# Trunking theory Calculate the grade of the service in terms of blocking. Statistical models of channel usage by subscribers. Initially developed for the [public switched telephone network](public%20switched%20telephone%20network.md) Not everyone makes a call at the same time! Same theory can be applied to mobile cellular networks. - How many control channels are needed per voice channel per cell? - [1G](../Telecommunications/1G.md) AMPS has 3 channels per cell but can support 56 voice channels! - We don't need alot of channel! We can guarantee a certain percentage of communication services (best case) Wifi doesn't aim for 0% [BER](bit%20error%20rate.md). ## Grade of Service The probability a call is blocked is the probability that when a random user attempts a call, there is no available channel to handle the call. ### Approaching blocked calls #### Lost calls cleared A busy signal is immediately given to the caller. The blocked call is rejected and dropped from the network. User waits a random amount of time and tries again. This is the focus of [TELE4652](../../../Spaces/University/TELE4652/MOCs/Mobile%20and%20Satellite%20Communications.md). #### Lost calls delayed Incoming calls finding all channels are being used, call will be held for a fixed delay to see if a channel becomes available. If no channel available, a busy signal is given to the caller. [^1] # References [^1]: