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

Hi Dan,

>> I'll get back to your comments later, but just a question for clarification:
>>
>> When you say "UDPTL over RTP", you are NOT referring to RFC 4612, right?
>
> I believe I am.  However, I thought there was an ITU specification for T.38 over RTP -- perhaps there is just that IETF specification.  

The latest version of T.38 also specifies the usage of T.38 over RTP.  

RFC 4612 defines the new MIME type and fmtp attribute values, also used in T.38, but refers to T.38 for the fax mechanism itself.

> Are you not a fan of RFC4612?

I'm a fan of Kelly Clarkson ;)

>> Or, did you mean to say "fax over RTP"? :)
>
> Maybe you could educate me on the difference.  My fax knowledge has faded with time.

When you use RTP, you don't use UDPTL. The UDPTL layer is "replaced" by the RTP layer, and the fax stuff is transported as an RTP payload type.

Regards,

Christer

> -----Original Message-----
> From: Dan Wing [mailto:dwing@cisco.com]
> Sent: 19. elokuuta 2013 20:43
> To: Christer Holmberg
> Cc: mmusic; mmusic-chairs@tools.ietf.org
> Subject: Re: [MMUSIC] Draft new: draft-holmberg-mmusic-udptl-dtls-00
>
>
> On Aug 19, 2013, at 6:03 AM, Christer Holmberg <christer.holmberg@ericsson.com> 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
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