Simultaneous VoIP Calls Capacity Over an 802.11 Ad Hoc Network

Voice over Internet Protocol (VoIP) over a wireless local area network (WLAN) is already an important Internet application. The data rate required for each VoIP stream depends on the used codec and the TCP/IP protocol overhead that typically add 98 bytes in the codec payload. As the G.726 codec has 80-byte payload (32 kb/s), the overhead represents 55% of the total packet size (178 bytes). This increases the raw data rate to 71.2 kb/s and limits the number of simultaneous VoIP calls. On the other hand, if the codec employed is G.729 the payload is much lower (20 bytes) and the raw data rate decreases to 47.2 kb/s, but the VoIP delay increases substantially due to the packetization time. There is a relationship between throughput and a target delay to investigate the maximum number of simultaneous VoIP calls in an 802.11b WLAN network in ad hoc mode operating with multihops. This paper analyses the simultaneous VoIP calls capacity to ad hoc network operating at 11 Mb/s in up to four hops.