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Musings on Mission-Critical Voice and the Project 25 ISSI

Author: Joe Boucher, Mutualink CTO

Date: 2015-05-04
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One of the questions asked of a FirstNet panel I was on at this past IWCE was "What are your biggest concerns about Mission-Critical Voice?”  I didn't get a chance to answer at the time, but this is an issue that deserves serious consideration by the public safety community.

One of the primary reasons that public safety agencies have trouble communicating with each other is that each agency has its own Land Mobile Radio (LMR) system that is typically dedicated to its own use. And since each LMR system may use different RF spectrum and underlying technology, these systems are very frequently not able to communicate with each other. This is fundamentally the "radio interoperability" problem plaguing first responders throughout our nation today.

There is a silver lining to the problem of many disparate LMR systems however: If one LMR system should fail or its spectrum becomes unusable, only that LMR system is affected while other systems in the vicinity continue to operate normally. Given the many LMR systems in a particular region or incident scene, this diversity effectively creates a very resilient and fail-safe network of systems; even in the largest disasters some LMR systems will still be operational.

Mission-Critical Voice will effectively use FirstNet's Band Class 14 (BC14) spectrum in an LMR-like fashion to allow direct voice communication between BC14-capable devices. The theory is that (in the future) all public safety agencies would be able to use that spectrum for voice comms instead of requiring a separate LMR system. However, if all public safety agencies at an incident scene are sharing the same spectrum (and LTE infrastructure if present), that's certainly putting all agencies' eggs in one basket and violates the "resilience through diversity" principle of highly-reliable systems.

In this scheme, a single failure can bring down all BC14 communications in the area. In addition to malfunctioning infrastructure components, there is always the possibility of bad actors; experiences at field trials have illustrated how easily a single rogue 700MHz transmitter can incapacitate the entire BC14 spectrum in an area.

So if neither a single shared system nor many disparate silos are the ideal solutions to public safety voice interoperability, then what is? Although there is certainly no single answer to this, one promising approach involves combining the two to gain the best of both while mitigating the disadvantages of each. If talkgroups from each disparate system were able to be quickly and easily inter-connected as needed, first responders would be able to communicate while still maintaining the resiliency of diverse systems. Such inter-connections would need to be secure enough for mission-critical use, easy enough for unskilled users to enable on-the-fly, and resilient enough to operate while disconnected from the network at large.

What if this inter-system capability was enabled by a secure network-centric framework that could utilize both on-scene and wide-area networks such as cellular, microwave, satellite, and of course BC14 LTE. In this model, instead of all agencies relying on BC14 as their primary mode of voice comms, they could use it as a secondary function to inter-connect their primary voice LMR systems. Of course, any on-scene agencies that do not have a primary LMR system could still use BC14 for their primary voice comms. Furthermore, on-scene inter-connects could be seamlessly bridged to remote systems/agencies via wide-area networks (if present).

The technology to do this exists today. And it can be deployed in an entire region for a fraction of the cost of migrating a single LMR system.

However, one of the primary obstacles to inter-connecting LMR systems is the lack of a fully-capable interface on each system. While the Project 25 Inter RF Subsystem Interface (ISSI) standard has been around for years, how many actual deployments has it seen, especially between disparate agencies? The biggest barrier to ubiquitous ISSI deployment seems to be the cost; purchasing the ISSI capability from some vendors is prohibitively expensive. This is understandable from the vendors' perspective - if you're not able to connect your LMR system to others, then you will be forced to expand your current system instead. Let's face it, some vendors want nothing more than to perpetuate our national interoperability crisis as long as possible; it's good business after all.

Perhaps what this country needs most is not a single frequency to rule them all, but vendors who consistently put First Responder safety before profits. To this end, it is end users that have the right to and should demand more from their vendors. Here's a proposal: Let's challenge radio system vendors to build the best, most competitive radio system they can, but with every system sold include a fully capable inter-system interface. Then agencies could enable inter-system interoperability at will, and radio systems will be chosen on their merits instead of being forced by anti-competitive vendor lock-in.

One can always dream...

For further information, you are invited to attend a Mutualink-sponsored Webinar, Collaborating in the FirstNet World, On Tues. May 12 from 1-11 PM PDT.  During this webinar, Mutualinnk hopes to engage in a lively industry discussion, rather than engage in a selling platform, with the goal of encouraging industry partners to creatively collaborate to answer first responders' needs for fully interoperable communications for enhanced situational awareness. For information, click here for the gotowebinar website to see details and sign-in.

Mutualink Chief Technology Officer Joe Boucher has been responsible for the architecture and development of the Mutualink Interoperability system. He has over 20 years of experience in telecommunications research and development, with 16 years of that focused on cutting-edge voice communications; he also holds several key Voice-over-IP (VoIP) and collaboration patents.  Mr. Boucher led the development of the world's first Voice-over-Broadband product.  His professional affiliations include Department of Homeland Security Public Safety VoIP Working Group (PSVWG) 2007; Public Safety Communications Research (PSCR) – Member of the Broadband Working Group; National Public Safety Telecommunications Council (NPSTC) Technology Committee.

This column originally appeared in “Urgent Communications” and is reprinted here with permission from Mutualink.




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