Public Safety Advocate: Looking Back and Looking Forward

As we enter the 21st month of the 25-year contract between FirstNet the Authority and FirstNet (Built with AT&T), the last three of this year’s Public Safety Advocates will examine what has already transpired and what may lie ahead for FirstNet in 2019. As you read these three Advocates, keep in mind that had the contract been awarded to a vendor that was focused simply on building out Band 14 (the public safety spectrum), this vendor would only have been required to have 60-percent of the network built out in metro areas at this point in time.

Instead, the RFP winner, AT&T, offered up all of its existing LTE spectrum plus Band 14. This had a significant impact on public safety communications. First, today, only 21 months into the contract, FirstNet (Built with AT&T) is providing far more than 60-percent coverage in metro areas with full priority access including pre-emption where and when needed. Further, AT&T has stated that as it continues to build out its own LTE network, the FirstNet network will also have access and when it starts building out its 5G system, FirstNet will be part of that, too.

The questions I will ask and try to answer are about Push-To-Talk (PTT), both on- and off-network, coverage that still needs to be completed in metro, suburban, and rural areas, and finally what lies ahead for 2019.

All this will be weighed against goals that created FirstNet: To have a Nationwide Public Safety Broadband Network (NPSBN) for public safety’s use including full pre-emption. We have not yet reached this goal but it is still in early in the development of the network. Some believe we can come close to achieving this goal but there will be some agencies that do not join FirstNet, at least in the next few years. I have to believe that as these agencies recognize the advantages of fully interoperable communications for the first time in the history of public safety communications, they will join in and this goal will eventually be realized.

In the meantime, departments that have chosen to embrace FirstNet (Built with AT&T) are already reaping the benefits. During the recent hurricanes and wildland fires, having access to both Land Mobile Radio (LMR) and FirstNet provided a number of advantages. The first is to have communications redundancy. In the Carolina’s when the LMR systems went down, FirstNet took up the slack. In other areas where FirstNet went down, LMR handled the load. Another critical aspect of FirstNet in major incidents is the ability to quickly and easily bring on other agencies. Again, during the hurricanes, FEMA and other agencies were equipped with FirstNet devices that enabled a level of coordination between local, state, and federal authorities that has been elusive thus far. Perhaps the greatest win for all is that FirstNet works tirelessly to bring in temporary cell sites and put existing sites back on the air. These efforts also benefit regular customers by providing service for them as well.

But there still is a lot left to do. The network will continue to be built out and open standards for elements such as push-to-talk and other features and functions of the network need to be put into place. Many of these are being worked on by a variety of companies and groups with the common goal of putting these services into use as quickly as possible.

Looking at PTT or “Mission-Critical” PTT

First, there are a number of pieces to Mission-Critical PTT or PTX (images, etc.).

  • An open standard is needed (3GPP has developed the standard, see below)
  • The network PTT is on must be mission-critical or public safety-grade (FirstNet is developing this but is not there yet)
  • A decision must be made about how many PTT vendors will be permitted on a given public safety network (see below)
  • The piece most people miss is that Multimedia Broadcast/Multicast Service (MBMS) must be implemented in the network (see below)
  • Off-network—simplex/talk-around must be as robust as LMR PTT, today’s Proximity Services (ProSe) does not begin to meet these requirements (see below)

If all five of these factors are met and implemented, we will have Mission-Critical PTT over broadband but this will not happen until after a great deal of work is completed. The standard is finished but has been revised and added to multiple times in multiple releases of the 3GPP LTE standard starting with release 13 and progressing through release 14 and 15. Now additional features and functions are still being included. Until we have vendors and network operators that implement PTT using the standard, we won’t know if it truly meets the requirements of the public safety community. However, after reviewing the specifications, it looks as though it will.

Next up is to determine how many vendors will be permitted on a given public safety network. The Critical Communications Association (TCCA) and others are holding plug-fests in which up to thirty-plus vendors are touting their interoperability. I was told by a TCCA official that he sees no reason any and all of these vendors should not be permitted to sell their PTT into the public safety network. However, even with plug-fests and standards, vendors have a habit of making “improvements” that render their products non-standard. If you recall, this was widely practiced after the P-25 digital standard was introduced and it took years of hard work to ensure devices were fully interoperable, but some vendors still include “over and above” enhancements in an attempt to gain an advantage.

