Re: [MEDIACTRL] FW: Race condition between msc-ivr dialogstart and SIP ACK

Some implementation issue.
FSM becomes complicated as two different events are required to initiate dialogstart with no ordering among them.
A more fundamental issue INVITE becomes a four way handshake. 
(Fourth event adding as extra identifier for confirming INVITE is over).

I think there are two issues here:

1. Unreliablity in protocol/mechanism. (Dialogstart will be sent after ACK deterministically)
2. Unreliability in implementation. (Control channel and UDP works on different process/threads etc in MS)

Unreliability in protocol/mechanism can only be removed by transport. In implementation it can exist.
e.g SCTP both dialogstart and ACK for a media session can be put inside same association. (IF INVITE is used with SCTP)

Regards,
Rahul

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----- Original Message -----
From: Stéphane Bastien <stephane@broadsoft.com>
Date: Tuesday, July 20, 2010 7:06 am
Subject: Re: [MEDIACTRL] FW: Race condition between msc-ivr dialogstart	and	SIP ACK
To: "mediactrl@ietf.org" <mediactrl@ietf.org>

> As long as we have two separate channels (one for SIP, one for 
> CFW), the race condition exists, regardless of the transport protocol.
> 
> I believe that an alternate solution is for the SIP INVITE 
> establishing the media session to provide an identifier which 
> informs the Media Server about which CFW channel will control the 
> media session. Then, when the media session is confirmed (i.e., 
> SIP ACK received), the Media Server can transmit a notification 
> over the CFW channel (i.e., media session is ready).
> 
> Le 2010-07-19 à 17:13, Eric Burger a écrit :
> 
> > Require TCP, TLS, or reliable SCTP only?  That is, no UDP allowed?
> > 
> > That might fly.  Comments from others, especially those that 
> today do not have TCP stacks?
> > 
> > On Jul 6, 2010, at 3:27 AM, RahulSrivastava 71616 wrote:
> > 
> >> Any automata which relies on time for success cases doesn't 
> look good.
> >> This problem is same if you use INFO/ACK (on UDP).
> >> INFO reaches earlier as compared to ACK then INFO is generally 
> queued (based on wait logic as described by you).
> >> 
> >> In long run I'll prefer reliable connecction to be used between 
> MS and AS.
> >> 
> >> Regards,
> >> Rahul
> >> 
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> >> 
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> >> ----- Original Message -----
> >> From: "WORLEY, Dale R (Dale)" <dworley@avaya.com>
> >> Date: Monday, July 5, 2010 11:41 pm
> >> Subject: Re: [MEDIACTRL] FW: Race condition between msc-ivr 
> dialogstart and SIP ACK
> >> To: Stéphane Bastien <stephane@broadsoft.com>, 
> "mediactrl@ietf.org" <mediactrl@ietf.org>
> >> 
> >>> ________________________________________
> >>> From: mediactrl-bounces@ietf.org [mailto:mediactrl-
> >>> bounces@ietf.org] On Behalf Of Stéphane Bastien
> >>> 
> >>> 5.       Application Server sends a SIP ACK with the answer 
> SDP to 
> >>> the Media Server
> >>> 
> >>> 6.       Application Server transmits over the control channel 
> an 
> >>> msc-ivr <dialogstart> with a connectionid of the media session 
> >>> established in step 5
> >>> 
> >>> The problem is what happens if the SIP ACK transmitted in step 
> 5 
> >>> gets lost in the network? One of the retransmissions of the 
> SIP 
> >>> ACK may eventually reach the Media Server, but will be 
> received 
> >>> later than the dialogstart from step 6. Yet, the Media Server 
> >>> can’t execute the dialogstart until the SIP ACK is received, 
> >>> otherwise the user gets media clipping.
> >>> 
> >>> I'm currently thinking of handling  this scenario by waiting 
> for a 
> >>> few seconds in step 6 if the SIP ACK is missing, and execute 
> >>> <dialogstart> as soon as the SIP ACK arrives. If the SIP ACK 
> does 
> >>> not arrive, the MS returns the msc-ivr status code 412 "Media 
> >>> stream not available". (Could we create an error code for this 
> >>> specific scenario to make it easier to detect by the AS?) An 
> >>> alternate approach would be for the AS to subscribe to the 
> state 
> >>> of a connectionid, and the Media Server would send a "Media 
> Stream 
> >>> Established" notification when receiving the SIP ACK in step 5.
> >>> ________________________________________
> >>> 
> >>> (Speaking as an individual.)
> >>> 
> >>> I'm not familiar with this particular application, but in 
> general, 
> >>> it's easier to implement a protocol if actions are taken on 
> when 
> >>> indications are received rather than based on timeouts.  So it 
> >>> would seem more robust and easier to code if we required the 
> MS to 
> >>> send an indication to the AS that it had received the answer 
> SDP, 
> >>> and the AS would then send the <dialogstart>.  But it appears 
> that 
> >>> the mechanism for doing that is having the AS specifically 
> >>> subscribe to the connectionid (carried in the SDP?) and then 
> wait 
> >>> for a notification, which adds several more steps.
> >>> 
> >>> Is there a way to do this which works the same way regardless 
> of 
> >>> which end sends the offer SDP?
> >>> 
> >>> Dale
> >>> _______________________________________________
> >>> MEDIACTRL mailing list
> >>> MEDIACTRL@ietf.org
> >>> https://www.ietf.org/mailman/listinfo/mediactrl
> >>> Supplemental Web Site:
> >>> http://www.standardstrack.com/ietf/mediactrl
> >>> 
> >> _______________________________________________
> >> MEDIACTRL mailing list
> >> MEDIACTRL@ietf.org
> >> https://www.ietf.org/mailman/listinfo/mediactrl
> >> Supplemental Web Site:
> >> http://www.standardstrack.com/ietf/mediactrl
> > 
> > _______________________________________________
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> > MEDIACTRL@ietf.org
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> > Supplemental Web Site:
> > http://www.standardstrack.com/ietf/mediactrl
> 
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