ETSI TS 123 179 specifies the functional architecture, procedures and information flows needed to support the mission critical push to talk (MCPTT) service including the common services core architecture for identity management, group management, and configuration management required to support the MCPTT voice service. Support for both MCPTT group calls and MCPTT private calls operating in on-network and off-network modes of operation is specified.

The corresponding service requirements are defined in 3GPP TS 22.179 [2].

The present document is applicable primarily to MCPTT voice service using E-UTRAN access based on the EPC architecture defined in 3GPP TS 23.401 [9]. Certain MCPTT functions such as dispatch and administrative functions could also be supported via non-3GPP access networks but no additional functionality is specified to support non-3GPP access.

The MCPTT service requires preferential handling compared to normal telecommunication services e.g. in support of police or fire brigade including the handling of prioritised MCPTT calls for emergency and imminent threats.

The MCPTT service can be used for public safety applications and also for general commercial applications e.g. utility companies and railways.

In the present document, MCPTT calls between MCPTT users on different MCPTT systems are considered, however, for roaming only EPC-level roaming and IMS-level roaming are considered i.e. partner MCPTT system based roaming (also known as "migration") is out of scope.