Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

6.2 Push-to-talk Over Cellular

Push-to-talk Over Cellular (PoC) is very similar to the well known walkie-talkie communication service. It provides a one-to-one or one-to-many speech service to a group of people in half-duplex mode, which means that only one participant can talk at a given time, while the others are listening. Like traditional walkie-talkie services, a session participant requests the floor by pressing a ‘talk button’ on its terminal. As the participant stops talking, he releases the talk button, allowing another participant to request the speech channel.

However, there are some basic differences with analogue or digital low-cost solutions which everyone can buy and easily deploy, due to the fact that PoC is not only supported by the terminal, but also relies on a full network infrastructure. The added value of PoC can be summarized by the two following points:

• PoC provision is not limited to a geographical area. The fact that PoC is supported on top of IMS architecture makes it available to every network subscriber attached to the network, regardless of its current location within the network coverage and access technology.
• In a PoC session, access to the speech channel is under the control of a PoC server and is not fully left on human being behaviour policy. This offers many possibilities to define evolved algorithms for speech access contention resolution. For example, a PoC server may queue and serve requests based on user priority, enforce specific service ...