What Happens When Trunk Systems Fail?

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What happens when a trunk system fails?

Where do the radio users go?

How do they communicate?

In this session, we’ll go over how trunk systems are supposed to work, what happens when they fail, and what can happen if an administrator plans for failure.




What You Need To Know

  • I was able to watch our new P25 system fail several months after it was populated with radios and users
  • These users were part of the county police system and they needed to fall back to cell phone communications while the system was offline
  • Trunk systems are a pool of frequencies with group of users called Talk Groups
  • All radios on the system listen to the control channel, which acts as a director, and tells all users what frequencies to go to and when to go.
  • What happens when that controller fails?
  • If the radio fails, we would have the alternative control channels kick in and resume control of the system.
  • The entire site could go offline or become an island site
  • Or we can have full loss of all trunking, and this is called Failsoft in a Motorola systems
  • When we are in fail soft mode, a system acts as a conventional repeater system
  • Radios are assigned a home frequency based on the talk group they are currently using.
  • The trunk system will send out a beacon to alert the radios they are supposed to fall into Failsoft mode, and all radios will beep to notify the end user they are in Failsoft.
  • As a scanner radio user, we would need to program the trunk system’s voice channels in our radios as conventioal frequencies in order to continue to hear the system once it is in Failsoft.
  • A good System Administrator would have thought of a backup plan and would have programmed a backup zone into all the radios on the system.
  • You might be able to find your local county’s radio guides by doing some google searching for the trunk system.



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