> -----Original Message-----
> From: Deepak Mohan [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, June 07, 2001 4:03 AM
> To: [EMAIL PROTECTED]
> Subject: [Sip-implementors] Spirals
>
>
> Hi,
> I am having some trouble understanding request spirals. I've
> checked the FAQ, but there is nothing on this. Can somebody
> either explain this to me, or point me to a link where this
> has already been discussed?
Sprials are defined in bis-03. They are requests that loop back to the same
proxy, but for which the request URI has changed.
Classic example:
[EMAIL PROTECTED] calls [EMAIL PROTECTED] Goes to the bigcompany.com proxy.
It proxies it to [EMAIL PROTECTED] The marketing.bigcompany.com
proxy invokes a CPL. The CPL has bob forwarding all his calls to
[EMAIL PROTECTED] This request is then proxied to the bigcompany.com
proxy. Now, this is a "loop", in the sense that the request has hit the same
server, but its a valid one. Its valid because the request URI the second
time around (sip:[EMAIL PROTECTED]) is not the same as the first time
around (sip:[EMAIL PROTECTED]). So, the proxy should accept this and
process it. This case is called a "spiral". Its called that since you can
think of a proxy network in two dimensions; one dimension is the set of
elements, and the other is the r-uri. The request returns to the same point
in the first axis, but a different point in the second. Much like a spiral
in 3D space, which returns to the same point in the X,Y axis, but a
different one in the Z.
Now, how does the proxy know this was a spiral, and not a loop? Using the
branch-ID. The branch-ID is supposed to contain a hash of the R-URI. So,
when the request arrives again at the proxy, it finds its previous Via entry
(because of the host name), and it matches. THen, it computes the hash of
the R-URI in the incoming request, and compares it to the hash in the branch
ID. If they are not the same, its a spiral. If they're the same, its a loop.
-Jonathan R.
---
Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Ave.
Chief Scientist First Floor
dynamicsoft East Hanover, NJ 07936
[EMAIL PROTECTED] FAX: (973) 952-5050
http://www.jdrosen.net PHONE: (973) 952-5000
http://www.dynamicsoft.com
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