If you recall, the premise of this network is that it is to be a nationwide fully-interoperable network. The thought of so many PTT vendors on it all needing to be included into the network servers seems to me to be defeating the concept and goals of this network. I would much rather see FirstNet or any public safety network and public safety work out a compromise to ensure there are fewer vendors and that none of them add “enhancements” to the standard unless every vendor adds them. Public safety has lived through many generations of LMR incompatibilities and we need to make sure public safety broadband meets the goals as set forth.


In order for FirstNet to be used for dispatch and for multiple PTT users within the same cell sector or site, the network must include multicast services but I do not know of any network anywhere that has implemented these services. Multicast is a necessity for both dispatch and multi-user PTT because it enables the network to be subdivided into segments and, within a segment, for the same information to be sent to multiple devices. However, there seems to be some confusion about when and if multicast will be implemented. That decision is up to FirstNet (Built with AT&T).

Off-Network Communications

For many years, the use of simplex or off-network one-to-one and one-to-many communications has been a mainstay of the public safety community. Many dispatches include identification of both the main command channel and at least one simplex channel to be used for the incident. As more public safety personnel arrive at a given incident, the number of simplex channels needed usually increases. During wildland fires, the use of simplex for each different function for each different division is critical. Today, most off-network communications are accomplished using 3- or 5-watt handheld radios with external antennas. They work and they work well.

The 3GPP off-network solution is called Proximity Services (ProSe). “Proximity” is a good word because today’s LTE devices are based on ¼ watt of power with the antennas inside the unit’s case. This is very limiting when it comes to distance and the ability to talk from outside a structure to inside. ProSe can rely on a relay between users but during an incident there is no guarantee the relay will remain in a viable position. Band 14 devices are permitted to use 1.25 watts, but in my estimation, that is still not enough power. Further, in order to provide off-network LTE, the device must have a separate transmitter or receiver built in (adding to the many already onboard). The frequency spread between the transmit and receive channels for cellular is quite wide, and it is not practical to spread an LTE receiver and transmitter that wide.

It seems to me that instead of the industry waiting for ProSe and finding out it will not satisfy public safety requirements for simplex, we should be spending our time on the integration of LTE and LMR as Harris has done and Sonim is about to do, and leave ProSe for what it might deliver to citizens including short-range, one-to-one or one-to-many for transferring files and such. Before ProSe is public safety ready, it must meet the criteria below.

These off-network tests that must be met before there is any chance of ProSe replacing LMR talk-around include:

  • Communications over a three- to-four block area with no relay (metro area)
  • Communications from street level to upper building floors at the furthest point from the street
  • Communications from street level to a sub-basement
  • In a wildland fire, the ability to reach all personnel attached to a division

If this can be accomplished without draining the device battery, and with the ability for both one-to-one and group calls, then perhaps ProSe has a place in public safety communications. If not, LMR should remain the standard and we should work with vendors that are blending LMR and LTE into a common device. This brings me to the missing link of PTT communications.

LMR/LTE Full Interoperability

Today, some departments have integrated their LMR systems with FirstNet. One of these is LA-RICS, which demonstrated this capability during the Rose Parade. The issues in cross-connecting LMR and LTE are many but there are a number of both easy/inexpensive and difficult/costly ways to accomplish this task.

The importance of these connections should not be overlooked. In the early stages of broadband LTE as it is being field-tested and used on today’s FirstNet, such connections are a valuable way of providing interoperability between agencies, departments, states, and federal agencies. Being able to interconnect LMR and LTE means all incoming units will be on a common system where PTT can be used to direct incoming units to where they need to be and to provide on-scene connectivity for the duration of the incident. In other words, PTT between LMR and LTE (FirstNet) becomes an extremely important element of the overall system. LMR systems are not being torn down and replaced by FirstNet, rather FirstNet is a partner with LMR and both systems need to work together seamlessly if at all possible.

What is ultimately needed is a way to cross-connect every LMR system with FirstNet in the United States and in other places to cross-connect LTE to Terrestrial Trunked Radio (TETRA). However, some decisions need to be made in order to accomplish this on a network basis. Will this decision be left to each agency? If that is the case, is each agency free to select the best solution in its judgement? Would it be enabled on a statewide and/or regional basis? And finally, could it be rolled into FirstNet so it is universal? There are several groups working on these issues now, but no decisions have been made.

