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------------------------ MOTOROLA TRUNKING SYSTEM ------------------------ 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?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.