For the latest draft of SD, see the following paper:

  Handley, M., and Jacobson, V., 
  SDP: Session Description Protocol.
  Internet draft draft-ietf-mmusic-sdp-01.{txt,ps}, 
  working draft.  
  URL http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.01.ps.

The release of sdr, a new session directory compliant with
draft-ietf-mmusic-sdp-01.{txt,ps}, is available from
ftp://cs.ucl.ac.uk/mice/sdr.  Also mirrored at
ftp://ftp.uoregon.edu/pub/src/multicast/sdr,
ftp://sauce.uio.no/mice-nsc/unsupported/sdr,
ftp://ftp.parc.xerox.com/pub/net-research/apps/sdr.