 When a customer is serviced at one node it can join another node and queue for service, or leave the network.For networks of "m" nodes, the state of the system can be described by an "m"–dimensional vector ("x"1, "x"2, ..., "x""m") where "x""i" represents the number of customers at each node.The simplest non-trivial network of queues is called tandem queues.