Modeling the Goodput of TCP NewReno in Cellular Environments
Gillies, Donald W.
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In this paper, we present an analytical model that characterizes TCP NewReno's goodput as a function of round-trip time, average time duration between handoffs, average number of packets reordered during a handoff, and the congestion window threshold. In cellular networks, the effective packet-loss probability for a flow experiencing handoffs is not exactly equal to the physical-layer packet-loss probability; it also depends on the frequency of handoffs and the number of packets that may arrive out of order at the receiver due to handoffs. With the emergence of technologies such as WiMax and Ultra Mobile Broadband (UMB), understanding the effect of handoffs and packet reordering on the goodput of TCP becomes very important for the designers of next generation cellular networks. Existing TCP throughput models cannot be used to understand the precise effect of handoffs and the resultant packed reordering on TCP's goodput. In this paper, we present a model of TCP NewReno goodput that captures the effect of handoffs. We validate the model by performing actual file transfers between different hosts that are connected by a router which emulates the wireless environment with handoff events and packet reordering.