Network Protection Codes Against Link Failures Using Network Coding

arXiv:0809.1258v2 [cs.IT] 21 Dec 2008 Network Protection Codes Against Link Failures Using Network Coding 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 Abstract—Protecting against link failures in communication networks is essential to increase robustness, accessibility, and reliability of data transmission. Recently, network coding has been proposed as a solution to provide agile and cost efficient network protection against link failures, which does not require data rerouting, or packet retransmission. To achieve this, separate paths have to be provisioned to carry encoded packets, hence requiring either the addition of extra links, or reserving some of the resources for this purpose. In this paper, we propose network protection codes against a single link failure using network coding, where a separate path using reserved links is not needed. In this case portions of the link capacities are used to carry the encoded packets. The scheme is extended to protect against multiple link failures and can be implemented at an overlay layer. Although this leads to reducing the network capacity, the network capacity reduction is asymptotically small in most cases of practical interest. We demonstrate that such network protection codes are equivalent to error correcting codes for erasure channels. Finally, we study the encoding and decoding operations of such codes over the binary field. I. INTRODUCTION Network coding is a powerful tool that has been used to increase the throughput, capacity, and performance of com- munication networks [15], [18]. It offers benefits in terms of energy efficiency, additional security, and reduced delay. Network coding allows the intermediate nodes not only to forward packets using network scheduling algorithms, but also encode/decode them using algebraic primitive operations (see [1], [4], [15], [18] and references therein). One application of network coding that has been proposed recently is to provide protection against link failures in overlay networks [9], [12]. This is achieved by transmitting combina- tions of data units from multiple connections on a backup path in a manner that enables each receiver node to recover a copy of the data transmitted on the working path in case the working path fails. This can result in recovery from failures without data rerouting, hence achieving agile protection. Moreover, the sharing of protection resources between multiple connections through the transmission of linear combinations of data units results in efficient use of protection resources. This, however, requires the establishment of extra paths over which the com- bined data units are transmitted. Such paths may require the This research was supported in part by grants CNS-0626741 and CNS- 0721453 from the National Science Foundation, and a gift from Cisco Systems. addition of links to the network under the Separate Capacity Provisioning strategy (SCP), or that paths be provisioned using existing links if using the Joint Capacity Provisioning strategy (JCP), hence reducing the network traffic carrying capacity. Certain networks can allow extra transmissions and the addition of bandwidth, but they do not allow the addition of new paths. In this scenario, one needs to design efficient data recovery schemes. Several previous approaches focused on solving this problem using additional extra paths at an overlay network level, or deploying ARQ protocols for the recovery of lost packets. In order to provide recovery from link failures in such networks, approaches other than using dedicated paths, or adding extra links must be used. In this paper, we propose such an approach in which we use network coding to provide agile, and resource efficient protection against link failures, and without adding extra paths. The approach is based on combining data units from a number of sources, and then transmitting the encoded data units using a small fraction of the bandwidth allocated to the connections, hence disposing of the requirement of having extra paths. In this scenario, once a path fails, the receiver can recover the lost packets easily from the neighbors by initiating simple queries. Previous solutions in network survivability approaches us- ing network coding focused on providing backup paths to recover the data affected by the failures [9], [10], [11]. Such approaches include 1+N, and M+N protections. In 1+N pro- tection, an extra secondary path is used to carry combinations of data units from N different connections, and is therefore used to protect N primary paths from any single link failure. The M+N is an extension of 1+N protection where M extra secondary paths are needed to protect multiple link failures. In this paper, we apply network coding for network protec- tion against link failures and packet loss. We define the concept of protection codes similar to error-correcting codes that

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