Re: T.38 session name in examples

Hello Kevin and Albrecht,

There's been a few issues on the T.38 call flows. There's this one and 
the use of a non-defined property value. There's aren't really 
appropriate for the H.248 series implementors guide. I'll make sure the 
Q.14/16 Rapporteur is aware of the issues and see how he wants to handle 
them.

Regards, Christian

Kevin Boyle wrote:
> I agree with Albrecht.  MGs must craft compliant SDP.  It is not the 
> MGC's responsibility to modify non-compliant SDP from an MG into 
> compliant SDP.
>  
> MGs that omit required lines are non-compliant to both RFC 2327 and 
> H.248.1.
>  
> Kevin
>
> ------------------------------------------------------------------------
> *From:* [email protected] [mailto:[email protected]] *On 
> Behalf Of *Schwarz Albrecht
> *Sent:* Tuesday, May 13, 2008 3:36 AM
> *To:* RUIKAR RAHUL A; [email protected]
> *Subject:* Re: [Megaco] T.38 session name in examples
>
> Agree to Kevin, this was also made more explicit in the past in an IG 
> ("In session descriptions sent from the MG to the MGC, the SDP must 
> comply with RFC 2327. "). See also H.248.1 V3 Amendment 1.
>  
> I may note that there are in the meanwhile many H.248 profile 
> specification which defining default values for the SDP o=, s= and t= 
> lines in MG-to-MGC directions.
>  
> Thus, the T.38 H.248 examples are incorrect in my understanding.
> But implementers should implement the protocol, and not examples.
> (T.38 was never officially reviewed by Q.3/16 wrt H.248 examples (as 
> far as I know)).
>  
>
>     ------------------------------------------------------------------------
>     *From:* RUIKAR RAHUL A
>     *Sent:* Dienstag, 13. Mai 2008 05:10
>     *To:* Kevin Boyle; [email protected]
>     *Cc:* Schwarz Albrecht
>     *Subject:* RE: [Megaco] T.38 session name in examples
>
>     Thanks for explanation.if "s" line is optional only in MGC->MG
>     direction and not in MG->MGC
>     but then I see that those attributes ( o,s,t ) are missing in
>     reply from gateway.
>     Now I have following doubt regarding this,
>     1) Should MG send RFC 2327 conformant SDP to MGC in reply ( eg.
>     adding missing o,s,t lines )
>     2) or is it MGC which has to manage these missing attribute and
>     add it to SDP which is to be sent out to remote side.
>      
>      
>     Example From Page No. 78 and 79
>      
>     MGC to MG1:
>     ====================
>     MEGACO/1.0 [123.123.123.4]:55555
>     Transaction = 11 {
>     Context = $ {
>     Add = DS0/1/1 {
>     Events = 1 {al/on, ctyp/dtone }
>     }, ; SCN termination prepared to listen for tones
>     Add = $ {
>     Media {
>     Stream = 1 {
>     LocalControl { Mode = ReceiveOnly, ReserveGroup = True, ReserveValue =
>     True},
>     Local {
>     v=0
>     c=IN IP4 $
>     m=audio $ RTP/AVP 18 0
>     v=0
>     c=IN IP4 $
>     m=image $ udptl t38
>     }; IP termination for audio } }}}}
>     Reply from MG1 -> MGC
>     =====================
>      
>     MEGACO/1.0 [124.124.124.222]:55555
>     Reply = 11 {
>     Context = 2000 {
>     Add = DS0/1/1, ; SCN termination added
>     Add = RTP/1 {
>     Media {
>     Stream = 1 {
>     Local {
>     v=0
>     c=IN IP4 124.124.124.222
>     m=audio 2222 RTP/AVP 18 0 ;MG1 supports both offered codecs
>     a=ptime:20
>     } ; IP termination added }}}}}
>      
>     Regards,
>     Rahul Ruikar
>     Alcatel-Lucent
>     Email: [email protected]
>     <mailto:[email protected]>
>     Alcanet: 2721 4732
>      
>
>     ------------------------------------------------------------------------
>     *From:* Kevin Boyle [mailto:[email protected]]
>     *Sent:* Tuesday, May 13, 2008 2:38 AM
>     *To:* RUIKAR RAHUL A; [email protected]
>     *Cc:* Schwarz Albrecht
>     *Subject:* RE: [Megaco] T.38 session name in examples
>
>     This misconception continues to pervade, and it is worrisome.
>      
>     The s= line (and other mandatory portions of the SDP
>     specification) are *NOT* optional in H.248.  They are only
>     optional in the MGC->MG direction.  In communications from the MG
>     to the MGC, the SDP must be conformant to RFC 2327. 
>      
>     The text in Clause 7.1.8 is explicit that the exceptions to SDP
>     are valid only in the MGC->MG direction.  This is to allow the MGC
>     to provide over- or under-specified SDP.
>      
>     Kevin
>
>     ------------------------------------------------------------------------
>     *From:* [email protected] [mailto:[email protected]]
>     *On Behalf Of *RUIKAR RAHUL A
>     *Sent:* Sunday, May 11, 2008 6:07 AM
>     *To:* [email protected]
>     *Cc:* Schwarz Albrecht
>     *Subject:* [Megaco] T.38 session name in examples
>
>     Just an observation about ITU-T Rec. T.38 (09/2005)
>     according to SIP RFC "s" line in SIP messages is mandatory, it is
>     missing in examples
>     given in document.
>     Though for H248 this attribute is optional but for messages
>     sent/received from/to SIP agent
>     shall have session name attribute present.
>      
>      
>     Regards,
>     Rahul Ruikar
>     Alcatel-Lucent
>     Email: [email protected]
>     <mailto:[email protected]>
>     Alcanet: 2721 4732
>      
>
> ------------------------------------------------------------------------
>
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