Several jurisdictions are looking to integrate the latest version of the Project 25 (P25) Inter Subsystem Interface (ISSI) into their statewide networks. Officials said the latest versions of ISSI products include more functionality and are easier to use than original versions.FirstNet Outlines Details Expected in State Plans, Information Portals
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The ISSI standard, first commercially implemented in 2010, aims to connect disparate P25 networks, regardless of vendor. For example, an ISSI gateway could connect a standalone Motorola Solutions P25 network to a Harris P25 network.
ISSI technology has not been widely deployed for various reasons including cost, complicated manual management and roaming from one P25 system to another, and lack of a Compliance Assessment Program (CAP) for the ISSI standard.
EF Johnson executives said the demand for the ISSI is increasing because of increased competition in the market. “Customers are being educated and learning more about the functionality, and there is more competition in the marketplace,” said Arindam Roy, EF Johnson director of product management for systems. “Customers are deploying systems from different vendors. As competition is growing, the need for interoperability between vendors is increasing. The vendors are working together to provide that seamless interoperability.”
Roy said that although there are no CAP interoperability tests yet, vendors are working with each other to test their ISSI products. “The vendors are working together to provide that seamless interoperability. As this demand grows and we see more deployments, you’ll see there is more push for CAP.”
The latest Harris P25 ISSI includes a site adjacency feature that allows radios to automatically roam between Radio Frequency Subsystems (RFSSs), said Tom Burkett, Harris Public Safety and Professional Communications (PSPC) product manager. “This means that the user’s radios can now receive the site adjacency information through the ISSI for sites on foreign RFSSs and its home system, which then provides them with information to spread the roaming decisions to sites beyond the home systems,” Burkett said. “For example, in the event of a car chase where an officer is traveling down an interstate and leaves his home system range, the officer would just need to focus on the incident and the radio would automatically transition to the new system without any intervention by the officer and he/she would be able to communicate the entire time with dispatch and other responding units. This feature is a large step up from the manual roaming that is available today, which requires that both systems support this feature to enable radios to roam.”
Tait Communications has a new ISSI that works between different vendors and will be undertaking further development work to expand support for Phase 2 operation, said Bill Fillman, Tait vice president of market development and solution engineering. EF Johnson’s Roy said the EF Johnson ISSI product has all the functionality that is part of the ISSI standard.
Both Missouri and Maryland have plans for the newest version of Motorola’s ISSI product, albeit linking one Motorola system to another Motorola system. Motorola’s latest product version of the technology eases management requirements, offers seamless roaming between networks and dynamically assigns unit identifications (IDs) compared to its original ISSI.1 product.
The state of Missouri plans to deploy Motorola’s ISSI 8000 system interface later this year to connect its statewide P25 VHF/700 MHz network to the Kansas City (Missouri) Police Department 800 MHz system, which is part of the Metropolitan Area Regional Radio System (MARRS). Motorola supplied both networks, and the upgrade requires both jurisdictions to have Motorola’s system 7.13 or a later version.
In July, the state of Missouri and the Kansas City Police Department are upgrading their P25 systems to 7.14 software. The ISSI packet gateway will be added to each system’s master site.
“ISSI.1 was an interim solution,” said Steve Devine, assistant director for the Missouri Statewide Interoperability Network (MOSWIN). “It wasn’t anyone’s perfect solution. It allowed baseband audio to be passed between systems, and roaming between systems required a knob change; there was no seamless transition between the systems. But it provided limited intersystem interoperability when implemented. It wasn’t a tool that made intersystem connections and roaming between systems easy from a system administration perspective but it did provide interoperability. Then the goal was to come up with a better ISSI, and that’s what we’re seeing in ISSI 8000.”
Devine said the updated ISSI is much easier to manage than the original product. A system administrator can pre-determine the parameters — unit IDs, talk groups, talk paths and sites — for one network’s users to have access to the other network. The update also includes an option to allow seamless roaming for users, removing the need for users to turn a knob on their radios to move to a neighboring radio system.
The ability for different systems using different system identifiers, regardless of the manufacturer, to be interconnected and promote interoperability is a powerful tool that can allow agencies to leverage all radio investments in their communities, not just those that were built by one agency. Using other agencies’ resources for interoperability or daily communications does, however, require the cooperation and approval of the other system administrator and owner, he said.
Devine said going forward that if the jurisdictions upgrade P25 system software at different times, the ISSI technology will still work. “This is the way it’s been explained to us,” he said. “These are our hopes.”
A Maryland First Responders Interoperable Radio System Team (Maryland FiRST) ISSI pilot is planned for mid-2015. The pilot will be with Prince George’s County, which deployed a P25 Phase 2 700 MHz system in 2010 and has limited coverage from Maryland FiRST, the statewide network. “This will allow us to test roaming characteristics as radios move from one system to the other,” said Ray Lehr, Maryland statewide interoperability director. “Both the county and state have recently upgraded to Motorola’s operating software version 7.14, which will allow for us to take advantage of the ISSI 8000 features.”
Lehr said communications officers could view the radio alias as well as a notation that a radio has roamed onto the system with Motorola’s latest ISSI technology. “This will increase awareness for dispatchers and incident commanders as multiple agencies work together on emergencies,” he said. “Maryland believes that this is a substantial benefit from the first-generation product that requires users to make manual changes in talk group selection.”
However, Lehr said there are still limitations, including no support for over-the-air programming (OTAP), over-the-air rekeying (OAR) and other features where data-driven functionality is required. “As an example, the ISSI standard does not allow for a radio to be remotely disabled when roaming off of Maryland FiRST,” Lehr said. “There are also limitations in the transmission of user location data when roaming from Maryland FiRST and onto a ‘foreign’ system. These are all important functions to support first responders, which are being addressed.”
If the initial pilot of ISSI proves successful, the state can decrease the number of sites it will deploy in other P25 Phase 2 jurisdictions. In Carroll County, for example, state plans originally called for deployment of FiRST equipment at six sites. With ISSI connectivity, the state can reduce that number to three sites in the county and receive a substantial amount of “on street” coverage from sites in surrounding counties. State system users would then only roam onto the Carroll County P25 system when they enter buildings in the county not receiving in-building signals from FiRST.
The state could use the ISSI to link a Motorola system with a Harris network in the future. St. Mary’s County has deployed a Harris P25 Phase 2 system and will present the first opportunity to test the upgraded ISSI capabilities between two different vendor’s systems.
“We currently operate Motorola APX radios in the Maryland State Police Barrack in St. Mary’s County, and they have tested their Harris radios on the MD FiRST system,” Lehr said. “While some small programming issues were encountered, both vendors’ engineering staff worked cooperatively to resolve those issues, and users are happy with the results of true P25 compatibility for voice transmissions.”
Maryland will share its results with other jurisdictions considering the ISSI, Lehr said. RCC Consultants’ Director Charles Bryson is the technical lead behind Maryland’s ISSI strategy.
“While ISSI is a standard, this does not mean that any given vendor currently supports all functionality, and it will take the support of both vendors to enable any given function,” said Tait’s Fillman. “The potential impact on traffic capacity of having Phase 1 radios roam on to a Phase 2 network needs to be understood in advance of the roaming, to avoid capacity issues.”
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