Hi,

A service provider supports the following SIP service:
A user could apply a primary number and serveral virtual numbers, for example, 
primary number is 213xxxxxx in Los Angeles, vitual numbers are 312xxxxxx in 
Orlando, 616xxxxxx in Michigan etc. He only register the SIP account of 
213xxxxxx on his SIP device, then Orlando's people just dial 312xxxxxx to call 
him, and similar process happens on 616xxxxxx.

Several months ago, I borrowed one SIP account from the provider to test the 
SIP service. In the incoming INVITE message from its proxy server, FROM header 
includes caller number, TO header consists of my primary number and REQUEST_URI 
is the same with TO header. I couldn't see any informations about virtual 
numbers in INVITE message.   

Now, I hear from the carrier has improved the SIP service, it is interesting 
that when calls from different virtual numbers are received, the ring tone(not 
ringback) of SIP device are diffenent. I don't know, but want to how the 
carrier realize it.

If the carrier realizes it by Multi-Line way as RFC4504 refers to, it isn't 
complex. But is it possible that the incoming INVITE message has nothing about 
virturl numbers but some parameters of ring tones? so my question is whether 
some parameters in SIP or SDP protocols could configure ring tone during SIP 
calls.

Thanks and regards,

luke
2006-12-04



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