Designing a rate-based transport protocol for wired-wireless networks

A large majority of the Internet traffic relies on TCP as its transport protocol. In future, as the edge of the Internet continues to extend over the wireless medium, TCP (or its close variants) may not prove to be appropriate. The key reason is in TCP’s inability to discriminate congestion losses from transmission losses. Since transmission losses are frequent in wireless networks, the penalty from loss misclassification can become high, leading to performance degradation. This paper presents an eXtended Rate-based Transport Protocol (XRTP), designed to support communication over lossy wireless media. We depart from the ack-based rate control paradigm. Instead, we try to estimate the network conditions by injecting probe packets at the sender, and then observing the spacing between packets that arrive at the receiver. We show that these observations can be useful indicators of available bandwidth, network congestion, and even the cause of packet loss. The inferences from the observations are utilized to regulate the transmission rate at the sender, leading to desirable properties of congestion control and loss discrimination. Simulation results show the efficacy of our proposed rate-based protocol in lossy wireless environments.