Improving TCP Performance through Pre-detection of Route Failure in Mobile Ad Hoc Networks

Ad Hoc 망에서 경로단절 사전감지를 통한 TCP 성능향상

  • Published : 2004.11.01

Abstract

Route failure is mainly caused by mobility of mobile host in ad hoc networks. Route failure, which may lead to sudden packet losses and delays, is losing the route from source to destination. In this situation, TCP assumes that congestion has occurred within the network and also initiates the congestion control procedures. Congestion control algorithm provides the means for the source to deal with lost packets. TCP performance in ad hoc environments will be degraded as TCP source cannot distinguish congestion from route failure. In this paper, we propose TCP-P as pre-detection approach to deal with route failure. TCP-P freezes TCP through pre-detection of route failure. Route failure information of the proposed mechanism is obtained not by routing protocol but by MAC protocol. The intermediated node, obtaining route failure information by its MAC layer, relays the information to TCP source and lets TCP source stop the congestion control algorithm. Results reveal that TCP-P responding with proactive manner outperforms other approaches in terms of communication throughput under the presence of node mobility.

Ad hoc망에서는 이동 호스트들의 움직임으로 인해 경로 단절이 발생한다. 전송 경로의 단절은 목적지까지의 패킷을 전송할 수 없는 상태이므로 패킷의 손실과 지연을 가져온다. 따라서 TCP와 같은 전송 프로토콜은 이를 망의 혼잡으로 간주하여 혼잡 제어 알고리즘을 구동한다. 혼잡 제어 알고리즘은 망의 혼잡을 피하기 위한 수단으로 사용되는데, 경로 단절 시 혼잡 제어 알고리즘이 동작하면 TCP 성능이 떨어진다. 이를 해결하기 위해 본 논문은 TCP-P (TCP Pre-freezing) 기법을 제안한다. TCP-P는 라우팅 프로토콜에서 경로 단절에 대한 정보를 얻지 않고, MAC 계층에서 직접 경로 단절을 감지한다. 그리고 경로 단절 정보를 소스에게 보내어 TCP를 Pre-Freezing 하고 혼잡 제어 알고리즘을 멈추게 한다. 따라서 경로 단절로 인한 패킷 손실을 막고, 경로 재설정 후에도 경로 단절 이전 상태로 전송을 재개할 수 있게 한다. 실험 결과 TCP-P는 ad hoc 망의 경로 단절 환경에서 Proactive하게 반응하며, 패킷 손실 측면에서 다른 TCP 향상 기법들보다 좋은 성능을 보였다.

Keywords

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