Call Setup Delays for Voice Communications on IEEE 802.11 Wireless LANs

The 12th IEEE Workshop on Local and Metropolitan Area Networks, Stockholm, Sweden, August 2002.

Abstract: PCF can be used to carry Constant Bit Rate (CBR) voice traffic between stations of the same BSS, while DCF supports their asynchronous data traffic. The number of voice users supported by PCF can be further increased by using silence detection at each voice user and a new management scheme on the AP's polling list, the so called Cyclic Shift polling process, that does not require any modifications on the wireless terminals access mechanism. Since the call establishment procedure uses a type of signalling protocol, in this paper we examined the call setup delay. For calculating the transmission probability of a station in any offered load, We used a modified Markov model in order to estimate the mean delay experienced by a voice station between the instant a call request is created and the time instant this call request is received by the AP, while part of the CFPR interval is devoted to PCF for handling already established calls. According to our numerical results, the mean delay of a call request received by the AP may vary from some tens of microseconds to some hundreds of milliseconds depending on many system parameters. The parameters that mainly affect the call setup delay are the number of wireless stations forming the BSS and the total offered load during DCF.

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