D-Link DCS-3511 User Manual page 52

Configuration
QoS/DSCP
DSCP-ECN defines 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 field to the IP header, called the DSCP (Differentiated Services Code Point). This is a 6-bit field
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 insufficient, especially for real-time streaming multimedia applications.
Quality can be defined as, for instance, a maintained level of bit rate, low latency, no packet dropping, etc.
D-Link DCS-3511/DCS-3530 User Manual 52