Chapter 10 Quality of Service (QoS)
VMG/XMG Series User’s Guide
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different kinds of forwarding. Resources can then be allocated according to the DSCP values and the
configured policies.
IP Precedence
Similar to IEEE 802.1p prioritization at layer-2, you can use IP precedence to prioritize packets in a layer-3
network. IP precedence uses three bits of the eight-bit ToS (Type of Service) field in the IP header. There
are eight classes of services (ranging from zero to seven) in IP precedence. Zero is the lowest priority
level and seven is the highest.
Automatic Priority Queue Assignment
If you enable QoS on the Zyxel Device, the Zyxel Device can automatically base on the IEEE 802.1p
priority level, IP precedence and/or packet length to assign priority to traffic which does not match a
class.
The following table shows you the internal layer-2 and layer-3 QoS mapping on the Zyxel Device. On the
Zyxel Device, traffic assigned to higher priority queues gets through faster while traffic in lower index
queues is dropped if the network is congested.
Table 77 Internal Layer2 and Layer3 QoS Mapping
PRIORITY
QUEUE
LAYER 2 LAYER 3
IEEE 802.1P USER
PRIORITY (ETHERNET
PRIORITY)
TOS (IP
PRECEDENCE)
DSCP
IP PACKET LENGTH
(BYTE)
0 1 0 000000
12
2 0 0 000000 >1100
3 3 1 001110
001100
001010
001000
250~1100
4 4 2 010110
010100
010010
010000
5 5 3 011110
011100
011010
011000
<250
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