POC, which is also termed as PTT (Push to Talk), leverages the flexibility of SIP (Session Initiation Protocol) and the efficiencies of packet switching to deliver media rich information in the format of voice, video and graphical information to individuals or a closed user group over cellular networks such as GSM, GPRS and UMTS. This module explains the architecture of POC solutions including the principle function and interfaces that will typically be employed in operators and carriers networks and which in the future will integrate into the IMS (IP Multimedia Subsystem). The concepts of addressing registration and session establishment are discussed as well as the subscription, notification and presence procedures that will be used to enhance POC services.
