Telecommunications Research Laboratories

Northern Telecom Limited

Alberta Telecommunications Research Centre

Tr Technologies Limited

Other

Nortel Networks Corporation

Wayne D Grover

John Doucette

Demetrios Stamatelakis

Adil Kodian

Ernst A Munter

Witold A Krzymien

James A McEachern

Thomas E Moore

Martin C Lefebvre

Lance Doherty

George D Fraser

Kwun Kit Leung

Joe P Dubuc

James B Slevinsky

Michael H MacGregor

Tommy Fong

Thuthuy Bach

G Dave Morley

Aden Grue

Ernest Y B Siu

Ganxiang Shen

Randy G Martens

Matthieu Arnold Henri Clouqueur

Rainer R Iraschko

A telecommunications network, comprising plural nodes connected by plural spans and arranged to form a mesh network. There is at least one pre-configured cycle of spare capacity established in the mesh network, the pre-configured cycle including plural nodes of the mesh network. The plural nodes of the pre-configured cycle are configured to protect a set of plural mutually disjoint working paths end to end.

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A communication network in which p-cycles are used to rapidly, simply and efficiently provide for the direct replacement of failed fiber sections with whole replacement fibers. As long as the loss budgets are adequate, entire DWDM wavebands can be restored with no switching or manipulation of individual lightpaths. Following a substitution transient, the DWDM layer would never know the break happened. In environments where fiber switching devices are low cost, and ducts are full of dark fiber, this could provide a very low cost alternative to protect an entire DWDM transport layer (or working capacity envelope) against the single largest cause of outage.

This disclosure introduces a significant extension to the method of p-cycles for network protection. The main advance is the generalization of the p-cycle concept to protect multi-span segments of contiguous working flow, not only spans that lie on the cycle or directly straddle the p-cycle. This effectively extends the p-cycle technique to include path protection, or protection of any flow segment along a path, as well as the original span protecting use of p-cycles. It also gives an inherent means of transit flow protection against node loss. We present a capacity optimization model for the new scheme and compare it to prior p-cycle designs and other types of efficient mesh-survivable networks. Results show that path-segment-protecting p-cycles ('flow p-cycles' for short) have capacity efficiency near that of a path-restorable network without stub release. An immediate practical impact of the work is to suggest the of use flow p-cycles to protect transparent optical express flows through a regional network.

Path segment protecting p-cycles

A novel alternative concept for handling dynamic provisioning changes and ongoing network reconfiguration and incremental reoptimization in general. A prime motivation is concern about the dependency of existing concepts for dynamic provisioning on the real-time coherence of databases of network state at diverse geographic locations. Not only is the continual updating of such global state everywhere in the network an intensive real-time load, but inevitable incoherencies pose hazards in network operation. The alternative proposal is a framework that makes use precise time synchronization and the computational power of network nodes to solve identical local instances of incremental reoptimization problems in situ. The new scheme removes the database coherency hazard, reduces signaling volumes, and increases resource efficiencies in service provisioning. It also provides a framework in general for continually ongoing incremental or (if desired) total reoptimization of network configuration.

Distributed synchronous batch reconfiguration of a network

A simple and effective pre-processing step to reduce the complexity of solving p-cycle network design problems involving pre-selecting candidate cycles based on their topological score (TS) and a priori efficiency (AE) is disclosed. The disclosure contains a case study that examines joint optimization of working routes with placement of p-cycles.

Method for design of networks based on p-cycles

A method for restoring traffic in a network. The network includes plural distinct nodes interconnected by plural distinct spans, each span having working links and spare links. Each node has a digital cross-connect switch for making and breaking connections between adjacent spans forming span pairs at a node. Cross-connections between spare links in adjacent spans are made such that sets of successive nodes through which the adjacent spans form span paths form closed paths. A method of finding and construction closed paths is described in which statelets are broadcast through the network. In a preferred method of implementation of the method, the statelet broadcast occurs not in response to a network failure, but across the entire network before any particular span failure and may be carried out during normal network operations as a continual re-configuration of the network.

Distributed preconfiguration of spare capacity in closed paths for network restoration

A novel alternative concept for handling dynamic provisioning changes and ongoing network reconfiguration and incremental reoptimization in general. A prime motivation is concern about the dependency of existing concepts for dynamic provisioning on the real-time coherence of databases of network state at diverse geographic locations. Not only is the continual updating of such global state everywhere in the network an intensive real-time load, but inevitable incoherencies pose hazards in network operation. The alternative proposal is a framework that makes use precise time synchronization and the computational power of network nodes to solve identical local instances of incremental reoptimization problems in situ. The new scheme removes the database coherency hazard, reduces signaling volumes, and increases resource efficiencies in service provisioning. It also provides a framework in general for continually ongoing incremental or (if desired) total reoptimization of network configuration. The proposal also points directions towards some new research questions such as implementation of optimization models for identical solution on disparate platforms and definition of a variety of incremental batch reoptimization problems. It is thought that this may be one of the first practical application concepts for transport network management that would involve on-line embedded use of operations research methods in communication networks.

