Understanding Qos - D-Link xStack DGS-3400 Series Reference Manual

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x Stack DGS-3400 Series Layer 2 Gigabit Ethernet M anaged Sw itch
Figure 4 - 1 An Example of the Default QoS Mapping on the Switch
The picture above shows the default priority setting for the Switch. Class-6 has the highest priority of the seven priority classes of
service on the Switch. In order to implement QoS, the user is required to instruct the Switch to examine the header of a packet to
see if it has the proper identifying tag. Then the user may forward these tagged packets to designated classes of service on the
Switch where they will be emptied, based on priority.
For example, let's say a user wishes to have a video conference between two remotely set computers. The administrator can add
priority tags to the video packets being sent out, utilizing the Access Profile commands. Then, on 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 results 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

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The xStack DGS-3400 Series supports 802.1p priority queuing. The Switch has 8 priority queues. These priority queues are
numbered from 6 (Class 6) — 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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