First responders are expected to begin utilizing mission-critical push-to-talk (MCPTT)-standard services over FirstNet and other LTE networks late this year, but industry representatives have myriad opinions about when MCPTT might supplant land-mobile-radio (LMR) as the solution for mission-critical voice communications.

AT&T officials have stated that MCPTT will be implemented on the FirstNet by the end of the year, and Verizon officials have set a similar timetable for MCPTT on its network with a dedicated public-safety LTE core. But all speakers on a wide variety of IWCE 2018 panels agreed that MCPTT will be used to augment LMR mission-critical voice services initially by extending coverage, offloading traffic and/or providing extra interoperability.

Push-to-talk over cellular (PoC) already is being used to replace LMR in non-mission-critical scenarios, but learning from those experiences eventually will impact acceptance of MCPTT-standard offerings, according to Chris Sambar, AT&T’s senior vice president for FirstNet.

“It will start with extended primary [users] in public safety, and it will move to first responders, in time,” Sambar said last month during an event sponsored by Sonim Technologies. “I don’t know how long that will take. I think there will always be a place for LMR, because it’s a great tool. I think [LMR] will start slowly moving to a backup technology, though. But it will take time.”

Most expect eventual public-safety transition to MCPTT over LTE, but timing remains in doubt

Sambar said he believes MCPTT over LTE will replace LMR for first responders’ mission-critical voice communications but declined to speculate when the transition would happen.

“I will never try to take something away from somebody that they use and depend on to save their life,” Sambar said. “Today, the primary communications device is a radio for public safety. Over time, I think that will change, and the primary communications device will be LTE.

“I don’t know what the timeline is on that. I would probably give a shorter timeline than somebody at, say, Motorola—they would say longer.”

Sambar said the adoption rate for MCPTT over LTE could differ significantly among various public-safety agencies. For instance, some cities with large budgets to fund LMR systems may utilize MCPTT as a secondary voice solution while continuing to rely on LMR as the primary mission-critical voice service for some time. But other budget-constrained may look to MCPTT as a mission-critical voice alternative earlier, he said.

“There are smaller agencies—in states that don’t necessarily have a lot of money—that already are asking some pretty hard questions of the land-mobile-radio [LMR] providers and us,” Sambar said. “[These agencies ask], ‘When’s it going to be robust enough to switch?’ and we tell them the truth: ‘It’s not there yet.’

“But it will be, and I don’t think it will take that long for mission-critical push to talk and for standards to be developed on things like pro se [proximity services, the 3GPP standard for direct-mode communications]. So, yes, that switch will happen. It just depends on how quickly.”

Several speakers at IWCE 2018 noted some key technological advancements that have set the stage for MCPTT over LTE being introduced this year. The base MCPTT standard was completed more than two years ago as part of LTE Release 13, and the LTE Release 15—a release that includes additional MCPTT features, including new LMR interoperability standards—has been “frozen” and is scheduled to be completed in June.

Perhaps the most important development in the MCPTT arena is the quality of service, priority and preemption (QPP) being promised to public-safety users on the FirstNet system being built by AT&T and on Verizon’s public-safety LTE core.

Another key is interoperability, both between MCPTT solutions and with legacy LMR systems. While there are several PoC applications that have been designed to meet the reliability needs of public safety, all PoC vendors have acknowledged that a limiting factor has been that the PoC solutions have not been guaranteed the network performance necessary to let them to serve the needs of first responders. That performance assurance is something FirstNet is designed to provide, according to Igor Glubochansky, AT&T’s assistant vice president of mobility management.

“[MCPTT is] only as mission-critical as the network it’s on, and FirstNet finally is beginning to build that mission-critical network,” Glubochansky said.