A SURVEY OF TCP ENHANCEMENTS FOR LAST-HOP WIRELESS NETWORKS

TCP continues to be an important transport-layer communication protocol that is typically tuned to perform well in traditional wired networks, where bit error rate (BER) is low and congestion is the primary cause of packet loss. The emergence of various mobile access networks has prompted researchers to look for suitable modifications to TCP so as to make it survive in the wireless era as well. Networks with wireless links and mobile hosts incur significant losses due to high BER, host motion, and handoff mechanisms. Mobile devices face temporary and unannounced loss of network connectivity when they move. They are likely to have scarce resources, and they react to frequent changes in the environment. Motion causes varying, increased delays and packet losses, while the network learns how to deliver packets to the new location of the host. TCP incorrectly interprets these delays and losses as signs of network congestion and throttles its transmission rate, causing degraded end-to-end performance. This article provides an in-depth survey of various TCP enhancements which are specifically targeted for last-hop wireless environments. The objective is to review the performance issues of TCP variations, when employed in last-hop wireless networks, and to provide a categorized analysis of different existing solutions comparatively, as we all know that it is difficult to create a "one size fits all" TCP for last-hop wireless networks.