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Mobile Backhaul by Esa Metsala, Juha Salmelin

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8.3 DSCP, Traffic Class, and Priority Bits

8.3.1 Differentiated Services

In the mobile backhaul, transport level quality of service (QoS) solutions are based on the Differentiated Services (DiffServ) approach which provides a relative service differentiation for connections aggregated into a limited number of well defined QoS classes based on the DiffServ code point (DSCP) encoded into each IP packet's header. 3GPP requires the use of DSCPs and a mapping of traffic categories into DSCPs as the means of transport layer QoS marking.

Traffic handling and scheduling decisions at the transport nodes are made based on the DSCP, that is, the network nodes differentiate the traffic based on its class marked by the DSCP. For each class a separate handling and forwarding policy is defined that is referred to as PHB (Per Hop Behaviour). Connections belonging to the same service class should be marked with the same DSCP in order to ensure the same level of service.

Differentiated Services (DS) classifies and conditions traffic at the network boundary (ingress), and assigns it to a behavior aggregate. The behavior aggregate is marked by a DS codepoint (DSCP). Network nodes then forward and schedule the packet according to the marked codepoint.

A DS domain consists of boundary nodes and interior nodes. Boundary nodes classify and condition traffic at the ingress. DS domain nodes then select the per-hop-behaviour according to the DS codepoint marking. A DS domain is managed typically by a single ...

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