Cross-connecting LMR and LTE needs to be thought out clearly. Should it be semi-automatic and controlled by the dispatch center? Should it be turned on at an incident by the incident commander or his/her assistant? Should it be live all the time? Perhaps a combination of these options would be appropriate depending on the needs of an agency or region. It would be preferable for the bridge to be set up and then using touch-tone commands from the field, turned on. My experience with dispatch center turn-on is unless the bridge is used fairly often and dispatch staff knows the system well, when and if it is needed there could be some delays involved in turning it on. Perhaps the best of both worlds would be to turn it on either from the field or through the dispatch center.

For P-25 to FirstNet integration, many vendors are recommending the Inter RF Subsystem Interface (ISSI) and Console Subsystem Interface (CSSI). Some vendors sell ISSI gateways for a reasonable amount of money ($40K or less) but some charge several-hundred-thousand dollars. At the low side of the interconnection puzzle there is an interface known as Radio over IP (RoIP) but today’s RoIP systems do not pass the FirstNet device’s location or the unit number for that device. Work is being done on “enhanced” RoIP but I don’t have more details.

Suffice it to say that there are under-$1,000 interfaces and upwards of $500,000 interfaces available depending on the type and the vendor. What is needed is an economical way of providing this interconnection so it can be acquired by any department that wants to use it. Some PTT vendors can and do supply ways to connect including the Motorola (Kodiak) and ESChat solutions from two PTT vendors approved by FirstNet. However, based on the importance of what needs to be done and how soon, common ground must be agreed upon and it needs to be an open standard so any vendor can install it between their radios and FirstNet regardless of whether they are analog or digital systems. If we can solve this problem quickly and inexpensively, it will go a long way toward providing the type of interoperability that is vitally important to first responders.

What Is Being Done

As mentioned, the TCCA with its Mission-Critical Open Platform (MCOP) group has been working on a number of plug-fests but they are concentrating on PTT and PTX over LTE, not LMR/LTE interoperability. However, the Public Safety Technology (PST) Alliance has two active working groups, one working on Mission-Critical PTT and one on LMR/LTE integration. Both groups have a number of highly qualified people working on these issues and are, at the moment, focusing on the near term (the next six months) to see how much headway they can make. It would be nice if there was more public safety representation on these committees, joining the PST Alliance is not expensive, and if the results are as meaningful as I think they will be, we will have made a lot of progress.

All of these efforts along with what is transpiring in the labs of the National Institute of Standards and Technology (NIST) and the Public Safety Communications Research division (PSCR) are, I hope, following the lead on the National Public Safety Telecommunications Council (NPSTC) report entitled, “Public Safety Land Mobile Radio Interoperability with LTE Mission Critical PTT,” published on January 8, 2018. It is well worth reading since it is the work product of a number of vendors, consultants, and public safety practitioners that really spells out the requirements.


As we approach the end of 2018, we should remember how far we have come since the RFP was awarded only 21 months ago. We should also look at the number of agencies on the network (more than 3,500 and growing) and consider network coverage and advances in coverage in these 21 short months. However, we should also call attention to what is missing in order to spur others to join and use this network. PTT is only one of several tasks remaining and it is imperative that we do a first-rate job of establishing PTT and PTT interoperability on the network.

Scott McNealy, who was president of Sun Microsystems, said a long time ago that a standard is not a standard until it is used and accepted as a standard. Mission-Critical PTT is not there yet and it will be a while longer before it is. Users are not those working on 3GPP standards in a lab somewhere, or even vendors that take part in the plug-fests. The users will be the public safety community, which has more than its share of skeptics. If they are burned once, they usually won’t be open to a second chance.

When and if public safety is willing to trust people’s lives to Mission-Critical PTT over FirstNet will be up to public safety and no one else. We saw during the hurricanes how valuable the service was in many ways and that it remained in operation or was returned to service as quickly as humanly possible. However, we must keep in mind that this is public safety’s network and public safety will decide if and when a technology or feature is worthwhile and, in the end, whether to trust lives to it.

Andrew M. Seybold
©2018, Andrew Seybold, Inc.


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