Public Safety Advocate: APCO, FirstNet, and PTT over LTE

Mid-month August, Denver hosted the annual Public Safety Conference. While those elected to APCO’s executive offices seem to be moving APCO more toward dispatch and training in that area, the show floor still represents what APCO has always been to me. It is an organization founded on the premise that public safety communications staffers needed a place to meet and discuss issues. Dispatchers and dispatch centers were a very important part of APCO for sure, but it now appears as though APCO is leaving its technical roots behind in favor of only one segment of the communications continuum. The good news is that the APCO show floor still represents all the various communications disciplines needed to provide public safety with end-to-end communications capabilities.

Only two short weeks after this gathering in Denver, Houston was hit by Hurricane Harvey. It is too soon for after-action reports since flooding and rescue efforts are still very much in the news, but preliminary numbers from the FCC indicate there were some call center outages, and some cell sites were offline, but not as many as might be expected. Of course, the FCC’s data was gathered during the height of the storm and may need to be revised as sites run out of fuel or connections to sites are damaged or flooded. The FCC does not maintain records on public safety LMR so there is no way at this point to compare and contrast the differences. However, listening to Houston Police and Fire Dispatch via the Internet it appears from a distance that their systems are fully functional and operational.

We also do not have any details regarding the Band 14 pre-FirstNet public safety LTE network that has been deployed and working in the Houston area for many months. As the rain subsides and the flooding ebbs, there will be plenty of after-action reports that will prove valuable to the entire public safety community. The head of the FirstNet Public Safety Advisory Committee (PSAC) is right in the middle of the Houston Public Safety communications scene and I think when this is over he, among others, will be able to provide some important information on what went right, what went wrong, and what needs to be improved before another incident occurs.


Meanwhile, FirstNet keeps adding opt-in states and territories and at last count it is up to sixteen early opt-in entities with more preparing to join them. This is a good sign because it indicates the state executives understand how important the entire project is. Of course, as everyone has been explaining, just because a state opts in, it does not mean any of the agencies within that state are required to take part in FirstNet. However, it appears as though more agencies that were concerned about AT&T’s coverage are feeling better after discussions with AT&T and FirstNet folks.

Push-To-Talk over FirstNet (PTT)

While all this is happening, there are still many questions about how FirstNet will be implemented. Although it seems to be understood, I have not seen public statements from either FirstNet or AT&T about how the issue of push-to-talk over FirstNet will be handled. The available choices seem to be as follows:

  • Limit push-to-talk on FirstNet to one of today’s available technologies
    1. Not a good move from an open market, innovation perspective
    2. Which one? Who chooses?
  • Permit multiple PTT services on FirstNet/AT&T broadband
    1. Unless steps are taken to provide full interoperability between vendors’ products this could result in less, not more interoperability
  • Permit multiple PTT services on FirstNet/AT&T BUT
    1. Require each vendor to prove 100% interoperability with all other PTT vendors on FirstNet
    2. Require all PTT vendors to open their bridges between LMR and LTE systems for all vendors. This is especially important for P25 digital to LTE PTT systems since the P25 RF Subsystem Interface (ISSI) pricing could make interoperability not very attractive for one or more PTT vendor

Obviously, the best correct answer is number three. Today a number of PTT over LTE systems have proven effective. Two of them, Kodiak and Wave, are owned by Motorola, then there is ESChat from SLA (and its license holders), and Harris with BeOn. Each of these PTT systems is up and running and while more companies have or are developing PTT over broadband, the vast majority of existing broadband PTT users are using one of these four systems.

3GPP’s standard is being revised but as far as I know all the vendors mentioned have committed in one way or another to being fully compliant with the 3GPP standard. The greatest hurdle for interoperable PTT services is not that each vendor will have to pass a test showing it is fully compatible, it will likely be a price/feature/function war between the vendors over whose ISSI interface to use. If you do a Google search for ISSI you will find its meaning as well as multiple instances of the following definition: “P25 ISSI is a non-proprietary interface that enables RF subsystems (RFSSs) built by different manufacturers to be connected together into wide-area networks so that users of different networks can talk to each other.” In reality, some vendors seem to have ignored the words, “non-proprietary interface,” when they designed their ISSI interfaces.

