4.1 General

22.1793GPPMission Critical Push to Talk (MCPTT)Release 17Stage 1TS

A Push To Talk service provides an arbitrated method by which two or more users may engage in communication. Users may request permission to transmit (e.g., traditionally by means of a press of a button). The Mission Critical Push To Talk (MCPTT) service supports an enhanced PTT service, suitable for mission critical scenarios, based upon 3GPP system services. The requirements for Mission Critical Push To Talk (MCPTT) service defined within can also form the basis for a non-mission critical Push To Talk (PTT) service.

The MCPTT Service is intended to support communication between several users (a group call), where each user has the ability to gain access to the permission to talk in an arbitrated manner. However, the MCPTT Service also supports Private Calls between pairs of users. The MCPTT Service builds on the existing 3GPP transport communication mechanisms provided by the 3GPP architectures to establish, maintain, and terminate the actual communication path(s) among the users.

The MCPTT Service also builds upon service enablers: Group Communications System Enablers and Proximity Services. To the extent feasible, it is expected that the end user’s experience to be similar regardless if the MCPTT Service is used under coverage of a 3GPP network or based on ProSe without network coverage. To clarify this intent, the requirements are grouped according to applicability to on-network use, off-network use, or both.

Though the MCPTT Service primarily focuses on the use of the 3GPP system there might be users who access the MCPTT Service through non-3GPP access technology, dispatchers and administrators are examples of this. Dispatchers and administrators are special users who have particular admin and call management privileges which normal users might not have. In MCPTT dispatchers can use an MCPTT UE (i.e., 3GPP) or a non-3GPP access connection to the MCPTT Service based on a "dispatcher and Administrator" interface. Through this interface a user is able to access and manage the services related to on the network and those common to on the network and off the network.

The MCPTT Service allows users to request the permission to talk (transmit voice/audio) and provides a deterministic mechanism to arbitrate between requests that are in contention (i.e., Floor control). When multiple requests occur, the determination of which user’s request is accepted and which users’ requests are rejected or queued is based upon a number of characteristics (including the respective priorities of the users in contention). MCPTT Service provides a means for a user with higher priority (e.g., MCPTT Emergency condition) to override (interrupt) the current talker. MCPTT Service also supports a mechanism to limit the time a user talks (hold the floor) thus permitting users of the same or lower priority a chance to gain the floor.

The MCPTT Service provides the means for a user to monitor activity on a number of separate calls and enables the user to switch focus to a chosen call. An MCPTT Service user may join an already established MCPTT Group call (Late call entry). In addition the MCPTT Service provides the User ID of the current speaker(s) and user’s Location determination features.

The users of an MCPTT Service may have more stringent expectations of performance than the users of a commercial PTT service.

MCPTT is primarily targeting to provide a professional Push To Talk service to e.g., public safety, transport companies, utilities or industrial and nuclear plants. In addition to this a commercial PTT service for non-professional use (e.g., groups of people on holiday) may be delivered through an MCPTT system. Based on their operational model, the performance and MCPTT features in use vary per user organization, where functionality which is more mission critical specific (e.g., Ambient Listening and Imminent Peril Call) might not be available to commercial customers.

MCPTT Users expect to communicate with other MCPTT Users as outlined above, however MCPTT Users also need to be able to communicate with non MCPTT Users using their MCPTT UEs for normal telephony services.