Motorola recently announced the first-ever deployment of Inter RF Subsystem Interface (ISSI) gateways between live P25 networks in Arizona, a test that could prove to be a significant step in the “network of networks” vision that many in public-safety communications believe would enhance interoperability and radio coverage.

Although Motorola has participated in ISSI demonstrations conducted at trade shows during the past year, the Arizona deployment marks the first time that ISSI gateways have been used to link two live networks—in this case, Motorola P25 networks owned by the city of Phoenix and the county of Yuma—said Bob Schassler, corporate vice president for Motorola’s government and public-safety products organization.

With both entities having P25 systems, Phoenix and Yuma personnel could talk on each system. However, if Yuma users entered the Phoenix footprint and began talking on that network, they would not be able to talk to users operating on the Yuma network, Schassler said. Installing an ISSI gateway—as well as two additional sites paid for by the state that linked the networks—resolved that issue, he said.

“Now, all of a sudden, you have an RF footprint for the county of Yuma folks that has expanded all the way to Phoenix and vice versa,” Schassler said during an interview with Urgent Communications. “You had two separate networks, and all of a sudden, from an end user’s perspective, those two networks look like one network now. So an end user doesn’t have to change a system on their radio or change stations or do anything like that. “

No mission-critical calls were delivered by the prototype ISSI gateways, but about 20 users conducted “extensive drive testing” to evaluate the technology, “which did exactly what they wanted it to do, as far as interoperability between the two systems and handoffs,” Schassler said. Motorola plans to make the ISSI gateway used in the test commercially available during the fourth quarter of 2009.

Helping drive state participation in the demonstration was Arizona Gov. Janet Napolitano, who is awaiting Senate confirmation of her new appointment to head the Department of Homeland Security as part of president-elect Barack Obama’s new administration.

“Our job is to magnify Arizona's innovation capacity to build a foundation for the future,” Napolitano said in a statement. “The Motorola ISSI gateway trial is an excellent example of driving innovation, which will enable our state with agency interoperability to best protect our residents and visitors.”

While the demonstration used the ISSI link to connect two Motorola P25 networks, the company is designing the ISSI gateway to work with P25 networks built by any vendor, Schassler said.

“We want to get it to the point where we know that there are no issues with Motorola P25 talking to a Motorola P25,” he said. “Once we get that to the point where there’s no software bugs or glitches and we feel like that’s a product where we know what we have from a development and reliability perspective, then we’ll be ready to introduce other P25 networks, knowing that, if the other networks comply to all the P25 standards and specifications that are there, it will also interoperate.”

For states that cover a large geographical area, using ISSI gateways to link networks built by local entities may be the most economical way for statewide systems to be built in the future, Schassler said.

“Conceptually, where this could go is that the dozen-plus P25 networks throughout the state of Arizona all get linked up with ISSI links,” he said. “Then, you could have one major footprint if you will.

“For Gov. Napolitano trying to get a statewide system, it’s a lot less investment by the state and a lot quicker to market with an interoperable system,” Scassler added. “It potentially could cut the investment in half and cut the time significantly as well, compared to building a statewide system from scratch for Arizona.”