ZyXEL Communications VMG1312-B Series, User Manual

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Chapter 10 Quality of Service (QoS)
VMG1312-B Series User’s Guide
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10.2 What You Need to Know
The following t erm s and concept s m ay help as you read t hrough t his chapt er.
QoS versus Cos
QoS is used t o priorit ize source- t o- dest inat ion t raffic flows. All packet s in t he sam e flow are given
t he sam e priorit y. CoS ( class of service) is a way of m anaging t raffic in a net work by grouping
sim ilar t ypes of t raffic t oget her and t reat ing each t ype as a class. You can use CoS t o give different
priorit ies t o different packet t ypes.
CoS t echnologies include I EEE 802.1p layer 2 t agging and DiffServ ( Different iat ed Services or DS) .
I EEE 802.1p t agging m akes use of t hree bit s in t he packet header, while DiffServ is a new prot ocol
and defines a new DS field, which replaces t he eight- bit ToS ( Type of Service) field in t he I P header.
Tagging and Marking
I n a QoS class, you can configure whet her t o add or change t he DSCP ( DiffServ Code Point ) value,
I EEE 802.1p priorit y level and VLAN I D num ber in a m at ched packet . When t he packet passes
t hrough a com pat ible net work, t he net working device, such as a backbone swit ch, can provide
specific t reat m ent or service based on t he t ag or m arker.
Traffic Shaping
Burst y t raffic m ay cause net work congest ion. Traffic shaping regulat es packet s t o be t ransm it t ed
wit h a pre- configured dat a t ransm ission rat e using buffers ( or queues) . Your Device uses t he Token
Bucket algorit hm t o allow a cert ain am ount of large burst s while keeping a lim it at t he average rat e.
T
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Traffic Rat e
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Traffic Rat e
( Befor e Traffic Shaping) ( Aft er Traffic Shaping)