Re: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

["Paul E. Jones" <[e-mail]>]

Christer,

 

I’m not trying to change the transport protocol.  I was asked about the
history of the RTP addition to T.38, so I provided that information along
with some of the reasons it was introduced.

 

That said, I do think it’s reasonable to consider using RTP if 3GPP is
considering using DTLS.  After all, DTLS is a change in transports, just as
using RTP would be.  Whether that is using RTP/DTLS or SRTP for security,
there are benefits in using RTP, such as the ability to report packet loss,
delay, jitter, etc. as is done for other RTP flows.  Plus, it would be
possible to switch between voice and fax within the same RTP media flow.

 

In any case, I was just asked for the history and I gave it.

 

Paul

 

From: Christer Holmberg [mailto:[e-mail]] 
Sent: Tuesday, September 03, 2013 6:57 AM
To: Paul E. Jones; 'Schwarz, Albrecht (Albrecht)'
Cc: 'mmusic WG'; [e-mail]
Subject: VS: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

 

Hi Paul,

You provide interesting input. However, 3GPP has chosen UDPTL as the
transport protocol for FoIP (and, as others have also indicated, UDPTL is
also the most common transport protocol for FoIP).

If you want to change the transport protocol for FoIP used in 3GPP, please
talk to your 3GPP folks. I don’t think this is the place.

The scope of the draft, and the work that we suggest, is to provide DTLS
security on top of the already used transport protocol for FoIP (i.e.
UDPTL).

Regards,

Christer

 

 

Lähettäjä: Paul E. Jones [ <mailto:[e-mail]>
mailto:[e-mail]] 
Lähetetty: 3. syyskuuta 2013 3:01
Vastaanottaja: 'Schwarz, Albrecht (Albrecht)'; Christer Holmberg
Kopio: 'mmusic WG';  <mailto:[e-mail]>
[e-mail]
Aihe: RE: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

 

Folks,

 

RTP was introduced primarily for use with SRTP, but it was not specified for
use with SRTP since there was contention with respect to how keying material
would be exchanged (e.g., SDES or something else).  The more important part
was just defining how to replace UDPTL as a transport.

 

During that time, we were also exploring why T.38 fax failed so often, an
area of work that seems to never end.  The biggest challenge with FoIP has
been timer expiry, corruption, and collisions on TDM links.  Fax machines
are sometimes slow to reply, there is delay end-to-end, and there are
sometimes gateways in the path that introduce a lot of delay.  All of those
have been contributors to timer expiry and failed fax calls.  In some
testing we did, we even saw T.38 converted to audio and then carried via
G.729.  As you can imagine, the end result was not very desirable.

 

So, T.38/RTP and Voice Band Data (VBD) (V.152) work was done to try to
address some of the transport issues we were seeing, not only with fax, but
also with other kinds of modulated signals.

 

Use of RTP would have been better than UDPTL for security reasons, of
course.  DTLS is certainly a possible candidate today, though not having
RTCP means that there is still some opportunity for packet loss to go
undetected.  We wanted those properties of RTP to help troubleshoot the
network – properties completely lacking in UDPTL.  (Yes, missing information
can be detected, but missing information might be a TDM-link issue or an IP
packet loss issue.  UDPTL cannot differentiate.)

 

Paul

 

PS – I fully support the use of PDF over SMTP, BTW. It really gives
customers a lot fewer headaches.

 

From: Schwarz, Albrecht (Albrecht)
[mailto:[e-mail]] 
Sent: Monday, September 02, 2013 5:05 AM
To: Christer Holmberg
Cc: mmusic WG; [e-mail] <mailto:[e-mail]> ;
Paul E. Jones
Subject: RE: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

 

Hello Christer,

I did follow the T.38 development in ITU-T a couple of years, but I have to
admit that I’m also missing the origins and history of T.4, T.30 and T.38 in
the 1990 decade.

The original requirement for secure fax transport was subject of the
application protocol itself (e.g. T.30) AFAIK. That’s why T.38 is silent on
that aspect.

The indication of RTP/SAVP in T.38 (2004) was listed just for completeness,
but not really motivated by T.38 security requirements (Paul may correct
me).

