[SIPForum-discussion] Possible responses to 180 Ringing Messages

[Rudra Kant Kanth]

Hi Stephan,

So, are there instances possible where we can have a BYE following after a
180 Ringing (apart from a CANCEL and PRACK)?

I have not seen such an instance myself. The only thing which I have seen
is that BYE request follows a CANCEL (that too only in race-conditions). I
think it's an unique Finding and I would be interested to see such a trace
where it depicts that even before the final response is received, a BYE is
sent ahead of CANCEL.

Regards,
Rudra

On Thu, Dec 22, 2011 at 10:20 AM, Stephen James <sjames_1958 at yahoo.com>wrote:

> PRACK, CANCEL, or BYE. Only PRACK is a true response the other two would
> be sent if the initiator wanted to terminate the session. CANCEL is most
> common, but BYE can be used if an early dialog has been established.
>
> Sent from my iPad
>
> On Dec 20, 2011, at 22:35, Bhanumati Behera <bbehera09 at gmail.com> wrote:
>
> Hi,
>      Three options are INVITE(in case of re-invite),CANCEL AND PRACK(It
> will  send when 100rel comes with 180 ringing)
>
> On Sat, Dec 17, 2011 at 11:01 PM, Rudra Kant Kanth <rudra.k1 at gmail.com>wrote:
>
>> Hi Amit and Albert,
>>
>> I have seen situations where 180 Ringing is followed up with PRACK as
>> reliable acknowledgement to the 180 Ringing.
>>
>> Though by default, the 180 Ringing doesn't need acknowledgement of
>> successful receipt by the far-end. However, when there is a "*required: 100
>> rel*" parameter in the 180 Ringing, then that 180 Ringing needs to be
>> acknowledged for successful receipt and thus a PRACK is sent by the UAS,
>> for which the client sends back 200 OK. However, in more generic cases, a
>> 180 Ringing would have 100 rel in the supported format.
>>
>> Thus,
>> PRACK is the ONLY VALID "RESPONSE" in this case. As Amit stated, all the
>> options were actually REQUESTS only.
>> But assuming the question is re-framed as what all are possible next
>> messages after a 180 Ringing, THEN among the options, we can have a CANCEL
>> coming in as well. If still I have to choose a 3rd option then, I would
>> choose an INVITE as my last option. The reason for choosing INVITE and not
>> BYE as my answer is that(based on my gut feeling):- in an event a user
>> decides to drop the call, he has to send a CANCEL. However, if the user
>> decides to change any of the entries in the INVITE headers (say contacts,
>> or codecs etc), it has to come up to the far-end client in form of INVITE
>> only.
>>
>> OK, another thing is that in race-conditions, you will also find a BYE
>> being sent in a CANCEL request call, but, this BYE HAS TO FOLLOW THE
>> CANCEL. It will never come before the CANCEL.
>>
>> So, PRACK, CANCEL and INVITE.
>>
>> Regards,
>> Rudra
>>
>>
>> On Wed, Dec 14, 2011 at 11:44 AM, AMIT ANAND <amiit.anand at gmail.com>wrote:
>>
>>> Hi Albert,
>>>
>>> Where did you get this question?
>>>
>>> If i were on your place i would say non of these,
>>>
>>> These all are requests and ideally there could be no response to a
>>> response.
>>>
>>> Except ACK any of other four can come in a call flow after 180.
>>>
>>> Cheers
>>> Amit
>>>
>>>
>>>
>>> On Fri, Dec 9, 2011 at 6:53 AM, Albert Etsebeth <umbrualbert at gmail.com>wrote:
>>>
>>>> Hi All
>>>>
>>>> I got this question in a exam, and its been driving me mad.
>>>>
>>>> Question:"what are valid responses to 180 ringing" (Choose 3)
>>>>
>>>> Options:PRACK / ACK / BYE /CANCEL /INVITE
>>>>
>>>> In my opinion there is only 2, PRACK and CANCEL
>>>>
>>>> Thanks
>>>>
>>>> umbru
>>>>
>>>>
>>>>
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>>>
>>>
>>> --
>>> Thanks
>>> Amit Anand
>>>
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>>
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