WTCP

Abstract: Wireless wide-area networks (WWANs) are characterized by very low and variable bandwidths, very high and variable delays, significant non-congestion related losses, asymmetric uplink and downlink channels, and occasional blackouts. Additionally, the majority of the latency in a WWAN connection is incurred over the wireless link. Under such operating conditions, most contemporary wireless TCP algorithms do not perform very well. In this paper, we present WTCP, a reliable transport protocol that addresses rate control and reliability over commercial WWAN networks such as CDPD. WTCP is rate-based, uses only end-to-end mechanisms, performs rate control at the receiver, and uses inter-packet delays as the primary metric for rate control. We have implemented and evaluated WTCP over the CDPD network, and also simulated it in the ns-2 simulator. Our results indicate that WTCP can improve on the performance of comparable algorithms such as TCP-NewReno, TCP-Vegas, and Snoop-TCP by between 20% to 200% for typical operating conditions.

Abstract: The transmission control protocol (TCP) used in the Internet has been mainly designed assuming a relatively reliable wireline network. The TCP assumes that any loss is due to congestion and consequently invokes congestion control measures. This has been shown to yield poor performance in the presence of wireless links as a large number of segment losses will occur more often because of wireless channel errors or host mobility. We present an efficient transmission control scheme (WTCP) that requires the base station to buffer data packets destined for the mobile host and retransmit lost packets. Through simulations, we show that our scheme yields better throughput than other existing proposals while maintaining the TCP's end-to-end semantics. One salient feature of WTCP is that it effectively hides the time spent by the base station to locally recover so that the TCP's round trip time estimation at the source is not affected. This is critical since otherwise the ability of the source to effectively detect congestion in the wireline network will be hindered.

Abstract: With the increased commercial deployment of wireless networks, the issue of service differentiation among flows in a wireless/wireline network is becoming important. While many wireline solutions for service differentiation depend on end to-end rate control upon packet loss, this approach does not work well for wireless networks because packet losses do not necessarily indicate congestion in the network in the wireless domain. In a related work, we presented WTCP, a reliable transport protocol that is designed to operate efficiently and fairly over wireless wide area networks. The rate control algorithm in WTCP is based on the use of the ratio of the inter-packet separation at the receiver and the sender as the metric for detecting and reacting to congestion. In this paper, we generalize the rate control mechanisms of WTCP to support both reliable and unreliable flows, and to provide service differentiation among flows. We present preliminary results using the ns2 simulator to show that our rate control algorithm provides service differentiation for low bandwidth wireless networks and scales well with the variations in the link loss characteristics.

Abstract: The wireless upgrading method includes steps: obtaining information of upgrade file from database of upgrade file; carrying out comparison between information of upgrade file and information of current file of logged wireless terminal, and sending out selectable prompting message based on the compared result; returning back file list to be upgraded to wireless terminal based on information of upgrading request sent from user; downloading and upgrading the upgrade files confirmed by user based on acknowledge information of user. Detecting software of wireless terminal by server end, the invention does not need client end to carry out active detection so as to simplify user's operation. The disclosed method and system can carry out automatic switching between WTCP and TFTP two communication protocols, and support breakpoint transmission.