ZyXEL Communications P-660HN-F1 15.5 QoS Technical Reference, 15.5.2 IP Precedence, 15.5.1 IEEE 802.1Q Tag

	Chapter 15 Quality of Service (QoS)
Table 86 Advanced > QoS > Monitor (continued)
LABEL	DESCRIPTION
Set Interval	Click this to apply the new poll interval you entered in the Poll Interval(s) field.
Stop	Click this to stop refreshing statistics.

15.5 QoS Technical Reference

This section provides some technical background information about the topics covered in this chapter.

15.5.1 IEEE 802.1Q Tag

The IEEE 802.1Q standard defines an explicit VLAN tag in the MAC header to identify the VLAN membership of a frame across bridges. A VLAN tag includes the 12-bit VLAN ID and 3-bit user priority. The VLAN ID associates a frame with a specific VLAN and provides the information that devices need to process the frame across the network.

IEEE 802.1p specifies the user priority field and defines up to eight separate traffic types. The following table describes the traffic types defined in the IEEE 802.1d standard (which incorporates the 802.1p).

Table 87 IEEE 802.1p Priority Level and Traffic Type

PRIORITY	TRAFFIC TYPE
LEVEL
Level 7	Typically used for network control traffic such as router configuration messages.
Level 6	Typically used for voice traffic that is especially sensitive to jitter (jitter is the variations in
	delay).
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.

15.5.2 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.

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