Congestion control for UDP/TCP flow in single-hop and multi-hop wireless networks

Abstract

Congestion occurs when the amount of incoming packets excess the network resources such as the buffer space and the network bandwidth. Once it happens, the elapsed time that a packet is successfully delivered to a destination increases substantially in networks. Moreover, the throughput decreases due to the increase of delay and the retransmission of the lost packets. To avoid network congestion, the suitable congestion control algorithm for the various network environment should be devised. The main purpose of the congestion control algorithm is to utilize the network bandwidth highly with allocating the network bandwidth fairly to flows. In this dissertation, we study on congestion control in two types of networks: single-hop wireless networks and multi-hop wireless networks. In addition, we also consider two types of flows: TCP flows and non-TCP flows for streaming applications. Lastly, we study the cross-layer approach for the power efficiency. Considering the characteristics of networks and flows, we propose congestion control algorithms as follows: First, we consider a congestion control algorithm over single-hop wireless cellular networks. The conventional TCP treats a packet loss as the incipiency of congestion. However, the wireless networks experience the packet loss due to wireless link error frequently. Then, even though congestion does not occur, a source unnecessarily reduces its transmission rate to avoid congestion and implements the retransmission. This causes the network performance to degrade significantly: low link utilization and severe unfairness. To solve this problem, for streaming realtime applications, which are mostly based on UDP, we propose TCP-friendly congestion control algorithm based on ECN messages. Through the ECN mechanism, we derive the congestion state irrespective of the wireless packet loss. Moreover, using TCP additive increase multiplicative decrease (AIMD) dynamic behavior on the average sense to set the transmis...