Protection Schemes for Two Link Failures in Optical Networks

arXiv:0811.1693v1 [cs.IT] 11 Nov 2008 Protection Schemes for Two Link Failures in Optical Networks Salah A. Aly and Ahmed E. Kamal Department of Electrical and Computer Engineering Iowa State University, Ames, IA 50011, USA Email: {salah,kamal}@iastate.edu October 29, 2018 Abstract—In this paper we develop network protection schemes against two link failures in optical networks. The motivation behind this work is the fact that the majority of all available links in an optical network suffer from single and double link failures. In the proposed network protection schemes, NPS2-I and NPS2-II, we deploy network coding and reduced capacity on the working paths to provide backup protection paths. In addition, we demonstrate the encoding and decoding aspects of the proposed schemes. Index Terms—Network Protection, Optical Networks. I. INTRODUCTION One of the main services of operation networks that must be deployed efficiently is reliability. In order to deploy a reliable networking strategy, one needs to protect the transmitted sig- nals over unreliable links. Link failures are common problems that might occur frequently in single and multiple operating communication circuits. In network survivability and network resilience, one needs to design efficient strategies to overcome this dilemma. Optical network survivability techniques are classified as pre-designed protection and dynamic restora- tion [13], [8]. The approach of using pre-designed protection aims to reserve enough bandwidth such that when a failure occurs, backup paths are used to reroute the transmission and be able to recover the data. Examples of this type are 1-1 and 1-N protections [2], [9]. In dynamic restoration reactive strategies, capacity is not reserved. However, when the failure occurs, dynamic recovery is used to recover the data transmitted in the links that are suffered from failures. This technique does not need preserved resources or provision of extra paths that work in case of failure. In this work we will provide several strategies of dynamic restoration based on coding and reduced distributed fairness capacities. Network coding is a powerful tool that has been recently used to increase the throughput, capacity, and performance of communication networks. Information theoretic aspects of network coding have been investigated in [12], [1]. Network coding allows the intermediate nodes not only to forward packets using network scheduling algorithms, but also en- code/decode them using algebraic primitive operations, see [1], [4], [12] and references therein. As an application of network coding, data loss because of failures in communication links can be detected and recovered if the sources are allowed to perform network coding operations. Network coding is used to maximize the throughput [1], [10]. Also, it is robust against packet losses and network failures [5], [11], [6]. Network protection against single and multiple link failures using adding extra protection paths has been introduced in [7], [8]. The source nodes are able to combine their data into extra paths (backup protection paths) that are used to protect all signals on the working paths plain carrying data from all sources. In both cases, p-cycles has been used for protection against single and multiple link failures. In this paper we design two schemes for network protection against one and two failed links in a network with n disjoint working paths: NPS2-I and NPS2-II. The approach is based on network coding data originated by the sources. We assume that network capacity will be reduced by a partial factor in order to achieve the required protection. Several advantages of NPS2-I and NPS2-II can be stated as: • The data sent from the sources are protected without adding extra paths. Two paths out of the n disjoint working paths will carry encoded data, and hence they are protection paths. • The encoding and decoding operations are achieved with less computational cost at both the sources and receivers. The recovery from failures is achieved immediately with- out asking the senders to retransmit the lost data. • The normalized network capacity is (n −2)/n, which is near-optimal in case of using a large number of connections. II. NETWORK MODEL In this section we present the network model and basic terminology. i) Let N be a network represented by an abstract graph G = (V, E), where V is a set of nodes and E be a set of undirected edges. Let S and R be sets of independent sources and destinations, respectively. The set V = V ∪ S ∪R contains the relay, source, and destination nodes. Assume for simplicity that |S| = |R| = n, hence the set of sources is equal to the set of receivers. ii) A path (connection) is a set of edges connected together with a starting node (sender) and an ending node (re- ceiver). Li = {(si, e1i), (e1i, e2i), . . . , (e(m)i, ri)}, 2 where 1 ≤i ≤n and (e(j−1)i, eji) ∈E for some integer m. iii) The node can be a router, switch, or an end terminal dependin

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