Port Traffic Controls

 

 

Guaranteed Minimum Bandwidth (GMB)

Table 13-1. Per-Port Outbound Priority Queues

 

 

802.1p Priority Settings in Tagged VLAN

Outbound Priority Queue for a Given Port

Packets*

 

 

 

 

 

1

(low)

1

 

 

 

2

(low)

2

 

 

 

0

(normal)

3

 

 

3 (normal)

4

 

 

 

4

(medium)

5

 

 

 

5

(medium)

6

 

 

 

6

(high)

7

 

 

 

7

(high)

8

*The switch processes outbound traffic from an untagged port at the "0" (normal) priority level.

You can use GMB to reserve a specific percentage of each port’s available outbound bandwidth for each of the eight priority queues. This means that regardless of the amount of high priority outbound traffic on a port, you can ensure that there will always be bandwidth reserved for lower-priority traffic.

Since the switch services outbound traffic according to priority (highest to lowest), the highest-priority outbound traffic on a given port automatically receives the first priority in servicing. Thus, in most applications, it is neces­ sary only to specify the minimum bandwidth you want to allocate to the lower priority queues. In this case, the high-priority traffic automatically receives all unassigned bandwidth without starving the lower-priority queues.

Conversely, configuring a bandwidth minimum on only the high-priority out­ bound queue of a port (and not providing a bandwidth minimum for the lower- priority queues) is not recommended because it may “starve” the lower- priority queues. (See the Note on page 13-24.)

13-23