â—¦ Transceiver type not supported in this software version.
â—¦ Not an Switch Transceiver.
Guaranteed minimum bandwidth (GMB)
GMB provides a method for ensuring that each of a given port's outbound traffic priority queues has a specified
minimum consideration for sending traffic out on the link to another device. This can prevent a condition where
applications generating lower-priority traffic in the network are frequently or continually "starved" by high volumes
of higher-priority traffic. You can configure GMB per-port and, in the case of the 2920 and 5400R switches, per
static trunk.
GMB operation
NOTE: Earlier software releases supported GMB configuration on a per-port basis. Beginning with
software release 15.18, the 2920 and 5400R switches also support GMB configuration on static
trunks. (GMB configuration is not supported on dynamic LACP or distributed (DT) trunks.
For application to static trunk interfaces (2920 and 5400r only), GMB enforcement is applied
individually to each port belonging to the trunk, and not to the trunk as a whole.
For any port, group of ports or, static trunks, you can use the default minimum bandwidth settings for each
outbound priority queue or a customized bandwidth profile. It is also possible to disable the feature entirely.
The switch services per-port outbound traffic in a descending order of priority; that is, from the highest priority to
the lowest priority. By default, each port (including each port in a static trunk) offers eight prioritized, outbound
traffic queues. Tagged VLAN traffic is prioritized according to the 802.1p priority the traffic carries. Untagged
VLAN traffic is assigned a priority of 0 (normal).
Table 16: Per-port outbound priority queues
802.1p Priority settings in tagged VLAN packets
1
Outbound priority queue for a given port
1 (low) 1
2 (low) 2
0 (normal) 3
3 (normal) 4
4 (medium) 5
5 (medium) 6
6 (high) 7
7 (high) 8
1
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
(including each port in a static trunk), you can ensure that there will always be bandwidth reserved for lower-
priority traffic.
Chapter 6 Port Traffic Controls 165
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