INS_CWGE24MS2_REV–
10/05/16 PAGE 54
INSTALLATION AND OPERATION MANUAL
CWGE24MS2
TECH SUPPORT: 1.888.678.9427
QoS Enhancement
You can configure the Switch to prioritize traffic even if the incoming packets are not marked with
IEEE 802.1p priority tags or change the existing priority tags based on the criteria you select.
The Switch allows you to choose one of the following methods for assigning priority to incoming
packets on the Switch:
» 802.1p Tag Priority - Assign priority to packets based on the packet’s 802.1p tagged priority.
» Port Based QoS - Assign priority to packets based on the incoming port on the Switch.
» DSCP Based QoS - Assign priority to packets based on their Differentiated Services Code
Points (DSCPs).
Note: Advanced QoS methods only affect the internal priority queue mapping for the Switch. The
Switch does not modify the IEEE 802.1p value for the egress frames. You can choose one of
these ways to alter the way incoming packets are prioritized or you can choose not to use
any QoS enhancement setting on the Switch.
802.1p Priority
When using 802.1p priority mechanism, the packet is examined for the presence of a valid 802.1p
priority tag. If the tag is present, the packet is assigned to a programmable egress queue based
on the value of the tagged priority. The tagged priority can be designated to any of the available
queues.
Ethernet Packet:
6
6
2
42-1496
4
DA
SA
Type / Length
Data
FCS
6
6
4
2
42-1496
4
DA
SA
802.1Q Tag
Type / Length
Data
FCS
802.1Q Tag:
2 bytes
2 bytes
Tag Protocol Identifier (TPID)
Tag Control Information (TCI)
16 bits
3 bits
1 bit
12 bits
TPID (0x8100)
Priority
CFI
VID
» Tag Protocol Identifier (TPID): a 16-bit field set to a value of 0x8100 in order to identify the
frame as an IEEE 802.1Q-tagged frame.
» Tag Control Information (TCI)
›
Priority Code Point (PCP): a 3-bit field which refers to the IEEE 802.1p priority. It indicates the
frame priority level from 0 (lowest) to 7 (highest), which can be used to prioritize different
