Egress QoS Configuration
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23. Egress QoS Configuration
23.1
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.
23.1.1
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.