A couple of weeks ago, I moderated a panel discussion about the InterRF Subsystem Interface, or ISSI, which is a component of the second phase of the Project 25 digital radio standard. Participating in the webinar -- which is archived on MRT's web site and can be viewed free of charge -- were Roy McClellan, director of standards and regulatory for EADS Secure Networks North America and the chairman of APCO's P25 ISSI Task Group; Craig Jorgensen, APCO P25 project director; and Charles Werner, chief of the Charlottesville, Va., fire department and a member of the SAFECOM Executive Committee.

The ISSI connects disparate P25-compliant systems by establishing roaming between authenticated users, including both individual and group calls, via an IP-based software protocol stack that can reside in the users' handsets or in a gateway device. (There's a lot more to it than that, but I'll let you get the full details by viewing the webinar -- McClellan and Jorgensen did an excellent job of explaining the deeper layers of how the interface works and Werner provided outstanding perspective on what it means to first responders.)

The most critical element from a first-responder perspective is that when a major incident occurs, agencies from across the affected region that are utilizing ISSI-compliant equipment can establish interoperable communications in a fraction of the time it takes to cross-patch or establish such communications via a non-ISSI-compatible gateway device. It's an interesting wrinkle considering that interoperability wasn't on the radar screen when P25 first was contemplated -- the initial goal of the standard was to drive down the cost of public-safety-grade digital radios. The idea was that allowing agencies to mix and match P25-compliant handsets would allow them to break the ties of proprietary systems, which in turn would force vendors to be more cost-competitive. "That changed after 9/11," Jorgensen said. Interoperability became a critical goal.

For the ISSI to effectively deliver interoperable communications, certain things must be in place. First is an IP network architecture. Traditionally, public safety has been wary of -- and even dismissive towards -- IP technology, largely because of concerns over latency, which can be a real problem when it comes to urgent communications. But Werner believes that mindset will change. "Public safety has had a resistance to move forward because there haven't been proving grounds to demonstrate that [IP] meets our needs. ... Once we are able to see and make sure the programs are in place to validate the working environment, I think you'll see public safety very quickly want to embrace [the] technology," he said. (According to McClellan, while no ISSI test lab currently exists, work is ongoing to develop an ISSI certification test.)

Planning also is a must for the ISSI to work as intended, McClellan said. "Operators have to pre-plan talk groups, they have to pre-plan who the allowed roamers will be, because ... you don't want to have a flood of people with compatible radios coming in and taking over your system," he said.

McClellan acknowledged that the ISSI will require more planning "than ever before" on the part of network managers, who also will have to constantly monitor their databases to ensure that they reflect "how you want the system to operate, who you want coming into your system." Though such a commitment might seem onerous to some agencies, McClellan stressed it will be worth the effort. "That's another level of management that in the long run could cost you more money but will provide you with a great deal of benefit."

I could go on and on, because what I've described here only scratches the surface of the chat these three had during the hour or so that we spent together. I know I learned a lot from this webinar, which currently is available 24/7 by clicking here. I am confident you will, too, and urge you to tune in. Besides, you can't beat the price.

E-mail me at gbischoff@mrtmag.com.