Rachna Asthana

p-Cycles: An overview

One of the most promising techniques of network protection i.e. p-Cycles (pre-planned, preconfigured-cycles) is reviewed in this paper. In this paper we provide a survey of the main work on p-cycles to date. The characteristics of p-cycles and various types of protection provided by them are discussed. Finally, some possible extensions or enhancements of the p-cycle concept are discussed.

Second Phase Reconfiguration of Restored Path for Removal of Loop Back in P-Cycle Protection

P-cycles are one of the most promising techniques used for span protection in optical networks. However when p-cycle is used to provide protection to any failed span, there may be overlapping of some nodes in the working path and in the restoration path provided by the p-cycle. These nodes are repeated in the restored path; hence redundant link capacity is used. These repetitions will form loops at the overlapping nodes. To remove these loops and release the redundant capacity, an algorithm is developed to reconfigure the restored path. This aspect of the p-cycle has not been discussed so far in the literature. The capacities required without reconfiguration and after reconfiguration have been compared. It has been found that with reconfiguration, considerable amount of capacity can be released, and the restored path length can also be reduced significantly

Distributed Protocol for Removal of Loop Backs and Optimum Allocation of p-Cycles to Minimize the Restored Path Lengths

p-Cycle-based protection is one of the most promising techniques of span protection in optical networks because of mesh-like efficiency and ring-like speed. We have presented a modified distributed cycle preconfiguration protocol (MDCPC) which reduces the computational complexities, by finding all the copies of the same p-cycle in single iteration. All the copies of the same p-cycle are aggregated together to reduce the number of switching fabrics and the amount of signalling traffic. Further, the restoration paths provided by the p-cycles are usually many hops long, as longer p-cycles provide better efficiency. Obviously, with longer p-cycles, the nodes in the working path may be repeated in the restoration path provided by the p-cycle. They will give rise to loop backs in the restored path. The restored path lengths will unnecessarily be longer due to these loop backs. If these loop backs can be removed, the restored path length will be reduced significantly, and redundant capacity will also be released. In the present work, a distributed protocol has been presented for the implementation of removal of loop back (RLB) algorithm to reconfigure the restored path. The reduction in the restored path length also depends on the fact that which p-cycle is being used to protect a particular path. The problem has been formulated as optimum p-cycle allocation (OPA) problem and solved with the Hungarian algorithm. The average lengths of the restored paths with and without RLB for the networks with 2.0 average nodal degree have also been derived.

Protection and Restoration in Optical Networks

Various protection and restoration techniques for IP over optical network framework have been surveyed in this paper. These schemes are based on different concepts. They have been classified according to the concepts used. An attempt has been made to identify mechanism to evaluate their relative performance. Further subjective comparison of various approaches of mixing, protection and restoration technique in various layers of networks has been presented.

Removal of Loop Back in p-cycle Protection: Second Phase Reconfiguration

P-cycles are one of the most promising techniques of span protection used in optical networks. However the protection path provided by p-cycle may contain some nodes, which are part of the working path also. When the p-cycle is used to provide protection to any failed span of the working path, then due to the common nodes in working path and protection path provided by p-cycle, there will be overlapping of these nodes in the restored path. These overlapping nodes will appear twice in the restored path, once in the working path and then in the protection path provided by p-cycle for the protection of any failed span. This repetition will make loops at the overlapping nodes. Hence redundant span capacity will be used. To remove these loops, and release the redundant capacity a scheme is developed to reconfigure the restored path. This aspect of the p-cycle has not been discussed so far in the literature. The released capacity is calculated and it has been found that significant amount of capacity is released. The average amount of released capacity with second phase reconfiguration, is in the range of 26% to 28% for the test network, depending upon the traffic distribution

A general algorithm to design sets of all possible one dimensional unipolar orthogonal codes of same code length and weight

This paper describe a general scheme to design all the uni-polar codes characterized by parameter (n, w). The binary sequence of length ‘n’ (‘n’ bits) and weight ‘w’ (number of bit ‘1’s in the sequence) with its n-1 circular shifted versions represent the same code. These codes can be further put in different subsets characterized by (n, w, λa, λc), where λa and λc are auto-correlation and cross-correlation constraint respectively. All the codes within a set are called orthogonal to each other. In reality, they are pseudo orthogonal as cross-correlation is non-zero. With parameter (n, w, λa, λc), there can be many sets each containing a number of orthogonal codes. All the codes in one set are always orthogonal to each other but not necessarily orthogonal to the codes in other sets. The code design scheme presented in this paper, can design all possible sets of codes. Users can select the code set as per their requirements. These uni-polar one dimensional orthogonal codes have their application in incoherent optical code division multiple access systems. The uni-polar optical orthogonal code can be generated by putting a single optical pulse at every position of bit ‘1’ and no pulses at the positions of bit ‘0’s in the sequence.

The effect of removal of loop back on the reliability of the restored paths provided by p-cycles

The p-cycles have been proved to be very effective technique of span protection due to its capacity efficiency and restoration speed. However, in most of the restored paths which are provided after the event of failure, many nodes and links are repeated. This repetition results in loop backs in the restored paths. These loop backs are totally undesirable and do not serve any purpose. In this paper we have performed a study to find out the effect of removal of loop back on the reliability of the restored paths. We have developed models for calculation of the reliability before and after removal of loop back. The reliability of the restored paths has been compared before and after the removal of loop backs. The results show considerable improvement in the reliability of the paths after loop back removal.