Im SMB documentation, a chapter like the one for GAiA "QoS Advanced QoS Policy Management - Differentiated Services (DiffServ)" does not exist, and i think that is because Embedded GAiA has only a subset of features implemented to keep the small footprint. The sk105722 reffered by you has Platform / Model : All, so i have asked for feedback concerning support on SMB devices. But according to sk104861, use of the feature has only been possible since R77.30 !
Further, in sk105380 i see for SMB:
Centrally managed SMB appliance can be configured to use Delay Sensitivity and Differential Services marking features only under Express QoS mode. Configuration is done in "Advanced" section of QoS action configuration window which is unique for Edge/SG80 appliances. Under Traditional QoS mode only Best Effort QoS class is supported, using other classes will disable QoS policy.
QoS supports marking the traffic with Differential Services (DiffServ) tags and preserving existing DiffServ tags. QoS does not support matching packets based on DiffServ tagging.
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