Why is Master Slave Determination Acknowledged In Both Direction? (Q74)

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The first ACK in the MSDSE delivers the results to the initiating EP; the second ACK informs the remote EP that the initiating EP has received the results. You can't do anything that depends on MSD until both sides know the results of the MSD and know that the other EP knows the results. Without the second ACK, the remote EP wouldn't know exactly when the initiating EP knew who was master and who was slave. It would have to wait some arbitrarily long amount of time before assuming that the initiating EP "knows," and this would simply not be practical. See C.2.1/H.245v5.