802.1P Settings - D-Link xStack Reference Manual

xStack® DGS-3120 Series Layer 2 Stackable Managed Switch Web UI Reference Guide
the receiving end, the administrator instructs the Switch to examine packets for this tag, acquires the tagged packets
and maps them to a class queue on the Switch. Then in turn, the administrator will set a priority for this queue so that
will be emptied before any other packet is forwarded. This result in the end user receiving all packets sent as quickly as
possible, thus prioritizing the queue and allowing for an uninterrupted stream of packets, which optimizes the use of
bandwidth available for the video conference.
Understanding QoS
The Switch supports 802.1p priority queuing. The Switch has eight priority queues. These priority queues are
numbered from 7 (Class 7) — the highest priority queue — to 0 (Class 0) — the lowest priority queue. The eight priority
tags specified in IEEE 802.1p (p0 to p7) are mapped to the Switch's priority queues as follows:
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Priority 0 is assigned to the Switch's Q2 queue.
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Priority 1 is assigned to the Switch's Q0 queue.
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Priority 2 is assigned to the Switch's Q1 queue.
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Priority 3 is assigned to the Switch's Q3 queue.
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Priority 4 is assigned to the Switch's Q4 queue.
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Priority 5 is assigned to the Switch's Q5 queue.
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Priority 6 is assigned to the Switch's Q6 queue.
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Priority 7 is assigned to the Switch's Q7 queue.
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 eight 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 Switch has eight configurable priority queues (and eight Classes of Service) for each port on the
Switch.
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 eight classes of service that may be used and
configured by the administrator.

802.1p Settings

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