Subject: [SIP] SIP Privacy Draft

From: William Marshall <[email-masked]>
Date: Thu, 1 Feb 2001 11:35:30 -0500 (EST)

Mark Watson's update on the privacy draft discussions reminded me
that I had an action item to bring to the list, regarding multiple
180 responses in a SIP session.

When a SIP call is delivered to a PSTN gateway, and thus to a PSTN
endpoint (B), B may have call forwarding established to (C).  In some
cases (which I admit to not understanding completely) the SS7 signaling
could identify endpoint B as a destination that is ringing, and later
identify endpoint C as an updated destination that is ringing.
Presumably if C forwards to D, and D forwards to E, etc etc etc, there
could be a whole sequence of indications received by the PSTN gateway
about ringing endpoints.

The question is whether these {may/should/shouldnot} result in multiple 
180-Ringing SIP responses.  I don't see anything in 2543 or 2543bis
that limits a UAS to sending a single 180 response, but it doesn't
seem like expected behavior.  So, {should/must} a standard UAC handle 
multiple 180 responses?

Bill Marshall
[email-masked]

_______________________________________________
This list is for continuing development of the SIP protocol.
The sip-implementer's list is the place to discuss implementation,
and to receive advice on understanding existing sip.
To subscribe to it, send mail to [email-masked] with
"subscribe sip-implementors" in the body.

---

From: "Henning G. Schulzrinne" <[email-masked]>
Date: Fri, 02 Feb 2001 14:56:04 -0500

> seem like expected behavior.  So, {should/must} a standard UAC handle

There are no restrictions on any 1xx responses, in terms of number,
ordering and type. Thus, any combination and sequence of 1xx has to be
handled correctly, including several 1xx with the same status code. The
spec says:

A server {\MAY} issue zero
or more 1xx responses, with no restriction on their ordering or
uniqueness. 

-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

---

From: Michel de Boer <[email-masked]>
Date: Mon, 05 Feb 2001 09:41:51 +0100

> could be a whole sequence of indications received by the PSTN gateway

SS7 identifies B as ringing and then forwards the call to C in the case
of call forwarding on no answer. A calls B. B rings several times but does
not answer the call. Then the call is forwarded to C. This is a common way
to implement a voice mailbox. You forward your call on no-answer to your
voice mail.
-- 
Michel de Boer
Lucent Technologies

Phone:  +31 35 687 3803
Fax:    +31 35 687 5822
E-mail: [email-masked]
Room:   BF203 (HVS)