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Communication engineering and systems
The use of the Internet to make phone calls is growing in popularity as the Voice over Internet protocol (VoIP) allows users to make phone calls virtually free of charge. The increased uptake of broadband services by domestic users will further increase the use of VoIP telephony. Furthermore, the emergence of low cost wireless networks (namely IEEE 802.11a/b/g WLANs) is expected to bring wireless VoIP into the mainstream. As the number of wireless hotspots increases more users will want to use VoIP calls wherever possible by connecting to open access points (AP). A major concern with VoIP is Quality of Service (QoS). In order for VoIP to be truly successful users must enjoy a similar perceived QoS as a call made over a traditional telephone network. There are many factors that influence QoS which include: throughput, packet delay, delay variation (or jitter), and packet loss. This thesis is an experimental study of the call capacity of an IEEE 802.11b network when using VoIP telephony. Experiments included increasing the number of VoIP stations and also increasing the level of background traffic until network saturation occurs. Results show that the network is capable of supporting at least 16 VoIP stations. Due to the operation of the IEEE 802.11 medium access control (MAC) mechanism, the AP acts as a bottleneck for all traffic destined for wireless stations, in that significant delays can be incurred by VoIP packets which can lead to a poor perceived QoS by users. Consequently the performance of the AP downlink is the critical component in determining VoIP call capacity.
Keegan, B.:An Experimental Analysis of the Call Capacity of IEEE 802.11b Wireless Local Area Networks for VoIP Telephony. M.Phil Thesis. Dublin, Dublin Insitute of Technology, 2005.