Ambiguity with MCPTT and [Not quite] Mission Critical PTT over LTE

Ambiguity with MCPTT and [Not quite] Mission Critical PTT over LTE

Even in 2025, after ten years of development of MCPTT ("Mission Critical Push to Talk"), truly mission-critical PTT rarely exists in the real world outside a lab. Not much has changed since I wrote the original version of this article in 2019.

As far as we and many users are concerned, "Mission-critical PTT" (MCPTT) is not mission-critical without a direct mode solution so the users may communicate when there is no network, or when the network fails.

Ideally, this will be an automatic function, so while the user may be aware of it, they do not have to switch their device into a different mode to be able to communicate.

Regardless of their success at plugtests and compliance with [some or most of] the 3GPP standard for MCPTT; until direct-mode/ProSe chipsets -  and just as importantly, direct mode frequencies - are readily available, MCPTT is just a label for an over-the-top solution. It is frustrating that vendors are self-labelling their solution "MCPTT" which, as Andy Seybold so aptly called it in 2017, still in 2025, is really "[Not quite] Mission Critical PTT over LTE".

Application providers are touting their solutions as MCPTT, but without the integration and interworking of the network, and ultimately, operation off the network; any PTT solution is an over-the-top solution. Most of the providers who tout their "MCPTT" solutions fail to advertise this, and potential users can be misled thinking if they buy "XYZ MCPTT" then they can bet their life on it because it's "MCPTT".

Some are even claiming to offer "MISSION CRITICAL PUSH TO TALK ACROSS ALL CELL CARRIERS..." This is certainly not the case (any cross-carrier solution today is still an over-the-top solution). 

Having said that, we congratulate the vendors, carriers and industry in general for their progress towards MCPTT.

The term "MCPTT" and "MCX" ("Mission Critical Services") is still misleading - even after a decade of work towards availability of devices, solutions and networks for a truly mission-critical standard.

A 2019 article correctly pointed out, "...we cannot speak on behalf of carriers on whether their networks meet mission-critical standards...;" while at the same time implying the testing referred to in the article is for a mission-critical solution. Any MCPTT solution relies on the network, and direct mode, for a full functioning solution, it's more than just the application provider.

Even Airbus is still promoting the need for maximum network availability in 2025, in their promotion of MCPTT. The article noteably ignores direct mode - it seems vendors won't emphasise the need for life-saving off-network comms if their products can't deliver it.

And L3Harris focuses on "Converged radios", alluding, like other industry bodies, that LMR is here to stay thanks to its availability of high-power talk-around, filling the MCPTT "direct mode" gap.

We would like to see more details in "MCPTT" and "MCX" providers' advertising. To us (and I'm sure many Firefighters, Police and other first responders); no solution will be truly mission-critical until it includes useable direct-mode (D2D or simplex) communications for ultimate fallback in the case of a complete network outage. While there are current and already rolled-out deployments of "MCPTT" and "MCX", there is a lack of clarity on how far the deployed "MCPTT" is actually going towards actually being mission-critical.

Further reading and references:

LTE Release 17 (with direct mode enhancements) expected late 2021

Airbus article, 3 requirements for mission critical communications

L3Harris presentation at ARCIA event, November 2024

Article by Ben Cosier, critical communications and PTT specialist

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