33.3. Fifo queue disc

33.3.1. Model Description

FifoQueueDisc implements the FIFO (First-In First-Out) policy. Packets are enqueued in the unique internal queue, which is implemented as a DropTail queue. The queue disc capacity can be specified in terms of either packets or bytes, depending on the value of the Mode attribute.

User is allowed to provide an internal queue before the queue disc is initialized. If no internal queue is provided, one DropTail queue having the same capacity of the queue disc is created by default. No packet filter can be added to a FifoQueueDisc.

33.3.1.1. Attributes

The FifoQueueDisc class holds the following attribute:

• MaxSize: The maximum number of packets/bytes the queue disc can hold. The default value is 1000 packets.

33.3.2. Validation

The fifo model is tested using FifoQueueDiscTestSuite class defined in src/traffic-control/test/fifo-queue-disc-test-suite.cc. The test aims to check that the capacity of the queue disc is not exceeded and packets are dequeued in the correct order.