Alcatel OmniPCX and Asterisk 1.4

Hi, I am a newbie to telephony in general, so I apologise for any incorrect terminology.

I am trying to link and alcatel pbx and asterisk.

I have set it up so that I can succesfully make calls from Asterisk to Alcatel.
However I can’t get the Alcatel to successfully make calls to Asterisk.

Every time I try I get the following message.

Call from ‘’ to extension ‘1000’ rejected because extension not found

I have found that if I edit sip.conf to include a context=blah in the [general] context then it appears to work. However this does not seem like the correct solution.

Can anyone help me understand why when the alcatel box sends a call to asterisk it doesn’t appear to be telling asterisk who it is and so the call does not end up inside my [alcatel] context inside sip.conf.