P.J. Cast. wrote: > Hi Benny, > > The issue is the sip proxy server expects the CallID > to be the same, so it can identify the forwarded call > as being part of the previous call. Else, it would be > a completely new transaction. Terminology: transaction: consists of a request, optional 0..n provisional responses and a final response. Thus every new INVITE request is a new SIP transaction. Its even a new SIP dialog as the the first INVITE transaction did not created a dialog. Thus, the relationship between the first INVITE and the second INVITE is only at application layer - not at SIP layer. A good SIP client should not automatically accept a 302 and make a new call but it should ask the user if it wants to make a new call to the provided URI. Maybe some clients reuse the call-id in the new call attempt, but others will not and IMO both is valid. A SIP proxy (or the billing system) should never rely on data provided by the SIP client. If you need full control over call setup and billing it is better to do the redirection in the proxy. do not trust user provided data (like call-id, tags, contact ...) blindly as this are very easy to spoof. > > For instance, a UserA dials UserB, but UserB is not > available and he has setup a forward to some PSTN > number. Consequently, Proxy returns 302 with new > number. > > Now, with the callid, the proxy can recognize that it > was a forward from UserB, so UserB is the party > responsible for it (and any billing/accounting > associated). > > With a new CallID, UserA would have to pay to be > forwarded. Not really optimal. Again: never expect all clients to act like you expect them. If you want to charge to call to user B then make the redirection in the proxy. > > For reference, both Xlite & Grandstream SIP Phones I > have used send the Invite in response to the callid > with the same CallID to maintain the transaction. > Though, they differ in how they send out the To and > Sip URI fields. > > It is pretty vital that this works by placing a call > with the same call id. Is there no way to control its pretty vital that you do not design your system by expecting all clients act the same way. > this? Perhaps it would be a simple matter to modify > pjsip? If so, where would you recommend > modifications... allow client to set the callid sounds > simplest. IMO you should fix the handling in your proxy. regards klaus
