Mobile systems primarily processing multimedia data are expected to become a dominant computing platform for a variety of application domains. The design of such systems imposes several new challenges, as it must consider demanding, dynamic, and multidimensional resource requirements and constraints, with energy becoming a first-class resource. At the same time, the ability of multimedia applications to trade off output quality for system resources and the difference between their peak and average demands offers a huge opportunity for optimization.

This paper presents a new TCP protocol, TCP-DCR, designed to tolerate channel errors in wireless networks. TCP-DCR employs the simple solution of allowing a link level retransmission scheme to recover the packets lost due to channel errors thereby limiting the response of the transport protocol to mostly congestion losses. TCP-DCR delays responding to a packet loss indication for a small period of time (one RTT) to allow the channel errors to be recovered by link level retransmission. We analyze TCP-DCR to show that the congestion response delay does not impact its performance and its fairness. We evaluate TCP-DCR through simulations and compare its performance with TCP-Reno, TCP-SACK and TCP-Westwood under different network conditions. Our results show that TCP-DCR offers significantly better performance when channel errors make a large contribution to packet losses in the network and when the round trip delays are large. We also present an analysis to show that protocol evaluation in the wireless networks is significantly impacted by the number of flows in the network.

Abstract. In this paper, we propose and evaluate TCP-DCR. TCP-DCR makes simple modifications to the TCP congestion control algorithm to make it more robust to non-congestion events. The key idea here is to delay the congestion response of TCP for a short interval of time £ , thereby creating room for local recovery mechanisms to handle any non-congestion events that may have occurred. If at the end of the delay £ , the event is not handled, then it is treated as a congestion loss. We evaluate TCP-DCR through analysis and simulations. The evaluation is done for three scenarios- a wireless network with channel errors, a wired network with packet reordering and a network with zero non-congestion events. The simulation results show that significant performance improvements can be achieved by using TCP-DCR in the presence of non-congestion events with zero or marginal impact in the absence of non-congestion events. TCP-DCR remains fair to the native implementations of TCP that respond to congestion immediately after receiving three dupacks. TCP-DCR is a simple, effective scheme providing a unified solution to several problems with minimal implementation overhead. 1

This paper presents a dependability oriented, fault tolerance based system design, development, and deployment approach. The approach relies on an architectural framework, which allows legacy software modules to be reused as the basic building blocks of a distributed dependable application. Different levels of replication and alternative adjudication strategies are implemented behind a unified interface. These can be configured for achieving the optimal compromise between dependability and performance, according to application, deployment environment, and fault characteristics. The suggested solution can be implemented on top of any CORBA infrastructure. The architecture has been developed and tested. Experimental results are presented and discussed.

Mobile systems primarily processing multimedia data are expected to become a dominant computing platform for a variety of application domains. The design of such systems imposes several new challenges, as it must consider demanding, dynamic, and multidimensional resource requirements and constraints, with energy becoming a first-class resource. At the same time, the ability of multimedia applications to trade off output quality for system resources and the difference between their peak and average demands offers a huge opportunity for optimization.

The increase in the availability of mobile computing devices has led to thedesign of communication protocols for multi-hop wireless networks. However, wireless networking poses implementation challenges due to character-istics such as resource constraints (e.g., battery power) and lossy links. Our research addresses the issue of energy-efficient multimedia communication insuch wireless networks by revisiting per-hop mechanisms.