ZyXEL Communications VSG1432-B101 - V1.10, Manual

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Chapter 10 Quality of Service (QoS)
VSG1432-B101 Series User’s Guide
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• The Monitor screen lets you view the ZyXEL Device's QoS-related packet
statistics ( Section 10.7 on page 165 ).
10.2 What 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.
Tr
af
fi
c
Time
Traffic Rate
Tr
a
ff
ic
Time
Traffic Rate
(Before Traffic Shaping) (After Traffic Shaping)