HP Network Direr Software Products manual Key Concepts

Key Concepts 627

The boundary nodes (shown in the Topology example) are complex classification devices and can perform the appropriate marking of packets. This means that any interior nodes that are simple classification devices are still able to determine the correct traffic prioritization to perform.

Queuing The first two aims of traffic prioritization (forwarding important traffic through the device faster than other traffic and reducing the risk of dropping important traffic) are provided by the queuing mechanism as follows:

1The classified traffic is queued for output on a particular port in multiple queues rather than in a single queue (as performed on devices that are not capable of traffic prioritization) and those queues are serviced in a particular way that favors the more important traffic over other traffic.

2Each of the queues is shared between one or more different types of traffic that have been defined as having a similar level of importance.

3If a particular queue fills up with packets then any further packets for that queue will be dropped until the queue is serviced. This will clear some of the packets from the queue.

4Packets are taken off the queues and transmitted out of the port according to the particular queue servicing mechanism that is in place. A device may support one or more of the various queue servicing mechanisms that are available, which include weighted round robin and strict priority queueing. Each of these queuing mechanisms has its own characteristics yet they are all aimed at ensuring higher priority traffic is processed and forwarded by the device quicker than other traffic.

An example of the results of a queuing servicing mechanism is illustrated in Figure 344. It shows how important traffic flows through the network quicker than the less important traffic and reduces the likelihood of the more important traffic being dropped. The device in the figure defines traffic as being gold, silver or bronze (gold being the most important) with a queue for each type of traffic.