Push-to-Talk over Cellular(PoC) is an IP-based voice service in General Packet Radio Service( GPRS). In this direct call voice service, switching is performed without establishing a connection through the dialing process.
The service uses always-on operation where subscribers are permanently connected to the Internet and transmits voice data to another subscriber without delay using the IP protocol. With push-to-talk, the subscriber presses a button and can immediately speak to one or more subscribers, as with walkie-talkie, but without range limitations.
For push-to-talk, the mobile terminal must support the Session Initiation Protocol( SIP), which handles call signaling in UMTS networks. The mobile subscriber receives a logical address that can be used to establish connections to IP services.
A prerequisite for push-to-talk operation is full IP continuity up to peer-to-peer connections. The Third Generation Partnership Project( 3GPP) is addressing this issue and defined IP multimedia services for peer-to-peer networks.
The Open Mobile Alliance( OMA) has standardized push-to-talk over cellular (PoC) for mobile networks.