textfiles/phreak/motorola.txt

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MOTOROLA TRUNKING SYSTEM
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This file is an over view of the Motorola Trunking system.

The concept:

   Trunking is a means of having a large amount of Two way radio users on a
few channels without the bother of waiting for the other users to clear a
channel or as in conventional repeaters having all other users on that
channel able to monitor your voice traffic.
  Interconnect to the telephone lines available as an option.This allows
phone calls to be made and recieved as well as dispatch.


The Equipment:

   Trunked systems in the U.S. currerently are all in the 800 MHZ range with
the systems being repeater type systems. The main differences is where to put
the logic and control package and what type of signalling system used. 

   The MOTOROLA system was designed with the logic in a central control unit
located at the base repeaters and a primarily digital format for signalling
between mobiles and the system. Data at 3600 baud is primarily used, also
used is 150 baud and 3 tones (1800 hz,105 hz,and 163 hz).


Terms used:

   For our uses we will suppose that the user is a rapid package delivery
service with roving supervisiors,roving expiditers,standard delivery people
and you the Boss.


FLEET: The entire group of mobile units and portables.

SUBFLEET: A user defined section of mobiles,portables, and or base units. A
subfleet can be just the delivery people and a base;or the Boss and his
supervisiors or any other combination needed. The mobile units can be fixed
to one subfleet or be able to move between subfleets.(numd<6D>r of subfleets
acsessable by a single mobile can be restricted). Up to 15 subfleets per
fleet and numbers of fleets are limited only  by the number of channels in
a system; to a max of 20 channels with 305 fleets.


We will now run through a call on a basic system. The system is 5 channels
with one channel dedicated to data. Data channel is 3600 baud only.

When the mobile is turned on it scans for the continuously transmitted
background data stream. This stream also contains the system Id. The mobile
if assigned to this system will decode the Id and sit on this channel. If a
conversation for this mobile is in progress then the mobile decodes the data
and joins the in progress conversation.

When the mic button is depressed the mobile sends on the data channel a
request for service(known as the inbound signaling word ,ISW.). The ISW
contains the following information: Fleet,Subfleet, and Unit ID.

The system hears the request and checks all channels for an activity. When
it finds one it sends back on the data channel the following:
FLEET,SUBFLEET,UNIT ID,AND CHANNEL INFORMATION. This is known as an Outbound
signalling word,OSW.

The OSW will send the mobile to a channel by programming its synthesiser.If
all channels are busy the OSW will cause a busy tone to be heard and a busy
lamp to light. The request will be held and the system will call back when
a channel is available.

With the requesting mobile now on the voice channel the system still sends
the OSW on the data channel and sends a 3600 baud handshake on the voice
channel. The handshake has Fleet, Subfleet and Unit Id in it.

When the requesting mobile decodes the handshake it responds on the voice
channel with 80 msec of 1800 hz tone.This tells the system that it is on the
voice channel.

The system responds by changing the handshake from 3600 to 150 baud data
using less devation. The 150 baud has in it Fleet and Subfleet data. The
system now sends all other mobiles that are in the same fleet and subfleet
to that voice channel. When they arrive they decode the fleet and subfleet
data and unmute the speaker to recieve the voice message. OSW still being
sent on data channel

The requesting mobile now switches to sending the subaudable connect tone
(105 hz) while voice is being transmitted.

The system hears the connect tone and holds the channel for that subfleet.

When the requesting mobile unkeys for the first time it sends a 200 msec of
disconnect tone(164 hz). It also hears the 150 baud data and unmutes the
speaker.

The disconnect tone starts a time out timer in the system.

All mobiles now on the voice channel may use the channel. Each time any
mobile keys up it sends only connect tone. This tone tells the system that
the channel is in use and resets the time out timer.

When the conversations are done the timeout timer will expire in the system
causing a disconnect data word to be sent on the voice channel.This mutes the
speakers of all the units on that voice channel and all units return to the
data channel. The OSW on the data channel is dropped.

The system will put that fleet id in the recent user queue.It will have first
call on the system instead of a new request by a different subfleet. This is
to ensure no waiting of a channel in the middle of a voice message if someone
lets the system drop out.

This system has a lot of nifty other features including what I call the Boss
call and the call from on high. As this is long enough already,I will save
them for another time.

If you have any questions leave a msg in the forum in section 3 and I will
be glad to give you any information I can.

JOE BARTLETT 70675,306  ALT.SYS.COMS.