Product Manual

DES-3526 / DES-3526DC Fast Ethernet Layer 2 Switch
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 has four priority queues. These priority queues are labeled as 3, the high queue to 0, the
lowest queue. The eight priority tags, specified in IEEE 802.1p are mapped to the Switch's priority
tags as follows:
• Priority 0 is assigned to the Switch's Q1 queue.
• Priority 1 is assigned to the Switch's Q0 queue.
• Priority 2 is assigned to the Switch's Q0 queue.
• Priority 3 is assigned to the Switch's Q1 queue.
• Priority 4 is assigned to the Switch's Q2 queue.
• Priority 5 is assigned to the Switch's Q2 queue.
• Priority 6 is assigned to the Switch's Q3 queue.
• Priority 7 is assigned to the Switch's Q3 queue.
For strict priority-based scheduling, any packets residing in the higher priority queues are transmitted
first. Multiple strict priority queues empty based on their priority tags. Only when these queues 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-3526 has four priority queues (and four Classes of Service) for each port on
the Switch.
Port Bandwidth
The bandwidth control settings are used to place a ceiling on the transmitting and receiving data rates
for any selected port. In the Configuration folder, click Port Bandwidth, to view the window shown
below.
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