Span protection has advantages in speed, locality of action and simplicity but requires that the failed span be located in real time. Recent work proposed rapid fault-localization via monitoring cycles (m-cycles). Span-protecting structures (such as p-cycles) operate and are designed separately from the monitoring cycles in this architecture. We have invented a method of designing survivable networks wherein a span protecting p-cycle network inherently includes the properties of a set of fault localizing m-cycles at zero or minimal additional network design cost. Results show that this can be achieved with the same localization effectiveness as separately designed m-cycle solutions, at little or no extra cost.

Self-fault isolation in transparent P-cycle networks

A method to increase the capacity efficiency of span-restorable mesh networking on sparse facility graphs. The new approach views the network as a 'meta-mesh of chain sub-networks'. This makes the prospect of WDM mesh networking more economically viable than with previous mesh-based design where the average nodal degree is low. The meta-mesh graph is a homeomorphism of the complete network in which edges are either direct spans or chains of degree-2 nodes. The main advantage is that loop-back type spare capacity is provided only for the working demands that originate or terminate in a chain, not for the entire flow that crosses chains. The latter 'express' flows are entirely mesh-protected within the meta-mesh graph which is of higher average degree and hence efficiency for mesh restoration, than the network as a whole. Nodal equipment savings also arise from the grooming of express lightpaths onto the logical chain-bypass span. Only the meta-mesh nodes need optical cross-connect functionality. Other sites use OADMs and/or glassthroughs. The resultant designs comprise a special class of restorable network that is intermediate between pure span restoration and path restoration. Most of the efficiency of path restoration is achieved, but with a span restoration mechanism which is more localized and potentially faster and simpler than path restoration. The concept lends itself to implementation with OADMs having a passive waveband pass-through feature to support the logical chain bypass spans for express lightpaths.

Design of a meta-mesh of chain sub-networks

Ongoing growth in transport demand is served while deferring or eliminating expenditure for additional capacity by reclaiming the protection capacity and inefficiently used working capacity in existing multi-ring network. Reclamation is through re-design of the routing and restoration in the network using mesh principles within the pre-existing ring capacities. The installed working and protection capacity of existing rings is viewed as a sunk investment, an existing resource, to be 'mined' and incorporated into a mesh-operated network that serves both existing and ongoing growth. A complete double or even tripling of demand could be supported with little or no additional capacity investment through the period of ring-to mesh conversion by ring-mining. An existing ring set may be converted to a target architecture of 'p-cycles' instead of a span-restorable mesh, through placement of straddling span interface units to convert ring ADMs to p-cycle nodal elements.

Evolution of a telecommunications network from ring to mesh structure

A method of designing a telecommunications network, the method comprising the steps of A) for all working demand flows required to be routed in the telecommunications network, finding an initial topology of spans between nodes in the telecommunications network that is sufficient for routing all working demand flows, while attempting to minimize the cost of providing the spans; B) given the initial topology of spans identified in step A, finding a set of additional spans that ensures restorability of working demand flows that are required to be restored in case of failure of any span in the initial topology of spans, while attempting to minimize the cost of providing additional spans; and C) starting with the initial topology of spans and the additional spans identified in step B, finding a final topology of spans between nodes in the telecommunications network that attempts to minimize the total cost of the final topology of spans, while routing all working demand flows and ensuring restorability of working demand flows required to be restored in case of failure of any span in the final topology of spans. A network so designed may be implemented in whole or in part.

Topological design of survivable mesh-based transport networks

A method of configuring a node in an IP network by creating a set of router table entries which form a set of virtually preconfigured cyclical routes, or p-cycles, within the IP network. This set of p-cycles is virtual in the sense that the only resources which they normally consume are routing table entries. No transmission capacity is required for them, unless/until they are used to carry packets (traffic.) These p-cycles sit idle and unused until a failure takes place. The routers surrounding the failure then use these p-cycles to route packets, which normally would be lost, around the failure. A router having an entry in its router table identifying the p-cycle, together with an associated port, is also disclosed, and also a data packet that may use a p-cycle to get to its destination.

Protection of routers in a telecommunications network

A method of providing restoration routes for protecting traffic in a mesh network is described. The method comprises the steps of generating a set of eligible restoration routes for each span in the network, establishing a bi-criteria objective function in terms of route length and capacity cost for selecting a set of restoration routes, and selecting a set of restoration routes for each span from the eligible restoration routes in dependence upon the bi-criteria objective function. Embodiments of the invention may be useful for shortening the lengths, in terms of hops, of existing restoration routes in a mesh-restorable network and in some cases with negligible spare capacity penalty.

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Edmonton, Canada

Wayne D Grover