Codan Radio P25 Training Guide - Manual (Page 26)

TRAINING GUIDE | P25 RADIO SYSTEMS
Chapter 2: P25 Interface Standards Page 18
INTER SUB-SYSTEM INTERFACE
The Inter Sub-System Interface (G) is under development.
The Inter Sub-System Interface (G) or ISSI permits multiple RF Sub-Systems to be interconnected
together into wide-area networks. The ISSI defi nes a multi-channel digital interface supporting standard
protocols to enable interoperability utilizing mobility management and wide-area service support
functionality. The interface is designed to give system designers the fl exibility to combine any number
of RF Sub-Systems of any size. The Inter Sub-System Interface also provides a common meeting
place for RF Sub-Systems of different technologies (TDMA, FDMA, micro-cell) and different RF bands.
This interface is optional, and need only be supported when intercommunication amongst and across
RFSS’s of Land Mobile Radio systems is desired.
Although a P25 subscriber radio may only operate freely among systems with the standard P25 common
air interface, the P25 ISSI has the potential to connect between different radio or telecommunications
networks as long as they also support the ISSI interface.
The ISSI messaging defi nes the basic structures to be shared among all equipped RFSS’s. The
ISSI can be supported on any possible networking confi guration, from a simple star confi guration to
a full mesh, to an intelligent network. This can consist of private links and network support, or may be
public links and network support confi gured as a private network. Any intervening network supporting
the information of an ISSI link needs to preserve the ISSI messaging packet, but may intermediately
represent the ISSI packet in whatever convenient form (e.g. ATM cell) is available.
The ISSI will support:
•
mobility and data management,
• wide area service control,
• service transport,
• end to end protection of signaling information,
• trunking.
• other network interconnection.