10.2 Queuing Options
10.2.1 First in, first out queuing overview

In its simplest form, FIFO queuing involves storing packets when the network is congested and forwarding them in order of arrival when the network is no longer congested. In some instances, FIFO is the default queuing algorithm and requires no router configuration. However, FIFO has several shortcomings. Most importantly, FIFO queuing makes no decision about packet priority; the order of arrival determines bandwidth, promptness, and buffer allocation. Nor does it provide protection against ill-behaved applications (sources). Bursty sources can cause long delays in delivering time-sensitive application traffic, and potentially to network control and signaling messages. These large file transfers and other high-volume network applications often generate series of packets of associated data. These related packets are known as packet trains.

As shown in the Figure, packet trains are groups of packets that tend to move together through the network. These packet trains can consume all available bandwidth and starve out other traffic.

FIFO queuing was a necessary first step in controlling network traffic, but today's intelligent networks need more sophisticated algorithms.