User Manual
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(Figure 5.8.1.1)
Users can select the QOS priority queue mechanism, the queue mechanism in two ways: weighted Fair
mode and strict mode.
Weighted Fair priority
Weighted Fair refers to this port sends message according to queue priority High, Medium, Normal and
low in proportion of 8:4:2:1 when some ports traffic is heavy. If sending speed is less than bandwidth, the
message of each priority queues can send normally; if the port keeps sending in full speed, then the rest
of the message of each priority queues will be discarded.
Strict priority
Strict priority: it refers to QoS deals with the message from high priority to low priority. If the low priority
queues is full but the message of high priority queues don‘t finish, the message of low priority queues will
be
discarded; but if the speed of high priority queue does not reach the port‘s wire speed, then message
of lower priority can send one by one, and the data may be lost because of shortage of bandwidth. The
ports always finish all messages of high priority queues first then allow the message of lower priority
queues
Port Priority
Default priority is based on port priority, default priority is different from COS and TOS, it did not have
relationship with data package, it had relationship with switch port‘s priority. If the port‘s priority is higher,
the data packet will be transferred at first.
When open port priority, must open inspect COS. The example: open inspect port, 1, 2, 3, 4 COS, divide
port 1, 2, 3, 4 in different priority, COS value corresponding priority no need to set up. Port 1, 2, 3, 4, port
1, the priority is the highest. When these
4 port ‗s receive data must transfer from other port, because the
limited of bandwidth, will be transferred according to priority queue mechanism(If use strict mode, then
port 1‘s data must be transferred over at first. If use Weighted Fair 8:4:2:1, the 4 port will be transferred
according 8: 4: 2: 1 ratio)
5.8.2 COS
IEEE P802.1p is the name of a task group active during 1995
–98 responsible for adding traffic class
expediting and dynamic multicast filtering to the IEEE 802.1D standard. Essentially, they provided a
mechanism for implementing Quality of Service (QoS) at the media access control (MAC) level. The
group's work with the new priority classes and Generic Attribute Registration Protocol (GARP) was not
published separately but was incorporated into a major revision of the standard, IEEE 802.1D-1998. It
also required a short amendment extending the frame size of the Ethernet standard by four bytes which
was published as IEEE 802.3ac in 1998.
