Method of preconfiguring optical protection trails in a mesh-connected agile photonic network
The method of pre-configuring the optical protect paths in an agile photonic network establishes a protection trail for each optical working path that may be set-up in the network. The pre-configuration is based on building an electrical layer (EXC) graph that takes into account all the connection demands in the network, and finding on this EXC graph a plurality of cycles. Next, the EXC cycles are validated at the optical layer, and are further validated against constraints. The method attempts to find an optimal cycles solution, without exhausting all possible variants.
1. In an agile network (APN) where each connection demand is automatically set-up along a respective working trail, each working trail having one or more successive optical working paths, a method of pre-configuring protect trails, comprising the steps of:
(a) at the electrical layer, preparing an electrical layer related (EXC) graph where each connection demand is represented by an EXC link;
(b) extracting a best valid cycle associated with a maximum number of EXC links from said EXC graph; and
(c) at the optical layer, pre-configuring said best valid cycle into protect trails, each of said protect trails being associated with an optical working path on said best valid cycle.
2. A method as claimed in claim 1 , further comprising the steps of:
(d) on a residual EXC graph obtained after extraction of said best valid cycle, identifying a next best valid cycle and extracting said next best valid cycle from said residual EXC graph; and
(e) repeating step (c) for said next best valid cycle, until all valid cycles are extracted from said residual EXC graph.
3. A method as claimed in claim 2 , wherein the number of iterations of step (e) is limited to a preset number of iterations.
4. A method as claimed in claim 2 , further comprising the steps of:
(f) on said residual EXC graph, identifying a valid group of EXC links and extracting said valid group as a complete cycle; and
(g) pre-configuring said valid group into protect trails, each protect trail associated with an optical working path represented by an EXC link on said group.
5. A method as claimed in claim 4 , further comprising the step of repeating step (g) for a next valid group, until all valid groups have been extracted from said residual EXC graph.
6. A method as claimed in claim 5 , further comprising the step of pre-configuring a 1:1 protect trail for each optical working path represented by an EXC link left on said residual EXC graph.
7. A method as claimed in claim 1 , wherein said step of extracting comprises:
finding a cycles basis for said EXC graph;
validating the cycles of said cycles basis;
identifying said best valid cycle; and
subtracting from said EXC graph all EXC links of said best valid cycle.
8. A method as claimed in claim 7 , wherein said step of identifying said best valid cycle comprises the steps of:
constructing a residual graph tree using for each branch a different cycle of said cycles basis as a first cycle to be extracted;
selecting from said residual graph tree a branch that extracts the maximum number of EXC links; and
identifying said respective first cycle as said best cycle.
9. A method as claimed in claim 7 , wherein said step of finding a cycles basis comprises the step of constructing a spanning tree for said EXC graph and finding a plurality of EXC cycles on said spanning tree.
10. A method as claimed in claim 7 , wherein said step of validating comprises the step of eliminating from said cycles basis all cycles that are not supported by an optical layer cycle in said APN.
11. A method as claimed in claim 10 , wherein said step of validating further comprises the step of eliminating from said cycles basis all EXC cycles that do not satisfy an optical layer constraint.
12. A method as claimed in claim 10 , wherein the number of cycles in said cycles basis is limited to a preset number of cycles.
13. In an agile network where a connection demand is automatically routed along an optical-layer trail, a trail having one or more optical working paths, a method of automatically re-routing said demand along a protect trail whenever an optical working path is affected by a fault, comprising:
generating an optical-layer cycle that has a plurality of successive optical paths;
for each optical path on said cycle, identifying a best remaining cycle associated with a maximum number of links of an associated EXC graph as a protect trail; and
pre-configuring a plurality of protection switching scenarios by associating each optical path on said cycle with a respective protect trail for enabling fast traffic recovery when any of said optical paths fail.
14. A method as claimed in claim 13 , wherein said step of generating comprises:
preparing the associated EXC graph where each user demand is represented by an EXC link;
finding a cycles basis for said EXC graph;
validating the cycles of said cycles basis;
identifying said optical-layer cycle among all valid cycles of said cycle basis; and
subtracting from said EXC graph all EXC links of said identified cycle.
15. A method as claimed in claim 14 , wherein said step of identifying said optical-layer cycle comprises:
constructing a residual graph tree using for each branch a different cycle of said cycles basis as a first cycle to be extracted;
selecting from said residual graph tree a branch that extracts the maximum number of EXC links; and
identifying said respective first cycle as said optical-layer cycle from said branch.
16. A method as claimed in claim 14 , wherein said step of finding a cycles basis for said EXC graph comprises constructing a spanning tree from said EXC graph, and identifying all fundamental cycles on said EXC graph.
17. A method as claimed in claim 14 , wherein said step of validating the cycles of said cycles basis comprises identifying a cycle of said basis as a valid cycle when said cycle is supported by an optical layer cycle; and when said optical layer cycle satisfies one or more constraints.
18. A method as claimed in claim 17 , wherein said step of finding a cycles basis further comprises identifying additional cycles on said EXC graph whenever the number of said valid cycles is less than a preset number.
19. In an agile photonic network (APN), a cycles management unit for sharing the protection bandwidth between a plurality of optical working paths, comprising:
a trail routing unit for automatically setting-up a working trail for each connection demand, said working trail having one or more successive optical working paths;
a cycles solution generator for providing a cycles basis for a given configuration of connection demands in said APN;
a cycles validating unit for identifying a best valid cycle in said cycles basis associated with a maximum number of links on a cycles graph; and
a cycles processing unit for associating each optical working path on said best valid cycle with a respective protect trail on said best valid cycle.
20. A cycles management unit as claimed in claim 19 , wherein said cycles processing unit maintains a list with the association between each optical working path and a respective protect trail.
21. A cycles management unit as claimed in claim 19 , further comprising means for storing a list of constraints used by said cycles validating unit.