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Question on Pause Frames and the FlexFabric module

Trusted Contributor

Question on Pause Frames and the FlexFabric module

Jeff had a FlexFabric module question:




    I have a question about pause frames on a FlexFabric mdule.    Would the SAN Ports on the FlexFabric module be affected by Pause Frames or do they have a different memory buffer for Fibre Channel?  




Jim replied:




My understanding is once a FCoE frame de-encapsulates the Fibre Channel (FC) from the Ethernet Frame, it is FC.

A Fiber Channel network is designed so that all capacity within the system is distributed and not oversubscribed. This is one of the many ways FC keeps from dropping frames, something that should never be allowed to happen in a FC world, because the underlying protocol at the FC4 layer, SCSI, will not tolerate it.

With Fiber Channel, each switch keeps track of how many credits it has available over each of its links. If it has credits, it sends data, decrements the credits and stops sending data when it runs out of credits. As it receives Receiver Ready frames, it replenishes its credits. At no time does it allow itself to use more capacity than it has agreed upon with the distant end.





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