FIFO simply queues processes in the order that they arrive in the ready queue. Queueing theory is the mathematical study of waiting lines, or queues. Markov chains are the basis for the analytical treatment of queues (queueing theory). There are several efficient implementations of FIFO queues. The service supports both unlimited queues and message traffic. The NIC may distribute incoming traffic between the receive queues using a hash function. ATS queues up taxis at the LAXit waiting area. There are three different methods to parallelize priority queues. If a recipient is not reachable, the SMSC queues the message for later retry. Another approach used is to send disproportionately more traffic from higher priority queues. Binary heaps are a common way of implementing priority queues. Stacks and queues may be modeled as particular kinds of priority queues. Long queues formed at polling stations. Parallelization can be used to speed up priority queues. Agendas are typically implemented as prioritised queues.