[Freeswitch-users] ReINVITE failure with ACK+SDP scenario

[Muhammad Shahzad]

I am not sure what you are trying to do here. You said we want to originate
two calls from your PABX to carrier through FS, i.e.

Call A: PABX -> FS -> Carrier -> User A
Call B: PABX -> FS -> Carrier -> User B

And then bridge them on FS, such that,

User A <- Carrier <- FS -> Carrier -> User B

I think there are easier ways to achieve this. But anyway in this scenario,

Since Call A does not have SDP, which means you are triggering Late SDP
Negotiation. Make sure you have enabled in sofia profile,

<param name="inbound-late-negotiation" value="true"/>


So, that FS does not Answer it with local SDP. Additionally you may need to
disable SOA,


<param name="enable-soa" value="false"/>


When 200 OK for Call A arrives (from carrier, through FS to PABX), you use
it as basis for SDP of INVITE in Call B. That's interesting..

When Call B is answered, you should use SDP in 200 OK as basis for SDP of
ACK in Call A. Otherwise you will get one way audio as expect.


Thank you.




On Fri, Jun 28, 2013 at 6:56 PM, BNML <bnml at andrexen.com> wrote:

> Hi all,
>
> I am having trouble with a transfert failure in a special scenario which
> i wasn't able to find documentation or configuration option solving it.
>
> I have a PBX creating two outbound call, it want to bridge them on the
> FreeSWITCH.
> It is sending a first INVITE without SDP and it will send the SDP in the
> ACK.
>
> (This is not breaking RFC3261 but I admit rarely seen scenario.
> http://tools.ietf.org/html/rfc3261#section-13.2.1 : "The UAC MAY choose
> to add a message body to the INVITE.". Looking at this scenario there
> is, indeed, at least one interesting scenario where it can helps
> avoiding creating another useless Re-INVITE transaction, see below)
>
> For the second call it is sending a re-invite with SDP.
> FreeSWITCH will understand and forward (because of "bypass_media") the
> second Re-INVITE but does never forward the first Re-INVITE (The one
> without SDP in the INVITE but in the ACK) to carrier, so this will end
> up in one-way-audio.
>
> A little schema to help :
>
> PBX                    FREESWITCH       COMMENT
> 1) INVITE (a-leg)                       [THERE IS NO SDP]
> 2)                     200 OK (fs-a-leg)[FreeSWITCH answer with the SDP
> information before any media update occurs, but my PBX is now aware of
> media informations]
> 3) INVITE+SDP (b-leg)                   [This is b-leg updated media
> information with previous 200 OK (fs-a-leg)]
> 4)                     200 OK (fs-b-leg)[My PBX updated media and has
> b-leg freeswitch media information that it will send in the ACK+SDP to
> finalize the both-legs Re-INVITE]
> 5) ACK (b-leg)                           [Acknoledgement of b-leg
> Re-INVITE transaction]
> 6) ACK+SDP (a-leg)                       [ *** problem *** it assume
> FreeSWITCH will update media information and forward to the carrier
> which it won't]
>
> The solution i imagine is FreeSWITCH SHOULD trigger a Re-INVITE either
> for the a-leg at INVITE (without SDP in "1") receiption (and update
> media information when receiving the ACK+SDP) _OR_ create a Re-INVITE
> transaction at "6" when receiving ACK+SDP. One way or another, I am
> supposing FreeSWITCH refuse to forward the INVITE without SDP at first
> maybe because of carrier compatibility ? If not, this seems the way to go.
>
> Has anyone faced such a scenario ? Am I rigth assuming a patch is needed
> ? If yes, any suggestions are welcome.
>
> Thanks you
>
> BNML
>
>
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-- 
Mit freundlichen Grüßen
Muhammad Shahzad
-----------------------------------
CISCO Rich Media Communication Specialist (CRMCS)
CISCO Certified Network Associate (CCNA)
Cell: +49 176 99 83 10 85
MSN: shari_786pk at hotmail.com
Email: shaheryarkh at googlemail.com
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