Quality of Service

The IEEE 802.1p standard uses eight levels of priority (0-7). Priority 7 is assigned to highest priority network traffic, such as OSPF or RIP routing table updates, priorities 5-6 are assigned to delay-sensitive applications such as voice and video, and lower priorities are assigned to standard applications. A value of 0 (zero) indicates a best effort traffic prioritization, and this is the default when traffic priority has not been configured on your network. The switch can filter packets based on the 802.1p values, and it can assign or overwrite the 802.1p value in the packet.

Figure 13 Layer 2 802.1q/802.1p VLAN tagged packet

Ingress packets receive a priority value, as follows:

•Tagged packets—the switch reads the 802.1p priority in the VLAN tag.

•Untagged packets—the switch tags the packet and assigns an 802.1p priority, based on the port’s default priority (/cfg/port x/8021ppri).

Egress packets are placed in a COS queue based on the priority value, and scheduled for transmission based on the scheduling weight of the COS queue.

Use the /cfg/qos/8021p/cur command to display the mapping between 802.1p values, Class of Service queues (COSq), and COSq scheduling weights.

>> 802.1p# cur

Current priority to COS queue configuration:

Number of COSq:

2

Priority

COSq

Weight

--------

----

------

0

0

1

1

0

1

2

0

1

3

0

1

4

1

2

5

1

2

6

1

2

7

1

2

99