A number of global PTT vendors are touting their solutions as MCPTT with no caveats. 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 in 2019 is an over-the-top solution).
More importantly, 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 commercially and readily available, it is frustrating that vendors are self-labelling their solution "MCPTT" which, as Andy Seybold so aptly called it in 2017, is still in 2019 "[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".
Having said that, we congratulate the vendors, carriers and industry in general for their progress towards MCPTT.
The term "MCPTT" is still misleading - even today after a number of years work towards availability of devices and solutions for a truly mission-critical standard.
The below article correctly points 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/ProSe, for a full functioning solution, it's more than just the application provider.
We would like to see more details in "MCPTT" 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 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", there is a lack of clarity on how far the deployed "MCPTT" is actually going towards true mission-critical.
Further reading and references: