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Abstract-Most standard implementations of TCP perform poorly when packets are reordered. In this paper, we propose a new version of TCP that maintains high throughput when reordering occurs and yet, when packet reordering does not occur, is friendly to other versions of TCP. The proposed TCP variant, or TCP-PR, does not rely on duplicate acknowledgments to detect a packet loss. Instead, timers are maintained to keep track of how long ago a packet was transmitted. In case the corresponding acknowledgment has not yet arrived and the elapsed time since the packet was sent is larger than a given threshold, the packet is assumed lost. Because TCP-PR does not rely on duplicate acknowledgments, packet reordering (including out-or-order acknowledgments) has no effect on TCP-PR's performance.Through extensive simulations, we show that TCP-PR performs consistently better than existing mechanisms that try to make TCP more robust to packet reordering. In the case that packets are not reordered, we verify that TCP-PR maintains the same throughput as typical implementations of TCP (specifically, TCP-SACK) and shares network resources fairly. Furthermore, TCP-PR only requires changes to the TCP sender side making it easier to deploy.

Simulation plays an important role in the verification of mobile wireless networking protocols. Recently several cities have either begun deploying or are completing plans to deploy large-scale urban mesh networks (LUMNets).On the other hand, the networking research community has little expertise in simulating such networks. While the protocols are simulated reasonably realistically, the propagation of wireless transmissions and the mobility of nodes are not. Today, simulations typically model propagation with either the free-space model or a "two-ray" model that includes a ground reflection. Such models are only valid in open space where there are no hills and no buildings. Since wireless signals at the frequencies used for mobile wireless networking are partly reflected off of buildings and partly is transmitted into the building, the presence of buildings greatly influences propagation.Consequently, the open-space propagation models are inaccurate in outdoor urban areas. Indoors, the open-space models are not even applicable. This paper presents guidelines for simulating propagation in such urban settings.Furthermore, extensive background discussion on propagation is also included. The techniques for propagation are validated against propagation measurements. The techniques discussed are implemented in a suite of tools that are compatible with protocol simulators and are freely available for use.

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