Simulation of a Backward Compatible IEEE 802.11g Network: Access Delay and Throughput Performance Degradation

With the emergence of Fiber to the X (FTTx) last-mile technologies, the capacity of access links has been significantly increased. A common scenario in Home, Enterprise or Public environments is a Wireless Local Area Network using such a link as the backhaul. Although devices compliant with the latest IEEE 802.11n standard extension for WLANs have been deployed, there is still a substantial number of Access Points (AP) using IEEE 802.11g \citeieee80211g-standard that provides a maximum transmission rate of 54 Mb/s. In scenarios where an 802.11g compliant AP uses a high capacity link as the backhaul, the wireless link may become a bottleneck and the wireless stations may not be using the full capacity available. At the time of first deployment of 802.11g compliant devices, the dominating standard was IEEE 802.11b \citeieee80211b-standard, providing maximal transmission rate of 11 Mb/s. In order to become commercially viable, IEEE 802.11g had to support presence of legacy 802.11b nodes in the network. Nowadays, 802.11b stations have been ruled out by the market but their presence is not uncommon. Hence, protection mechanisms developed in order to support backward compatibility in 802.11g networks are still widely used to allow support for association of legacy nodes.

This paper investigates the performance degradation of an 802.11g network in scenarios where at least one legacy station is associated with the AP. For that purpose a custom event-driven simulator was developed in C programming language. Consistency of the simulator was checked by comparative studies with analytical and simulation results from \citesakurai-mac-delay. These results are presented in Section \refconsistency-check.

Contribution of our work is twofold. Firstly, we present the access delay performance degradation of an 802.11g network for different number of nodes due to backwards compatibility. The BSSBasicRateSet is a set of transmission rates, communicated within the network (BSS), from which each rate must be supported by all nodes wanting to associate with an AP. Thus, if the AP supports legacy stations, it includes some or all of the 802.11b transmission rates in the advertised BSSBasicRateSet. Hence, the impact evaluation of the minimal rate in BSSBasicRateSet on this delay is detailed. Secondly, in order to extend \citevassis-, we evaluate channel throughput in saturation conditions in g-only, as well as backward compatible network scenarios using different protection mechanisms. These results are presented as a function of minimal transmission rate in BSSBasicRateSet.