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Site Trunking is, hands down, the most misunderstood component of the statewide 800 MHz system and of any shared communication system. When the system goes into Site Trunking, many users think that the radio system is down. This is an inaccurate perception. When the radio system goes into Site Trunking , it is still working, but at reduced capacity.
Even though the system is working as designed, a system in Site Trunking can frustrate users out in the field and in the dispatch center. A clear understanding of Site Trunking concepts and practices will alleviate some of that frustration and can help users recognize when their radio goes into that mode.
Each radio in a shared system, such as Indiana’s 800 MHz SAFE-T system, affiliates with one site (tower) at a time in one Zone Controller and to one talkgroup. Sites are linked by T-1 lines, phone lines or microwave, which creates a network of repeated connectivity. Under normal circumstances, the system operates as a Wide Area network, which allows users to communicate not only with others affiliated with the same site, but also with those affiliated with other sites across the network. Users can communication across cities, counties and even across the state.
When connectivity to the T-1 line, phone line or microwave is severed, the system goes into Site Trunking. The site will continue to “trunk” on channels at that site and users affiliated with that site can communicate with other users affiliated with the same site. They cannot, however, communicate with users affiliated with a different site and vice versa since their connectivity has been temporarily severed.
Each dispatch center should have a site trunking plan and should test and exercise this plan! IPSC recommends:
IPSC is available to help agencies understand site trunking, create site trunking plans, and determine if the system is optimally configured for your agency needs. IPSC also has the ability to remotely place a site into Site Trunking for testing and exercises! Use the contact links below to request assistance.
MYTH #1: The site is completely down when in Site Trunking. FACT: The site is still operational, and users of that site can communicate normally. Users cannot, however, communicate with those affiliated with other sites since their connection has temporarily been severed.
MYTH #2: It is necessary to report the site to the NOC. FACT: It is not necessary to report Site Trunking issue to the Network Operations Center (NOC). The NOC and Motorola are notified immediately when a site goes into Site Trunking. The only exception to this rule is if the site continuously goes in and out of Site Trunking. Then report the issue.
MYTH #3: IPSC controls all the T-1 lines that connect the towers. FACT: IPSC does not have control over the T-1 lines. The T-1 lines are controlled by the telephone company.