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Exchange 2007


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We are trying to get PBXnSIP to play nice with Exchange 2007.


Everything works great but there two long delays during the SIP setup that results in about a 10 second total delay before the Exchange auto attendant starts talking.




Thru ugly low level packet traces it really seems that the Exchange server is just sitting there waiting.


I called MS and they tried for days to help but we could find no problems.


Then I got out the handy dandy telnet app and connected to port 5060 and pasted an INVITE to the Exchange server.


To my surprise it just hung out ... for about 5 seconds (which it does twice during a connection leading to the 10 second delay).


If I telnet and paste and then manually press ENTER it immediately works.


If I telnet and paste an extra CR+LF it just sits there for 5 seconds.


Is it a possible timing issue?


I've actually seen this trying to simulate an SMTP connection via Exchange.


Telnet/paste and it can't take it.


Doing the same thing to a Linux machine running exim and it eats it right up.


Does that make any sense?

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I got it figured out.


We like to live on the edge so we installed our PBXnSIP server of Vista x64.


Crazy aye?


Well ... I didn't trust just pasting the INVITE in via telnet so I made me a quicky program to do the same thing.


After repeated attempts to break it ... I couldn't.


Every bit-o-info in the packet was an exact duplicate of what PBXnSIP sent but my program wouldn't break.


That is until I ran it from the Vista machine.


Tried the program from WinXP, Win2003R2, Vista 32bit and Vista 64bit.


Each Vista machine "hung".


Packet traces showed a strange ACK being sent by Vista machines immediately after the INVITE.


Google told me about all the niffty enhancements to the TCP stack that Vista brought to the table.


What's this ... Auto-Tuning the receive window size ... hmm ...


From a command prompt:


netsh interface tcp set global autotuninglevel=disabled


After that single command ... we're now back on track.

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