Chapter 10 Quality of Service (QoS)

•The Monitor screen lets you view the ZyXEL Device's QoS-related packet statistics (Section 10.7 on page 169).

10.2What You Need to Know

The following terms and concepts may help as you read through this chapter.

QoS versus Cos

QoS is used to prioritize source-to-destination traffic flows. All packets in the same flow are given the same priority. CoS (class of service) is a way of managing traffic in a network by grouping similar types of traffic together and treating each type as a class. You can use CoS to give different priorities to different packet types.

CoS technologies include IEEE 802.1p layer 2 tagging and DiffServ (Differentiated Services or DS). IEEE 802.1p tagging makes use of three bits in the packet header, while DiffServ is a new protocol and defines a new DS field, which replaces the eight-bit ToS (Type of Service) field in the IP header.

Tagging and Marking

In a QoS class, you can configure whether to add or change the DSCP (DiffServ Code Point) value, IEEE 802.1p priority level and VLAN ID number in a matched packet. When the packet passes through a compatible network, the networking device, such as a backbone switch, can provide specific treatment or service based on the tag or marker.

Traffic Shaping

Bursty traffic may cause network congestion. Traffic shaping regulates packets to be transmitted with a pre-configured data transmission rate using buffers (or queues). Your ZyXEL Device uses the Token Bucket algorithm to allow a certain amount of large bursts while keeping a limit at the average rate.

Traffic Rate

Traffic Rate

Traffic

Time

Traffic

Time

(Before Traffic Shaping)

(After Traffic Shaping)

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VSG1435-B101 Series User’s Guide