with a
cost associated with a wavelength pass-through operation and the
other link marked as a "wavelength conversion" link with a cost
associated with a wavelength conversion operation.
[0045] In embodiments, the plurality of nodes comprises at least
one wavelength pass-through optical node configured to transmit
incoming data on an ingress optical link at the first wavelength as
outgoing data on an egress optical link at the first wavelength
only, and at least one wavelength conversion optical node
configured to transmit incoming data on an ingress optical link at
a second wavelength as outgoing data on an egress optical link at
one or more wavelengths different to the second wavelength. In such
embodiments, performing the network graph expansion process
comprises, for at least one physical egress link of at least one
wavelength conversion optical node, expanding the at least one
physical egress link into at least one of a virtual wavelength
pass-through egress link, wherein a predetermined pass-through cost
is assigned to the operation of the respective wavelength
conversion optical node passing through data on an ingress link to
the virtual wavelength pass-through egress link at the same
wavelength, and a virtual wavelength conversion egress link,
wherein a predetermined wavelength conversion cost assigned to the
operation of the respective wavelength conversion optical node
converting data on an ingress link to one or more different
wavelengths on the virtual wavelength conversion egress link. In
such embodiments, the least cost path calculation process is
carried out on the basis of the expanded network graph
representation of the network comprising virtual wavelength
pass-through and virtual wavelength conversion egress links.
[0046] In embodiments, the predetermined wavelength conversion cost
is higher than the predetermined wavelength pass-through cost.
[0047] Having separate links for both costs simplifies the
processing for grouping together equal cost routes according to
embodiments. In embodiments employing connectivity matrices, a
connectivity matrix used to determine cross connectivity between
links then only has to deal with which wavelengths are
"transmitted" on each egress link without having separate costs for
each wavelength.
[0048] FIG. 2 shows a physical link between two optical nodes with
available wavelengths marked according to embodiments.
[0049] FIG. 3 shows that the physical link of FIG. 2 has been
replaced in the expanded graph representation of the optical
network with two links each with the same available wavelengths,
but with different cost metrics for each link depending on whether
the link is using wavelength conversion or wavelength pass-through
according to embodiments.
[0050] Embodiments employ a routing mechanism which builds upon
standard Dijkstra where paths are expanded from the least cost
route first (utilizing a processing heap to maintain efficient
ordering of paths based on cost). Standard Dijkstra expands from
each node once because it is only concerned about the least cost
path to that node and it expands using the least cost paths first.
However, embodiments may employ multiple possible routes to a node
due to the different costs for different groups of wavelengths.
Embodiments make gains over a simple graph expansion for every
single possible wavelength by keeping groups of wavelength-paths
together that have identical costs.
[0051] Embodiments comprise, for each ingress link to a node,
keeping track of the least cost paths for a group of possible
wavelengths for each link. FIG. 4 shows an example application of
such embodiments where it can be seen that for each ingress node,
the expansion paths that are used to reach that node are noted,
along with the cost of the path and the available wavelengths for
that particular path. As with Dijkstra, all paths are put on a
processing heap and expanded least cost first. For the example
embodiments depicted in FIG. 4, it can be seen that path ADG has a
cost of 2 and available wavelengths of L1, L2 and L3; path ACFG has
a cost of 3 and available wavelengths of L4 and L6; and path ABEFG
has a cost of 4 and available wavelengths of L5 and L10. In this
example embodiment, each link has an equal cost, but this need not
be the case and in other embodiments, the costs for different links
may vary.
[0052] Embodiments comprise expanding a path by selecting a
particular egress link and selecting wavelengths on the egress link
based on the selected wavelengths on the ingress link, the
available wavelengths on the egress link and whether the link
represents a wavelength conversion virtual link or a wavelength
pass-through virtual link.
