Public Safety Advocate: Why Are We Waiting for a PTT Interoperability Solution?

A number of committees are working toward solving both the Land Mobile Radio (LMR)/LTE Push-To-Talk (PTT) interoperability issues and LTE/LTE PTT interoperability issues. Meanwhile, the 3GPP standards body is crafting 3GPP TS 23.283, Mission-Critical Communication Interworking with Land Mobile Radio Systems, or the Interworking Function (IWF). The IWF is to be the interface that will provide solid interoperability between Mission-Critical Push-To-Talk (MCPTT) and LMR networks.

IWF specifications are intended to support a broad range of LMR technologies, effectively allowing MCPTT to interoperate with most of today’s LMR systems. Sounds good, however, in practice it will be an extremely complex implementation, beyond that of any interoperable systems in use today. There are no IWF implementations in existence at this time, which makes sense since there are no fully-compliant MCPTT systems in existence. Some Over-The-Top (OTT) broadband push-to-talk systems including Motorola and ESChat are successfully deploying P25 interoperability via Inter-RF Subsystem Interface (ISSI). Motorola has also introduced Critical Connect, a subscription-based (SaaS) interoperability hub that will connect Motorola’s LMR and LTE PTT solutions.

Implementing the IWF will be a massive task, which we assume will be offered in an SaaS model as well, similar to Motorola’s offering. The IWF will be managed by the wireless carrier, which also represents numerous risks. This is foreign ground for any wireless carrier, and one must question whether they really want to be (or should be) in this position. Fulfilling the IWF will be a task larger than implementing MCPTT itself. 

Even though IWF specifications have been released, so far, no company I know of has deployed the IWF interface. It also appears that while designed to solve MCPTT to P25 and Tetra interface issues, IWF does not address other issues, and addresses still others with limited functionality. This includes the large number of analog FM LMR systems still in use in the United States and it is not clear if IWF requires ISSI as a P25 interface, which can cost an agency anywhere from $40K to more than $500K depending on the vendor. I am hearing that several vendors either have contracts to start implementing IWF or have actually begun an implementation. I, for one, don’t know if IWF, if it existed today, would truly resolve the interoperability issues that are before us.

Remember, the goal, at least as I see it, is to enable LMR and FirstNet/LTE networks to pass push-to-talk traffic between an LMR network and the FirstNet/LTE network. This is a very important goal and one that, as far as I am concerned, is taking far too long to accomplish. We should already be in a position to connect every public-safety LMR network to FirstNet in both directions. However, this is only one part of the equation and it is needed now, not years into the future. In an ideal world, all of the different PTT vendors’ offerings that are available on FirstNet should be able to interoperate with all the others. 

Some technologists say once Mission-Critical Push-To-Talk becomes the standard of the land, other PTT venders will simply fold their tents and go away. This is not realistic. Today, existing FirstNet-approved PTT vendors already have a huge share of the available market and I, as well as others, don’t see every agency on FirstNet simply moving over to a different PTT platform. Further, until 100-percent of the public-safety agencies are using FirstNet (a goal that may never be fully realized), MCPTT will not handle cross-network communications. However, several vendors with over-the-top PTT products do. PTT works well on FirstNet and all of the vendors that have FirstNet-approved products provide very fast and functional PTT services. Some interoperate with several of the others, and every vendor, so far, has been able to provide cross-LMR/FirstNet connectivity in one form or another. 

Where We Are Today

  1. IWF is not a reality but it is being developed. Once it is available, it will still have to pass muster to determine whether it actually meets the needs of the public-safety community. 
  2. FirstNet has announced Mission-Critical PTT and it is becoming available. I consider today’s version to be the foundation of what MCPTT can become over time once it can compete with PTT applications already in the market and when it is capable of interoperating with LMR PTT systems. 
  3. There are seven certified PTT platforms currently running on FirstNet; three are fully interoperable and others could be interoperable if there was a desire by the vendor to make that happen.
  4. Some technologists and pundits are still trying to push public safety to a FirstNet-only environment (please note that even FirstNet (Built with AT&T) is not among them). However, they continue to miss the fact that LMR supports off-network communications and while MCPTT does provide support, it is not in a way that would be of any use to the public-safety community.
  5. Still other technologies and pundits are fond of saying we will reach full PTT interoperability in the future. Perhaps this is true, but I have to ask, “Why do we have to wait for the future?”

We have the brightest and best wireless engineers anywhere in the world, vendors that can build devices purposefully for public safety that are also attractive to the general public, and vendors busy building FirstNet and LMR into one device. What we don’t have is a standard, and some people say we should wait for one. I like to reference Scott McNealy, one of the founders of Sun Microsystems (now owned by Oracle). Scott and his folks built great machines and a great operating system. Oftentimes, he was called out for not building to “standards,” and his comeback was, “A standard is ONLY a standard when people use it!” 

Where We Need to Be

Things are moving fast in the world of technology. It took more than ten long, hard years for what is now known as FirstNet to be passed into law, another five years before a contract was awarded to build and operate the FirstNet network, and today, three years later, we still have not solved the most critical interoperability issue facing public safety. Push-to-talk is and will remain the most important method of communications used by public safety. Data, video, text, and other forms of transmissions that are enabled by FirstNet add to the total scope of communications for public safety, but at the end of the day, PTT over LMR and over FirstNet is the fastest and most important method of communications in the field. 

