This is a survey on polling systems, focussing on the basic single-server multi-queue polling system in which the server visits the queues in cyclic order. The main goals of the paper are: (i) to discuss a number of the key methodologies in analyzing polling models; (ii) to give an overview of recent polling developments; and (iii) to present a number of challenging open problems.
Assumption 7The service order within each queue is First-Come First-Served (FCFS). This assumption was almost universally made in the polling literature until the work of Wierman et al. (2007). In Sect. 7, we will discuss non-FCFS service orders.Assumption 8 The times to switch from Q i , i = 1, 2, . . . , n, to the next queue are assumed to be i.i.d. random variables, generically denoted by S i , with distribution S i (·) and LST σ i (·). All switchover times are assumed to be independent of each other and of the interarrival and service times. When the switchover times between successive queues are all zero, a special situation arises. If the system has become empty after a visit to, say, Q i in the case of zero switchover times, then the server is assumed to visit queues Q i+1 , . . . , Q n (which now takes zero time) and stay in front of Q 1 (see Sect. 4). In the case of non-zero switchover times, the server is assumed to keep switching in an empty system.
Assumption 9As soon as a customer has been served, it leaves the system. At some places, we briefly mention the case of customer routing; a served customer might rejoin the same queue, or join another one.