Messages arrive at a group of service channels in accordance with a time-dependent Poisson process. An arrival either (1) immediately begins k-stage Markovian service if an empty channel is reached, or (2) balks and enters a retrial population if the channel sought is busy. Diffusion approximations to the number of messages in service (each stage) and in the retrial population are derived by writing stochastic differential (I+0) equations. Steady-state distributions are found and compared with certain simulation resultssupported in part by the National
Science Foundation, Grant AG46 7, at the Naval Postgraduate School, and the Air Force Office of Scientific Research, Grant AFOSR74-2642, at Carnegie Mellon University.http://archive.org/details/gaussianapproxim00gaveN
