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52D-Link DCS-7110 User Manual
Conguration
QoS/DSCP
DSCP-ECN denes QoS at Layer 3 (Network Layer). The Differentiated
Services (DiffServ) model is based on packet marking and router queuing
disciplines. The marking is done by adding a eld to the IP header, called the
DSCP (Differentiated Services Code Point). This is a 6-bit eld that provides
64 different class IDs. It gives an indication of how a given packet is to be
forwarded, known as the Per Hop Behavior (PHB). The PHB describes a
particular service level in terms of bandwidth, queuing theory, and dropping
(discarding the packet) decisions. Routers at each network node classify
packets according to their DSCP value and give them a particular forwarding
treatment. For example, how much bandwidth should be reserved.
Quality of Service refers to a resource reservation control mechanism, which
guarantees a certain quality to different services on the network. Quality
of service guarantees are important if the network capacity is insufcient,
especially for real-time streaming multimedia applications. Quality can be
dened as, for instance, a maintained level of bit rate, low latency, no packet
dropping, etc.