• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.10 s.352
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• pp.79-89
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• 2006

TCP is the most widely used transport protocol in Internet applications that guarantees a reliable data transfer. But, in the wireless multi-hop networks, TCP performance is degraded because it is designed for wired networks. The main reasons of TCP performance degradation are contention for wireless medium at the MAC layer, hidden terminal problem, exposed terminal problem, packet losses in the link layer, unfairness problem, reordering problem caused by path disconnection, bandwidth waste caused by exponential backoff of retransmission timer due to node's mobility and so on. Specially, in the mobile ad-hoc networks, discrepancy between a station's transmission range and interference range produces hidden terminal problem that decreases TCP performance greatly by limiting simultaneous transmission at a time. In this paper, we propose a new MAC algorithm for mobile ad-hoc networks to solve the problem that a node can not transmit and just increase CW by hidden terminal. In the IEEE 802.11 MAC DCF, a node increases CW exponentially when it fails to transmit, but the proposed algorithm, changes CW adaptively according to the reason of failure so we get a TCP performance enhancement. We show by ns-2 simulation that the proposed algorithm enhances the TCP performance by fairly distributing the transmission opportunity to the failed nodes by hidden terminal problems.

• Journal of KIISE:Information Networking
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• v.29 no.1
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• pp.65-76
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• 2002

QoS routing is a routing technique for finding feasible path that satisfies QoS requirements required by application programs. Since QoS routing determines such paths in terms of dynamic network state, it satisfies the requirement of applications and increases the utilization of the network. The overhead is, however, generated by routers to exchange the information of the dynamic state of network. In order to reduce this protocol overhead, a timer based update mechanism is proposed in which router checks the change of the network status periodically and network state information is exchanged if the change is greater than a certain value. Using large update period makes, though, routing performance irresponsive to the parameters which determine the update of the network state of the router. In addition to this, large update period may result in inaccurate network state information at routers and cause resource reservation failure. The resource reservation failure generates additional overhead to cancel the resource reservation of the part of the path. In this paper, we propose mechanisms enhancing the existing network state update policy with respect to these two problems. Performance of the proposed schemes are evaluated through a course of simulation.