GS2210 Series User’s Guide
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H A P T E R
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Differentiated Services
39.1 Differentiated Services Overview
This chapt er show s you how t o configur e Different iat ed Ser vices ( DiffSer v) on t he Swit ch.
Qualit y of Ser vice ( QoS) is used t o pr ior it ize source- t o- dest inat ion t raffic flow s. All packet s in t he
flow ar e given t he sam e pr ior it y. You can use CoS ( class of serv ice) t o give differ ent pr ior it ies t o
differ ent packet t ypes.
DiffSer v is a class of ser vice ( CoS) m odel t hat m ar ks packet s so t hat t hey r eceive specific per- hop
t r eat m ent at DiffSer v- com pliant net w or k devices along t he r out e based on t he applicat ion t ypes
and t raffic flow. Packet s ar e m ar ked w it h DiffSer v Code Point s ( DSCPs) indicat ing t he level of
ser vice desir ed. This allow s t he int er m ediar y DiffSer v- com pliant net w or k devices t o handle t he
packet s different ly depending on t he code point s w it hout t he need t o negot iat e pat hs or r em em ber
st at e infor m at ion for ever y flow. I n addit ion, applicat ions do not have t o r equest a par t icular ser vice
or give advanced not ice of w her e t he t raffic is going.
39.1.1 What You Can Do
•
Use t he D iffSe r v scr een (
) t o act ivat e DiffSer v t o apply m ar king r ules
or I EEE 802.1p pr ior it y m apping on t he Sw it ch.
•
Use t he D SCP scr een (
) t o change t he DSCP- I EEE 802.1p m apping.
39.1.2 What You Need to Know
Read on for concept s on Differ ent iat ed Ser vices t hat can help you configur e t he scr eens in t his
chapt er.
DSCP and Per-Hop Behavior
DiffSer v defines a new DS ( Differ ent iat ed Ser vices) field t o r eplace t he Ty pe of Ser vice ( 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 ser vice levels and
t he r em aining 2 bit s ar e defined as cur r ent ly unused ( CU) . The follow ing figur e illust rat es t he DS
field.
Figure 230
DiffServ: Different iat ed Service Field
DSCP is backward com pat ible w it h t he t hree precedence bit s in t he ToS oct et so t hat non- DiffSer v
com pliant , ToS- enabled net w or k device will not conflict w it h t he DSCP m apping.
DSCP (6 bits)
CU (2 bits)
