Default priority is also the port based priority. Default priority is quite different from COS and TOS, it has
nothing to do with data packets but port priority of the switch. When port priority is high, the data packets
transmitted from this port will faster than other ports.
COS
Priority tag in 802.1P includes 8 kinds (0-7). The corresponding priority includes 4 kinds (High, Medium,
Normal, Low).
In device’s default settings, data with priority tag 0 and 1 will be in queue Low, data with 2 and 3 will be in
queue Normal, data with 4 and 5 will be in queue Medium and data with 6 and 7 will be in queue High.
DSCP
DiffServ system need every transmitting message with different classification in the network. Classification
information is comprised in the head of IP message. former 6 bits of TOS is used to comprise the
classification information.
Now the defined DSCP we have here includes: default DSCP, the value is0; class selector DSCP, the value is
(8,16,24,32,40,48,56); expedited forwarding(EF), has the characteristics of low delay, The recommended
DSCP for expedited forwarding is 46(101110);assured forwarding(AF), The AF behavior group defines four
separate AF classes with Class 4 having the highest priority. Within each class, packets are given a drop
precedence (high, medium or low). The combination of classes and drop precedence yields 12 separate
DSCP encodings,((10,12,14), (18, 20, 22), (26, 28, 30), (34, 36, 38)).
The device defines value (0-15) as Low priority queuing, the first queuing, value (16-31) as Normal priority
queuing, the second queuing, value(32-47) as Medium priority queuing, the third queuing and the
value(48-63) as High priority queuing.
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Configuring the System
33
