The QoS framework allows network administrators to configure the router to meet the real
time requirements for voice and video. For a complete solution the QoS framework is supported
on both the Ingress and Egress interface. The QoS Framework supports the following domains:-
1. TOS
2. DSCP
3. VLAN
4. WME (WLAN only)
To support these domains the QoS Framework introduces a virtual concept of Class of Service(CoS).There are
six levels of service available named and prioritized as follows:-
CoS1 > CoS2 > CoS3 > CoS4 > CoS5 > CoS6
The network admin needs to define Ingress TCA that maps the Domain to CoSx. The framework also allows the ability
to classify packets on the basis of the type of data. Currently the following fields can be used to
classify packets:-
1. Source Mac Address
2. Source IP Address/Source Net
3. Destination IP Address/Destination Net
4. Source Port (Range is supported)
5. Destination Port (Range is supported)
6. Protocol
Once a packet has been classified on the Ingress the network admin needs to configure the Egress to do the reverse
i.e. CoSx to Domain Mappings.
The QoS Framework also provides the following shaping algorithms:-
1. PRIOWRR
This is a priority based WRR algorithm operating on CoS2-CoS6. CoS1 queues are highest priority and are
not controlled by the WRR algorithm.
2. Rate Based Shaper
The PRIOWRR algorithm does not account for the packet size. This algorithm rate shapes the traffic
of a class over a specific interface. All CoSx traffic is assigned a specific rate to which data will be
shaped to. Example: If CoS1 is configured to 100Kbps then even if 300Kbps of CoS1 data is being transmitted
to the interface only 100Kbps will be sent out.
3. Low Latency Shaper
This is similar to the above algorithm except that CoS1 is not rate limited. So in the example above CoS1
data is not rate limited to 100Kbps but instead all 300Kbps is transmitted. The side effect is that a
misconfigured stream can potentially take all bandwidth.
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