On Apr 12, 2008, at 12:18 PM, Francois Audet wrote: > Every single endpoint that I've seen does NOT use a Tel URI per se, > but > rather, a Tel URI embedded in a sip URI as per RFC 3261/19.1.6. > > Insisting on Tel URI seems kind of out of touch with reality.
So they're functionally limited. Explain to me what you would send in a 302 response to redirect the UAS to call a certain phone number on it's own dime. I don't believe we have a way to do this, and I have always believed it to be a critical use case for real integration (and no, today's "telephony over IP" services are not really integrated, which is why Gizmo customers call Vonage customers through multiple PSTN gateways). Here's a use case: Let's say Gizmo and Vonage some day figure out how to peer at a SIP level. Assuming we maintain current billing models: Alice is a Gizmo customer. As such, she pays Gizmo per minute on calls going to the PSTN, but calls to IP destinations (which don't use Gizmo's bandwidth) are not charged to her. Calls coming from the PSTN are also not charged to her. Bob is a Vonage customer. As such, he pays Vonage per minute on calls going to the PSTN, but calls to IP destinations (which don't use Vonage's bandwidth) are not charged to him. Calls coming from the PSTN are also not charged to him. Alice calls Bob. Bob wishes to redirect Alice to call the premium telephone destination 1-900-HELP-DSK. This is an expensive service to Bob, but perhaps he thinks Alice is willing to pay for it or already has a service contract allowing her to call the service for free. If Bob wanted to pay for this call, he would proxy Alice through a Vonage gateway, but provide credentials so that the call is charged back to him. Bob does not wish to pay from his account . But in this case, let us assume that Bob does NOT want to pay for Alice's call to the help desk. The obvious way to do this is for Bob to send a 300 class response, probably a 302. But remember that Bob's system has no knowledge of Alice's PSTN routing model, and outside of a domain name, no knowledge of Gizmo's service at all. So what should go into the 302 as a Contact: header field value? It can't be "sip:[EMAIL PROTECTED]" or even "sip:[EMAIL PROTECTED];user=phone " because Alice presumably doesn't have permission to use Vonage's gateways. Perhaps Bob's system could guess that Gizmo might understand ""sip:[EMAIL PROTECTED] " or maybe ""sip:[EMAIL PROTECTED];user=phone" and use this to reach an appropriate gateway. But what if Alice gets better rates by using a local phone line on her FXO port to reach that phone number? What if, unknown to Bob, there's an ENUM entry for +19004357375 that would have allowed Alice to call that number directly over SIP instead of using a gateway at all? Similar (and perhaps less contrived) use cases can be constructed around REFER -- how doe we ask somebody in a different domain to call a PSTN destination? How do you think this should work? The only way I'm aware of that we have to express the desired semantic is to redirect the call to "tel:+19004357375" and let Alice's UA figure out how it wants to get there. -- Dean _______________________________________________ Sip mailing list https://www.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip
