19216811.liveUser Manual
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Quality of Service
Quality of service allows network administrators to configure the routers to meet the real
time requirements for voice and video.
Different networks use different QoS markings like:
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ToS network: ToS bits in the IP header
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VLAN network: priority bits in the VLAN header
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DSCP network: uses only 5 bits of the CoS
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WLAN: WLAN QoS header.
The QoS framework is supported on all the above domains. How do you make them talk
to each other? How can you make sure the priority from one network is carried over to
another network? Class of service (CoS) is introduced as the common language for the
QoS mappings. When QoS is enabled, the router has full control over packets from the
time they enter the router till they leave the router. This is how it works: The domain
mapping (ToS bits, priority bits, etc.) of a packet needs to be translated to CoS when the
packet enter the router, and vice versa, the CoS of a packet needs to be translated back
to the domain mapping when the packet leaves the router.
There are some additional terms you should get familiarize with:
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Ingress: Packets arriving into the router from a WAN/LAN interface.
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Egress: Packets sent from the router to a WAN/LAN interface.
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Trusted mode: Honors the domain mapping (ToS byte, WME, WLAN user priority).
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Untrusted mode: Does not honor domain mapping. This is the default QoS setting.
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Traffic Conditioning Agreement (TCA): The TCA needs to be defined for each
interface:
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Ingress mappings (Domain =>CoS)