Dexiang Wang, Arvindhan Kumar, Madhan Sivakumar , and Janise Y. McNair

1. AFault-tolerantbackbonenetworkArchitectureTargetingtime-criticalcommunicationforAvionicwdmlansAFault-tolerantbackbonenetworkArchitectureTargetingtime-criticalcommunicationforAvionicwdmlans Dexiang Wang, Arvindhan Kumar, MadhanSivakumar, and Janise Y. McNair Wireless And Mobile Systems Laboratory at University of Florida http://www.wam.ece.ufl.edu Algorithm for any S-D pair lightpath setup: Initial stage: include all links in the torus structure, S=Φ, i=1 While i ≤ 4, find the shortest path Path(i) in the current structure, S = S U Path(i), remove all the links in Path(i) from the torus structure, i=i+1 Output S as the lightpath set Abstract Probabilistic Study of 4×4 Torus with Two-terminal Disconnection (TTD) Probability as Fault-tolerance Performance Metric • This work focuses on the design and analysis of a torus-based backbone architecture targeting to meet the low delay and high reliability requirements of avionic time-critical communications The calculation of two-terminal disconnection (TTD) probability is given by (1) • Improved connection reliability Scenario 1: source and destination not in the same row and column • Four non-overlapping lightpaths for arbitrary source-destination (S-D) pairs are setup by a proposed greedy algorithm with the goal of maximizing two-terminal reliability (TTR), which makes the network able to tolerate at least three arbitrary link failures without losing connectivity • A wavelength assignment and reuse (WAR) scheme is proposed to reduce by half the wavelength requirement for all-to-all communication in a case study of 4×4 torus • Both probabilistic analysis and packet-level simulation reveal that the proposed architecture can survive over 3 critical failures with negligible packet delay variation (due to lightpath length difference) Probability of TTD VS Probability of single link failure (f) Scenario 2: source and destination in the same row or column • TTD probability distribution across the torus from node 11 Introduction & Motivation 11 14 12 13 21 24 22 23 31 34 32 33 41 44 42 43 Wavelength Assignment & Reuse (WAR) Reduces Number of Wavelengths Required Probabilities of TTD from node 11 to all other nodes (f = 0.1) • Impact of network link failures on connection reliability Wavelength requirement is reducedby half by carefully developing lightpaths. Following is an example for 4×4 torus in which two source-destination pairs can share one wavelength without lightpath overlapping and therefore wavelength requirement goes from 120 to 60. • The hostile aerospace environment imposes many design challenges to the avionic optical on-board communication systems especially in the aspect of fault tolerance • Torus is explored to be a good architectural candidate in this work due to its connectivity richness, structural symmetry and ease of routing There are in total 5 S-D positional relationships in 4×4 torus. For 2 of them (left below) the redundant lightpaths can be built in the same wavelength graph. For other 2 of them, 2 S-D pairs of the same positional relationship can merge their lightpaths in one wavelength graph (middle and right below) Previous Work Probability of TTD conditioned on varied number of link failures • Network connectivity reliability has been studied and it has been proved that evaluation of all-terminal and two-terminal reliabilities is NP-hard problem for a general graph • Centralized on-line routing and wavelength assignment (RWA) algorithms have been developed targeting minimum blocking probability to a new traffic session • Capacity provisioning based failure recovery has been studied based on run-time failure detection and resource reallocation • However, they are either centralized in nature and hence not suitable for distributed implementation or requiring noticeable failure response time and hence not satisfying time constraint of avionic time-critical communications • We propose a “zero-response-time” and distributed fault-tolerant architecture. Packet-level Simulation With varied numbers of link failures occurring on critical spots between nodes 11 and 12, the communication can survive over 3 critical failures with negligible packet delay variation (due to lightpath length difference) for all three types of traffic patterns. Average packet latency VS Number of critical link failures For the last case, if the 4 lightpaths are allowed to be built on two wavelengths, 2 wavelengths can accommodate 4 S-D pairs’ lightpath setup as below. The unutilized links in 2 wavelength graphs can be assigned for lightpath setups of other 2 S-D pairs Redundant Lightpath Setup Algorithm Maximizes 2-terminal connection reliability Future Work • Objective: maximize the connection reliability and minimize signal attenuation and propagation delay • The probability of disconnecting a source-destination pair: Potential future research includes an analysis of the approximation ratio of the lightpath setup algorithm, an all-terminal reliability (ATR) analysis and a complete all-to-all network simulation Acknowledgements • p is the link operation probability, also the complementary probability of link failure (f). l1, l2, l3, l4 denote the numbers of hops of the four non-overlapping lightpaths • By observing smaller l1, l2, l3 and l4 lead to lower Pdisconnection, a greedy lightpath setup algorithm is proposed: The authors would like to acknowledge that this material is based upon work supported by the United States Navy, under Award No. N68335-06-C-0386-P00001, and RSoft Design Group, Inc.