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Quality of Service Overview
•
Priority Transmit Queue (TxQ) with configurable forwarding behavior
•
In‐bound and/or outbound rate Limiter (IRL) per transmit queue
•
Outbound rate shaper per transmit queue
The CoS configuration for each service can be easily viewed using the CoS setting tables. Ports are
bundled into port groups with the group assigned to a CoS, significantly cutting down on
operational overhead and complexity.
CoS Priority and ToS Rewrite
The two parameters configurable for CoS priority are 802.1p and Type of Service (ToS). Each CoS
can be mapped to an 802.1p priority and a ToS rewrite value. The 802.1p parameter is:
•
A subset of ToS with values 0–7 (upper 3 bits of the 8 bit ToS field)
•
Supported in both layer 2 and layer 3
The ToS parameter is:
•
An 8‐bit field with values 0–255
•
Supported in layer 3 only
•
Also referred to as the Differentiated Services Code Point (DSCP) when limited to the lower 5
bits of the field
Figure
assignments (shown here using DSCP terminology).
QoS priority/ToS configuration:
•
Derives its characteristic requirements from the end‐system application.
•
Is configured on the edge device the application is connected to
•
Is propagated through the network in the protocol packet header
February 22, 2008
1 displays the relationship between your application, priority level, 802.1p, and ToS
Page 3 of 29
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