ZyXEL Communications zyxel 14.8 Technical Reference

Chapter 14 Quality of Service (QoS)

14.8 Technical Reference

The following section contains additional technical information about the P-870HN- 51D features described in this chapter.

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 68 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.

DiffServ

QoS is used to prioritize source-to-destination traffic flows. All packets in the flow are given the same priority. You can use CoS (class of service) to give different priorities to different packet types.

DiffServ (Differentiated Services) is a class of service (CoS) model that marks packets so that they receive specific per-hop treatment at DiffServ-compliant network devices along the route based on the application types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs) indicating the level of

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