MCPTT is 3GPP’s answer to the issues discussed in the previous topic, namely, an open standard PTT over LTE specification that meets the mission-critical requirements as identified in the U.S. by the National Public Safety Telecommunications Council (NPSTC), including a plan for integrating LMR and LTE.

In response, both carrier-based and OTT PTToC vendors have announced plans to modify or upgrade their own offerings to the MCPTT standard and FirstNet/AT&T has insisted that its PTT will be fully compliant. Deployments of MCPTT to public safety have begun, so MCPTT will be tested in real life situations.

Does this mean that the issue has been settled about whether PTToC is mission-critical? Not quite.

First, let’s remember that most of the devices available today for MCPTT are standard consumer products. Not public safety grade, not rugged, and not built with dedicated PTT or emergency alert buttons. Over time this will undoubtedly change.

Second, unless MCPTT runs over LTE networks that support quality of service, call prioritization and call pre-emption, the reliability and availability of communication will still not meet public safety expectations. FirstNet does have the right features, but many public networks do not.

Third, there is the question of interoperability between LTE networks and between LTE and legacy LMR. While FirstNet provides interoperable communications for all of its subscribers, the ability of FirstNet subscribers to MCPTT outside of FirstNet, either to other LTE networks or to legacy LMR systems is a point of continuing discussion.

Finally, Direct Mode for LTE is still a challenge. To meet this 3GPP created a specification for LTE Proximity Services (ProSe) that define how to achieve device-to-device communications for voice (MCPTT), data (MCDATA) and video (MCVIDEO). However, typical LTE devices are designed to transmit at low power (generally around a quarter of a watt) at high frequencies through internal antennas, so the range of ProSe is quite limited. LMR radios, with higher transmission power, external antennas, and use of lower frequencies (with superior propagation) do a lot better in Direct Mode.

In the US, FirstNet will be a powerful promoter and proving ground for MCPTT and provide the necessary experience for future improvements to PTT over LTE.

So, although PTT over LTE is not yet fully mission-critical, the gap is closing fast.