E F Johnson Company 2425M70 Benutzerhandbuch

9-3

Frame Sync Seek Period - Selects the amount of time the radio listens for a frame sync 
sequence before a packet is transmitted. Times are 0 to 5000 msec., in increments of 50 
msec. The default is 750 msec. 

Tx Short Random Range - Selects the maximum amount of time the radio waits to 
transmit once the first qualified FS is received indicating the channel is clear. Times are 
50 to 500 msec., in increments of 50 The default is 50 msec. 

Tx Long Random Range - Selects the upper range of the random range. When the 
radio detects a busy, the radio uses a random time within this range (Back off delay) to 
determine when to retransmit the packet. Times are 50 to 5000 msec., in increments of 
50 msec. The default is 2000 msec. 

Tx Response Random Range - Selects amount of time radio waits before rechecking a 
channel's status once a busy channel status symbol has been received. Only applies to 
ACKs. Times are 50 to 1000 msec., in increments of 50. The default is 1000 msec.

The radio connects from its MDP Interface to the RS232 COM port of the computer using 
the P25 Mobile Data Peripheral (MDP) Interface cable.

In order for the radio to access data service on a trunking system, it must be a valid user on 
the system and it must be affiliated to an RF site. Once this is accomplished, the radio 
must request data services from the trunked system through the process of context 
activation; a data registration of the radio with the system. Context activation is initiated 
from the radio. 

In an EFJohnson Technologies mobile radio, context activation is automatically initiated 
when the user selects a P25 trunking system with either data registration enabled or OTAR 
enabled. During a context activation, the mobile radio attempts to access a packet data 
channel (PDCH) at the site and send it its request for data services. If the context 
activation is successful, the mobile subscriber will receive a response containing a IP 
address. This IP address will be used by the mobile radio as a source IP address for all 
inbound data messages sent, and is used by the host application as the destination IP 
address for all outbound data messages.

If for some reason the context activation fails, the mobile radio will not be allowed to use 
data services on the trunked system. If a PPP link is established between the portable 
computer and mobile radio without the radio context activated, any data transmitted by the 
computer to the radio is ignored.