FPIC ISSI/CSSI Focus Group Releases Features and Functions White Paper on P25 Patching and Regrouping


Author: Brian Heitman, Cybersecurity and Infrastructure Security Agency (CISA), FPIC Federal Lead Coordinator

The Federal Partnership for Interoperable Communications (FPIC) has released the Patching and Dynamic Regrouping: Project 25 (P25) Inter-RF Subsystem Interface (ISSI) and Console Subsystem Interface (CSSI) Features and Functions document. This is the second document in a P25 informational series focused on this specific ISSI/CSSI function that provide critical life-saving and interoperable communications capabilities to public safety users. This document - along with other documents in the series – is a byproduct of discussions within the FPIC ISSI/CSSI User Focus Group and is intended to increase awareness of P25 features, terminology, and implementation considerations specific to ISSI/CSSI deployment. 

Properly enabling and using group regrouping across an ISSI or CSSI – and thus across multiple P25 systems – can be technically and operationally complicated and challenging. While most end users and system operators understand how to patch and regroup their users within a single system, the FPIC ISSI/CSSI User Focus Group—a P25 user group of ISSI/CSSI early-adopters—found that the complexities can quickly become overwhelming for those looking to use these features across multiple systems.

With the publication of this document, P25 system planners and administrators can advance their understanding of the technology and potential roadblocks identified by other users. Readers can expect to learn more about patching and regrouping terminology, technical and operational considerations, potential use cases, implementation variables, applicable standards, and available resources.

To learn more about P25, ISSI and CSSI, and the FPIC, please visit cisa.gov/safecom/fpic or contact FPIC@cisa.dhs.gov.