10.1 Queuing
10.1.2 The need for traffic prioritization

The need to prioritize packets arises from the diverse mixture of protocols and their associated behaviors found in today’s data networks. Different types of traffic that share a data path through the network can affect each other.

Depending on the application and overall bandwidth, users may or may not perceive any real performance degradation. For instance, delay-sensitive, interactive, transaction-based applications may require a higher priority than, say, a file transfer to satisfy users. Voice and desktop videoconferencing requires a specified amount of bandwidth to perform acceptably. If your network is designed so that multiple protocols share a single data path between routers, prioritization may be a requirement.

Prioritization is most effective on WAN links in which the combination of bursty traffic and relatively lower data rates can cause temporary congestion. Depending on the average packet size, prioritization is most effective when applied to links at T1/E1 bandwidth speeds or lower. If there is no congestion on the WAN link, there is no reason to implement traffic prioritization.

It is important to note that prioritization is effective on WAN links that experience temporary congestion. If a WAN link is constantly congested, traffic prioritization may not resolve the problem. Adding bandwidth might be the appropriate solution.