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 takes place 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 a 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. TheThird Generation Partnership Project (3GPP) is addressing this issue and has 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.