Key Points of QoS Deployment

QoS is used to identify special traffic (such as VoIP, VIP, voice, and video traffic) and increase their priority to ensure that the special traffic is preferentially scheduled and reliably forwarded. QoS is typically applied to high education and enterprise campus scenarios to differentiate traffic of users. For example, traffic of VIP users is preferentially scheduled, and VoIP traffic is preferentially processed to ensure call quality.

Based on the services and scale of the campus network, key points of QoS deployment for improving the priority of special traffic are as follows:

• Identify special traffic.

  Identify characteristics of special traffic and match the traffic with traffic classifiers.

  Identify the interface through which special traffic passes and the traffic direction to determine the location where the traffic policy is applied.

• Determine the priority of special traffic.

  Packets transmitted over different networks carry different QoS precedence fields. For example, the EXP field is used on a Multiprotocol Label Switching (MPLS) network, the 802.1p field is used in a virtual local area network (VLAN), and the DSCP field is used on an IP network. When the device connects different types of networks, it maps external precedence fields (including 802.1p, MPLS EXP, and DSCP fields) of all the received packets to internal priorities. When the device sends packets, it maps internal priorities to external priorities. There are eight CoS values, that is, eight per-hop behaviors (PHBs): CS7, CS6, EF, AF4, AF3, AF2, AF1, and BE listed in descending order of priority. Select a proper priority based on the actual requirements for the packet delay, jitter, or packet loss ratio.