Chapter 15. Enabling Class of Service (COS)

In a basic network, all traffic is treated the exact same way. Packets come into your routers, and packets go out of your routers, and it really doesn't matter what kind of packets they are or what their transport requirements are.

Class of service allows you finer control over the traffic in your network. By grouping similar types of traffic, you can treat each class of traffic in a specific way, granting preference to traffic that is less tolerant to jitter, delay, and packet loss. Essentially, class of service lets you determine which traffic in your network is a first class passenger and which traffic has to ride economy.

Knowing What Pieces a COS Configuration Requires

The basic idea behind Class of Service (COS) is that you examine traffic entering your network to determine what type of traffic it is. Once you know the type of traffic (voice traffic, data traffic, traffic tied to a particular customer, and so on), you can mark that traffic accordingly. As those packets flow through your network, each router can then identify the traffic and make decisions on how to handle it based on its type. In this manner, all of your delay-sensitive traffic can be forwarded faster, or your critical traffic may be less likely to be dropped in times of congestion.

COS is how you control jitter and delay in your network. But what exactly are jitter and delay?

  • Jitter is the variation in delay over time. The primary contributor to jitter is the variability ...

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