This was written to help all radio users on the Regional Radio System understand what to do in the case their radios begin to display "Site Trunking". On March 01, 2016 Galveston County transitioned from the analog smartzone radio system to the new P25 digital simulcast system. The Galveston County P25 digitial simulcast system consists of four towers within Galveston County, the Galveston Tower, the Texas City Tower, the Ginger Road Tower and the League City Tower. The way that simulcast works is that the central site controller sees all four towers as a single site. This results in better and more efficient radio communications. The Simulcast System is connected to the central site controller and that central site controller acts as the manager for radio traffic on the system. As long as the network is in place and connection to the site controller is active the radios will be able to communicate throughout the entire coverage of the regional system and not just within Galveston County.
If a significant failure causes the Simulcast System to lose it's connection to the central site controller (possibly due to a zone controller failure, a fiber line cut or sometimes scheduled maintenance), the simulcast site will operate independently in “site trunking” mode. The radio display will alternate between “SITE TRUNKING” and the name of the selected talkgroup. It is important to understand that when the simulcast system is "site trunking" the four towers in Galveston County are isolated from the rest of the network. This could cause potential radio communication issues. Normally nearly all radios within Galveston County would be affiliated to the Simulcast System so site trunking should not effect most radios in the field. However if a radio roams outside the simulcast and then affiliates to another tower, that radio will not communicate with radios on the simulcast system. For example if the Simulcast system is "site trunking" and your radio is affiliated to the Friendswood tower then your radio would not be able to communicate with the radios still affiliated to the simulcast system.
In order to alleviate this potential problem during "site trunking" all radios have been programmed to include several backup zones. These zones are programmed to operate on only a single tower. The procedure to follow during "site trunking" is to have all radio users in the field manually switch their radios to the GC SIMULCAST zone. This way all radios will be on the same tower for the duration of the "site trunking" event and no calls will be missed. When the connection to the site controller has been restored all radio users can then switch back to the main zone and begin to operate in wide area once more.
Site Trunking is handled in a similar way for radio dispatchers in the PSAPs. On a day to day basis a dispatcher will operate from the front folder which contains all the talkgroups that the dispatcher needs for communications. If a significant failure causes the radio tower sites to lose their connection to the prime site (possibly due to a zone controller failure, a Fiber line cut or sometimes scheduled maintenance), the Simulcast towers can operate as an independent cell in “site trunking” mode. If this happens it is important for the dispatchers to select the backup folder and operate from there for the duration of the event. Backup folders are directly tied to radios in the radio room of the various PSAP's. These radios are selected to operate only on the GC Simulcast cell and will not "roam" to another tower. This way all radios in the field and the dispatch consoles will be on the same tower for the duration of the "site trunking" event and no calls will be missed.
If you have any questions about "site trunking" or what to do if this happens please call the Communication District at (409) 935-3911.
Click here to watch a short Youtube video clip explaining how to swtich to your radio to the GC Simulcast zone.