[SIPForum-discussion] Regarding 491 request pending

Santosh Iyer spi6281 at yahoo.com
Tue Oct 2 15:59:05 UTC 2012

My earlier response may have been slightly incorrect, I missed the part where the 183 had the answer. But in addition to having the answer rfc 3311 section "5.1 Sending the update" has the following stipulation(Pasted Below). So the chances are that this was rejected because it was not sent reliably or just that the UA is not rfc3311 complaint and cant handle an UPDATE.
------------------------  and for the callee:

      o  If the UPDATE is being sent before the completion of the  INVITE transaction, and the initial INVITE contained an offer, the
UPDATE cannot be sent with an offer unless the callee has         generated an answer in a reliable provisional response, has         received a PRACK for that reliable provisional response, has      not received any requests (PRACK or UPDATE) with offers that it
has not answered, and has not sent any UPDATE requests      containing offers that have not been answered.
--- On Mon, 10/1/12, Prem chandiran <toprem.m at gmail.com> wrote:

From: Prem chandiran <toprem.m at gmail.com>
Subject: Re: [SIPForum-discussion] Regarding 491 request pending
To: "Santosh Iyer" <spi6281 at yahoo.com>
Date: Monday, October 1, 2012, 7:36 AM

Hi Santosh,Thanks for your reply, In the below issue UA1 is B2BUA and sends UPDATE request to UA(which itself a B2BUA). 
Regards,Prem Chandiran M

On Mon, Oct 1, 2012 at 4:16 AM, Santosh Iyer <spi6281 at yahoo.com> wrote:

Technically only the UAC can generate an UPDATE, an UAS cannot. UAC generates anUPDATE to update the offer. even the excerpt that you have pasted from rfc 3311 implies that a UAC generated the UPDATE and the UAS generated the answer. Hope that answers your question

--- On Sat, 9/29/12, Prem chandiran <toprem.m at gmail.com> wrote:

From: Prem chandiran <toprem.m at gmail.com>
Subject: [SIPForum-discussion] Regarding 491 request pending
To: discussion at sipforum.org

Date: Saturday, September 29, 2012, 2:29 AM

Hi All,
may i know why 491 request pending is sent for UPDATE, as per rfc 33 11 "If an UPDATE is received that contains an offer, and
 the UAS has generated an offer (in an UPDATE, PRACK or INVITE) to which it has not yet received an answer, the UAS MUST reject the UPDATE with a 491 response." below is the call flow

UA                                                   UA1

|                                                      ||          INVITE(with offer)                  |

------------------------------------------> ||                                                      |

|      100 Trying                                 | <-------------------------------------------|

|                                                      ||      183 (with Answer)                      |

 <-------------------------------------------||                                                      |

|      UPDATE(With Offer)                    | <-------------------------------------------|

|                                                      ||        491 Request Pending                 |

------------------------------------------> |

UA sends an offer in invite for that UA1 respond with answer in 183 then UA1 triggers UPDATE with offer UA is sending 491. Please let me know what might be wrong. 

Thanks  all...

Regards,Prem Chandiran

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