Skype public API - difference between Alter Call and Set Call?

I am looking over the Skype public API and I am not sure what the difference between these two commands if the Skype call status is RINGING:

ALTER CALL 8 ANSWER

vs

SET CALL 8 STATUS INPROGRESS

The same goes for hanging up a call that is IN开发者_开发技巧PROGRESS. Whats the difference between these two?

ALTER CALL 8 HANGUP

vs

SET CALL 8 STATUS FINISHED

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To my experience so far, there is not any difference between those two commands in terms of their effects.