This report provides an overview of common wireless network technologies used today, with emphasis on data transmission. Wireless networks are becoming increasingly used for Internet communications. As discussed in the report, the TCP protocol may experience performance degradations over wireless networks, due to non-congestion related packet loss and varying round trip times. To this end, many enhancements for TCP to the link and transport layer have been proposed. A selection of these are presented and discussed in relation to the wireless network technologies.

The demand for wireless access to the Internet has grown rapidly making the performance of TCP in wireless environments an important issue. We present experimental measurements of the performance of TCP over GSM. The measurements were captured over a real GSM network connected to a controlled radio environment. A range of radio conditions were considered with a focus on the interaction between TCP and the GSM link layer. Even for very poor radio conditions, only neglible negative interaction effects were found.

Investigating the wireless Internet is a nontrivial task dueto the complexity of wireless systems and the many protocolinteractions that appear. In this paper we present a measurementtestbed that allows us to investigate the performanceof Internet traffic over a real GSM network but witha controlled radio environment and traffic load. A detailedperformance evaluation of TCP over GSM is presented. Arange of radio conditions are considered with a focus on theinteraction between TCP and the GSM link layer. With respectto efficient protocol layer interaction, the results showthat high variability in round trip times is more problematicthan poor radio conditions. How the testbed has been extendedfor GPRS and planned measurements for this systemare also discussed.

Wireless Internet access over GPRS, the packet-oriented extension to GSM, provides for higher data rates and more efficient network utilization compared to circuit-switched access. The performance of the Internet protocols in GPRS is dependent not only on the quality of the radio link, but also on the buffering in the GPRS network. In this paper we investigate the impact of buffering on TCP performance. Measurements are conducted in a GPRS testbed consisting of real network nodes with real protocol implementations. When the buffer between the fixed and the wireless networks is large, then the round trip times may become very long. Measurements with different buffer settings indicate that the buffer could be decreased in order to reduce the queuing delay, without degrading the throughput. Measurements of concurrent packet- and circuit-switched traffic show that buffered data is flushed immediately as the GPRS traffic is preempted by circuit-switched calls. When resources are available again, the lost data must be retransmitted. In many cases this could be avoided by guarding the data with a timer