proxying to a SIP Server located behind the firewall

Hi,
I have a query reg. siproxd. Does it support forwarding calls to a SIP 
server located behind the firewall? Explaining furthur, let us assume I 
have a firewall (configured on a Linux machine) with a public IP. Behind 
the firewall, I have a SIP server with a Private IP (which can 
communicate with the Internet using NAT). Now if someone places a SIP 
call to the Linux machine (ruuning SIPFwd), can it proxy it to the 
private SIP server and start a conversation?

My real problem is that I have only one public IP. If I do port 
forwarding of SIP port (5060) in the firewall to the internal SIP 
server, then users can call the SIP server directly by calling 
account-v+aXH1h/sVxuYUHNOcvv81aTQe2KTcn/@public.gmane.org (assuming "account" is a user in the SIP 
server). But then my users will be forced to use the name "account" as 
the username. What I want them to do is use 
"rahul-v+aXH1h/sVxuYUHNOcvv81aTQe2KTcn/@public.gmane.org". So I essentially need rewriting of the SIP 
url by siproxd.

Is this feasible with siproxd? ? if not, could you suggest me any SIP 
software (other than full blown PBXs such as Asterisk) which will help 
me achieve this functionality?

Thanks and Regards,
Rahul.


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