Further, we should only refer to T.38 2010 (due to the well known issue with
V.34G3 fax).

 

That said, like to suggest following revision proposal to clause 1 and
references, see below.

Regards,

Albrecht

 

PS

Cc’d ITU-T Q.15 SG16, which is technology owner of T.38 in current Study
Period.

 

 

1.  Introduction
 
There are three transport options for T.38 fax-over-IP, called “T.38
transport modes” [ITU.T38.2010]. T.38 transport mode “UDPTL/UDP”
[ITU.T38.1998] is the predominant protocol for fax transport in
   IP networks.  The protocol stack for fax transport using UDPTL is
   shown in Table 1.
 
                      +-----------------------------+
                      |           Protocol          |
                      +-----------------------------+
                      | Internet facsimile protocol |
                      +-----------------------------+
                      |            UDPTL            |
                      +-----------------------------+
                      |             UDP             |
                      +-----------------------------+
                      |              IP             |
                      +-----------------------------+
 
                Table 1: Protocol stack for UDPTL over UDP
 
T.38 itself does not support integrity and confidentiality protection,
because supposed to be subject of the application layer.  
 
NOTE 1: Encryption of end-to-end facsimile transfer between fax devices
was/is historically part of the application layer, such as [ITU.T.30] in
case of group 3 facsimile equipment (G3FE). See e.g., T.30 “Annex H -
Security in facsimile G3 based on the RSA algorithm”
 
Hence, none of the three T.38 transport modes was required to support
additional security.
 
NOTE 2: Keeping in mind that T.38 communication was/is normally limited
between T.38 endpoints located in IP-PSTN gateways (due to G3FE) besides
Internet-Aware Fax (IAF) devices). 
   
UDPTL does not offer integrity and confidentiality protection.  To
   enable integrity and confidentiality protection, [ITU.T38.2004]
   specifies fax transport over RTP/SAVP.  However, fax transport over
   RTP/SAVP is not widely supported.
 
   The 3rd Generation Partnership Project (3GPP) has performed a study
   on how to provide secure fax in the IP Multimedia Subsystem (IMS),  which
concluded that secure fax shall be transported using UDPTL over
   DTLS.
NOTE 3: Because, 1st limited end-to-end scope (“IMS domain only”) and 2nd
support of transport security due to the assumption of unsecured facsimile
data at application layer. 

 

 

…

 

   [ITU.T38.1998]

              International Telecommunications Union, "Procedures for

              real time Group 3 facsimile communication between

              terminals using IP Networks", ITU-T Recommendation T.38,

              1998.

 

   [ITU.T38.2004]

              International Telecommunications Union, "Procedures for

              real-time Group 3 facsimile communication over IP

              networks", ITU-T Recommendation T.38, 2004.

   [ITU.T38.2010]
              International Telecommunications Union, "Procedures for
              real time Group 3 facsimile communication between
              terminals using IP Networks", ITU-T Recommendation T.38,
              2010.
 
<https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-T.38-201009-I!!PDF-
E&type=items>
https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-T.38-201009-I!!PDF-E
&type=items 

 

 

 

-----Original Message-----
From:  <mailto:[e-mail]> [e-mail] [
<mailto:[e-mail]> mailto:[e-mail]] On Behalf
Of Christer Holmberg
Sent: Donnerstag, 29. August 2013 10:17
To: Dan Wing
Cc: mmusic WG
Subject: Re: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

 

Hi Dan,

 

The protocols listed in draft-ietf-tls-applayerprotoneg-01 are used without
SIP/SDP, so using such mechanism makes sense for those protocols.

 

In SIP, SDP is used to negotiate the media (including nonsecure fax), and I
see no reason why we should introduce a new mechanism for secure fax. 

 

Regards,

 

Christer

 

 

-----Original Message-----

From: Dan Wing [ <mailto:[e-mail]> mailto:[e-mail]] 

Sent: 28. elokuuta 2013 20:41

To: Christer Holmberg

Cc: mmusic WG

Subject: Re: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

 

 

On Aug 22, 2013, at 2:37 AM, Christer Holmberg <
<mailto:[e-mail]> [e-mail]>
wrote:

 

> Hi Dan,

> 

> Regarding the 3GPP SA3 study, the information I gave was a little
misleading. From a security perspective SRTP would be fine.

