Method and system for design and routing in transparent optical networks
View Patent ↗The present invention relates to a method and system for design and routing in telecommunications networks having transparent elements such as photonic switches. Transparent optical networks transmit signals optically, performing both switching and amplification photonically. As a result, transparent networks may be more economical than conventional “opaque” optical networks that convert signals to electronic form at each network node because they do not require as much equipment for performing optical-electrical conversion. However, transparent networks pose new operational challenges. Physical-layer impairments that are repaired by optical-electrical-optical (OEO) regeneration can accumulate along (transparent) connection paths. To effectively deploy and utilize transparency, mechanisms to assure that impairment-feasible paths exist and can be identified in the network are required. The present invention provides: 1) a method for locating OEO-regeneration capability to assure the existence of impairment-feasible paths in a network and 2) a method for identifying impairment-feasible connection paths in a network of transparent and OEO-capable nodes. The first is a method related to network design, which models the design problem as a variation of a connected dominating set problem. The second is a method related to network routing, which transforms the impairment-aware routing problem into a shortest-path problem in an expanded network. The design methodology of the present invention employs both domination and connectability concepts to enable sparser placement of OEO regeneration capability within networks. Further, the routing methodology of the present invention provides a mechanism for finding feasible routes with respect to impairment constraints while minimizing the use of OEO interfaces to assure such feasibility.
1. A method for locating optical-electrical-optical (OEO) regeneration capability in an optical network having at least one transparent element, said method comprising:
creating a domination graph for said optical network;
creating a connectability graph for said optical network;
identifying a set of nodes that forms a dominating set in said domination graph that remains connected in said connectability graph when all other nodes are removed from said connectivity graph; and
locating OEO capability at nodes in said optical network corresponding with identified set of nodes.
2. The method according to claim 1 , wherein said domination graph and said connectability graph are constructed using information about the network topology of said optical network and in accordance with constraints defining impairment-feasible paths within said optical network.
3. The method for locating optical-electrical-optical (OEO) regeneration capability in an optical network having at least one transparent element, said method comprising:
creating a domination graph for said optical network;
creating a connectability graph for said optical network;
labeling each node in said domination graph with undominated status;
labeling each node in said connectability graph with unconnected status;
establishing a list of OEO locations, initially set to empty;
determining the number of nodes dominated by each node in said domination graph;
selecting one node that dominates the most nodes;
performing the following scanning operation on said selected node;
add said selected node to said OEO list;
update the labels of the selected node to dominated in said domination graph and connected in said connectability graph;
update labels for all nodes connected to said selected node to dominated in said domination graph and connected in said connectability graph;
determine if any undominated nodes still exist and repeat said scanning operation for the connected node that dominates the most undominated nodes;
repeating said step of determining if any undominated nodes still exist, until no undominated nodes exist; and
placing OEO capability at each node on the final OEO list.
4. The method according to claim 3 , wherein said domination graph and said connectability graph are constructed using information about the network topology of said optical network and in accordance with constraints defining impairment-feasible paths within said optical network.
5. A method for identifying impairment-feasible paths between a first node and a second node in an optical network that contains at least one transparent element, said method comprising:
selecting at least one measurable parameter related to impairment accumulation along paths in said optical network;
setting a maximum constraint on said measurable parameter; and
constructing an impairment graph between said first node and said second node by,
defining feasible states for said first node, said second node and for each node between said first node and second node by assuring that said maximum constraint is not exceeded;
representing said first node, said second node and each node between said first and second node by sets of in and out designations for at least one feasible impairment state of each node;
constructing a directed link from the in designation of an impairment state of a node to the out designation for a new impairment state of the same node if the node may be crossed transparently, where the new impairment state records the change for each measurable parameter related to crossing said node transparently;
constructing a directed link from the in designation of an impairment state of a node to the out designation for a new impairment state of the same node if regeneration can be performed at the node, where the new impairment state resets each measurable parameter to zero;
constructing a directed link from the out designation of an impairment state of a node to the in designation for an impairment state of an adjacent node of said optical network, where the impairment state at the in designation records the change for each measurable parameter related to traversing said link;
wherein said impairment graph represents impairment-feasible paths between said first node and said second node.
6. The method according to claim 5 , wherein said maximum constraints are set on both total distance and total number of intermediate nodes traversed.
7. The method according to claim 5 , wherein said maximum constraints are set on numbers of in-line and node amplifiers traversed.
8. The method according to claim 5 , wherein said impairment graph is used to minimize the cost of performing OEO regeneration within the optical network by applying costs to links between in designations and out designations of nodes, where said cost reflects the cost of regenerating at the associated node within said optical network.
9. The method according to claim 5 , wherein said impairment graph is used to minimize said measurable parameters by associating costs related to said parameters with links in said impairment graph.
10. The method according to claim 5 , further including the steps of identifying a least-cost impairment-feasible path from all of the impairment-feasible paths represented on said impairment graph.
11. The method of claim 10 , wherein step of identifying a least-cost impairment-feasible path comprises solving a shortest-path problem.