NIST and NTIA's Institute for Telecommunications Sciences (ITS) are working with DHS's SAFECOM Program to support the emergency response community and industry in their effort to accelerate the development of Project 25 (P25) standards for interoperable communications.
One of the the keys to achieving near-term interoperability of P25 Radios is to bridge between potentially non-interoperable RF systems using standard IP-based Protocols. In P25, this bridge is referred to as the Inter-RF Sub-System Interface (ISSI). The ISSI suite comprises protocols that are built on top of Session Initiation Protocol (SIP) for call control signaling and Real-Time Transport Protocol (RTP) to support Push to Talk (PTT).
NIST's Advanced Network Technologies Division is supporting Project 25 by developing tools and technologies for testing and measuring ISSI equipment and infrastructure. Such tools include the Department of Commerce ISSI Evaluation and Test System (DIETS) which serves as an ISSI reference implementation and an ISSI test and evaluation framework.