Gangxiang Shen

Extending the p-cycle concept to path segment protection for span and node failure recovery

The paper introduces an extension to the method of p-cycles for network protection. The p-cycle concept is generalized to protect path segments of contiguous working flow, not only spans that lie on the cycle or directly straddle the p-cycle. The original span protecting use of the p-cycle technique is extend to include path protection or protection of any flow segment along a path. It also gives an inherent means of protecting working flows that transit a failed node. We use integer linear programming to study the new concept and determine its inherent capacity requirements relative to prior p-cycle designs and other types of efficient mesh-survivable networks. Results show that path-segment-protecting p-cycles (flow p-cycles) have capacity efficiency near that of the shared backup path-protection (SBPP) scheme currently favored for optical networking. Because its protection paths are fully preconnected and because it protects path segments (not entire paths), it has the potential for both higher speed and higher availability than SBPP. We also develop capacity optimization models to support 100% restoration of transiting flows through failed nodes. Only a very small additional spare capacity is needed to achieve both 100% span and intermediate node-failure restorabilities, and a very high transiting traffic restorability can be accomplished for node failure restorability given spare capacity only for span-failure protection. An immediate practical application is to suggest the use of flow p-cycles to protect transparent optical express flows through a regional network.

Performance study on a WDM packet switch with limited-range wavelength converters

We consider a slotted WDM packet switch with limited-range wavelength converters. The performance of this switch is studied using simulations with various types of data traffic. Results show that the slotted WDM packet switch with a small range of wavelength conversion capability can achieve a performance close to that of a switch with the full range of wavelength conversion capability.

Efficient heuristic algorithms for light-path routing and wavelength assignment in WDM networks under dynamically varying loads

This paper presents heuristic algorithms that may be used for light-path routing and wavelength assignment in optical WDM networks under dynamically varying traffic conditions. We consider both the situations where the wavelength continuity constraint is enforced or not enforced along a light-path. The performance of these algorithms has been studied through simulations. We also compare their performance with that of a simpler system that uses fixed shortest-path routing. Our proposed algorithms provide lower blocking probabilities and are simple enough to be applied for real time network control and management. The heuristic algorithms are computationally simple and efficient to implement and provide good wavelength utilisation leading to efficient usage of the networks resources.

Architectural design for multistage 2-D MEMS optical switches

Next-generation wavelength routing optical networks requiring optical cross connects (OXC) in the network have the ability to direct optical signals from any input interface to suitable output interfaces by configuring their internal embedded optical switch matrices. Microelectromechanical systems (MEMS) switches are regarded as the most promising technology to achieve such functionality. We consider the construction of a multistage MEMS switch network with single two-dimensional (2-D) MEMS switch blocks. A power loss model is developed that calls on a single MEMS block that is then used to develop the model for a three-stage Clos network. An effective model for maximum loss difference between calls is also developed. Based on these, the paper also proposes three connection patterns [Max + Min greedy (MMG), compressed extended generalized shuffle 1 (C-EGS-1), and compressed extended generalized shuffle 2 (C-EGS-2)] to connect outlet ports and inlet ports between two neighboring stages in a three-stage Clos network. These connection patterns are proved to be optimal and efficient enough to reach the minimums of both the maximum power loss of calls and the maximum loss difference between calls.

Design and performance of protected working capacity envelopes based on p-cycles for dynamic provisioning of survivable services

