First Hands on With QoS

As I dive deeper into the VoIP world, I'm starting to learn just how important QoS (Quality of Service) is in a network. QoS is a complicated topic and for good reason, not only because the configuration can be quite involved, but also their can be a lot of corporate politics involved. QoS comes into play when a network is congested, instead of having a router just drop random packets that it can't route you can prioritize which specific packets should be sent from most important to least important. With the least important being sent to the "bit bucket (gone forever)" most likely. With this said RTP voice traffic is very time sensitive, when there is latency it upsets the way it is sent to the receiving end and in turn usually upsets the end user as it can cause echoing, dropped calls, and a plethora of other issues.

You should prioritize voice and video traffic before other traffic in most environments...well unless the CEO steps in and demands that his e-mail and internet traffic is more important than any other traffic! There are essentially 3 steps to configuring QoS:

1. Identify and match packets with the class-map command
2. Prioritize traffic with the policy-map command
3. Assign the QoS policy to the impacted interface with the service-policy command

You can see a sample configuration in the picture above that I was messing around with in GNS3.