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Re: [PWE3] PWE3 new WG items? PW QoS


Busschbach, Peter B (Peter) wrote:
Peter>- Are segments set up in a random order or is there a need 
for a certain sequence of message?






Scott> For scaling and robustness you can't require a certain order of setup.


Scott,

Assume one wants to set up a multi-segment from A via B and C to D to carry ATM traffic. Suppose that the segment between B and C is set up independently from the other two segments. Then it is possible that B indicates to C that it accepts a maximum number of ATM cells per frame equal to N1. Subsequently, B could learn from A that A accepts a maximum number of ATM cells per frame equal to N2. If N2 is smaller than N1, there is a problem. B might have to repackage frames it receives from C to make sure it doesn't exceed N2 cells in the frames it forwards to A.

Based on this example, it seems obvious to me that B has to receive a PW setup message from A before it can forward it to C and C has to receive a setup message from B before it can forward it to D. In other words, there is a clear order.




Hi Peter,



Agree with your observation.  Even though the ordered setup is a sensible 
approach and makes life easier to establish a multi-segment pseudowire, it's 
still up to the stitching nodes, B and C in this case, to decide what the 
aggragated events should be to trigger its signaling.  For example, they need 
other resources to get ready before start signaling and they can wait 
indefinitely before start signaling.



Therefore, the ordered setup seems to be more of an implementation specific 
issue for the stitching nodes rather than an item to be standardized.



---Wei






Peter 


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