Evaluation of migration support for indirect transport protocols

TCP as a reliable transport protocol is tuned to operate efficiently within traditional networks. Within wireless communication scenarios, TCP's congestion avoidance mechanism is falsely triggered by higher bit error probabilities of wireless links and disruptions due to handoffs within cellular communication networks. To separate wired and wireless subpaths of a hybrid communication path the indirect transport protocol model has been introduced. It subdivides the end-to-end transport connection into several subconnections, operating over wired subpaths and over wireless subpaths. Thus, the negative effects of the wireless subpath do not influence the transport connection operating over the wired part of the network. Interconnection of transport connections is realized by so called transport gateways. Due to the potential mobility of wireless attached stations, the migration of transport gateways to network nodes located nearby the current location of the mobile stations is needed. The migration approach presented by Bakre and Badrinath (1995) interrupts transport communication by up to 1.4 seconds. Our approach reduces communication pauses to 75 milliseconds. This is achieved by the so called delayed migration approach, that enables transport layer communication while state information of the transport protocol is transferred to the new gateway. To support the delayed migration approach modifications of the Mobile IP proposal are required. These modifications and performance measurements are presented in this paper.