asterisk users - Nov 2004 - Huge ten second audio delay on SIP channel

I have two Asterisk servers interconnected with IAX (non-trunk). I place a
call on Server B (using DIAX) which goes to an extension on Server A and
terminates with a Dial to a local SIP phone (Sipura SPA 2200).

The SIP phone rings immediately but when it is answered there is a delay of
about 10-15 seconds on the line.

However, if I put an Answer() just before the final Dial(SIP/..) command on
Server A's extension, there is the normal tens of millisecond delay in the
Audio. Clearly undesirable for billing reasons but does anyone know what on
earth is going on!?

I am using a recent CVS.

Thanks
Peter

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