This chapter illustrates the usefulness of analytical modeling for studying a component of a local area network (LAN), in this case the control scan time. It gives an introduction to queuing techniques for the modeling of computer communication networks. The token bus distributed processing system consists of processors connected to interface units which, in turn, are connected by a common communication medium-the global bus. The allocation of the bus is controlled by the cyclic passing of tokens in a sequential manner from lowest numbered interface unit (IU) to the next highest until all numbered IUs have been interrogated and serviced. The analytical models developed for the token bus will be presented in an order reflecting an increasing degree of complexity and, consequently, a relaxation of the corresponding mathematical assumptions. The Honeywell experimental distributed processing system consists of processors connected to interface units that are joined by a bit-serial global bus. Bus allocation is governed by the vector-driven proportional access mechanism.