PSTA: P25 DFSI Best Integration Protocol for LMR/LTE Interoperability
Tuesday, August 06, 2019 | Comments

A Public Safety Technology Alliance (PSTA) subcommittee identified the Project 25 (P25) Digital Fixed Station Interface (DFSI) as the best integration protocol standard for LMR and Long Term Evolution (LTE) interoperability. The subcommittee said an enhanced radio over IP (RoIP) protocol could also be developed to address DFSI’s shortcomings.

The PSTA LMR/LTE Interoperability Subcommittee outlined its recommendations in a report released this week.

The committee, established to identify integration protocol standards suitable for public-safety users operating across LMR and broadband PTT technology, made the recommendations based on input from PSTA industry and public safety. Additional input on the recommendations is welcome, a PSTA statement said.

“Cost of implementation is always an important consideration in public safety, and the subcommittee decided on DFSI as the primary recommendation from the PSTA because it is an affordable solution that fills the stated need for a viable and broad open standard,” said LMR/LTE Interoperability Subcommittee member Andy Seybold.

The report said the P25 Inter RF Subsystem Interface (ISSI)/Console Subsystem Interface (CSSI) is “technically ideal but very expensive.”

Using the P25 DFSI as an LMR gateway protocol has several advantages, outlined in the report, along with five shortcomings. The report said the DFSI has provisions for “manufacturer extensions” that allow extending the protocol’s capabilities to address many of the shortcomings.

The report also said an enhanced RoIP protocol could also address the limitations. “The challenge will be to have a new protocol recognized and published as an open standard by an SDO (standards development organization), which could be a two- to five-year process,” the report said. “The subcommittee is considering the DFSI for the short term by virtue of it being an existing, extensible standard, and potentially RoIP for the long term with the hope to be entirely suitable for the intended application.”

“It is critical to have seamless voice communication between legacy LMR systems and public-safety LTE-based communications as we see more and more first responders relying on LTE each day,” said Jeff Johnson, PSTA board member.

PSTA said the subcommittee will update its recommendations as necessary. No timeline for final recommendations or future work was given, but the report said the subcommittee plans to draft DFSI extensions to address three of the shortcomings to enable integration with analog FM LMR systems and to fully examine the capabilities of an enhanced RoIP protocol. “We plan to draft DFSI extensions to address the remaining shortcomings, and perhaps publish a draft standard of an enhanced RoIP protocol in the subsequent sprints,” the report said.

A joint working group of the Alliance for Telecommunications Industry Solutions (ATIS) and Telecommunications Industry Association (TIA) is also working on LMR to LTE interworking and released a draft architecture document. More details are in the February 2019 issue of MissionCritical Communications.

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