Protection against link errors and failures using network coding in overlay networks

We propose a network-coding based scheme to protect multiple bidirectional unicast connections against adversarial errors and failures in a network. The end nodes of the bidirectional connections are connected by a set of shared protection paths that provide the redundancy required for protection. Suppose that ne paths are corrupted by an omniscient, computationally unbounded adversary. Under our proposed protocol, the errors can be corrected at all the end nodes with 4ne protection paths. More generally, if there are ne adversarial errors and nƒ failures, 4ne + 2nƒ protection paths are sufficient. The number of protection paths only depends on the number of errors and failures being protected against and is independent of the number of unicast connections

Protection against link errors and failures using network coding

We propose a network-coding based scheme to protect multiple bidirectional unicast connections against adversarial errors and failures in a network. The network consists of a set of bidirectional primary path connections that carry the uncoded traffic. The end nodes of the bidirectional connections are connected by a set of shared protection paths that provide the redundancy required for protection. Such protection strategies are employed in the domain of optical networks for recovery from failures. In this work we consider the problem of simultaneous protection against adversarial errors and failures. Suppose that n_e paths are corrupted by the omniscient adversary. Under our proposed protocol, the errors can be corrected at all the end nodes with 4n_e protection paths. More generally, if there are n_e adversarial errors and n_f failures, 4n_e + 2n_f protection paths are sufficient. The number of protection paths only depends on the number of errors and failures being protected against and is independent of the number of unicast connections.Comment: The first version of this paper was accepted by IEEE Intl' Symp. on Info. Theo. 2009. The second version of this paper is submitted to IEEE Transactions on Communications (under minor revision). The third version of this paper has been accepted by IEEE Transactions on Communication

Overlay Protection Against Link Failures Using Network Coding

This paper introduces a network coding-based protection scheme against single and multiple link failures. The proposed strategy ensures that in a connection, each node receives two copies of the same data unit: one copy on the working circuit, and a second copy that can be extracted from linear combinations of data units transmitted on a shared protection path. This guarantees instantaneous recovery of data units upon the failure of a working circuit. The strategy can be implemented at an overlay layer, which makes its deployment simple and scalable. While the proposed strategy is similar in spirit to the work of Kamal '07 & '10, there are significant differences. In particular, it provides protection against multiple link failures. The new scheme is simpler, less expensive, and does not require the synchronization required by the original scheme. The sharing of the protection circuit by a number of connections is the key to the reduction of the cost of protection. The paper also conducts a comparison of the cost of the proposed scheme to the 1+1 and shared backup path protection (SBPP) strategies, and establishes the benefits of our strategy.Comment: 14 pages, 10 figures, accepted by IEEE/ACM Transactions on Networkin

Algebraic approaches to distributed compression and network error correction

Algebraic codes have been studied for decades and have extensive applications in communication and storage systems. In this dissertation, we propose several novel algebraic approaches for distributed compression and network error protection problems. In the first part of this dissertation we propose the usage of Reed-Solomon codes for compression of two nonbinary sources. Reed-Solomon codes are easy to design and offer natural rate adaptivity. We compare their performance with multistage LDPC codes and show that algebraic soft-decision decoding of Reed-Solomon codes can be used effectively under certain correlation structures. As part of this work we have proposed a method that adapts list decoding for the problem of syndrome decoding. This in turn allows us to arrive at improved methods for the compression of multicast network coding vectors. When more than two correlated sources are present, we consider a correlation model given by a system of linear equations. We propose a transformation of correlation model and a way to determine proper decoding schedules. Our scheme allows us to exploit more correlations than those in the previous work and the simulation results confirm its better performance. In the second part of this dissertation we study the network protection problem in the presence of adversarial errors and failures. In particular, we consider the usage of network coding for the problem of simultaneous protection of multiple unicast connections, under certain restrictions on the network topology. The proposed scheme allows the sharing of protection resources among multiple unicast connections. Simulations show that our proposed scheme saves network resources by 4%-15% compared to the protection scheme based on simple repetition codes, especially when the number of primary paths is large or the costs for establishing primary paths are high

Implementation of linear network coding over a flexible emulator

This dissertation has the main objective of study and implement network coding (NC) techniques in a flexible emulator, programmed in a language that allows the coexistence of entities running parallel code, in order to emulate each node independently. The dissertation starts with the study of NC’s concept and with the characterization of the different type of coding methods, with a focus on linear network coding (LNC). . A flexible Java emulator (named Net Genius) was developed, which not only allows numerous topologies of networks, but also different types of coding. In addition, the emulator allows to emulate the networks in two different modes: with a distributed network or with a centralized network. In order to present the differences between the LNC approach and the traditional approach used in packet networks (based in routing tables), the emulator allows the user to choose between these two types of approach, assessing the impact of having network coding over user-defined networks. When implementing LNC, the concept of generations of packets was introduced in order to avoid combining packets from different sources. Leveraging on this, the transfer matrix at each node is calculated based on the coded packets and not based on the information stored in each node. In addition to this, a mechanism to code packets at the source was implemented, as well as a mechanism to introduce errors in the connection links. This allowed to emulate networks with different link error probabilities, in order to assess the resilience of the different approaches to the presence of failures.Esta dissertação visa estudar e a implementar técnicas de network coding (NC) num emulador flexível, programado numa linguagem que permita a coexistência de entidades a correr código em paralelo por forma a simular cada nó de forma independente. Este trabalho começa com estudo do conceito de NC e da caracterização dos diferentes tipos de métodos de codificação, focando-nos essencialmente no linear network coding (LNC). Optou-se por criar um emulador flexível em Java (designado por Net Genius), que não só permite várias topologias de redes, mas também vários tipos de codificação. Além disso, o emulador permite emular as redes em dois modos diferentes, um modo com uma rede distribuída e outro com uma rede centralizada. De modo a evidenciar as diferenças entre a abordagem LNC e a abordagem tradicional (sem codificação), o emulador permite escolher o tipo de abordagem em cada emulação, o que permite estudar o impacto do NC em redes definidas por utilizadores. Procedeu-se à implementação de técnicas LNC e introduziu-se um conceito de gerações de pacotes, de modo a evitar a codificação de pacotes de diferentes fontes. A par disto, a matriz de codificação é calculada com base nos pacotes codificados e não com base na informação guardada em cada nó. Por último, implementou-se um mecanismo para codificação de pacotes na fonte e um mecanismo de introdução de erros nos links, permitindo emular a rede com diferentes probabilidades de erro, sendo possível ver como as abordagens resistem à existência de falhas nas ligações