AT&T and Verizon have been conducting a sort of press release duel in recent months with regard to public safety communications. Verizon traditionally has had the largest share of that market, but AT&T gained a tremendous edge when it won contracts and spectrum to build out a nationwide mobile broadband network on which public safety users would have priority.

Verizon has been telling public safety users they can still use Verizon for connectivity, while AT&T has touted exclusive features available only to FirstNet subscribers. Both companies have made vague references to public safety and FirstNet interoperability, but it wasn’t clear what either of them meant by interoperability, so Telecompetitor pressed them for details.

Here’s what we learned.

FirstNet Interoperability

The FirstNet network consists of two key pieces. One piece is the radio access network (RAN) that AT&T is building using spectrum known as Band 14 in the 700 MHz band. The other piece is the core network, which will be largely wireline infrastructure, including data centers, connecting FirstNet RANs nationwide. In exchange for agreeing to invest $40 billion in the network, AT&T gained exclusive use of the spectrum and $6.5 billion toward network costs from the U.S. government.

As AT&T explained, non-FirstNet subscribers will be able to reach FirstNet subscribers and vice-versa.

“When a FirstNet user calls or emails a public safety user on another carrier’s network, the communication will go from the FirstNet device, through the RAN, to the FirstNet core to the other carrier’s network,” an AT&T spokesperson said. If a non-AT&T public safety user calls or sends an email to an AT&T public safety user, “traffic would simply flow the other way,” the spokesperson said. A Verizon spokesperson explained the traffic flow in essentially the same manner.

Once traffic to and from public safety users reaches the FirstNet core, “it is now on a dedicated physically separate core, with no commercial traffic,” the AT&T spokesperson explained.

AT&T declined to comment on whether the company would charge other carriers for traffic delivered to the FirstNet core or whether it would use a “bill and keep” approach in which carriers do not exchange interconnection fees.

The FirstNet RAN

AT&T commercial customers can use capacity on the FirstNet RAN when it is not in use by public safety, but public safety users get priority. If AT&T has not yet built out the FirstNet spectrum in an area, FirstNet subscribers in that area get priority on AT&T’s existing commercial wireless network.

Customers of other carriers, however, will not be able to use the FirstNet RAN, according to AT&T.

A Verizon spokesperson noted that Verizon offers several devices that work on the Verizon network and can also work in the FirstNet band but confirmed that those devices will only work in the FirstNet band if customers have a service plan with FirstNet. He added that because smartphones are single SIM devices, they will only use the network that the SIM supports.

“If the device supports Band 14 as well as Verizon bands, the SIM card would need to be replaced with a FirstNet SIM and the user/agency would need to subscribe to FirstNet to access the FirstNet network,” he explained.

FirstNet Core Capabilities

While traffic originating on other carrier’s networks may traverse the FirstNet core, the AT&T spokesperson noted that some capabilities enabled by that core are only available to FirstNet subscribers – and comments from Verizon suggest that could be the next battleground between the two carriers with regard to public safety.

Among the features only available to FirstNet subscribers are additional priority levels and an incident management portal, which enables authorized users to reassign priority levels and give priority to non-public safety users such as utility or transportation companies, as appropriate, the AT&T spokesperson noted. Future capabilities will include z-Axis location-based services, which can help pinpoint individual floors within a building, as well as something AT&T calls “mission-critical Push-to-Talk.”

Asked if there are any other issues pertaining to FirstNet interoperability with other networks that still must be resolved, the Verizon spokesman said the company believes that “all public safety first responders should have access to the applications they need to complete their mission, regardless of which network they are on.

“Any public safety applications should be available to first responders on any network,” the Verizon spokesperson continued.

He added that priority and preemption capability should be consistently applied on Verizon or FirstNet public safety users and “recognized end to end, even between networks.”

Finally, he said, “as mission critical features are introduced later this year, these should be built using 3GPP standards and be available for interoperability across Verizon and FirstNet customers.”

The AT&T spokesperson said FirstNet “will be interoperable with other commercial networks according to 3GPP industry standards.”

No Rural Update from AT&T

We asked AT&T this week if the company had signed up any rural carriers to build part of the FirstNet RAN and the spokesperson had no information for us on that. One of the requirements of AT&T’s deal with the government is that the company must use rural network operators to build at least 15% of the network.

The AT&T spokesperson noted, however, that the company has a commitment to build out 20% of its rural coverage target in the first year, 60% in the second year, 80% in the third year, 95% in the fourth year and 100% by the fifth year.

Updated to include additional information from AT&T