TCP over multihop 802.11 networks: issues and performance enhancement
Proceedings of the 6th ACM international symposium on Mobile ad hoc networking and computing
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The probe traffic is an essential tool to an end user in the Internet to monitor the network condition and estimate the available bandwidth. For example, the widely used TCP protocol adds one more packet to the current sending rate at every round-trip-time to explore the potential network capacity. The probe traffic should be aggressive enough to get a meaningful feedback. In the meanwhile, it should not be too aggressive to affect the stability of the network. Thus, it is critical to find a right probe traffic scale with respect to a given network environment. In this research, we investigate several emerging networking environments and applications, in which the probe traffic scale plays an interesting and important role. First, we investigate TCP over 802.11 multihop ad hoc networks. The network participants in 802.11 networks are involved in a complicated cross-layer interaction. It is observed that the inappropriate scale of TCP probe traffic induces the over-reaction of on-demand ad hoc routing protocol and hurts the quality of end-to-end connection. So, we propose limiting the growth rate of TCP window to prevent the over-reaction of the routing protocol. The proposed scheme is analytically tractable, and a dramatic improvement of TCP performance and network stability can be achieved in various 802.11 multihop networks. Next, we investigate layered video multicast for live webcasting to a multitude of heterogeneous viewers. We introduce a congestion control strategy based on the usage of thin layers to suppress the side-effects of the coarse granularity of layer partition commonly found in the typical layered multicast. The strategy is directly applicable to the layered video format in the standard track like MPEG4-FGS to achieve an improvement in TCP-friendliness and network fairness. Based on our research as stated above, we conclude that the scale of the probe traffic is a critical factor to be considered in the design of networking and application systems in the next generation IP networks.