Subject: [Megaco] About the Fax call Flow

From: "Zahid Anwar" <[email-masked]>
Date: Tue, 09 Oct 2001 15:33:18 +0800

Hello 
Thanks for the comments, but there is a little confusion.

The faxtone is the CNG (the T30 fax calling tone).
The CED or the (V21 flags) is notified to the MGC by the called gateway via the reply to the Audit Capabilities request sent earlier by the MGC not shown in this example. That is why the MGC knows that the termination supports T38. Please elaborate on the redundancy you have mentioned since I believe this is the minimal call flow possible and you cannot eliminate the remote descriptors.  
As far as modifying the physical terminations from RTP to UDPTL is concerned do you think it is necessary? Afterall we have modified the ephmeral terminations.

Regards,
Zahid Anwar,
Design Engineer
CET
-----Original Message-----
From: "Miao, Kai" <[email-masked]>
Date: Mon, 8 Oct 2001 11:30:15 -0400 
To: "'Zahid Anwar'" <[email-masked]>, [email-masked]
Subject: RE: [Megaco] Fax call Flow for discussion and comments required

> Anwar,
>  
> I have the following questions regarding your FaxFlow example:
>  
> 1) Is the Faxtone either CNG or CED? Or it goes by CED only?
>  
> 2) If Redundancy has to be considered, do we need to use RED in your
> example?
>  
> 3) Modify is used to change from RTP to UDPTL. How is the TDM termination
> (for exampe, EC, TG, etc.) modified? Done under the hood?
>  
> 4) What about teardown? Could you include that also in your example?
>  
> Kai Miao
> Intel  
> 
> -----Original Message-----
> From: Zahid Anwar [mailto:[email-masked]]
> Sent: Monday, October 08, 2001 3:19 AM
> To: [email-masked]
> Cc: [email-masked]
> Subject: [Megaco] Fax call Flow for discussion and comments required
> 
> 
> 
> In reply to the message posted asking about fax callflow. I propose the
> following callflow. But there are a few confusions for example exchange of
> SDP formats, sequence of messages and about the fax package id which is not
> specified in the RFC. Comments on the following callflow is requested from
> all. Any help would be greatly appreciated.
> 
> 
> Messages Exchanged between MGC and Gatways in order to establish Fax call
> between GW1 and GW2. It is assumed that both gatways are registered, codecs
> have been exchanged and a normal call has been established and both
> terminations are in on-hook state at this point. 
> 
> The caller termination at MG1 detects a fax tone and notifies the MGC. 
> 
> MG1 to MGC 
> 
> MEGACO/1 [125.125.125.111]:55555 
> Transaction = 50005 { 
> Context = 1 { 
> Notify = Phy/1 {ObservedEvents =1234 { 
> 19990729T22020002:faxpkg/faxtone}}}} 
> 
> The MGC sends a notify reply. 
> 
> MGC to MG1 
> 
> MEGACO/1 [123.123.123.4]:55555 
> Reply = 50005 { 
> Context = 1 {Notify = Phy/1}} 
> 
> MGC sends a modify to the caller sending it the fax codec in the local of
> the the media descriptor. 
> 
> MGC to MG1: 
> MEGACO/1 [123.123.123.4]:55555 
> Transaction = 50006{ 
> Context = 1{Modify = Eph/1{Media{ 
> Stream = 1{ 
> Local{ 
> v=0 
> c=IN IP4 0.0.0.0 
> m=audio 3456 RTP! /AVP 0 
> a=ptime:30 
> }}}}}} 
> 
> 
> MG1 sends a reply filling the attributes of its particular fax codecs in the
> local descriptor 
> 
> MG1 to MGC: 
> MEGACO/1 [124.124.124.222]:55555 
> Reply = 50006 { 
> Context = 1 { 
> Modify= Eph/1{Media { 
> Stream = 1 { 
> Local { 
> v=0 
> o=faxgw1 2890846 2890846 IN IP4 ift.here.com 
> c=IN IP4 125.125.125.111 
> m=image 15002 udptl t38 
> a=T38FaxVersion:0 
> a=T38maxBitRate:14400 
> a=T38FaxFillBitRemoval:0 
> a=T38FaxMaxBuffer:72 
> }}}}}} 
> 
> 
> MGC sends a modify signal to GW2 to ask it to play fax tone 
> 
> MGC to MG2 
> MEGACO/1 [123.123.123.4]:55555 
> Transaction = 50007 { 
> Context = 1{ 
> Modify = phy/2 { 
> Signals {faxpkg/faxtone}}}} 
> 
> MG2 sends a modify reply 
> 
> MG2 to MGC 
> 
> MEGACO/1 [123.123.123.4]:55555 
> Reply = 50007 { 
> Context = 1 {Modify = Phy/2}} 
> 
> Now the MGC asks MG2 for its codes filling the codes of the caller in the
> remote 
> 
> MGC to M! G2: 
> MEGACO/1 [123.123.123.4]:55555 
> Transaction = 50008{ 
> Co ntext = 1{ 
> Modify = Eph/1{Media{Stream = 1 { 
> Local{ 
> v=0 
> c=IN IP4 0.0.0.0 
> m=audio 3456 RTP/AVP 0 
> a=ptime:30 
> }Remote{ 
> v=0 
> o=faxgw1 2890846 2890846 IN IP4 ift.here.com 
> c=IN IP4 125.125.125.111 
> m=image 15002 udptl t38 
> a=T38FaxVersion:0 
> a=T38maxBitRate:14400 
> a=T38FaxFillBitRemoval:0 
> a=T38FaxMaxBuffer:72 
> }}}}}} 
> 
> 
> MG2 sends a reply 
> 
> MG2 to MGC: 
> MEGACO/1 [124.124.124.222]:55555 
> Reply = 50008 { 
> Context = 1 { 
> Modify= Eph/2{Media { 
> Stream = 1 {Local { 
> v=0 
> o=faxgw1 2890846 2890846 IN IP4 ift.here.com 
> c=IN IP4 125.125.125.111 
> m=image 15002 udptl t38 
> a=T38FaxVersion:0 
> a=T38maxBitRate:14400 
> a=T38FaxFillBitRemoval:0 
> a=T38FaxMaxBuffer:72 
> }}}}}} 
> 
> MGC sends the codes of MG2 to MG1 
> 
> MGC to MG1: 
> MEGACO/1 [124.124.124.222]:55555 
> Transaction = 50009 { 
> Context = 1 { 
> Modify= Eph/1{Media { 
> Stream = 1 { 
> Remote 
> { 
> v=0 
> o! =faxgw1 2890846 2890846 IN IP4 ift.here.com 
> c=IN IP4 125.125.125.111 
> m=image 15002 udptl t38 
> a=T38FaxVersion:0 
> a=T38maxBitRate:14400 
> a=T38FaxFillBitRemoval:0 
> a=T38FaxMaxBuffer:72 
> 
> }}}}}} 
> 
> MG1 replies to MGC 
> 
> MEGACO/1 [124.124.124.222]:55555 
> Reply = 50009 { 
> Context = 1 { Modify = Eph/2}} 
> 
> 
> 
> Regards
> 
> 
> Zahid Anwar.
> 
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