As an alternative to the shared backup path protection (SBPP) method, wen develop a framework for dynamic provisioning of survivable services through the usen of p-cycles to form a protected working capacity envelope (PWCE) within whichn dynamic provisioning of protected services is greatly simplified. With a PWCE,n arbitrarily fast dynamic service demands can be handled with much less complexityn (in terms of database maintenance and state update dissemination) than with SBPP.n Only a simple open-shortest-path-first (OSPF) topology view of nonexhausted spans inn the envelope is required. If a new path can be routed through the envelope, it isn protected by virtue of being routable. This is in contrast to needing a fulln database of the network state so that the end user can set up a shared backupn protection path under SBPP. In addition, dissemination of spare capacity sharingn updates occurs only on the time scale of the nonstationary evolution of the demandn statistics, not like SBPP, which occurs on the time scale of individual connectionn arrivals or departures. During statistically stationary periods there is non dissemination of spare capacity sharing updates whatsoever with an envelope that isn well matched to its load. The PWCE concept thus offers some new trade-offs betweenn operational simplicity and spare capacity efficiency. Under the PWCE conceptn p-cycles are of particular interest for consideration because, although manyn protection techniques can be the basis of PWCE operation p-cycles offer the uniquen combination of ring-like protection times with the capacity efficiency ofn shared-mesh networks. But, in addition, p-cycles offer a further important propertyn for a transparent optical network: that of providing fully pre-cross-connectedn protection paths. Because all protection paths are preconnected structures, opticaln transmission path integrity can be validated before failure and is not of suchn concern as it is in schemes where optical replacement path segments of severaln wavelength channels would have to be assembled on the fly (without the benefit ofn o-e-o between stages). The main contribution of this work is the detailedn implementation and simulation of test networks operating under PWCE and designedn with novel envelope volume maximizing formulations. A wide range of network capacityn environments were considered to find that p-cycle-based PWCE is close to SBPP inn blocking performance while simultaneously offering much simpler operation and an faster restoration speed.

Operation of WDM networks with different wavelength conversion capabilities

We study the impact of wavelength conversion capability on wavelength routing WDM networks with fixed shortest-path routing. We propose a method for implementing wavelength routing in a WDM network with partial wavelength conversion capability. Simulation results show that such partial wavelength conversion networks provide a performance in between that of wavelength continuous networks and those with full conversion capability. In addition, it can be seen that only limited wavelength conversion capability is enough to provide a performance close to that of a network with full conversion. Analytical and simulation bounding results for the full and no conversion cases have also been provided.

Extending the p-cycle concept to path-segment protection

This work introduces a significant extension to the method 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 protection use of p-cycles. It also gives an inherent means of transit flow protection against node loss. We develop 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 have capacity efficiency near that of a path-restorable network is to suggest the use of flow p-cycles to protect transparent optical express flows through a regional network.

Segment-based approaches to survivable translucent network design under various ultra-long-haul system reach capabilities (Invited)

One of the most practical architectural options for optical networking is a so-called translucent network based on a predominance of optically transparent switch nodes and a smaller number of strategically placed opaque (electronic core) switch nodes. In such a network it is technically easier to assume failure detection at the opaque nodes only and thus natural to consider viewing the transparent path segments between opaque nodes as the entities to be protected for network survivability, as opposed to single spans or entire end-to-end paths. We develop and test capacity-design models to compare this type of segmentbased restoration scheme with conventional schemes. More important, however, a fast, nearly optimal, algorithm is proposed that can determine the placement of opaque nodes so that the fewest possible number is needed that ensures complete translucent reachability and single-failure survivability on the basis of the corresponding transparent path segments. Our data and methods also reveal the trade-off between the transparent reach obtainable by an ultra-long-haul (ULH) system and the corresponding number of opaque nodes required in the network (including survivability considerations), and thus we attain important insights to guide the relative allocation of research and development efforts on ULH systems as opposed to optical‐electronic‐optical cross-connect cost reduction.

Exploiting forcer structure to serve uncertain demands and minimize redundancy of p-cycle networks

We study the forcer concept in the context of p-cycle based networks. A simple but efficient forcer analysis method is proposed specifically for span-restorable networks in general. Besides identifying forcers, the method is also capable of exploiting extra servable working channels given an initial network spare capacity budget designed for pre-existing working capacities. We find that a large number of extra working channels can be served with no increase in the pre-planned spare capacity budget. This attribute of p-cycle protected networks can be used to enhance their ability to serve unforeseen demand patterns or provide an expanded envelope of protected working capacity within which dynamic demand is servable without blocking due to exceeding the protected working capacity limits.

Crosstalk analysis for limited-wavelength-interchanging cross connects

Identifies crosstalk sources in limited-wavelength-interchanging cross connects (L-WIXC) and calculates the power penalty imposed by this. Specifications for the components used in the L-WIXCs can then be determined for obtaining a specified level of system performance.