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 over LTE (MCPTT) service supports an enhanced PTT service, suitable for mission critical scenarios, based upon 3GPP Evolved Packet System (EPS) 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 is a service that can be used for public safety applications and general commercial applications (railways, utility companies etc.). The MCPTT Service is intended to support group communication, where each user has the ability to gain access to the permission to talk. Additionally, MCPTT Service also supports private calls between users.

The MCPTT Service is based on existing 3GPP transmission communication mechanisms provided by EPS architectures to establish, maintain, and terminate the actual communication path(s) between users.

MCPTT High Level Architecture
As shown above, MCPTT core comprises three main servers namely 

  1. MCPTT originating participating server
  2. MCPTT controlling server and 
  3. MCPTT terminating participating server 

to establish, update and to terminate sessions. Services given by MCPTT rely on IMS. MCPTT works as application servers on the top of IMS. In addition to this, MCPTT interacts with PCF/PCRF for quality of service negotiation. As a whole, MCPTT system is made up of:

  • MCPTT Servers
  • Group Management Server
  • Configuration Management Server
  • Key Management Server
  • Identity Management Server and
  • Control Room