Subject: Questions about draft-ietf-fax-fulladdr-06.txt

From: Hiroshi Tamura <[email-masked]>
Date: Tue, 25 May 1999 09:29:21 +0900

Allocchio san,

I have questions about draft-ietf-fax-fulladdr-06.txt.
In the paragraph 5.1 there are several examples.

>   A pstn-mbox address in Germany for an hypotetical XYZ service, using 
>   global-phone, with ISDN sub-addr-spec 1234 and written-sep ".":
>
>     XYZ=+49.81.7856345/ISUB=1234

In this example, does the offramp gateway make a call to ISDN, not PSTN ?

>   A pstn-mbox address in Italy for fax service, using local-phone, 
>   dialed from an MTA in Germany, (international access code "00", 
>   with ISDN subaddress 9823, with T.33 subaddress "4312" and without
>   pause or written-sep:
>
>     FAX=003940226338/Isub=9823/T33S=4312

In this example, does the offramp gateway make a call to ISDN and send
a fax ? Does the gateway use G4fax protocol, not G3fax one ?
I know SUB(nearly equal to T33S) can be mapped in CDCL in T.62.
Is this your intension ?

I would like to know these meanings exactly.

There are no clear identifier or something about the selection
between ISDN and PSTN. In the fax service there are large differences
in protocols to use between G3Fax(PSTN) and G4Fax(ISDN).
Isn't it necessary ?

Regards,
--
Hiroshi Tamura, Ricoh Company, LTD.
Mail: [email-masked]
Tel: +81-462-28-7459  Fax: +81-462-28-7500 (SUB/F-code 5727)

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From: Claudio Allocchio +39 040 3758523 <[email-masked]>
Date: Thu, 27 May 1999 12:11:03 +0100

> In this example, does the offramp gateway make a call to ISDN, not PSTN ?

Yes, exactly: the offramp gateway calls an ISDN destination (you cannot 
distinguish an ISDN number from a PSTN number, unless you know the 
internal numbering convention of the service provider).

> a fax ? 

Yes, the offramp gateway calls an ISDN number, issues an ISDN 
sub-address to send a fax, and when talking to the fax device sends the 
T.33 subaddress. 

Does the gateway use G4fax protocol, not G3fax one ?
> I know SUB(nearly equal to T33S) can be mapped in CDCL in T.62.

Actually, there is no implied significance about the used (G3 or G4) fax 
protocol in the addressing session. However I ask our ietf-fax collegues 
more experts than me in G3/G4 internal protocol to aswer more exactly 
your previous question.

> in protocols to use between G3Fax(PSTN) and G4Fax(ISDN).

You are correct. They are very different. However I think we should not 
make this distinction in the "addressing" section. In fact the addressing 
elements should only be the items needed by the offramp gateway to 
correctly reach the final destination. It is the gateway than which needs 
to understand that it is reaching an ISDN or PSTN destination. This could 
be by examining the presence of ISUB elements (which automatically tells 
about an ISDN destination): in this case also T33S means "SUB" from T.62

If the destination address does not specify ISUB, there is of course no 
way from the address to understand if the destination is PSTN or ISDN. In 
this case, how the fax gateway should decide about G3 or G4? I suppouse 
just negotiationg them when esteblishing the connection. In traditional 
fax to fax only communication you do not know if you're dialling a PSTN 
or an ISDN number from your fax machine... However, as above, I ask the 
group members about advice in this field. I think we do not need to 
distinguish the two cases in the addressing, but I may be wrong!

regards
Claudio

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From: Hiroshi Tamura <[email-masked]>
Date: Fri, 28 May 1999 18:44:07 +0900

Allocchio san,

Thank you for your reply.
I understood your opinion.

There are the comments I would like to say.

(Of course this depends on implemenataion.)

Case 1:

If an offramp gateway has only ISDN connection(no PSTN connection)
and the LHS field has the "ISUB",
the gateway at first makes a call as the number is for G4fax.
(Bearer capability of setup is "unrestricted ditigal information".)

If the first call fails and it gets the appropriate cause values,
the gateway makes a call as the number is for G3fax.
(Bearer capability of setup is "speech".)

Case 2:

If an offramp gateway has only ISDN connection(no PSTN connection)
and the LHS field does not have "ISUB",
the gateway does not know if the number is for G3 or G4.

Someone make the first call to be for G4fax and if failed, 
the second for G3fax.
Others make the opposites.

In case 2, it is convenient to have the identifier for ISDN.
If it exists, only one call is enough.
But, some actions can be done without it.
For the time being, I do not have problems.

>> distinguish the two cases in the addressing, but I may be wrong!

You are not wrong. Partly I answer it as the above.

Anyway, thanks.