[0053] In embodiments, performing the network graph expansion
process comprises, at the least one wavelength conversion optical
node, selecting wavelengths on the virtual wavelength pass-through
egress link and virtual wavelength conversion egress link of the at
least one wavelength conversion optical node on the basis of the
wavelengths selected on the ingress link, the available wavelengths
on the physical egress link and whether the egress link is a
virtual wavelength pass-through egress link or a virtual wavelength
conversion egress link.
[0054] In some embodiments, identifying the subset of one or more
wavelengths for a given node in the one or more nodes comprises
determining the intersection between the selected wavelengths on
the ingress link of the given node and the available wavelengths on
the physical egress link of the given node, and the pruned subset
of one or more identified wavelengths comprises the wavelengths
which are determined not to be in the intersection.
[0055] In embodiments, performing the network graph expansion
process comprises, at the least one wavelength conversion optical
node, selecting wavelengths on the virtual wavelength conversion
egress link of the at least one wavelength conversion optical node
to be all of the available wavelengths on the physical egress link
of the at least one wavelength conversion optical node.
[0056] In embodiments, prior to performing the wavelength pruning
operation, the available wavelengths on each of the first virtual
wavelength pass-through egress link and the second virtual
wavelength conversion egress link of the at the least one
wavelength conversion optical node comprise the available
wavelengths on the physical egress link for the at least one
wavelength conversion optical node. If a node in the network cannot
perform optical wavelength pass-through or optical wavelength
conversion, then the corresponding virtual link can be omitted from
the expanded network graph representation of the optical
network.
[0057] In embodiments, the wavelengths on the egress link are
selected such that, if the egress link is a wavelength pass-through
link then the selected wavelengths are the intersection of the
selected wavelengths on the ingress link and the available
wavelengths on the egress link, and if the egress link is a
wavelength conversion link then the selected wavelengths are the
complete set of available wavelengths on that link.
[0058] For example, the two egress links in a part of an optical
network shown in FIG. 5A are being expanded and pruned where
possible. The wavelength pass-through link will have wavelengths L1
and L3 selected, whereas the wavelength conversion link will have
wavelengths L1, L3, L5 and L6 selected. Such a pruned expansion is
depicted in FIG. 5B.
[0059] Note that in embodiments when expanding the egress link, it
can be guaranteed that the cost of the paths on the ingress link
are the cheapest cost for the selected wavelengths (since Dijkstra
expands cheapest paths first, it is guaranteed that only higher or
equal cost routes will use those wavelengths on that link). Once
those wavelengths are selected, those wavelengths can be pruned
from the list of available lambdas on the ingress link; this means
that future path calculations that traverse that link from other
path/wavelength combinations do not consider the pruned wavelengths
as available.
[0060] In embodiments, only the least cost route for each
wavelength is stored, so although there are multiple costs
associated with each ingress edge, each wavelength will appear on
only one cost grouping. Note that there is additional overhead in
performing the wavelength pruning, however, this pruning is
distinct from the actual cost ordering and therefore does not
affect the processing heap used for the network graph expansion.
This means that this processing can be pushed to another
thread/core; in some embodiments, suitable locking is applied to
ensure pruning for a set of wavelengths between two nodes has
completed before expanding any further routes between the two same
nodes.
[0061] Some embodiments comprise, prior to performing the network
graph expansion process, identifying at least one wavelength
available on at least one optical link which has an associated
available bandwidth which falls below a predetermined minimum
bandwidth threshold, and pruning the identified at least one
available wavelength from the available wavelengths on at least one
optical link from the network graph representation of the optical
network
[0062] In such embodiments, an available bandwidth pruning
operation is performed on the network graph representation of the
optical network to remove wavelengths whose available bandwidth
does not meet one or more required constraint(s) imposed by a
required bandwidth for one or more routes.
[0063] In some embodiments, in response to the available bandwidth
pruning operation leaving the at least one optical link with no
further available wavelengths, the at least one optical link is
pruned from the network graph representation of the optical
network.
