[VOIPSEC] Really RTP is end-to-end?

[Dan Wing]

> From a SRTP standpoint having DTMF digits carried inband (RFC 2833)
> is less than ideal as each hop would need to decrypt and re-encrypt
> the media at each hop just to detect the presence of DTMF digits.
> Is there a way to carry DTMF digits out of band like other protocols
> can do?  I mean you can encrypt media right through the asterisk box
> in H.323

Yes, it's called KPML.  The document is 
http://www.ietf.org/internet-drafts/draft-ietf-sipping-kpml-07.txt, 
which is in the RFC Editor's queue.  Abstract:

   This document describes a SIP Event Package "kpml" that enables
   monitoring of DTMF signals and uses XML documents referred to as Key
   Press Markup Language (KPML).  The kpml Event Package may be used to
   support applications consistent with the principles defined in the
   document titled "A Framework for Application Interaction in the
   Session Initiation Protocol (SIP)".  The event package uses SUBSCRIBE
   messages and allows for XML documents that define and describe filter
   specifications for capturing key presses (DTMF Tones) entered at a
   presentation-free User Interface SIP User Agent (UA).  The event
   package uses NOTIFY messages and allows for XML documents to report
   the captured key presses (DTMF tones), consistent with the filter
   specifications, to an Application Server.  The scope of this package
   is for collecting supplemental key presses or mid-call key presses
   (triggers).

-d