Design Reference

VSP 4000 supports two-rate, three-color marking for policers as described in RFC 2698.
Policers mark packets as Green, Yellow, or Red. Red packets are dropped automatically. Out
of profile packets cannot be re-marked to a lower QoS level.
The system can perform rate metering only on a Layer 3 basis.
Traffic shapers buffer and delay violating traffic. These operations occur at the egress level.
Virtual Services Platform 4000 supports traffic shaping at the port level.
QoS interface considerations
Four QoS interface types are explained in detail in the following sections. You can configure
an interface as trusted or untrusted, and for bridging or routing operations. Use these
parameters to properly apply QoS to network traffic.
Trusted and untrusted interfaces
You can configure an interface as trusted (core) or untrusted (access). The default is trusted
(core).
Use trusted interfaces (core) to mark traffic in a specific way, and to ensure that packets are
treated according to the service level of those markings. Use a core interface if you need control
over network traffic prioritization. For example, use 802.1p-bits to apply desired class of service
(CoS) attributes to the packets before they are forwarded to the access node. You can also
classify other protocol types ahead of IP packets.
A core port preserves the DSCP and 802.1p-bits markings. The device uses these values to
assign a corresponding QoS level to the packets.
Use an access port to control the classification and mapping of traffic for delivery through the
network. Untrusted interfaces require you to configure filter sets to classify and re-mark ingress
traffic. For untrusted interfaces in the packet forwarding path, the DSCP is mapped to an IEEE
802.1p user priority field in the IEEE 802.1Q frame, and both of these fields are mapped to an
IP Layer 2 drop precedence value that determines the forwarding treatment at each network
node along the path. Traffic that enters an access port is re-marked with the appropriate DSCP
and 802.1p markings, and given an internal QoS level. The switch performs this re-marking
based on the filters and traffic policies that you configure.
The following logical table shows how the system performs ingress mappings for data packets
and for control packets not destined for the Control Processor (CP).
Table 14: Data packet ingress mapping
Enable
DiffServ
Access
DiffServ
802.1p
Override
Routed
Packet
Tagged
Ingress
Packet
Internal
QoS
Derived
From
Egress
Packet
DSCP
Derived
from
Egress
Packet
802.1p
Derived
from
1 0, L3T=1 0, L2T=1 1 1 DSCP Stays
untouched
iQoS
QoS design guidelines
132 Network Design Reference for Avaya VSP 4000 February 2014
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