ZyXEL Communications ADSL2+4 用户手册

 Chapter 13 Quality of Service (QoS)

P-660H-T1v3s User’s Guide

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.

If you enable QoS on the P-660H-T1v3s, the P-660H-T1v3s 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 P-660H-T1v3s. On the P-660H-T1v3s, traffic assigned to higher priority 
queues gets through faster while traffic in lower index queues is dropped if the 
network is congested.

Level 5

Typically used for video that consumes high bandwidth and is sensitive to 
jitter.

Level 4

Typically used for controlled load, latency-sensitive traffic such as SNA 
(Systems Network Architecture) transactions.

Level 3

Typically used for “excellent effort” or better than best effort and would 
include important business traffic that can tolerate some delay.

Level 2

This is for “spare bandwidth”. 

Level 1

This is typically used for non-critical “background” traffic such as bulk 
transfers that are allowed but that should not affect other applications and 
users. 

Level 0

Typically used for best-effort traffic.

Table 41   IEEE 802.1p Priority Level and Traffic Type

Table 42   Internal Layer2 and Layer3 QoS Mapping

0

1

0

000000

1

2

2

0

0

000000

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