I have been participating in two committees from two different organizations. Both of these fully understand the importance of communications for the first-responder community, but the work drags on and on. Once a report is completed, it will have to be turned over to a standards body to wrestle into a standard or it will have to be embraced by The FirstNet Authority and the Public-Safety Advisory Committee (PSAC), then moved forward. Perhaps I am being too impatient, but I wonder why we have not yet addressed this issue and fixed it when it is clear that voice in the form of push-to-talk is the most important feature of public-safety communications and agencies using different flavors of PTT cannot communicate with each other.

Why do we have to wait for a “standard” passed by a body made up of mostly commercial broadband providers (networks and vendors) and a few public-safety types? When a standard was passed, why wasn’t work begun? Several vendors will follow a standard and most likely add some “neat” features, but will they really fix the LMR-to-FirstNet/LTE and FirstNet-to-FirstNet interoperability issues? If IWF won’t truly meet the needs of the public-safety community, where will we go from there and how much longer will it take? Or if one flavor of IWF meets the needs of the public-safety community but it has been implemented in several different ways, how do we identify the best way to provide true interoperability?

The good news is that I recently learned about several organizations (companies) that are working on different approaches to solve these interoperability issues. One thing they have in common is that they are not looking for only MCPTT-compliant (on-network) solutions. The are looking for approaches that take into consideration that there are and will continue to be several types of PTT on an agency’s premises, on-network, and in the cloud, as they work on ways to once and for all solve the interoperability issues and deliver a solution that works but is not years away.

As FirstNet (both The Authority and the network) moves forward, it is completely dedicated to the public-safety community as are vendors, various organizations, and most standards bodies that serve public safety. Everyone involved is dedicated to providing the public-safety community with what it wants and needs in the way of communications. Other issues that need to be addressed include Next-Generation 9-1-1 (NG911) funding, reversal of the T-Band giveback, ensuring that 4.9 GHz remains in the hands of public safety, and other concerns of equal importance. However, in my estimation, push-to-talk full interoperability in the field must be given the highest priority. We could see a solution not in five years but in one or two, certainly sooner than if we simply wait while the standards wheels keep grinding away.

Winding Down

What Is the FCC Thinking Now?

The FCC is apparently moving on the 4.9-GHz issue. As you may remember, the Public Safety Spectrum Alliance (PSSA, is committed to retaining the 50 MHz of 4.9-GHz currently in the hands of the public-safety community by asking the FCC to license this spectrum to The FirstNet Authority. Instead, the FCC has frozen the 4.9-GHz spectrum from accepting new public-safety licenses, and according to the Chairman at the September 30, 2020, FCC open meeting, the FCC intends to propose issuing licenses for the 4.9-GHz spectrum to each state. This is a disaster waiting to happen and perhaps the worst decision to come out of the FCC in a very long time. 

Radio waves don’t stop at state borders, the plan is extremely premature, and I don’t believe what the FCC is doing will work anyway. Even though a follow-on notice states public safety will be protected, the “frequency coordinator” will be the major spectrum holder in each state. In other words, the company with the greatest incentive in each state will be responsible for coordinating who will make use of the spectrum for what purpose, and then working with surrounding states. Just think about the issues that will arise state-to-state and the differences state-to-state in what the spectrum will be used for, then trying to protect existing public-safety users! I do not understand how the FCC Commissioners can even consider this to be a viable option.

Radio Club of America

The Radio Club of America, a well-known and highly-respected organization, has been in continuous operation since 1909 and its members are from all communications disciplines. I have been a member of the RCA for many years and have had the good fortune to know Fred Link (the father of two-way radio). Fred was a long-term member and supporter of the Radio Club, and he proposed that I join the organization. It was the right move. I have met many of the folks who are and had been driving various communications segments including broadcast, commercial, public safety, amateur radio, and many other disciplines.  

Over the years, I have served on the board of directors, was elevated to Fellow in 1997, and was awarded the Club’s Sarnoff Citation in 2010. Every year, the Club holds elections and this year, Don Root, who has been exceedingly active in public-safety communications, is running for a position on the board. Don recently retired from many, many years at the County of San Diego working in the area of radio communications. He has also been deeply involved with the National Public Safety Telecommunications Council (NPSTC) and he spearheaded the committee that came up with the official names for the public-safety interoperability channels. I plan to vote for Don and if you are a member of RCA, I hope you will as well. 

If you are not a member and would like to learn more, I encourage you to visit the RCA website. I believe you will find it worthwhile to support the RCA. I especially appreciate that the Club spends a great deal of time supporting schools and other youth organizations in its efforts to turn the younger generation on to radio communications—an area that is imperative to the future of wireless communications.

Until next week…

Andrew M. Seybold
©2020, Andrew Seybold, Inc.


1 Comment on "Public Safety Advocate: Why Are We Waiting for a PTT Interoperability Solution?"

  1. This is like asking ‘why do we need a P25 standard for LMR’. Yes, there should be an IWF standard to avoid proprietary implementations and monopolies. All vendors and carriers should be able to interoperate using a standard

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