Public Safety Advocate: Push-To-Talk Is Public Safety’s Lifeline

At the time the Public Safety Alliance (PSA) set its sights on acquiring spectrum and some funding for a nationwide broadband network, most Members of Congress and their staffers had never used Push-To-Talk (PTT). However, most of them had been using cell phones since they became available, or they grew up using them. As a result, most users did not understand the differences between PTT and cellular. The most significant of these is that push-to-talk is near-instantaneous and cellular is text dialogue.

That was around 2012 as work was beginning on FirstNet.  Many more people have joined the public safety community since then and many of these brought a great deal of knowledge they had accumulated by working with broadband networks and smart devices. However, a number of new professionals had no awareness of the difference between push-to-talk and other services available on FirstNet and other networks. Therefore, I think it is an appropriate time to update the technologies and discuss current differences between them.

Today there are multiple push-to-talk Land Mobile Radio (LMR) systems and a variety of flavors of push-to-talk over broadband are being used on the FirstNet network.

Public safety began using push-to-talk in the 1930s. After the war, more vendors became involved in land mobile radio or “wireless communications” as it was then called. In the early days of LMR, push-to-talk was easy to implement. All of the radios were analog FM, and the push-to-talk features and functions in one radio worked with all other LMR devices. However, nothing stays the same and everything changes. Over the ensuing years, there have been many advances so working with LMR has become a bit more complicated.

LMR matured and new forms of technology such as P25 conventional, P25 trunked, satellite receivers, simulcast systems, and more were added. LMR push-to-talk devices no longer talk to all other LMR push-to-talk devices.

Further, smartphones have built-in spectrum and select the best available frequencies at any given time for the network and phone to work in concert.

On the other hand, until recently, LMR was confined to small segments of radio spectrum and a single device could not be used on multiple public safety frequencies.

The public safety community grew up with low band, VHF, UHF, the addition of the T-Band portions of 800-MHz spectrum, and lastly, the addition of 700-MHz spectrum.

Because LMR devices could not talk from one band to another, we ended up with the situation that created the need for a Nationwide Public Safety Broadband Network (NPSBN). After years of effort, the public and the US Government finally began to understand that there were issues facing the public safety community that do not come into play with commercial broadband.

The Value of Push-To-Talk

Push-to-talk is near-instantaneous communications between two or more radios (LMR-to-LMR). Because it is nearly instantaneous, PTT can be used over an LMR network, or unit-to-unit when needed or outside of network coverage. The most important elements of push-to-talk are “attack time” and “volley time.” Attack time is the time between depressing the radio’s push-to-talk button and when the user can talk over an established push-to-talk link. Volley time is the time from when the “talker” releases the PTT switch and the next user can respond.  

With analog LMR, there is no readily available confirmation indicator on the radio to let users know if they have connected with the network or, when in simplex, if the person on the other end can hear the conversation. In the newer LMR digital and FirstNet worlds, when the push-to-talk button is activated, there is usually a very short delay followed by an acknowledgment beat indicating that the radio has established contact with the network.

The push-to-talk applications available on FirstNet and other broadband networks offer many advantages to LMR push-to-talk. Most support location information for people on the call and, in many cases, preconfigured or instantaneously configured groups of people who need to be in the same conversation.

Where PTT Is Today

LMR push-to-talk remains a vital communications link for public safety activities. Since land mobile radio systems are local, countywide, regional, or a few statewide, push-to-talk conversations are limited to the coverage of the LMR network.

Broadband coverage is nationwide, so the applications that provide push-to-talk will work coast-to-coast. Today there is an increasing need to integrate broadband push-to-talk with LMR push-to-talk to add yet another layer of flexibility.

Where PTT Should Be

When I ponder where we should be with public safety push-to-talk, what comes to mind is the telegraph system that ran across our nation, usually along railroad lines. This network used a system of dots and dashes developed by Samuel Morse to indicate letters and symbols. Only one language (Morse code) was used nationwide from the early days and everyone on the network could hear and understand everyone else. Unfortunately, we are a long way from having the nationwide capabilities that were available to Western Union in the early days of the telegraph.

