Quality of Service
This chapter covers the following topics:
- Architectural overview
- Configuration of quality of service
- Deployment scenarios
- Monitoring quality of service
In a standard IP network, all packets are processed identically based on best effort. The network devices usually ignore the importance or criticality of the data that is passing through the network. This creates problems in deployments where time-sensitive traffic, such as voice and video packets, is delayed or dropped because the network devices do not prioritize it over other traffic. The feature of prioritizing some traffic over other traffic is known as quality of service (QoS).
QoS is useful in the following network deployments:
- You run voice, video, and data traffic on the same network. Because voice and video streams are time sensitive and do not tolerate network delays, QoS policies must be implemented to ensure traffic prioritization.
- You run data applications such as time sensitive databases that require traffic prioritization if there is congestion on the network.
- You want to prioritize management traffic, such as Telnet or SSH, so that you do not lose access to the network devices if there is an outbreak of a new virus in the local network.
- You are a service provider and want to offer different classes of service (CoS) to your customers based on their needs.
- You have virtual private networks (VPNs) deployed and you want to prioritize or rate-limit traffic going over the VPN tunnel.
Many different types of QoS mechanisms are available in the Cisco devices, such as the following:
- Traffic policing
- Traffic prioritization
- Traffic shaping
- Traffic marking
QoS is useful in policing and prioritizing packets only when there is congestion in the network. For end-to-end QoS, all network devices along the path should be QoS capable.