User`s manual

Chapter 1 Overview
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For more information regarding the use of VLAN tags, see the Support for 802.1Q
Tag-Based VLAN Switching section below.
The switch also enables the user to configure the egress scheduling mode:
 Strict priority mode: all top priority frames are egressed out of a port until that
priority's queue is empty, then the next lower priority queue's frames are
egressed. In other words, whenever a queue has a frame to transmit, it goes
out to the link before any frame in any lower-priority queue.
The strict priority mode guaranties minimum latency for the traffic assigned to a
queue, but can cause the lower priority queues to be starved out, because it may
prevent them from transmitting any frames, but on the other hand ensures that all
the high priority frames egress the switch as soon as possible.
 Weighted fair queue mode: 8, 4, 2, 1 weighting is applied to the four priorities.
This approach prevents the lower priority frames from being starved out with
only a slightly increased delay to the higher priority frames.
However, only idle bandwidth is used for lower priority frames: to ensure that the
bandwidth assigned to a certain traffic class does not decrease below the
assigned value, when congestion occurs any class cannot more than the assigned
bandwidth.
1.6.3.6 Support for Port-Based VLAN
The Ethernet switch supports user-defined port-based VLANs. A port-based VLAN
is a logical group of ports defined by the user: traffic within the VLAN is forwarded
Note:
As an alternative to using the information carried by each
frame to determine the QoS during its forwarding by the
switch, the user can assign a fixed priority to any port.
Therefore, when the QoS feature is not enabled, the
egress priority of any frame received through a certain
port is determined only by the user-configured priority of
the frame ingress port. This fixed priority can be
independently selected for each port.