DGS-3700-12/DGS-3700-12G Series Layer 2 Gigabit Ethernet Switch User Manual
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Figure 4 - 1 Mapping QoS on the Switch
The picture above shows the default priority setting for the Switch. Class-7 has t he highes t priorit y of the eight pr iorit y
queues on the Switch. In order to implement QoS, the user is req uired to inst ruct t he S witch to exam ine the h eader of
a packet to see if it has the proper identifying tag tagged. Then the us er may forward these tagged packets to
designated queues on the Switch where they will be emptied, based on priority.
For example, lets say a user wishes to have a videoconference betwee n two remotely set computers. The
administrator can add priority tags to the video packets being s ent out, utilizi ng the Access Profile comm ands. Then,
on the receiving end, the administrator instructs the Switch to examine pac kets for this tag, acquires the tagged
packets and maps them to a class queue on the Switch. Then in turn, the adm inistrator will set a priority for this queue
so that will be emptied before any other packet is forwarded. T his resul ts i n the end user r eceiv ing a ll pac k ets sent as
quickly as possible, thus prioritizing the queue and allowing for an uni nterrupted stream of packets, which optimi zes
the use of bandwidth available for the video conference.
Understanding QoS The Switch has eight priority queues. These priority queues are label ed f rom 0-7, with 7 be ing t he hi ghest pr iorit y and
0 the lowest priority queue. The eight priority tags, specified in IEEE 802.1p are m apped to the Switch's priorit y tags
as follows:
Priority 0 is assigned to the Switch's Q2 queue.
Priority 1 is assigned to the Switch's Q0 queue.
Priority 2 is assigned to the Switch's Q1 queue.
Priority 3 is assigned to the Switch's Q3 queue.
Priority 4 is assigned to the Switch's Q4 queue.
Priority 5 is assigned to the Switch's Q5 queue.
Priority 6 is assigned to the Switch's Q6 queue.
Priority 7 is assigned to the Switch's Q7 queue.