Subject: [Sipping] How can INVITE and ACK contain message bodies??

From: [email-masked]
Date: Fri, 12 Oct 2007 12:13:57 +0530

Hi All,
        Help me in interpreting the meaning and the flow of the following 
test case.

SIP_CC_TE_CE_V_008:
Ensure that the IUT on receipt of an INVITE request including a message 
body with
a content-Disposition header not set to session value includes in its 
first 2xx 
response an initial offer session description. 

From the above test case I could understand that if the 
Content-Disposition header 
value is not session (in the Incoming INVITE) then the 2xx for the INVITE 
contains 
an intial offer.

 Does the test-case mean that the offer in the INVITE request is rejected 
and a 
new offer is sent again in 2xx response to the INVITE????

But with reference to following statements from RFC 3261, 

 "When a user agent client desires to initiate a session (for example,
   audio, video, or a game), it formulates an INVITE request.  The
   INVITE request asks a server to establish a session.  This request
   may be forwarded by proxies, eventually arriving at one or more UAS
   that can potentially accept the invitation.  These UASs will
   frequently need to query the user about whether to accept the
   invitation.  After some time, those UASs can accept the invitation
   (meaning the session is to be established) by sending a 2xx response.
    If the invitation is not accepted, a 3xx, 4xx, 5xx or 6xx response is
   sent, depending on the reason for the rejection.  Before sending a
   final response, the UAS can also send provisional responses (1xx) to
   advise the UAC of progress in contacting the called user."

If the INVITE cannot be accepted then a failure response must be sent.

Also under the section 13.2.1 in RFC 3261 it has been quoted that,

"The restrictions of the offer-answer model just described only apply
   to bodies whose Content-Disposition header field value is "session".
   Therefore, it is possible that both the INVITE and the ACK contain a
   body message (for example, the INVITE carries a photo (Content-
   Disposition: render) and the ACK a session description (Content-
   Disposition: session))."

With respect to the above statements, how can both INVITE and ACK contain
a body message.  The possibilities that come to my mind are

1) INVITE had an offer and was responded to in 2xx, then  ACK also 
contained
the message body.... 
 ---> so did the ACK have a new offer ???.... how will the offer in ACK be 
answered???

2) INVITE had an offer and was not answered in  2xx . But  ACK contained a 
message 
body.
---> But this cannot happen.. A UA cannot generate a new offer until the 
previous offers
are answered.

3) INVITE had an offer. It was rejected(but was not communicated with any 
error response)
Now 2xx contains a new offer and been answered in the ACK.
--> Now both INVITE and ACK contains message body. But is this behavior 
correct??
How will a UAC know that the offer sent in INVITE was rejected and he is 
receiving a 
new offer in 2xx( for which he has to answer in ACK).

Please correct me if I my understanding is not right and clarify me on the 
same.

Thanks and Regards,
 Preethi..
------------------------------------------------------------------------------
Preethi Sadasivan,
Software Engineer,
ARICENT ,
Bangalore.
tel: +91-80-41069118
------------------------------------------------------------------------------

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---

From: Paul Kyzivat <[email-masked]>
Date: Fri, 12 Oct 2007 08:05:21 -0400

One way this could happen is for the INVITE to contain a body of some 
type other than an SDP offer. For instance,

INVITE ...
...
Content-Disposition:render;handling=optional
Content-Type:text/plain

IGNORE THIS

	Paul

[email-masked] wrote:
> 
> Hi All,
>         Help me in interpreting the meaning and the flow of the 
> following test case.
> 
> *SIP_CC_TE_CE_V_008:*
> *Ensure that the IUT on receipt of an INVITE request including a message 
> body with*
> *a content-Disposition header not set to session value includes in its 
> first 2xx *
> *response an initial offer session description. *
> 
> value is not session (in the Incoming INVITE) then the 2xx for the 
> INVITE contains
> an intial offer.
> 
>  Does the test-case mean that the offer in the INVITE request is 
> rejected and a
> *   If the invitation is not accepted, a 3xx, 4xx, 5xx or 6xx response is
>   sent, depending on the reason for the rejection. * Before sending a
>    Therefore, *it is possible that both the INVITE and the ACK contain a*
> *   body message* (for example, the INVITE carries a photo (Content-
>  ---> so did the ACK have a new offer ???.... how will the offer in ACK 
> be answered???
> 
> 2) INVITE had an offer and was not answered in  2xx . But  ACK contained 
> a message
> body.
> 3) INVITE had an offer. It was rejected(but was not communicated with 
> any error response)
> Please correct me if I my understanding is not right and clarify me on 
> the same.
> 
> Thanks and Regards,
> Preethi..
> ------------------------------------------------------------------------
>