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User's Manual - 45
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 level, the switch will handle video packets rst.
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 offer a "best-effort." Users can think of CoS as "coarsely-grained" trafc control and QoS as
"nely-grained" trafc 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