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BP1037 Transitioning to DCB with EqualLogic PS series Storage Solutions 9
2.3.2 Enhanced Transmission Selection (ETS)
Enhanced Transmission Selection is a mechanism for guaranteeing a minimum percentage of
bandwidth to a traffic class. A traffic class contains one or more CoS’s defined using VLAN Q-tag. Each
traffic class is then assigned a percentage of bandwidth (with setting granularity down to 10%). All
traffic class bandwidths must add up to 100%; no oversubscription is allowed.
The bandwidth percentage defined is a minimum guaranteed bandwidth for that traffic class. If a traffic
class is not currently using all of its minimum allocation, then other traffic classes may use it. However,
as soon as the original traffic class requires its bandwidth again, the other traffic flow may be throttled
to allow recovery to the minimum level allocated for that class. This is accomplished through the use
of PFC. PFC will issue a pause for the required traffic classes in a manner to allow the bandwidth to be
regained while minimizing the probability of dropped frames occurring in the throttled traffic classes.
An important note to consider when deciding on bandwidth percentages for each traffic class is that
the required accuracy of the ETS algorithm is only plus or minus 10%. If the setting for a particular
traffic class is not set with this in mind, it may not receive all the bandwidth expected.
Figure 2 Enhanced Transmission Selection