Subject: RE: [Megaco] Fax over IP

From: Pellegrino Jose Luis <[email-masked]>
Date: Fri, 30 Nov 2001 15:50:31 -0300

We have written in black the Spanish version  and in blue the  English one.

Hi Fernando,

Comentaré qué hemos hecho en Telefónica al respecto. Espero te sirva.
En Telefónica, para trasnmisiones de Fax, hemos utilizado el criterio
explicado mas abajo para MGCP. Creemos que ese criterio es válido para
MEGACO (Al final de este mail detalles). Si bien los comandos son
diferentes, la idea conceptual entre ambos protocolos es la misma. De hecho
hay muy pocas diferencias entre ambos protocolos

In order to clarify your doubt, I will coment, what we have done in
Telefónica to implement  FAX transmission  over IP . I hope it will be
usefull for you.
In Telefónica, we have used the criteria explained below  for MGCP. We think
we can use the same criteria for MEGACO (see at the end of this mail). Of
course the comands are different, but the conceptual idea is the same.

				1- what we have done for MGCP:

-El MGC utilizará el parámetro RequestedEvent para indicar el package y los
eventos  que el MG deberá observar y notificar. Preferentemente dicho
parámetro irá en el comando CRCX. Opcionalmente podrá ir en el comando
NotificactionRequest (RFC2705 pag 33),  o en el MDCX.

-The MGC will send a RequestedEvent parameter to indicate to MG the Package
and the events to detect and notify (for example Fax tone and Modem tone).
The MGC will include this parameter in a CRCX or in a MDCX.

-R: G/mt(N), G/ft(N)  (notificar inmediatamente la presencia de tono de fax
y de modem). El MGC podrá introducir espacios a entre un evento y otro, por
ejemplo a continuación de una "coma".

-R: G/mt(N), G/ft(N) (The MG must notify inmediately to the de MGC the
detection of the fax tone o modem tone). The different events may be
separates by a coma

Nota: para este y todos los comandos, el El MG deberá interpretar
correctamente el comando con o sin dichos espacios.

-La detección del evento será noticada por el MG mediante un comando Notify
indicando el Request Identifier corrrespondiente al comando que es
respondido, el package y los eventos detectados. Notar que siempre debe
enviarse el "package" (G en el ejemplo), ya que algunos eventos son comunes
en mas de un package.

-The MG will send a Notify including the Request Identifier (In MEGACO is
the same) to correlate the request comand (CRCX) and the Notify Comand, the
package (in this case it is a General Package), and the events detected (may
be Fax tone).

-El MGC enviará un MDCX modificando los parámetros necesarios. En el ejemplo
anterior:
a: PCMA, e:off , s:off  (Cambiar codec a g.711, desactivar la supresión de
silencios y la cancelación de eco).

-The MGC will send a MDCX modifying the parameters. In the example:
a: PCMA, e:off , s:off  (Change codec to g.711, deactivate the silence
suppresion and de echo cancelation).

It´s important to notice this: The MGC modifies the parameter in the two MG
envolved. This is the reason why we request the MG not to modify anything by
itself. It only notify, then the MGC modifies both MG's.

				2- Our recommendation for MEGACO

The MGC will include an AuditValue parameter in ADD comand or in a Modify
comand (while the call is been stablished), to indicate to MG the Package
and the events to detect and notify (for example Fax tone and Modem tone). 
After detecting the event requested (fax tone for example), the MG willl
send a Notify command including an ObservedEvents Descriptor, to notify the
MGC .

We think that the MG must not modify anything by itself. The MGC is who will
modify the parameter in both MG (the one which has detected the event, for
example de originating MG,  and the other one, the receiving one). 

We think this is  the way we can be sure that the two MG will use the same
codec (G.711 in this example), 
	
	We have noticed that some of MGC sends the RequestedEven (MGCP) or
the AuditValue (MEGACO) parameter to the called MG. In fact it works as
well as it would be sended to the calling one.

	This situation is the same we have observed when the calling uses a
text phone from an ordinary line (H.248 Annex F) and then the call is routed
to a Trunk Gateway.

Respect to the second question, we have observed that the usual procedure
is:

1- receive only to the calling (ADD). May be inactive too.
2- sendreceive to the called (ADD)
3- sendreceive to the calling (MODIFY).

Respect to third question, sorry I don´t have any  MEGACO Scenario at this
moment.

 Cordial saludo/best regard

JOSE LUIS PELLEGRINO
Tecnología Conmutación yTerminales
Hipólito Yrigoyen 1556 6º piso contrafrente
* [email-masked]
TELEFONICA DE ARGENTINA
*54 11 4332-2606
FAX: 54 11 4381-8301

> -----Mensaje original-----
> De:	Fernando Vallejo Lazaro [SMTP:[email-masked]]
> Enviado el:	Viernes 30 de Noviembre de 2001 05:02
> Para:	[email-masked]'
> Asunto:	[Megaco] Fax over IP
> 
> Hi all, 
> 
> Some questions have arised when thinking about the FAX over IP with Megaco
> 
> 
> 1) When a fax is establishing a call it first dials the digits of the
> remote fax. 
> The MGC may decide to use G.723 but afterwards when the originating MG
> detects the inital tone of a fax (2100 Hz) 
> it usually has to change to G.711 for quality reasons. How do we notify to
> the MGC the change of a codec? 
> How we could notify it is a fax call? Otherwise we will send the tone in
> G.711 and the other side expects 
> it in G.723... 
> 
> 2) Moreover, the MG originating may be in ReceiveOnly, but we have to send
> the initial fax tone 
> and the MG terminating may be in SendOnly and it has to send an answer
> tone without 
> picking up  the phone, doesnt it? 
> 
> 3) Does anybody have a scenario of a fax call or where can I find it? 
>   
> 
> Thanks in advance 
> Fernando 
>   
> -- 
> Fernando Vallejo Lazaro
> Phone:  +34 91 330 8279
> SW  Wireline ASD-Madrid
>        ALCATEL
>  

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