Codan Radio P25 Training Guide - Manual (Page 40)

TRAINING GUIDE | P25 RADIO SYSTEMS
Chapter 3: P25 Technical Information Page 32
Emergency indicator
The Link Control word (LDU1) contains the 1 bit Emergency indicator fi eld. The Emergency indicator
is embedded in group voice messages to indicate an emergency condition.
The emergency indicator bit is designed to be selectable by a switch or programming in the subscriber
units. The emergency indicator bit can be set as follows:
%0 routine, non-emergency condition
%1 emergency condition
(See Chapter 4; Figure 4-6)
Link Control Format
The Link Control Format is an 8 bit fi eld contained in the Link Control Word (LDU1). The Link Control
Format is used to specify content of the Link Control Word. The Link Control Format is not accessible
to the user.
(See Chapter 4; Figure 4-6)
Packet Data Unit Digital Codes
There are other digital codes used in the Packet Data Unit such as the Service Access Point Identifi er
(SAP Identifi er), Full Message Flag (FMF), etc. These digital codes are defi ned in more detail in
Chapter 4: Anatomy of the Common Air Interface.
P25 VOICE MESSAGE OPTIONS
P25 Radio Systems process voice messages in a variety of modes. P25 radio systems operate in
both P25 digital mode and conventional analog mode. Voice messages can be sent over a 12.5 KHz
bandwidth analog channel using standard analog call procedures with analog signaling (CTCSS, DCS,
etc.). Some manufacturers also have equipment that will allow operation in 25 KHz analog bandwidth.
P25 voice messages can also be sent in P25 digital mode. P25 voice messages can be sent in either
encrypted (secure) or unencrypted (clear) mode. The secure / clear operation is typically an option that
is required to be installed in the subscriber units.