[0064] In such embodiments, after an available bandwidth pruning
operation has been performed on the network graph representation of
the optical network to prune wavelengths from a given link, if
there are no longer any available wavelengths on the given link,
then the given link is removed entirely from the network graph
representation of the network. Such embodiments reduce the total
number of edges (and possibly nodes) in the least cost path
calculation.
[0065] An example optical network where optical links have
different bandwidth capabilities is depicted in FIG. 6. The optical
network depicted in FIG. 6 has a similar topology to that depicted
in FIG. 1; in FIG. 6, however, each of the available wavelengths on
a link has an associated available bandwidth for transmission of
data at the respective wavelength. For example, as can be seen in
FIG. 6, the link between nodes A and B has available wavelengths of
L1, L2 and L5 which have available bandwidths of 2000, 2100 and
3000 respectively, whereas the link between nodes C and D has
available wavelengths of L1, L2 and L3 which have available
bandwidths of 200, 210 and 300 respectively. The available
bandwidths for wavelengths on the links are given in arbitrary
units, but could for example comprise hertz.
[0066] FIG. 7 depicts the optical network of FIG. 6 after an
available bandwidth pruning operation has been performed on the
network graph representation of the optical network. In this
example, the required bandwidth for each of the paths was 1000
(arbitrary units), such that any wavelengths with available
bandwidths less than 1000 are pruned from the network graph
representation of the optical network. In this example, the
available bandwidth pruning operation removed all available
bandwidths from the link between node A and node D, the link
between node C and node D, and the link between node C and node E,
so these links are pruned from the network graph representation of
the optical network entirely.
[0067] Some embodiments involve wavelength assignment where paths
through the network are selected. Some such embodiments comprise,
for each path produced by the least cost path calculation process,
performing a wavelength assignment operation to select wavelengths
for navigating each of the links comprised in the respective path
in a reverse direction to the least cost path calculation process;
in such embodiments, the output of the wavelength assignment
operation comprises path configuration data for the optical
network.
[0068] For a given selected path, each egress link in the selected
path has a new set of wavelengths that could be valid based on the
selected ingress wavelengths and the available egress wavelengths.
Once the path is selected, the actual wavelength assignment is
established by selecting wavelengths navigating the path in reverse
applying one or more wavelength assignment rules.
[0069] In embodiments, one such wavelength assignment rule
comprises for the last link in the expanded graph representation of
the network, a wavelength is chosen from the list of selected
wavelengths. In some embodiments, all wavelengths are treated with
equal weight, such that the selection of the wavelength is
arbitrary. In other embodiments, different wavelengths have
different weightings and some wavelengths are preferentially
selected over other wavelengths. In some embodiments, it may be
preferential to select a specific wavelength.
[0070] In embodiments, another such wavelength assignment rule
comprises, for the previous link, if the node is acting as a
wavelength pass-through node then the wavelength on this (ingress)
link should be the same as the other (egress) link, whereas if the
node is acting as a wavelength conversion node then an arbitrary
wavelength is chosen from the list of selected wavelengths on this
(ingress) link. In alternative embodiments, instead of an arbitrary
choice, one or more wavelengths could be preferentially chosen over
one or more other wavelengths.
[0071] In embodiments, performing the wavelength assignment
operation for a given path comprises, for a given egress link of a
given node, if the given node comprises a wavelength pass-through
optical node configured to transmit incoming data on an ingress
optical link at the first wavelength as outgoing data on an egress
optical link at the first wavelength only, then the wavelength
assigned for the ingress link to the given node is the same as the
selected wavelength on the ingress link.
[0072] In embodiments, performing the wavelength assignment
operation for a given path comprises, for a given egress link of a
given node, if the given node comprises a wavelength conversion
optical node configured to transmit incoming data on an ingress
optical link at a second wavelength as outgoing data on an egress
optical link at one or more wavelengths different to the second
wavelength, then the wavelength assigned for the ingress link to
the given node is chosen arbitrarily from the list of selected
wavelengths on the ingress link. In alternative embodiments,
instead of an arbitrary assignment, one or more wavelengths could
be preferentially assigned over one or more other wavelengths.
