ZyXEL Communications EX5501-B0 User Manual page 168

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 57 Internal Layer2 and Layer3 QoS Mapping
LAYER 2
PRIORITY
IEEE 802.1P USER
QUEUE
PRIORITY (ETHERNET
PRIORITY)
0 1
1 2
2 0
3 3
4 4
5 5
EX5501-B0 / AX7501-B0 / PX7501-B0 User's Guide
Chapter 10 Quality of Service (QoS)
LAYER 3
TOS (IP
PRECEDENCE)
0
0
1
2
3
168
IP PACKET LENGTH
DSCP
(BYTE)
000000
000000 >1100
001110 250~1100
001100
001010
001000
010110
010100
010010
010000
011110 <250
011100
011010
011000