Planet XGS3-24042 User Manual download pdf (Page 179)

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Chapter 20 Egress QoS Configuration

20.1 Introduction to Egress QoS

In traditional IP networks, all packets are treated in the same way. All network equipments treat them by the

first-in-first-out policy and try best effort to send them to the destination. However, it does not guarantee the

performance like reliability and transmission delay. Network develops so fast that new demand has been

raised for the quality of service on IP network with the continual emergence of new applications. For example,

delay-sensitive services like VoIP and video put higher demands on packet transmission delay and users

cannot accept too long transmission delay (by contrast, E-mail and FTP services are not sensitive to the time

delay). In order to support services with different service requirement like voice, video and data service, the

network is required to be able to distinguish between different communications and provide appropriate

service. The traditional best-effort IP network cannot identify and distinguish various kinds of communications

while this ability is the very premise of providing differentiated services for different communications.

Therefore, the best-effort service mode of traditional network cannot meet the demand of applications. The

emergence of QoS techniques is committed to solve this problem.

Egress PolicyMap is the QoS policy in egress which performs QoS control of packets in the egress direction

and provides better service for specified network communication with kinds of techniques. Egress PolicyMap

includes class-map and policy-map, of which class-map is used for selecting packets to operate and

policy-map is used for specifying the operation to use. Not all equipments support Egress QoS currently.

20.1.1 Egress QOS Terms

Egress QoS: Achieving QoS on egress of port.

Inner_vid: VLAN ID brought by the TAG near the header of network layer when double TAGs exist.

Outer_vid: VLAN ID brought by the TAG near the header of network link layer when double TAGs exist. The

TAG is considered to be outer tag by default when only one TAG exists.

Outer_tpid: Protocol type of the network link layer header indicating the type of outer tag.

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