Today, work is being done to develop push-to-talk broadband applications that will use the 3GPP push-to-talk standard across networks along with tools needed to integrate this standard with land mobile radio.

Meanwhile, a number of existing push-to-talk applications are approved and running on FirstNet. We do not have a single nationwide push-to-talk system that can be used by every public safety entity that is a member of FirstNet. What we do have is the basis for a nationwide public safety network. Now we need nationwide push-to-talk capabilities.

As I see it, a single, nationwide PTT application is much further away now that some members of FirstNet have decided not to wait any longer and to move on with their preferred push-to-talk application from a specific vendor. In many cases, these agencies have integrated this system with their LMR push-to-talk service. Meanwhile, a number of companies and organizations are still working toward push-to-talk interoperability. Now there is another issue to be resolved before we can continue: how to serve a public safety community when different flavors of push-to-talk and LMR integration are in play.

One option being floated is to use a cloud-based system to provide interoperability between different vendors’ push-to-talk systems. I am not a fan of this approach because using multiple, different types of push-to-talk and a cloud-based solution would introduce many more potential points of failure into a system that is intended to provide interoperability.

Where Do We Go from Here?

We should all be working on answering this question before we go any further. With some pre-planning, I am confident we can develop a fully-interoperable nationwide push-to-talk broadband system connected to multiple LMR systems across the United States.

While serving as a panelist at several events, I have suggested one approach might be to put all the vendors in a room to come up with a solution and a timeframe for its implementation. There are ways to roll out a nationwide push-to-talk system more quickly and easily than what we have been doing.

From the beginning, the promise of FirstNet was a Nationwide Public Safety Broadband Network that provides fully interoperable communications for voice, data, text, video, and pictures. Today, FirstNet is a robust network capable of handling all the traffic public safety wants and needs. I will remain optimistic about finding a way, soon, to provide the operational interoperability that is sorely needed by our public safety community.

Winding Down

First, it’s great to be back writing and back to work. I look forward to returning to publishing the Advocate on a regular schedule again. That being said, next week many of us will be at the Vision 2022 FirstNet Users Summit in Las Vegas so, once again, there won’t be an Advocate next week.

As I was thinking about this week’s article, I remembered the many times I stood in front of a group of firemen and/or law enforcement personnel and talked about the differences between LMR being on the network or in simplex mode.

Several examples stand out. Most often I heard complaints from battalion chiefs or incident commanders who were on one side of an engine and were not able to communicate with someone on the other side of the engine. This problem is almost always because the radios are set to network operation. In the network setting, the originating radio would be talking to a repeater many miles away and then that repeater would be transmitting back to the person on the other side of the truck. When radios that are close to each other are trying to communicate over the network there are usually problems, which is why the users need to switch to simplex operation.

Another instance was when there was a reported missing swimmer at a beach in Santa Barbara and the county and city sent a number of engines. The crews were walking up and down the beach trying to determine if there was in fact someone in the water. As I listened to the radio traffic that day, it was obvious that while they were standing on the beach they were trying to communicate with each other via a repeater system miles away. What’s more, the beach was at the bottom of what might be considered a rather large hill that blocked the signal.

Recently, there was a serious incident where the authorities blamed not being able to communicate with each other on their radios and/or the network. I wonder if they had thought to switch to simplex.

Many departments understand the differences between how network and off-network communications work and they use off-network communications as much as possible. Fire Department New York (FDNY) is a good example and there are others. Perhaps as LMR push-to-talk and FirstNet push-to-talk become more entwined, moving to a simplex channel will become more automatic.

Meanwhile, I hope to see you at Vision 2022. If you are attending, please say hello, and I would like your feedback about my Advocate columns suggestions of topics you would like me to write about.

Back in two weeks…

Andrew M. Seybold, Sr.
©2022, Andrew Seybold, Inc.

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