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An essential component of any trunked mobile radio system is the signalling protocol used for the purpose of call establishment. The paper presents computer simulation results of one such protocol designed for use with dedicated signalling channels and incorporated within the Advanced Mobile Phone Service. The latter is a high-accuracy cellular-structured mobile radio system currently being implemented by AT & T in Chicago, Illinois. In particular, the paper examines the signalling channel blocking probability, the effect of varying system parameters on this blocking probability and the mean delays encountered in obtaining a signalling channel. Also of concern is the influence of the signalling protocol on the subsequent voice-channel blocking probability. To this end, a fixed voice-channel assignment scheme and an Erlang B service discipline were included in the simulation model. It is determined that if two or more automatic reattempts to gain access to the system are permitted, then only one signalling channel per cell is required in order to maintain the signalling-channel blocking probability below 2% for all traffic loads likely to be encountered in practice.