The Specs Behind LTE-Advanced Pro’s Mission Critical Communication

One reason for referring to 3GPP Release 13 as ‘LTE-Advanced Pro” is that this version of the specification finally has everything in place for Mission Critical Communication, the LTE based successor to 2G TETRA networks designed in the 1990’s and used by public safety organizations in many countries today. One of the first countries that will use LTE-Advanced Pro’s Mission Critical Communication is the UK and a contract has already been awarded to Everything Everywhere. Time to have a look at the specs for Mission Critical Push to Talk (MCPTT), the central feature for public safety organizations.

In summary, Mission Critical Push To Talk (MCPTT) is the packet switched replacement for TETRAs circuit switched push to talk functionality which itself at the time was a replacement for push to talk over analog radio. While one might think that Push to Talk is a simple service, that might have been true in the analog days. Not anymore, as a lot of features have accumulated around it. Talking about the details in a single blog post won’t be possible but if you are interested here’s a list of specification documents in the order you should have a look at them:

The first and foremost specification document on the subject is 3GPP TS 23.179 – ‘Functional architecture and information flows to support mission critical communication services; Stage 2’. Stage 2 means it does not contain the requirements (that’s stage 1) but describes how the requirements are implemented in practice. While being a higher layer description document, 23.179 is nevertheless 220 pages long which gives you an idea of how much stuff has accumulated around just pressing a push to talk button to tell something to a group.

For further details the following specifications are recommended:

  • 23.468: Group Communication Service (GCS) AS (Application Server) – Stage 2 (The MCPTT server is an instantiation of the GCS AS!)
  • 24.379: MCPTT Protocol definition
  • 24.380: MCPTT – Floor Control
  • 24.381: Group Management
  • 24.382: Identity and Configuration Management
  • 24.980: IMS Profile support for MCPTT
  • 23.303: ProSe Stage 2 (Proximity Services)
  • 3GPP TS 36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (see chapter 15 for eMBMS)