[0073] In embodiments, the least cost path calculation process is
performed on the expanded network graph representation of the
network in a forward direction from a first node in the network to
a second node in the network and the wavelength assignment
operation is performed on the expanded network graph representation
of the network in a reverse direction from the second node in the
network to the first node in the network.
[0074] In embodiments, performing the wavelength assignment
operation for a given path comprises for the ingress link of the
second node, arbitrarily assigning a wavelength from a list of
selected wavelengths on the ingress link of the second node. In
alternative embodiments, instead of an arbitrary assignment, one or
more wavelengths could be preferentially assigned over one or more
other wavelengths.
[0075] An example wavelength assignment operation for a given path
is depicted in FIGS. 8A and 8B according to embodiments. FIG. 8A
shows the given path before the wavelength assignment operation has
been carried out where the selected wavelengths are specified on
each link, and the nodes are marked according to whether they are
acting as a wavelength conversion node or a wavelength pass-through
node.
[0076] Starting from the final link on the path, wavelength L5 is
selected on the link between node D and node C (in this example, an
arbitrary choice from the list of wavelength L5 and wavelength L7).
Node C is a wavelength pass-through node so the wavelength on the
link between node C and nod B is also selected as wavelength L5.
Node B is a wavelength conversion node so the wavelength on the
link between node B and node A is selected as wavelength L1 (in
this example, an arbitrary choice from the list of wavelength L1,
wavelength L2, wavelength L3 and wavelength L4). FIG. 8B shows the
given path after the wavelength assignment operation has been
carried out.
[0077] In some embodiments described herein, the routing process
excludes routing back to a node that is already in the route, for
example routing from node X-Y-Z-Y, where routing back to Y is
disallowed. Such embodiments prevent routing loops that could make
the graph expansion too unwieldy.
[0078] However, in some embodiments by allowing a small (for
example fixed) number of repeat nodes (or selecting repeatable
links or nodes), it is possible to engineer routes with `hairpins`
or similar forms to utilize an optical node that is able to perform
wavelength conversion for navigating through another section of the
network that is unable to perform wavelength conversion, but where
it may be required due to lack of available wavelengths.
[0079] Embodiments comprise performing the network graph expansion
process such that at least one wavelength conversion optical node
configured to transmit incoming data on an ingress optical link at
a second wavelength as outgoing data on an egress optical link at
one or more wavelengths different to the second wavelength and at
least one ingress optical link thereto and at least one egress
optical link therefrom form the tip of a hairpin in the network
graph representation of the optical network in order to provide
wavelength conversion capabilities in at least one part of the
optical network where it would otherwise not be possible to provide
wavelength conversion capabilities due to a lack of available
wavelengths in the at least one part of the optical network.
[0080] Bi-directional Dijkstra is an extension to the basic
Dijkstra algorithm whereby the network graph representation is
expanded simultaneously from both a source and destination until
the two expansion processes meet. This can greatly reduce the
overall number of expansions. Some embodiments make use of such a
bi-directional approach with some modifications. Bi-directional
Dijkstra only needs both expansion directions to meet at a
particular node. In embodiments, expansion beyond a common node is
carried out to find a common expansion link (i.e. the link needs to
overlap from both sides of the expansion); such features are
employed in embodiments because the selected wavelengths on a
particular link from both directions of the expansion should
overlap.
[0081] In embodiments, the least cost path calculation process is
performed as a bi-directional least cost path calculation process
on a network graph representation of the optical network, the
bidirectional least cost path calculation process comprising a
forward direction network graph expansion process starting at a
first node in the network and a reverse direction network graph
expansion process starting from a second, different node in the
network; in such embodiments, the forward and reverse direction
network graph expansion processes continue until they meet at a
common optical link between two optical nodes in the network.
