| Summary: | 碩士 === 國立政治大學 === 資訊科學學系 === 96 === A Mobile Ad hoc Network (MANET) MANET is composed of a group of mobile computing devices (nodes) that are equipped with Wireless LAN (WLAN) capability. Nodes can transmit packets to each other to construct Intranet without any base station. In an MANET environment, the communication links are unstable due to various reasons. Error rate is higher and bandwidth is smaller than fixed networks. Running regular TCP protocol on MANET will suffer from serious performance degradation in MANET.
To handle packet lost, regular TCP can only retransmit lost packets from the source. However, when error rate is high, several retransmissions may be needed to transmit a packet to its destination successfully. As a result, the effective bandwidth is much lower and the average time to transmit a packet will be much longer.
Considering that most applications on MANET prefer shorter transmission time to higher bandwidth, this thesis proposes Hop-by-Hop TCP protocol aiming to accelerate the transmission of packets. Hop-by-Hop TCP makes every intermediate node in the transmission path running a local TCP to guarantee the transmission of each packet on each link. The retransmission of a lost packet is right at the transmitting end of the link where the packet is lost. It doesn't need to retransmit a lost packet from its source node. It takes less time in average to transmit a packet to its destination in a high error rate environment.
We evaluate the performance of our approach by simulation using NS-2 simulator. Our experiments show that our proposed protocol outperforms TCP Reno by 25.7% in throughput and 25% reduction in average transmission time. The fairness requirement is also achieved while our proposed protocol coexists with other major TCP variants.
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