> 

> The focus of the SA3 study was on how to provide security for the existing
fax transmission mechanism, which uses UDPTL/UDP.

> 

> 3GPP already mandates IMS terminals to support UDPTL/UDP for unsecure fax.
And, new terminals (supporting secure fax) are still required to also
support unsecure fax, in order to communicate with legacy terminals when
unsecure fax is sufficient. 

> 

> So, using UDPTL/DTLS/UDP for secure fax makes more sense, as it avoids
implementing different mechanisms for secure and unsecure fax -
UDPTL/DTLS/UDP only requires a new layer between UDPTL and UDP, it does not
require changing the upper layers (UDPTL and above).

> 

> Hopefully this clarifies :)

 

(Sorry for my delay.  I was on vacation.)

 

Thanks for the clarification.

 

 

Back to your document, it says:

 

   Since the DTLS record layer "application_data" packet does not

   indicate whether it carries UDPTL, or some other protocol, the usage

   of a dedicated DTLS association for transport of UDPTL needs to be

   negotiated, e.g. using the Session Description Protocol (SDP)

   [RFC4566] and the SDP offer/answer mechanism [RFC3264].

 

   Therefore, this document specifies a new <proto> value [RFC4566] for

   the SDP "m=" line [RFC3264], in order to indicate UDPTL over DTLS in

   SDP messages [RFC4566].

 

Have you considered doing UDPTL negotiation in the DTLS handshake itself,
using  <http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg>
http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg?  That seems
ideally suited for indicating the application layer protocol, perhaps in
addition to the SDP signaling described in your I-D.

 

-d

 

 

> 

> Regards,

> 

> Christer

> 

> 

> 

> 

> 

> -----Original Message-----

> From: Dan Wing [ <mailto:[e-mail]> mailto:[e-mail]]

> Sent: 19. elokuuta 2013 20:43

> To: Christer Holmberg

> Cc: mmusic;  <mailto:[e-mail]>
[e-mail]

> Subject: Re: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00

> 

> 

> On Aug 19, 2013, at 6:03 AM, Christer Holmberg <
<mailto:[e-mail]> [e-mail]>
wrote:

> 

>> Hi,

>> 

>> We have submitted a new draft, draft-holmberg-mmusic-udptl-dtls-00, which
defines usage of UDPTL over DTLS, in order to provide secure fax.

>> 

>> The draft was previously submitted to DISPATCH. Based on discussions with
the ADs and chairs, it was decided that it shall be submitted to MMUSIC
(note that no DTLS extensions are needed).

>> 

>> As is indicated in the draft, 3GPP has performed a study on how to 

>> provide secure fax in the IMS, and the outcome was that secure fax shall
be transported using UDPTL over DTLS.

> 

> Got a pointer to that study?  Seems easier to carry UDPTL over RTP, which
would allow the RTP to be secured using SRTP (and thus the UDPTL would be
secured using SRTP).  There is a spec floating around to do exactly that
(carry fax over RTP so that SRTP can secure it).  Advantage of using SRTP to
secure fax is it separates the keying mechanism from security, so that
Security Descriptions / MIKEY / DTLS-SRTP / whatever-is-invented-in-2020
will work just as effectively for voice as for fax.  And also that upgrading
from a voice call to a "fax" call has no additional complexities due to
security ("please press START to begin the fax transmission").

> 

> -d

> 

> 

>> However, there is nothing "3GPP/IMS specific" about the mechanism, as
UDPTL is commonly used for fax also elsewhere.

>> 

>> Regards,

>> 

>> Christer

>> _______________________________________________

>> mmusic mailing list

>>  <mailto:[e-mail]> [e-mail]

>>  <https://www.ietf.org/mailman/listinfo/mmusic>
https://www.ietf.org/mailman/listinfo/mmusic

> 

 

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