[0082] For example, consider the following forward (from left to
right in the upper part of FIG. 9) and reverse path (from right to
left in the lower part of FIG. 9) expansions which overlap on the
"pass-through" link between node C and node D as depicted in FIG. 9
according to embodiments. Note that in the reverse path
calculation, the selection of wavelengths on the ingress link
(where the ingress link refers to the true ingress link if the path
was taken in the forward direction) is calculated based on the link
type of the egress link and the available wavelengths on the
ingress link. In the example of FIG. 9, for the ingress link
between node C and node D, the egress link between node D and node
E is a wavelength conversion link; this means that the selected
wavelengths for the link between node C and node D can be the full
list of available wavelengths on the link between node C and node
D.
[0083] In the example depicted in FIG. 9, the overlapping link
between node C and node D has wavelengths L2 and L3 in common.
[0084] The selection of a single wavelength for each link can be
performed in the reverse direction of each of the calculated routes
starting from the overlapping link. For example, wavelength L2 can
be selected as an arbitrary wavelength (or alternatively, a
preferentially selected wavelength) from the list of common
wavelengths in the overlapping link between node C and node D. From
this, the wavelengths for each portion of the path can be chosen as
depicted in FIG. 10; here the two portions of the path are for the
forward direction, from the ingress of node A to node B to node C
and the common link between node C and node D depicted in the upper
part of FIG. 10, and for the reverse direction, from the egress of
node E to node D and the common link between node D and node C
depicted in the lower part of FIG. 10). From this, both the forward
route and the reverse route can be combined to form a single
complete route as depicted in FIG. 11.
[0085] Embodiments comprise configuring one or more nodes in the
plurality of optical nodes to route data according to the path
configuration data generated for the optical network.
[0086] Embodiments comprise a network of optical nodes configured
to route data on the basis of path configuration data generated
according to the embodiments described herein.
[0087] In some embodiments, a constraint based routing approach may
be used for multi-constraint based routing by utilizing heuristics
to provide faster convergence on an approximate solution. For
example, a mechanism for handling multiple constraints might
involve additional graph pruning to remove nodes that do not meet
any of the individual constraints. Another example may comprise
routing which involves applying a heuristic (such as Lagrangian
Relaxation) to provide modified cost metrics that include
constraint information.
[0088] The standard Dijkstra algorithm does not lend itself to
multi-threaded (or multi-core) processing since there is
effectively a single calculation for each routing-front expansion
which needs to be completed and added to a processing heap before
selecting the next route expansion node (Dijsktra always expands
from the least cost node). However, unlike standard Dijkstra,
embodiments described herein contain multiple expansion processes
that could at least in part be run on multiple threads. This is
extremely useful when utilizing multi-core processors to maximize
performance of the graph expansion.
[0089] In some embodiments, a main expansion processing thread
handles the expansion of the lowest cost path on the heap. As part
of the node expansion, the wavelengths on each egress link are
calculated. In embodiments, this wavelength expansion is handled on
a separate thread which can significantly reduce the impact of
handling the wavelength calculations.
[0090] In embodiments, the network graph expansion process and the
subset identification and bandwidth pruning operation are carried
out at least in part in parallel by separate processing threads. In
embodiments, the network graph expansion process and the wavelength
assignment process are carried out at least in part in parallel by
separate processing threads. In embodiments, the subset
identification and bandwidth pruning operation and the wavelength
assignment process are carried out at least in part in parallel by
separate processing threads.
[0091] Although the wavelength expansion may be handled separately
from the main graph expansion thread, in some embodiments locking
is employed to ensure that only one thread is updating the
wavelength data for any given node at any one time. There may
therefore be some situations where a wavelength expansion thread
blocks the main expansion processing thread for a period of time.
