RCA THOMSON SpeedTouchTM (Wireless) Business DSL Router - Manual (Page 20)

Chapter 3
Basic QoS Concepts
E-NIT-CTC-20041213-0013 v0.5
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3.2 Differentiated Services
Introduction Differentiated Services (DiffServ) is an architecture which allows service providers to
offer different kinds of services to different customers and their traffic streams.
Differentiated Services is a framework for scalable service discrimination and allows
an approach to modular IPQoS objectives for the needs of various types of
applications.
The premise to DiffServ networks is that routers within the core of the network are
capable to forward the packets of different traffic streams in different Per-Hop
Behaviours (PHB). The PHB for the packets is indicated by a Differentiated Services
Codepoint (DSCP) in the IP header. The DiffServ architecture does not use any
signalling between the routers but all the forwarding behaviour is defined by using
the DSCP.
Terminology Before we continue we will explain the abbreviations used in this section.
 Behaviour Aggregate (BA):
Is a collection of packets with the same Differentiated Services codepoint, thus
receiving the same PHB, crossing a DiffServ node in a particular direction.
 Differentiated Services CodePoint (DSCP):
Is the value in the IP header in the DS field, used to select the PHB.
 Per-Hop Behaviour (PHB):
Is the forwarding behaviour for the packet applied at DiffServ compliant nodes
to a DiffServ BA.
 Service Level Specification (SLS):
Is a set of parameters and their values which together define the service offered
to a traffic stream by a DiffServ domain.
 Traffic Conditioning Specification (TCS):
Is a set of parameters and their values which together specify a set of classifier
rules.