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Community Member

cos and qos

Hi all, I am soon to implement qos, can anyone tell me the difference between qos and cos, is cos used on older switches? and on most new devices is it all qos ? also when running this, does it have to be on every port on every switch btween the connection ?


Re: cos and qos


Actually Cos can be called as a subset of QoS.

In a layer 2 trunk frame, you have 3 bits that define class of service(COS).

When you manipulate this prioritising traffic, you are actually implementing QoS

HTH, rate if it does


Community Member

Re: cos and qos

can you explain a little further for me ? i am still unsure

Community Member

Re: cos and qos

Quality of service refers to control mechanisms that can provide different priority to different data flow.

Ex. At the ethernet layer i.e Layer2 the frame uses the Class of Service in 802.1p and ISL. Qos can be used to place frames in different Queues based on the priority set in 802.1p. This allows each queue to have different service levels. Each queue can have a threshold set. The thresholds act as the starting point for the packet to be dropped.

At layer 3 we have the ToS(Type of Service or IP Precedence). Many implementations provide for the mapping of the ToS to CoS. This provides for an end to end priority for the traffic flow.

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