Design and Implementation for SIP-based Push-to- Talk Services over 802.11 Networks

Push-to-Talk (PTT) is a service that allows users using mobile phones in a way like walkie-talkie. All big telecommunication vendors and operators consider PTT an emerging application. 3GPP and OMA regulate the PTT specifications on the basis of Session Initiation Protocol (SIP) to assure interoperability. However, current PTT services are dedicated to cellular phones. We would like to realize PTT services with popular 802.11 wireless networks and VoIP services. Thus, in this paper, we implement a PTT system that works in 802.11 networks. Moreover, we interconnect it with GPRS network to compare the performance in-between these two heterogeneous networks. Simulation result shows that the latency to hear the talk calling from GPRS network to 802.11g network is only about 1~2 seconds while that of from 802.11g network to GPRS network is 6 seconds. Index Terms – Push-to-Talk (PTT), Session Initiation Protocol (SIP), Wi-Fi Network, 802.11.