User Manual

SGD-SB2025NT-TUM, Part 1
Jan 12 Page 12 INTRODUCTION
In the Tx direction (outgoing), the TM constructs the P25 frames from the voice data bit stream
coming from the Central NI or DFSI in IP packets or from the voted Station NI if in Talkthrough
(T/T) mode. The TM sends out the P25 frames in IP packets to every Station NI on the channel.
In non-P25 mode, the packets from the Central NI or voted Station NI are basically replicated for
each Station NI. In the Rx direction (incoming), the TM reads the data in the packets to determine
the mode of signal. For P25 signals, the TM checks for errors and applies error correction.
Received Signal Strength Indication (RSSI) information is used for signal quality comparison
measurements, so that the site offering the best incoming signal is selected or voted.
The site that is presenting the best quality signal will be selected and data packets passed to the
Central NI or DFSI, which will decode the plain or P25 audio as appropriate and output analogue
audio to the console system with any corresponding signalling.