[Serusers] Re: [Asterisk-Users] INFO/DTMF retransmissions in * not absorbed?
andres at telesip.net
Tue Feb 24 04:15:05 CET 2004
I certainly welcome and applaud your comments and suggestions. But I
could not continue to push this issue as an asterisk "bug" since the RFC
did not back me up. Absorbing these SIP INFO retransmissions is more
like a common sense thing/feature that should be implemented in asterisk
rather than an RFC violation, since the RFC is quite vague. If anybody
has the knowledge to implement this feature I can certainly help test it.
Jiri Kuthan wrote:
>thanks for your reply. I beg to disagree, here are the arguments:
>1) Having INFO is imho a useful thing: it allows elements out of the
> media path to control DTMF-based service logic. Otherwise, you
> will end up processing media which affects bandwidth and latency
> noticably and does not scale.
>2) Apart from the out-of-order argument, reprocessing retransmissions
> is a bug worth fixing. It is responsibility of transaction layer
> to absorb UDP retransmissions and never let app see them.
> (Similarly like TCP does not pass retranmissions to apps.) I think
> there are more cases for proper transaction processing other than just
>3) out-of-order delivery may or may not be an issue: gnerally, one would
> need to mainain a kind of playout buffer like for RTP. O-o-o delivery
> does not matter to me personaly since I send DTMF/INFO in stop-and-go mode.
> (BTW, I think the text in the RFC is not entirely correct, re-INIVITE
> should not cause CSeq gaps. Nevertheless, the RFC does not prevent
> anybody from implementing an "INFO playout buffer").
>On Sun, 22 Feb 2004, Andres wrote:
>>Been there. We switched from INFO to RFC2833 for this same reason.
>>Take a look at:
>>Not only retransmissions are affected but out of order packets too.
>>This behaviour can be partly blamed on the RFC:
>>"In addition, the INFO method does not define additional mechanisms
>>for ensuring in-order delivery. While the CSeq header will be
>>incremented upon the transmission of new INFO messages, this should
>>not be used to determine the sequence of INFO information. This is
>>due to the fact that there could be gaps in the INFO message CSeq
>>count caused by a user agent sending re-INVITES or other SIP
>>Jiri Kuthan wrote:
>>>I'm wondering whether people know if there could be a problem
>>>with * receiving retransmissions of INFO/DTMF requests.
>>>I'm trying to play DTMF via INFO to *. If it takes a 200 reply too
>>>long to come back, the request is retransmitted. Whenever this
>>>happens, the IVR down in PSTN reports that the number sequence
>>>This makes me guess that * turns INFO retransmissions into new
>>>DTMF digits on the PSTN part.
>>>Does anybody have the same experience? Is it a known problem?
>>>Are there any patches?
>>>Jiri Kuthan http://iptel.org/~jiri/
>>>Asterisk-Users mailing list
>>>Asterisk-Users at lists.digium.com
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