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m @ c i s c o . c o m Absfract-Concurrent Multipath Transfer (CMT) uses the Stream Control Transmission Protocol's (SCTP's) multihoming feature to distribute data acmss multiple end-to-end paths in a multihomed SCTP association. We propose five retransmission policies for CMT. We demonstrate the occurrence of spurious retransmissions in CMT with all of the five policies, and propose an amendment to the timeout retransmission mechanism to avoid spurious retransmissions We also modify the Cwnd Update for CMT (CUC) algorithm to allow better cwnd growth in CMT with the different retransmission policies. We then evaluate the retransmission policies using ns-2 simulations, and discuss the distributions of trffic that result. We operate under the strong assumptions that the receiver's advertised window does not constrain the sender, and that the bottleneck queues on the end-to-end paths used in CMT are independent

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We evaluate three retransmission policies for transport protocols that support multihoming (e.g. SCTP). The policies dictate whether retransmissions are sent to the same peer IP address as the original transmission, or sent to an alternate peer IP address. Each policy presents tradeoffs based on the paths' bandwidth, delay, loss rate, and IP destination reachability. We find that sending all retransmissions to an alternate peer IP address is useful when the primary IP address becomes unreachable, but often degrades performance in non-failure scenarios. On the other hand, sending all retransmissions to the same peer IP address as the original transmission reverses the tradeoffs. We balance the tradeoffs by proposing a hybrid policy that sends fast retransmissions to the same peer IP address as the original transmission, and sends timeout retransmissions to an alternate peer IP address. We show that even with extensions which we proposed to improve the policies' performance, the hybrid policy is the best performing policy in failure and non-failure scenarios. q

The stream control transmission protocol is a new standard for generalpurpose transport proposed by the Internet Engineering Task Force. SCTP addresses application and security gaps left open by its predecessors, TCP and UDP.

References 1, 5 introduce a transport protocol that o ers partially ordered service for multimedia applications. This paper investigates how m uch the selection of a linear extension a ects system performance in a partially ordered service. We rst show h o w t o identify better linear extensions of a partial order, and then determine the performance gains by using such linear extensions at the time of transmission. To quantify linear extensions of a partial order, we propose a new metric pBuf -metric that is derived from bu ering probabilities. Since pBuf -metric is complex to calculate, a simpli ed version called -metric is also investigated. An OPNET simulation shows that for certain partial orders, a linear extension optimized according to these metrics provides some delay, and signi cant bu er utilization improvements over a non-optimal linear extension. Thus, prudent transmission order selection in a partially ordered service does improve system performance. Results also show that, in general, -metric is as e ective a s pBuf -metric in identifying better linear extensions of a partial order.

We present a new model for testing real-time protocols with multiple timers, which captures complex timing dependencies by using simple linear expressions involving timer-related variables. This new modeling technique, combined with the algorithms to eliminate inconsistencies, allows generation of feasible test sequences without compromising their fault coverage. The model is specifically designed for testing to avoid performing full reachability analysis, and to control the growth of the number of test scenarios. Based on extended finite state machines, it is applicable to languages such as SDL, VHDL, and Estelle. The technique models a realistic testing framework in which each I/O exchange takes a certain time to realize and timers can be arbitrarily started or stopped. A software tool implementing this technique is used to generate test cases for the U.S. Army wireless standard MIL-STD 188-220.