Understanding Qos - D-Link DES-6500 Manual

Understanding QoS

The Switch has eight priority classes of service, one of which is internal and not configurable. These priority classes of
service are labeled as 6, the high class to 0, the lowest class. The eight priority tags, specified in IEEE 802.1p are mapped
to the Switch's priority classes of service as follows:
Priority 0 is assigned to the Switch's Q2 class.
•
Priority 1 is assigned to the Switch's Q0 class.
•
Priority 2 is assigned to the Switch's Q1 class.
•
Priority 3 is assigned to the Switch's Q3 class.
•
Priority 4 is assigned to the Switch's Q4 class.
•
Priority 5 is assigned to the Switch's Q5 class.
•
Priority 6 is assigned to the Switch's Q6 class.
•
Priority 7 is assigned to the Switch's Q6 class.
•
For strict priority-based scheduling, any packets residing in the higher priority classes of service are transmitted first.
Multiple strict priority classes of service are emptied based on their priority tags. Only when these classes are empty, are
packets of lower priority transmitted.
For weighted round-robin queuing, the number of packets sent from each priority queue depends upon the assigned weight.
For a configuration of 8 CoS queues, A~H with their respective weight value: 8~1, the packets are sent in the following
sequence: A1, B1, C1, D1, E1, F1, G1, H1, A2, B2, C2, D2, E2, F2, G2, A3, B3, C3, D3, E3, F3, A4, B4, C4, D4, E4, A5,
B5, C5, D5, A6, B6, C6, A7, B7, A8, A1, B1, C1, D1, E1, F1, G1, H1.
For weighted round-robin queuing, if each CoS queue has the same weight value, then each CoS queue has an equal
opportunity to send packets just like round-robin queuing.
For weighted round-robin queuing, if the weight for a CoS is set to 0, then it will continue processing the packets from this
CoS until there are no more packets for this CoS. The other CoS queues that have been given a nonzero value, and
depending upon the weight, will follow a common weighted round-robin scheme.
Remember that the DES-6500 switch has 7 configurable priority queues (and seven Classes of Service) for each port on the
Switch.
DES-6500 Chassis-based Layer 3 Ethernet Switch Manual
NOTICE: The Switch contains eight classes of service for
each port on the Switch. One of these classes is reserved
for internal use on the Switch and is therefore not
configurable. All references in the following section
regarding classes of service will refer to only the seven
classes of service that may be used and configured by the
Switch's Administrator.
85