Quality of Service (QoS): Managing Bandwidth More Effectively

Introduction

But if the packet is in a VLAN-tagged environment, then the above setting is also added to the packet as an 802.1p priority for use by downstream devices and applications (shown in table 6-3). In either case, an IP packet can also carry a priority policy to downstream devices by using DSCP-marking in the ToS byte.

Table 6-3.Mapping Switch QoS Priority Settings to Device Queues

Priority Setting

Outbound Port

802.1p Priority Setting Added

Queue Assignment in Downstream Devices With:

 

Queues in the

to Tagged VLAN Packets

8 Queues

3 Queues

2 Queues

 

Switch

 

Leaving the Switch

 

 

 

 

 

1

Queue 1

1

(low priority)

Queue 1

Queue 1

 

2

 

2

 

Queue 2

 

Queue 1

0

 

 

 

Queue 3

 

 

Queue 2

0

(normal priority)

Queue 2

 

3

 

3

 

Queue 4

 

 

4

 

 

 

Queue 5

 

 

Queue 3

4

(medium priority)

Queue 3

 

5

 

5

 

Queue 6

 

Queue 2

6

 

 

 

Queue 7

 

 

Queue 4

6

(high priority)

 

 

7

 

7

 

Queue 8

 

 

 

 

 

 

 

 

 

 

Classifiers for Prioritizing Outbound Packets

 

 

N o t e O n U s i n g

ProCurve recommends that you configure a minimum number of the available

M u l t i p l e

QoS classifiers for prioritizing any given packet type. Increasing the number

C r i t e r i a

of active classifier options for a packet type increases the complexity of the

 

possible outcomes and consumes switch resources.

 

 

Packet Classifiers and Evaluation Order

The switches covered by this chapter provide six QoS classifiers (packet criteria) you can use to configure QoS priority.

6-9