Bridging Systems Interface

Bridging Systems Interface is a standard protocol for communicating with physical interfaces which attach analog or digital voice radios to digital data networks—known as 'Radio over IP'--to make easier the use of remote radios by local users, and the sharing of radios by multiple users, in the service of improving emergency communications interoperability. The standard is promulgated by the SAFECOM program in the US Department of Homeland Security's Office for Interoperability and Compatibility, specifically, the VoIP Working Group .
Technical Details.
The working group has broken down the problem of moving public safety communications audio over data (usually TCP/IP) networks into 5 specific interface points:
To quote the working group's pseudo-RFC standards proposal :
This interface is based on SIP, the Session Initiation Protocol, and the document provides standardized mappings between that protocol and the actual functions that are provided by individual radio hardware, whatever those might be.