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| 1.2 |  | Key Characteristics of Scalable Internetworks |
| 1.2.3 |  | Making the network responsive |

End users notice network responsiveness as they use the network to perform routine tasks. Users expect network resources to respond quickly, as if network applications were running from a local hard drive. Networks must be configured to meet the needs of all applications, especially time delay sensitive applications such as voice and video. The IOS offers traffic prioritization features to tune responsiveness in a congested network. Routers may be configured to prioritize certain kinds of traffic based on protocol information, such as TCP port numbers. Traffic prioritization ensures that packets carrying mission-critical data take precedence over less important traffic.

If the router schedules these packets for transmission on a first-come, first-served basis, users could experience an unacceptable lack of responsiveness. For example, an end user sending delay-sensitive voice traffic may be forced to wait too long while the router empties its buffer of queued packets.

The IOS addresses priority and responsiveness issues through queuing. Routers that maintain a slow WAN connection often experience congestion. These routers need a method to give certain traffic priority. Queuing refers to the process that the router uses to schedule packets for transmission during periods of congestion. By using the queuing feature, a congested router may be configured to reorder packets so that mission-critical and delay sensitive traffic is processed first. These higher priority packets are sent first even if other low priority packets arrive ahead of them. The IOS supports four methods of queuing, as described in the following sections:

- First-in, first-out (FIFO) queuing
- Priority queuing
- Custom queuing
- Weighted fair queuing (WFQ)

Only one of these queuing methods can be applied per interface because each method handles traffic in a unique way.

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