RE: [Sip-implementors] what is spiraling

[Chris Boulton]

From 3261 :-   Loop: A request that arrives at a proxy, is forwarded, and later          arrives back at the same proxy.  When it arrives the second          time, its Request-URI is identical to the first time, and other          header fields that affect proxy operation are unchanged, so          that the proxy would make the same processing decision on the          request it made the first time.  Looped requests are errors,          and the procedures for detecting them and handling them are          described by the protocol.   Spiral: A spiral is a SIP request that is routed to a proxy,          forwarded onwards, and arrives once again at that proxy, but          this time differs in a way that will result in a different          processing decision than the original request.  Typically, this          means that the request's Request-URI differs from its previous          arrival.  A spiral is not an error condition, unlike a loop.  A          typical cause for this is call forwarding.  A user calls          [EMAIL PROTECTED].  The example.com proxy forwards it to Joe's          PC, which in turn, forwards it to [EMAIL PROTECTED]  This          request is proxied back to the example.com proxy.  However,          this is not a loop.  Since the request is targeted at a          different user, it is considered a spiral, and is a valid          condition.     So an illegal loop is a request that is re-visiting un-changed while a legal (spiral) will have altered it’s routing decision (R-URI has been altered by another proxy).   HTH,   Chris.     -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: 04 September 2002 18:00 To: [EMAIL PROTECTED] Subject: [Sip-implementors] what is spiraling   Hi all, Could you tell me what is spiraling, and what is the difference between  "loop" and "spiraling"?  Thank you. 　　                        [EMAIL PROTECTED] 　　　　　　　　　　  　   2002-09-05