FirstNet PTT technical progress highlighted by AT&T at APCO 2022

FirstNet PTT—the mission-critical-push-to-talk (MCPTT) service launched in 2020—continues to evolve with the development of much-anticipated features like LMR interoperability and broadcast technology that will support one-to-many calls, an AT&T official said during a presentation at the recent APCO 2022 event in Anaheim, Calif.

FirstNet users can use numerous different push-to-talk (PTT) applications that leverage the connectivity provided by the nationwide public-safety broadband network (NPSBN), but FirstNet PTT—developed by Samsung—is designed to meet the 3GPP standard for mission-critical services (MCX), according to Robert Fowler, AT&T’s product-management specialist for FirstNet LTE mission-critical services (pictured above on the left, with Mike Newburn).

“The solution is a high-prioritized solution on the network,” Fowler said during the APCO presentation. “One of the key differences between FirstNet Push to Talk and any application you might download off of Google Play or off of iTunes is that this is really a core network service—it is not an application. It is part of the LTE network, fully integrated with an enhanced packet core.

“So, it’s not an external entity that’s connected to the FirstNet network. It’s an integral part of the FirstNet solution. Therefore, we can prioritize the service moreso than you can any standard, over-the-top application. It delivers on the 3GPP promise of a low-latency, high-performing audio-quality service, and you’ll note that, if you test the service out yourself.”

Indeed, those who have tested FirstNet PTT overwhelmingly have applauded the performance and audio-quality aspects of the push-to-talk offering since it was introduced in March 2019. However, relatively few have indicated that they would use FirstNet PTT, in large part because the MCPTT offering did not allow interoperable communications with LMR radio systems.

But that situation appears to be changing rapidly. Today, FirstNet PTT interoperability can be provided with a radio-over-IP (RoIP) solution, and AT&T is testing a FirstNet solution developed by Catalyst that uses standards included in Release 12 of the 3GPP standard for LTE.

In addition, interoperability using the interworking function (IWF)—the LMR-LTE interoperability technology included in Release 17 of the 3GPP standard—will be introduced later this year, according to Fowler.

“IWF is part of the MCX infrastructure, so each of the solutions has a different approach,” he said. “Down the FirstNet PTT approach, we’re using Samsung and Etherstack core software. So, ISSI guys—with a premier network-infrastructure player—are building IWF.

“We’re going to go to controlled introduction this year. We’re excited about it.”

Other vendors are developing IWF solutions or others that are functionally similar, but Fowler said that the FirstNet PTT deployment of the Samsung-Etherstack technology could be the first IWF deployment in the world on a large-scale basis.

“As far as I know, this will be the first actual deployment of one. I have not seen any press on anyone saying that they’ve done it—even with TETRA, which is where you would expect something to happen, but it didn’t. We’re really excited about doing it.”

FirstNet also is in the process of deploying eMBMS—the 3GPP technology that supports broadcast communications, including one-to-many PTT calls, Fowler said.

“We haven’t announced broadly the availability [of eMBMS] … We’re still working through some of the technical aspects of it, but we have it in test cities,” Fowler said.

“We have deployed it in 20 cities, and we’re testing it out with the PTT service.”

Fowler noted that deploying eMBMS broadly in the network is not the only challenge to making the technology useful; eMBMS also requires support from the user device, which will display when eMBMS is being used. And eMBMS will not be used for all PTT calls—current unicast systems are adequate in most situations, so eMBMS will be invoked into service only when needed to relieve traffic on the FirstNet system, he said.

“The times when eMBMS is most useful is when you have a concentration of users coming into a service area, which is the way public safety responds,” Fowler said. “When they come together, you’ll have to start slicing off a network piece—that’s what eMBMS does—so that everyone has access.

“You use up less resources [with eMBMS], and it’s more efficient. You don’t have to worry about crowding out the cell infrastructure and so on.”

AT&T officials stated early this year that they hoped to make FirstNet PTT operationally practical on iPhones and other devices that utilize the iOS operating system from Apple. No Apple devices feature a dedicated push-to-talk button, and one iOS release proved problematic for PTT applications.

“Some of the things that they did to their application prevented push-to-talk applications from coming to the foreground, taking over the speaker, and behaving like a PTT app,” Fowler said.

Recently, Apple released a “framework” that was expected to address some of the PTT issues. The Apple framework proposal is a “first step,” but “it doesn’t really deliver a lot of functional,” according to Fowler.

“It looks like [Apple iOS developers are] trying to improve the notification mechanisms within iOS to help support push to talk, but it assumes that PTT is a black box and that we don’t need anything else from them, which is not the case at all,” he said. “We need a lot more. We would like a lot more support from their OS to deliver an improved user experience, and we’re conveying that back to them.

“We reviewed their beta documentation, and now we’re sending them back [responses. We’re saying,] ‘Here’s our comments on that. You’re making a step in the right direction, but here’s what we really need.’”

Fowler described the work with Apple in the PTT realm as “evolving,” which also may be an accurate description of FirstNet PTT’s place in the push-to-talk marketplace. Fowler declined to say how many users subscribe to FirstNet PTT today but noted that the service is “in the adoption phase” at the moment.

All statements during Fowler’s presentation at the APCO 2022 event referred to the FirstNet PTT service developed by Samsung. FirstNet users also have the option of using another MCPTT-platform service—the Rapid Response offering from Motorola Solutions that was developed with the carrier-integrated software purchased from Kodiak as its foundation.

“This is a parallel product,” Fowler said. “FirstNet is offering different PTT solutions, because there are differences in their deployment and in their user experience. FirstNet Rapid Response leverage our relationship with Motorola that we’ve had on Enhanced Push to Talk, which started as an enterprise solution but is available to FirstNet [users] as well.

“It’s the evolution of the Motorola product toward all of the MCX capabilities. So, it’s a sister solution.”