D-Link DCS-7517 User Manual page 52

Configuration
QoS (Quality of Service)
Quality of Service refers to a resource reservation control mechanism, which
guarantees a certain quality of transmission 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. It gives you the ability
to prioritize traffic and guarantee a certain level of performance. It can also help
you control the amount of bandwidth each application may use, and thus provide
higher reliability and stability for your 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 have QoS enabled.
CoS
IEEE802.1p defines a QoS model at OSI Layer 2 (Data Link Layer), which is called
CoS, Class of Service. It adds a 3-bit value to the VLAN MAC header, which indicates
prioritization from 0~7 (eight different classes of service are available). The priority
is set up on the network switches, which then use different queuing disciplines to
forward the packets.
Please follow the steps below to enable CoS:
1. Click Enable CoS.
2. Enter the VLAN ID of your switch (0~4095).
3. Choose the priority for each application (0~7). Higher values will provide higher
priority.
Note:
• A VLAN Switch (802.1p) is required. Web browsing may fail if the CoS settings
are 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." You 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.
D-Link DCS-7517 User Manual 52