[SIPForum-discussion] Possible responses to 180 Ringing Messages

[Bhanumati Behera]

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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