This probably has nothing to do with Asterisk, but I'm hoping someone can point me in the right direction.... My senario is.... Phone A is a hardware SIP phone Phone B is a hardware SIP phone Phone C is a Microsoft RTC API SDK endpoint (http://msdn.microsoft.com/library/default.asp?url=/downloads/list/clientapi.asp) All three are registered with the latest release version of Asterisk. A phones B. B phones C. B hangs up, A is connected to C. This all works fine, however there is a wait of about 10 seconds between B handing up, and A being connected to C. I've compared traces between C being an RTC endpoint, and C being a SIP phone. The SIP phone seems to send more ACKs than the RTC endpoint. However the trouble with the RTC is that all the SIP commands have been abstracted out, so I can't just send my own ACKs. Then again, these ACKs can't be essential as the transfers do work with the RTC endpoint, it's just that I get this 10 second delay. Any ideas are very welcome. And before you say it, the project I'm working on has insisted I use the Microsoft RTC, so no changing library 'm afraid. :-( Jerry