Differentiated Services; Differentiated Services Overview - ZyXEL Communications GS2210-8 User Manual

39.1 Differentiated Services Overview

This chapt er shows you how t o configure Different iat ed Services ( DiffServ) on t he Swit ch.
Qualit y of Service ( QoS) is used t o priorit ize source- t o- dest inat ion t raffic flows. All packet s in t he
flow are given t he sam e priorit y. You can use CoS ( class of service) t o give different priorit ies t o
different packet t ypes.
DiffServ is a class of service ( CoS) m odel t hat m arks packet s so t hat t hey receive specific per- hop
t reat m ent at DiffServ- com pliant net work devices along t he rout e based on t he applicat ion t ypes
and t raffic flow. Packet s are m arked wit h DiffServ Code Point s ( DSCPs) indicat ing t he level of
service desired. This allows t he int erm ediary DiffServ- com pliant net work devices t o handle t he
packet s different ly depending on t he code point s wit hout t he need t o negot iat e pat hs or rem em ber
st at e inform at ion for every flow. I n addit ion, applicat ions do not have t o request a part icular service
or give advanced not ice of where t he t raffic is going.
39.1.1 What You Can Do
• Use t he D iffSe r v screen (
or I EEE 802.1p priorit y m apping on t he Swit ch.
• Use t he D SCP screen (
39.1.2 What You Need to Know
Read on for concept s on Different iat ed Services t hat can help you configure t he screens in t his
chapt er.
DSCP and Per-Hop Behavior
DiffServ defines a new DS ( Different iat ed Services) field t o replace t he Type of Service ( ToS) field in
t he I P header. The DS field cont ains a 6- bit DSCP field which can define up t o 64 service levels and
t he rem aining 2 bit s are defined as current ly unused ( CU) . The following figure illust rat es t he DS
field.
Figure 230 DiffServ: Different iat ed Service Field
DSCP is backward com pat ible wit h t he t hree precedence bit s in t he ToS oct et so t hat non- DiffServ
com pliant , ToS- enabled net work device will not conflict wit h t he DSCP m apping.
C
HAPTER

Differentiated Services

Sect ion 39.2 on page 334) t o act ivat e DiffServ t o apply m arking rules
Sect ion 39.3.1 on page 336) t o change t he DSCP- I EEE 802.1p m apping.
DSCP (6 bits)
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CU (2 bits)
3 9