This issue needs to be resolved fairly soon and agreed upon between FirstNet/AT&T and the public safety community. If this is not resolved soon, buying decisions for agencies in opt-in states could be delayed until this entire PTT issue is sorted out. If there is to be a standard interface between different vendors’ PTT over LTE systems, who will write the specifications (or do we simply assume the 3GPP standard will be the only specification needed)? Who is to make decisions over the PTT issue? Does it fall under the purview of FirstNet or will AT&T be able to determine this issue? To be fair, this will be a contentious decision regardless of how it turns out and hopefully the PSAC and FirstNet will have the final world on this topic.

The number of public safety agencies already using PTT over LTE is not known but there many. So far, bragging rights for the vendor with the most public safety PTT users are unclaimed but if I had to guess I would put ESChat and Kodiak on an even keel, with Motorola’s Wave and Harris’ BeOn in the next spots. Most PTT over LTE in use today in the public safety community is aimed at the brass rather than the troops. Dispatch functions and day-to-day PTT functions for public safety field operations still employ existing Land Mobile Radio (LMR) PTT systems that have been around for many years.

PTT over LTE is currently an administrative tool. Many who don’t always wear uniforms and who spend as much time with elected officials and out in public don’t want to have to carry both an LMR radio where they have to constantly adjust the volume and potentially miss an important message. In many agencies, these LMR devices have been replaced with a broadband commercial device that serves the upper echelon and those in other types of jobs well (i.e., fire inspectors and detectives). They have a smartphone that can be used to notify them if there is a major incident and if they want to listen to the LMR PTT or talk to their field commanders, all they have to do is enable that PTT feature on their smartphone.

PTT over FirstNet

Will the type of PTT over LTE user, or PTT user, or FirstNet user change over the next few years? My guess is not much. PTT over FirstNet will remain mostly a tool for higher-level public safety users and over time, will probably become a way to provide multi-agency interoperability between disparate LMR systems. That is, FirstNet PTT will be the system that will tie all of the different LMR channels present at an incident together and will be the bridge for providing interoperable PTT services. Once an incident is under control or terminated, the FirstNet LTE PTT system will go back to mostly administrative voice communications. This will give agencies time to become familiar with connecting LMR and LTE networks together, and it will continue to enable those in charge of a department to carry only one device.

That of course, begs the question of when and if FirstNet PTT will replace LMR systems. If you ask first responders you will probably be told that PTT over LMR will remain their lifeline for a very long time. However, if you ask non-public safety technologists, the answer will be that PTT over FirstNet will be ready to replace LMR PTT within the next few years. I don’t know about you but I come down on the side of the public safety community. This is especially true since PTT over FirstNet does not offer any type of off-network PTT and there is a lot of doubt about LTE FirstNet ever being able to offer off-network voice communications that will rival what LMR off-network simplex communications can do today.

Agency Decisions

States opting in is a good thing. However, the most important part of the puzzle is how many public safety agencies within those states will sign up for FirstNet/AT&T service. With better AT&T coverage, the move to AT&T works with these agencies on back-end logistics and training. After AT&T/FirstNet have made their PTT over LTE choice clear, agencies will be able to truly weigh their options and make up their minds. Signing up based on only one of the above parameters might result in unhappy users later on when some of the other options are clarified and might not fit with some agencies’ actual requirements.

Agencies don’t have to worry about the state opt-in or opt-out decision. Once a state has opted in the time clock stops ticking and the agencies have, basically, all the time they want and need to make up their minds. Of course, the sooner the decision is made to join the FirstNet system, the better off everyone will be when it comes to attaining a much higher level of interoperability than is generally available today.

Andrew M Seybold
©2017 Andrew Seybold, Inc.


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