D-Link DCS-6116 User Manual page 50

Section 3 - Configuration
Note:
• The VLAN Switch (802.1p) is required. The web browsing may fail if the CoS
setting is incorrect.
• Class of Service technologies do not guarantee a level of service in terms of
bandwidth and delivery time. They only offer a "best-effort." Users can think
of CoS as "coarsely-grained" traffic control and QoS as "finely-grained" traffic
control.
• Though CoS is simple to manage, it lacks scalability and does not offer end-to-
end guarantees since it is based on L2 protocol.
QoS (Quality of Service)
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.
The following are the main benefits of a QoS-aware network:
• The ability to prioritize traffic and guarantee a certain level of performance to the data flow.
• The ability to control the amount of bandwidth each application may use, and thus provide higher reliability and stability on the network.
Requirements for QoS:
To utilize QoS in a network environment, the following requirements must be met:
• All network switches and routers in the network must include support for QoS.
• The network video devices used in the network must be QoS-enabled.
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.
D-Link DCS-6116 User Manual 50