CANOGA PERKINS 9171 Configuration Guide - Manual (Page 208)

CanogaOS Configuration Guide
31-2
Other frame types cannot carry Layer-2 CoS values.
CoS values range from 0 to 7 and 7 is the highest priority.
DSCP Value
Differentiated Services Code Point (DSCP) is a 6-bit value used to classify the priority of
Layer-3 packets upon entry into a network.
DSCP values range from 0 to 63, 63 being the highest priority, 0 being best-effort traffic.
IP-Precedence Value
IP-Precedence is a 3-bit value used to classify the priority of Layer-3 packets upon entry
into a network.
IP-Precedence values range from 0 to 7, 7 being the highest priority.
EXP Value
EXP value is a 3-bit value used to classify the priority of MPLS packets upon entry into a
network.
MPLS EXP values range from 0 to 7, 7 being the highest priority.
Classification
Classification distinguishes one kind of traffic from another by examining the fields in the
packet. The process generates an internal priority for a packet, which identifies all future
QoS actions to be taken on the packet.
Each packet is classified upon entry into the network. At the ingress, the packet is
inspected, and the priority is determined based on ACLs or the configuration. The
Layer-2 CoS value is then mapped to a priority value.
The classification is carried in the IP packet header using 6 bits or 3 bits from the
deprecated IP TOS field to carry the classification information. Classification can also
occur in the Layer-2 frame.
Classification is enabled only if QoS is globally enabled on the switch. By default, QoS is
globally disabled, thus, no classification occurs.
Classification occurs on an ingress physical port, but not at the switch virtual interface
level.
Classification can be based on CoS/DSCP/IP-Precedence, default port cos, or class
maps and policy maps.
Shaping
Shaping is to limit the rate at which packets pass through the shaper by buffering
packets that exceed a defined rate and sending those packets later. The goal is that,
over time, the rate of transmission will be smoothed out to the defined rate.
Shaping has the following attributes:
• Shaping can occur only on a physical port basis
• Shaping can occur on egress interface.
Policing
Policing determines whether a packet is in or out of profile by comparing the internal
priority to the configured policer.