From: "Smith, Nathan" <[EMAIL PROTECTED]> Quick question on what the "correct" behaviour of a SIP redirect server is expected to be, in a Voice Telephony environment where the redirector is used solely to spread call load over a number of dedicated Application Servers:
Initiating AS Redirector Destination AS INVITE-----------------> <-------------100 Trying <-------------180 Ringing * <-------------302 Moved Temp ACK--------------------> INVITE----------------------------------------> <------------------------------------100 Trying <------------------------------------180 Ringing <------------------------------------200 OK ACK-------------------------------------------> In general, there is nothing forbidding a "redirect server"(*) from returning any provisional response. And as Jerry Yin says, the redirector may want to use a 180 to carry early media to provide an announcement. But if it is anannouncement for a redirection, the provisional response should be 181 Call Is Being Forwarded. But in this case, at this point in the call, the call is *not* ringing, so the redirector should *not* send 180 Ringing. In most cases, the 302 will be returned immediately, so no 18x response is needed to inform the UAC what is happening. If early media for an announcement needs to be carried, 181 is an obvious choice, or perhaps 182, or if there is no better choice, 183. (*) Generally, people classify SIP agents into "user agents" which terminate dialogs, and "proxies" which pass requests through to other agents. But a redirect server is in an even narrower class, which neither terminates requests nor passes them through, it only generates non-2xx responses to them. Dale _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
