ABSTRACT
Queues can be formed at the nodes of a network or on its arcs. The simplest form of a queueing network is a set of parallel servers supplying substitutable services. An arriving customer selects one of these queues, or balks. In the case of a central planner, customers are routed to the servers. Another simple topology is that of serial or tandem queues. In this case services are complementary and customers typically need all of them. More complicated topologies involve selection of substitutable routes with each supplying complementary services. Further complications arise when routes have different source and destination nodes. For example, it is possible for customers to leave a serial network at any node. In the case of complementary services some variations dictate a given order while others don’t.