Such blocking events would be infrequent, however, for a large
graph expansion.
[0092] Embodiments comprise measures including methods, systems and
computer program products for generating path configuration data
for an optical network. A least cost path calculation process is
performed on a network graph representation of the optical network
to generate path configuration data for the optical network. The
optical network comprises a plurality of optical nodes connected by
optical links including at least one wavelength pass-through
optical node configured to transmit incoming data on an ingress
optical link at a first wavelength as outgoing data on an egress
optical link at the first wavelength only, and at least one
wavelength conversion optical node configured to transmit incoming
data on an ingress optical link at a second wavelength as outgoing
data on an egress optical link at one or more wavelengths different
to the second wavelength.
[0093] In such embodiments, performing the least cost path
calculation process comprises performing a network graph expansion
process on a network graph representation of the optical network to
obtain an expanded network graph representation of the optical
network. Performing the network graph expansion process comprises,
for at least one physical egress link of at least one wavelength
conversion optical node, expanding the at least one physical egress
link into a virtual wavelength pass-through egress link where a
predetermined pass-through cost is assigned to the operation of the
respective wavelength conversion optical node passing through data
on an ingress link to the virtual wavelength pass-through egress
link at the same wavelength, and a virtual wavelength conversion
egress link where a predetermined wavelength conversion cost is
assigned to the operation of the respective wavelength conversion
optical node converting data on an ingress link to one or more
different wavelengths on the virtual wavelength conversion egress
link. The least cost path calculation process is carried out on the
basis of the expanded network graph representation of the network
comprising virtual wavelength pass-through and virtual wavelength
conversion egress links.
[0094] The above embodiments are to be understood as illustrative
examples of the disclosure. Further embodiments of the disclosure
are envisaged.
[0095] Embodiments described herein employ average cost values for
optical links. In some situations, using an average cost per link
might not provide an accurate reflection of the real network. In
further embodiments, multiple path calculations are performed using
a for example) random selection of averages and comparing results
with real cost metrics inserted after the path calculation.
[0096] Yet further embodiments involve adding additional virtual
links into the graph representation of the network for different
conversion scenarios. In such embodiments, instead of employing two
types of virtual links, three types of virtual link could be
employed, for example wavelength pass-through, wavelength
conversion (no reframing), and reframing (wavelength may or may not
require conversion). The latter two types of virtual link could be
referred to as two different types of translation virtual links. In
such embodiments, each physical link would be split into three
virtual links (or even more if different layers of reframing are to
be handled differently).
[0097] In embodiments, embodiments are carried out by apparatus (or
`device` or `system`) such as a network node, switch, server, etc.
Embodiments may be carried out in a distributed manner across
multiple apparatus. Such apparatus may for example comprise a
computerized device which may for example comprise a processor
and/or processing system. One or more of the aspects of the
embodiments described herein with reference to the drawings
comprise processes performed by an apparatus. In embodiments, the
apparatus comprises one or more processing systems or processors
configured to carry out these processes. In this regard,
embodiments may be implemented at least in part by computer
software stored in (non-transitory) memory and executable by the
processor, or by hardware, or by a combination of tangibly stored
software and hardware (and tangibly stored firmware). Embodiments
also extend to computer programs, particularly computer programs on
or in a carrier, adapted for putting the above described
embodiments into practice. The program may be in the form of
non-transitory source code, object code, or in any other
non-transitory form suitable for use in the implementation of
processes according to embodiments. The carrier may be any entity
or device capable of carrying the program, such as a RAM, a ROM, or
an optical memory device; etc.
[0098] It is to be understood that any feature described in
relation to any one embodiment may be used alone, or in combination
with other features described, and may also be used in combination
with one or more features of any other of the embodiments, or any
combination of any other of the embodiments. Furthermore,
equivalents and modifications not described above may also be
employed without departing from the scope of embodiments, which is
defined in the accompanying claims.
* * * * *