Introduction to Quality of Service (QoS)

A Quality of Service (QoS) network policy refers to the network-wide controls available to:
  • Ensure uniform and efficient traffic-handling throughout your network, while keeping the most important traffic moving at an acceptable speed, regardless of current bandwidth usage.

  • Exercise control over the priority settings of inbound traffic arriving in and travelling through your network.

Adding bandwidth can be a good idea, but is not always feasible and does not completely eliminate the potential for network congestion. There will always be points in the network where multiple traffic streams merge or where network links change speed and capacity. The impact and number of these congestion points will increase over time as more applications and devices are added to the network.

When network congestion occurs, it is important to move traffic on the basis of relative importance. However, without QoS prioritization, less important traffic consumes network bandwidth and slows down or halts the delivery of more important traffic. Without QoS, most traffic received by the switch is forwarded with the same priority it had upon entering the switch. In many cases, such traffic is normal priority and competes for bandwidth with all other normal-priority traffic, regardless of its relative importance to your organization's mission.