Subject: [Sipping] Question about SIP support for real-time fax

From: Eiji Tomimura <[email-masked]>
Date: Fri, 02 Aug 2002 17:01:37 +0900

Dear all,

I resubmit this question since it has got no answer yet.

A about draft-ietf-sipping-realtimefax-00.txt,

In section 5.1 "Internet fax device  fax only support" call sequence, it
shows a diagram to establish T.38/UDPTL session from the beginning. We tried
this scenario and realized the following thing:

--
(1) In case both SIP-UA are telephony gateway which are configured to
support fax only, T.38/UDPTL session are established as the section 5.1
represents.

(2) FAX machines tries to negotiate their capability by exchanging CNG and
CED tones.

(3) As T.38/UDPTL session basically doesn't have a capability to pass
through CNG or CED tones, this negotiation fails.

(4) The Calling FAX machine terminate fax call as it cannot get CED response
from the callee side. Then, FAX fails.

---

So, if FAX machines need CNG/CED exchange to start fax, this call scenario
is not appropriate. Instead, we should always use section 5.2 call scenario,
which use voice stream to exchange CNG/CED first.

So, my questions is that, is section 5.1 is appropriate from fax machines'
and T.38 session's perspective?

If not, I would like to recommend to remover section 5.1 of
draft-ietf-sipping-realtimefax-00.txt, and allows only the procedure
described in section 5.2.

Regards,
- Eiji Tomimura

-- 
Eiji Tomimura 
Senior Engineer 
Systems Technology Dept., Information Technology R&D Laboratories
Sumitomo Electric Industries, Ltd.
Phone: +81-6-6466-5609  Fax: +81-6-6466-5732  Email: [email-masked]

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