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Analysis of the draft IEEE 802.11 wireless local area network (WLAN) standard is needed to characterize the expected performance of the standard's ad hoc and infrastructure networks. The performance of the medium access control (MAC) sublayer, which consists of Distributed Coordination Function (DCF) and Point Coordination Function (PCF), is determined b y simulating asynchronous data traffic in a 1 Mbps ad hoc network, and asynchronous data and packetized voice traffic in a 1 Mbps infrastructure network. The simulation models incorporate the effect of burst errors, packet size, RTS threshold and fragmentation threshold on network throughput and delay. The results show that the IEEE 802.11 WLAN can achieve a reasonably high efficiency when the medium is almost error-free, but may degrade appreciably under harsh fading. The results also show that time-sensitive traffic such as packet voice can be suppol-ted together with other intensive traffic such as packet data. However, an echo canceler is required f o r packet voice systems.

We are on the threshold of witnessing an explosion of portable and mobile terminals capable of sending and receiving multimedia traffic. Currently, the standard being worked out by the IEEE 802.11 committee to support wireless connectivity in the local area network appears to be the most promising one. IEEE 802.11 protocols support both scheduling and random access techniques operating simultaneously, called Point Coordination Function (PCF) and Distributed Coordination Function (DCF), respectively. In this paper, we study the interactions between PCF and DCF when voice and asynchronous data traffic needs to be supported. We investigate the dimensioning problems of various parameters, and provide the general rule of thumb of the default values. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx SPIE Vol. 2917/481 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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This paper describes the use of a transparent TCP gateway to improve the performance of applications operating in a shared secure satellite environment. Typically, a satellite gateway is installed at each end of the satellite link, and the gateways process all tra@c traversing the link. With the proliferation of virtual psivate network (YPN) technologies, multiple encrypted tunnels can be established over a satellite link. If transparent TCP gateways are used to optimize application performance, a pair of gateways are required at the egress points of each tunnel. Many TCP gateways perform poorly in this situation because they do not implement congestion control on their 'satellite ' sides, resulting in network congestion between the sending gateways and the satellite uplink. Our approach is to use Space Communications Protocol Standards (SCPS) transparent transport layer gateways, which are capable of implementing a variety of congestion control schemes on their terrestrial and satellite sides. By using a variant of the TCP Vegas congestion control algorithm, the gateways can comniunicate indirectly (by detecting changes in packet round-trip times) to eficiently share the satellite bandwidth, Results show that this improves performance over end-to-end TCP without congesting the network between the gateways and the uplink as would pure rate-control.