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User's Manual - 71
Network > QoS (Quality of Service)
Advanced Mode
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.
The following are the main benets of a QoS-aware network:
■
The ability to prioritize trafc and guarantee a certain level of performance to the data ow.
■
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 models
CoS (the VLAN 802.1p model)
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 the frame priority level from 0
(lowest) to 7 (highest). The priority is set up on the network switches, which then use different queuing
disciplines to forward the packets.
Below is the setting column for CoS. Enter the VLAN ID of your switch (0~4095) and choose the priority
for each application (0~7).
If you assign Video the highest priority level, your network switch will handle video packets rst.
NOTE:
► A VLAN-capable Switch (802.1p) is required. 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 offer a “best-effort.” Users can think of CoS as “coarsely-grained” trafc control and QoS as
“nely-grained” trafc control.
► Although CoS is simple to manage, it lacks scalability and does not offer end-to-end guarantees since
it is based on L2 protocol.