We can set up radio systems to utilize a control concept called transmission trunking.
This type of trunking service facilitates the automatic sharing of channels in a multiple repeater system. Advantages of trunking include less waiting time to access the system and increased channel capacity for a given quality of service. Since the probability of all channels being busy at the same instant is low, the chance of being blocked is much less than when only one channel can be accessed. Trunking concepts are based on the presumption that a large number of individual subscribers do not use the system at the same time.
A repeater is held for only the duration of the transmission with dispatch calls. This means that an entire conversation consisting of several transmissions may occur on several channels. Transmission trunking provides maximum system efficiency because the time between transmissions can be used by others. Some special calls, such as telephone calls, hold the repeater for the duration of the call.