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Class of Service (CoS) 63
Class of Service (CoS)
This section describes the Class of Service (CoS) Queue Mapping and CoS Interface
Configuration features.
CoS Queue Mapping
You can configure ports as trusted or untrusted.
Trusted ports have the following features:
z Takes at face value certain priority designation for arriving packets
z Trust only applies to packets that have that trust information
z
Can only have one trust field at a time

802.1p User Priority (default trust mode - Managed through Switching configuration)

IP Precedence
 IP DiffServ Code Point (DSCP)
Untrusted ports have the following features:
z
No incoming packet priority designation is trusted, therefore the port default priority value
is used
z
All ingress packets from Untrusted ports, where the packet is classified by an ACL or a
DiffServ policy, are directed to specific CoS queues on the appropriate egress port. That
specific CoS queue is determined by either the default priority of the port or a DiffServ or
ACL.
z
Used when trusted port mapping is unable to be honored - i.e. when a non-IP packet
arrives at a port configured to trust IP precedence or IP DSCP
Packets arriving at the port ingress are inspected and their trusted field value is used to
designate the CoS queue where the packet is placed when forwarded to the appropriate egress
port. You configure a CoS mapping table to associate the trusted field value with the desired
CoS queue.
The three internal traffic class queues available are:
z
Queue 2 - Minimum of 50% of available bandwidth
z Queue 1 - Minimum of 33% of available bandwidth
z Queue 0 - Lowest priority, minimum of 17% of available bandwidth
For untagged traffic, you can specify default 802.1p priority on a per-port basis.
NOTE: From the Web interface, you map IP Precedence and IP DSCP values to the internal
traffic classes on the QoS > Class of Service > Mapping Table Configuration page
and you map 802.1p priority values to the traffic classes on the Switching > Class of
Service > 802.1p Priority Mapping page.