Radio interoperability has long been the stated — and often elusive — goal of the public-safety sector. At last month's Association of Public-Safety Communications Officials annual conference in Baltimore, Cisco Systems gave interoperability a twist by demonstrating the ability to link analog and digital two-way radios, voice-over-IP phones, wireline phones, wireless phones and satellite phones. EADS and Raytheon JPS also participated in the APCO demonstration.

“We call that ‘network-of-networks’ interoperability,” said Lindsay Hiebert, senior solutions marketing manager for Cisco's emerging technologies group. “For the first time, first responders not only have the ability to leverage their RF radio network but also multiple networks, including commercial cellular, wireless mesh and satellite networks.”

To accomplish this, Cisco leveraged its experience in VoIP and PBX communications, according to Larry Metzger, a Cisco technical leader. “The problem we typically run into is that when we try to cross-band the resources of one agency to those of another statically, we limit the number of users on those resources and tremendously lower the overall system capabilities,” Metzger said. “So we created a mechanism based on what we learned in building IP networks between Internet service providers to create a toolkit that allows the sharing of those resources dynamically when they're needed.”

Cisco also leveraged the Inter-RF Subsystem Interface (ISSI) that was part of the second phase of the Project 25 digital radio standard. The ISSI was created to link P25-compliant devices manufactured by disparate vendors, but the ability to also use the standard to let radio and non-radio handsets communicate with each other wasn't envisioned originally, Metzger said.

Hiebert added that because the P25 ISSI standard is based on open IP protocols, “it was easy to extend” to this application.

A big advantage of the linking capability is that first responders in the field will be able to tap into expertise that normally wouldn't be available to them. For example, emergency medical personnel responding to a chemical spill would be able to speak over their radios with medical experts gathered around a VoIP speakerphone in a hospital conference room to get guidance on how to treat victims at the scene and how those victims should be triaged.

“Let's say I'm a public-safety officer responding to a domestic dispute,” Metzger said. “I arrive at the scene and the domestic dispute is in a language I don't recognize. What do I do? I can simply patch together an expert in that language who's talking to me on his cell phone. Without that capability, I'd be at a complete disadvantage and unable to deal with the situation, which could have simply been that someone fell in the bathroom, but they weren't able to communicate that” because of the language barrier.

An additional advantage of the capability is that it gives public-safety agencies a migration path to digital radio, Hiebert said, because digital handsets can be added incrementally as analog handsets are retired, and users of both still will be able to communicate with each other.

A timetable for the platform's availability remains to be set, Hiebert said.

Of course, the ISSI's primary function is to link P25-compatible devices, and that ability was on full display at APCO as well. EADS, EFJohnson, Motorola and M/A-COM combined to demonstrate interoperable communications between each company's handsets, an event that EADS' Roy McClellan, chairman of the ISSI working group, called “historic.”

“We had people coming by the first day just to look at the booth to see the four infrastructure guys' equipment in the same place — without their hands around each other's necks,” McClellan joked.

He added that curiosity soon gave way to surprise and then excitement.

“We had a lot of key players out of government and other places come to witness this, and the first time we did it, the people couldn't contain themselves — they just started applauding,” McClellan said. “We had 800, 400, 700 and 150 MHz all tied together.” McClellan acknowledged that the surprise had more to do with a “level of distrust” regarding the four vendors rather than a lack of faith in the interface.

“People really didn't believe it,” he said. “[They wondered], ‘Are these guys really going to tie their systems together and make it work? Just because they created a spec doesn't mean they're serious about it.’ One of the purposes of the demonstration was to show that everyone is indeed serious.”