Message Trunking:
Message trunking is the earliest form of call signaling with its roots in Type I trunking. When message trunking is used the station will hold for a period of time after the subscriber unkeys their microphone. This period between unkeying, and when the station actually drops the call, is called hangtime. [I believe the default hangtime is half a second.] During this time the system still reserves the station for the previous group, private, or data call. At the end of the hangtime the disconnect tone is sent causing all radios to return to the control channel.
One problem with Message trunking is with subscriber replies. During this hangtime a subscriber, no matter whether they are a valid or invalid subscriber, can make a call. This allows for malicious use of the system.
Transmission Trunking:
Transmission trunking differs from Message in that there is no hangtime. Once the subscriber unkeys their mic the station drops the call and all radios return to the control channel. This makes for the most efficient use of channels within the system.
PTT-ID Trunking:
PTT-ID trunking is built upon message trunking yet fixes the problem of authentication for replying subscribers. Any time a subscriber wishes to reply to a call in progress or in hangtime it must send its information in to the control channel first before it can make the call. Once the replying subscriber is given a call grant he or she can continue their call. This maintains a totally closed system based on the SAC database.
©2003 Wayne Hayes
To contact me: 2microwave6 -> thebriarpatch.org
05/12/2007
All trademarked names are property of their original owner and are used here for educational purposes only.