QoS provided by the IEEE 802.11 wireless LAN to advanced data applications: a simulation analysis

IEEE 802.11 is a Media Access Control (MAC) protocol which has been standardized by IEEE for Wireless Local Area Networks (WLAN). The IEEE 802.11 MAC protocol offers two types of services to its users: synchronous and asynchronous. This paper thoroughly analyzes, by simulation, the asynchronous part alone, when each station feeds the MAC protocol with data traffic patterns (in the following referred to as advanced data traffic) that are very close in shape to those generated by a terminal accessing, for example, the WWW service. Although the analysis shows that the performance of the IEEE 802.11 with advanced traffic is considerably worse than with Poissonian traffic, we can conclude that IEEE 802.11 still performs satisfactorily. Furthermore, our analysis is broadened to include higher medium capacities up to 10 Mbit/sec. This part of the analysis shows that the IEEE 802.11 MAC protocol is not adequate to work at speeds planned for the upcoming ATM Wireless LAN. 1.0 Introduction The IEEE 802.11 is a standard for a WLAN covering both Physical and MAC layers ([IEEE95], [LaMa95]). A key issue of this standard is that a mobile host is able to communicate with any other mobile or wired host in a transparent manner. In other words, an IEEE 802.11 WLAN appears to layers above the MAC layer as any other IEEE 802.X LAN (e.g. Ethernet or Token Ring). This means, in particular, that the mobility aspects are handled at the MAC level or below. Workshop on Nomadic Computing Geneva (CH) April 5, 1997 2 A performance analysis for the IEEE 802.11 WLAN is reported in [Chha96] where the authors take into account the decentralized nature of communication between stations, the possibility of capture, and the presence of hidden stations. They also study the impact of spatial characteristics on system performances. Both parts (synchronous and asynchronous) of the IEEE 802.11 MAC protocol have been analysed in [Viss95]. A comparison of the IEEE 802.11 MAC protocol with HIPERLAN [ETSI95], the ETSI proposal for wireless LANs, can be found in [Wein97]. The aim of this paper is to further advance the previous analysis on the asynchronous part of the IEEE 802.11 standard. In fact, since we expect that relevant data applications serviced by WLANs are very likely to resemble today's WWW applications, in our performance analysis we use data traffic models which are very similar to those recently proposed in the literature ([Deng96], [Crov95]) for these type of applications (i.e., WWW applications). Furthermore, since discussions at an international level for a MAC protocol of an ATM Wireless LAN have just began, we also analyse whether or not the IEEE 802.11 MAC protocol is suitable for operating at higher channel speeds. Although data integrity is a key requirement for data transmission, we assume an error free radio channel despite the fact that we are dealing with a very unreliable environment. This is because in the present paper we are focusing on multiple access aspects of the IEEE 802.11 MAC protocol as measured by the average access delay experienced by messages transmitted over data connections. The paper is organized as follows. Section 2.0 describes the IEEE802.11 MAC Protocol. Section 3.0 describes the simulation environment while results are reported in Section 4.0. Section 5.0 concludes the paper. 2.0 IEEE 802.11 Wireless Network Standard In this section we only report those aspects of the standard which are relevant for our analysis. Specifically, Section 2.1 introduces the terminology and topology adopted for an IEEE 802.11 WLAN, whereas Section 2.2 describes the MAC Protocol. See [IEEE95] for details. Workshop on Nomadic Computing Geneva (CH) April 5, 1997 3 2.1 Network Topology An IEEE 802.11 WLAN generally consists of Basic Service Sets (BSSs) which are interconnected by a Distribution System (DS) to form an Extended Service Set (ESS) as shown in Figure 1.