Consider a single server queueing system in which customers arrive in a Poisson process with rate λ. These customers are identified as primary calls. If the server is free at the time of a primary call arrival, the arriving call begins to be served immediately and leaves the system after service completion. Otherwise, if the server is busy, the arriving customer becomes a source of repeated calls (a customer in orbit, a customer in pool, etc.). The pool of sources of repeated calls may be viewed as a sort of queue. Every such source produces a Poisson process of repeated calls with intensity μ. If an incoming repeated call finds the server free, it is served and leaves the system after service, while the source which produced this repeated call disappears. Otherwise, the system state does not change.