How to notify SIP client when there is an incoming call on another phone

is it possible to notify a SIP client when there is an incoming call on another phone? I know that there are the SUBSCRIBE and NOTIFY commands but I have found no event package for signaling incoming calls.

Background: for a SIP-capable telephony system, I would like to provide an application that displays information about开发者_JS百科 the caller (e.g. name, address, contracts, etc.) when the phone rings. The phones are external to the PC; they are not soft-phones.

-Frank

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The dialog event package (RFC4235) is what you're after. The key realisation is that dialog's get established when the first non-100 response is received on an INVITE transaction.

A dialog is in the early state until the INVITE is answered with a final response but that doesn't matter as the dialog event package is designed to send notifications for early dialogs just the same as for answered dialogs.

Finding servers or providers that supprt the dialog event package is another matter. The best softphone that I have come across for SIP events is the Bria, as far as servers go sip2sip and my own sipsorcery have some level of support for the dialog event package although I must admit I have left out early dialog notifications.