A comparative experimental study of media access protocols for wireless radio networks

We conduct a comparative experimental analysis of three well known media access protocols: IEEE 802.11, CSMA, and MACA for wireless radio networks. Only static ad-hoc networks are considered. The experimental analysis was carried out using GloMoSim: a tool for simulating wireless networks. The main focus of experiments was to study how: (i) the size of the network, (ii) number of open connections, (iii) the spatial location of individual connections, (iv) speed with which individual nodes move, and (v) protocols higher up in the protocol stack (e.g. routing layer) affect the performance of the media access sublayer protocols. The performance of the protocols was measured w.r.t. four important parameters: (i) number of received packets, (ii) average latency of each packet, (iii) long term fairness, and (iv) throughput. The following general qualitative conclusions were obtained; some of the conclusions reinforce the earlier claims by other researchers. (1) Typically, all protocols degrade significantly at higher packet injection rate. Moreover, the degradation often happens rather sharply. (2) In general while the performance of 802.11 was better than CSMA at lower injection rates, the performance of 802.11 is worse than that of CSMA at higher injection rate - on the other hand, CSMA assigns inequitable amount of resources; in this regard 802.11 performs quite well. (3) MACA typically was dominated either by CSMA or by 802.11 w.r.t. any of the performance measures. (4) Protocols in the higher level of the protocol stack affect the MAC layer performance. The main general implications of our work is that no single protocol dominated the other protocols across various measures of efficiency. In other words the performance of protocols depends on all of the parameters mentioned above.