I have a question regarding qos over frame-relay .
Let's say we dont use the same classification and marking on both sides of the network.
On side A you put traffic X in REAL-TIME class (dscp=ef) and on side B you put traffic X in DATA class (dscp af41) , so the marking and classification is not the same.....
What will happens in case of congestion of the frame-relay link ?
Second question , is the qos mechanism on the cisco router ALWAYS active or is it just active when you have congestion on the link ?
This is result of poor design. One thing you have keep in your mind when designing QOS is desing end to end QOS solution, not the one you are talking about. No administrator would like to have same category of traffic marked differently within their network. They would also ensure that no one sending wrongly marked packets when they are connected to other networks. QOS design should be neatly defined in terms of boundary and consistent markings for traffic types.
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Hey Thomas -
1) Your QOS congestion management or avoidance mechanism is completely independant of your global marking scheme. Hence, router A's congestion management (for example) will treat packets in accordance with their markings in relation to what you have specified for the policy to do - ie. guarantee bandwidth, police etc. If you change markings before packets reach router B, router B could care less. It is still going to simply follow whatever QOS policy you have configured. If you tell it to guarantee 10Mb for DSCP EF, it makes no difference if EF was classified VoIP at previous points in the network, but now is being utilized for FTP marking.
Quite simply - the router will do what you tell it to do at each point in the network.
2) "Second question , is the qos mechanism on the cisco router ALWAYS active or is it just active when you have congestion on the link ?".....Depends. Congestion avoidance (such as policing / shaping) will occur irrespective of how utilized your interface is. Congestion management (such as CBWFQ) only kicks in during times of congestion. Then theres WRED, which is also congestion avoidance....WRED sits somewhere between policing and CBWFQ in that it only starts at a predefined threshold, and ramps up in force as congestion increases.