Trunking is a system that allows multiple users to share a limited number of frequencies. By using a process known as "time-division multiple access" or TDMA, trunking allows each user to have full use of a frequency for a short period of time, then hands off the frequency to another user. This process is similar to how cell phones work, and allows many more people to use a given number of frequencies than would be possible without trunking. In addition, trunked systems often make use of "dynamic channel assignment" which further increases the efficiency of the system by automatically reassigning channels as needed to accommodate changes in usage patterns.