EADS North America introduced last week at the Association of Public-Safety Communications Officials conference in Orlando a solution that leverages the recently approved inter-RF subsystem interface, or ISSI, protocol to establish interoperable communications between disparate Project 25 devices. The company demonstrated interoperability between a P25 800 MHz trunked system and a P25 VHF system using the solution at its booth during the APCO conference.

The P25 ISSI Interface is unique in that it requires no new hardware or infrastructure and ties together multiple P25-compatible systems without a proprietary gateway, said David Cerqua, general manager of EADS Secure Networks North America. “It’s as simple as switching to a talk-group channel,” Cerqua said, adding that non-P25-compliant radios still can be patched in through a gateway.

Cerqua said that the ISSI standard—supporting digital encrypted voice communications between multiple vendor systems using standard IP protocols for voice transport (real-time transport protocol, or RTP) and signaling (session initiation protocol, or SIP)—represents the future for P25.

“IP-based and standards-based solutions are the building blocks customers are longing for regarding interoperability,” Cerqua said.

In addition to supporting individual and group push-to-talk calls across multiple networks, the ISSI standard also supports authentication and registration of roaming radios. This allows a network to track and control its radios when they are under another network’s coverage and to control visiting radios based on interagency agreements, according to an EADS white paper published in June.

While it might seem that EADS moved with lightening speed to produce the interface a little more than a month after the ISSI standard was approved, the reality is that the interface was developed on a parallel path with the standard, according to Roy McClellan, who directs EADS regulatory and standards efforts and is chairman of the Project 25 APIC ISSI Task Group.

“We worked on it almost simultaneously,” McClellan said. “Since we worked on the standard, we understand it. And as a major contributor, we know what it’s supposed to do.”

McClellan believes the ISSI standard should be a requirement for any new public-safety radio system.

“Open standards are the key to unite agencies’ day-to-day operations, regardless of frequency or manufacturer.”