ISSI and CSSI Implementation Guidance

Author: Jim Downes, Cybersecurity and Infrastructure Security Agency (CISA)

The Federal Partnership for Interoperable Communications (FPIC), in conjunction with SAFECOM and the National Council of Statewide Coordinators (NCSWIC), has published a guidance document for the emergency communications user community concerning implementation of Project25 (P25) Inter-RF Subsystem Interface (ISSI) and Console Subsystem Interface (CSSI) technologies.

As the public safety community continues to recognize the importance of land mobile radio (LMR) operability and interoperability, interest in ISSI and CSSI technology has increased. Given this heightened interest in both technologies, the FPIC developed an ISSI/CSSI User Focus Group to:

  • Explore the ISSI/CSSI technology offerings;
  • Document successful deployments, existing challenges, and impediments to deployments;
  • Illustrate the complexities of ISSI/CSSI implementations; and
  • Identify actionable solutions for addressing implementation challenges.

The ISSI/CSSI User Focus Group developed the Best Practices for Planning and Implementation of P25 Inter-RF Subsystem Interface (ISSI) and Console Subsystem Interface (CSSI): Volume I to address pre-planning, partnerships, and governance practices that are essential for planning an ISSI and/or CSSI implementation. The document—which is the first in a series of “best practices” documents—includes a one-page “Best Practices Checklist,” incorporating important steps such as developing a thorough understanding of what ISSI- and CSSI-enabled systems can and cannot do, and coordinating ISSI governance with existing systems management and governance. Volume 1 also details benefits of interoperability enhancements and the potential for infrastructure sharing through an ISSI/CSSI for those agencies interested in implementing either or both technologies.

The best practices contained in Volume 1 are an extensive collaborative effort of the FPIC ISSI/CSSI User Focus Group, which primarily consists of non-federal (state and local) public safety entities. The Joint SAFECOM-NCSWIC Technology Policy Committee also reviewed and approved the document prior to approval by the SAFECOM and NCSWIC Executives Committees (ECs).

The Best Practices for Planning and Implementation of P25 Inter-RF Subsystem Interface (ISSI) and Console Subsystem Interface (CSSI): Volume I document is available at For those interested in learning more about ISSI and CSSI implementation, or for those interested in FPIC-related activities, please visit for more information.

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