Cisco 8620, Справочное руководство

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Cisco Video Surveillance 8620/8630 IP Camera Reference Guide
Chapter 5 Configuration
Network > QoS (Quality of Service)
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.
You can enable CoS and/or QoS/DSCP.
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.
In 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 first.
Note • A VLAN Switch (802.1p) is required. Web browsing may fail if the CoS setting is incorrect.
•
The Class of Service technologies do not guarantee a level of service in terms of bandwidth and
delivery time; they offer a “best-effort.” You can think of CoS as “coarsely-grained” traffic control
and QoS as “finely-grained” traffic 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.
QoS/DSCP (the DiffServ model)
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 Codepoint). 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, queueing 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
to reserve for it.
Use the setting options of DSCP (DiffServ Codepoint) to specify the DSCP value for each application
(0~63).