Internet DRAFT - draft-civanlar-pointer

draft-civanlar-pointer



  Internet Engineering Task Force           Civanlar & Cash - AT&T
  INTERNET DRAFT                            June 24, 1999
  File: draft-civanlar-rtp-pointer-00.txt   Expires: December, 24 1999


                RTP Payload Format for Real-Time Pointers


                           STATUS OF THIS MEMO

  This document is an Internet-Draft and is in full conformance with all
  provisions of Section 10 of RFC2026.

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                                 Abstract

  This document describes a payload format for transporting the
  coordinates of a pointer that may be used during a presentation in
  real-time using RTP [1].

  1. Introduction

  In most presentations, significant information is conveyed through the
  use of viewgraphs and a pointer. This makes accurate transmission of
  them vital in remote conferencing. Using regular video of a
  presenter's display for this purpose is problematic because, while the
  viewgraphs require a high spatial resolution, the pointer movements
  need to be sampled and transmitted at a high temporal resolution so
  that the presenter's pointing actions can be displayed synchronously
  with the corresponding audio and video signals, e.g.  when a speaker
  points at two alternatives in sequence and says "this one is better
  than this." To satisfy both of these requirements, at least S-VHS
  quality video may need to be used. Codecs that can compress S-VHS



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  video effectively in real-time are expensive, and transmitting such
  video uncompressed requires very high bandwidths.

  A much simpler and economical system can be designed by capturing and
  transmitting the pointer coordinates separately [2]. The pointer
  coordinates with respect to a displayed viewgraph can easily be
  obtained in electronic presentation systems. For presentations
  prepared for optical systems, such as transparencies for overhead
  projectors, an arrangement where the viewgraph is captured in a frame
  buffer on a computer can be used to associate the pointer coordinates
  with the displayed viewgraph. For capturing transparencies, printed
  material, or even three dimensional objects, a document camera and a
  personal computer or workstation based video capture card can be used.
  This arrangement can handle electronic viewgraphs by feeding the video
  output of the computer that displays them to the video capture card
  through an appropriate converter also. (A side benefit of this is that
  it allows using a presenter’s own computer to transmit electronic
  viewgraphs without connecting it to, for example, an intranet.) The
  captured image is then displayed along with the capturing computer's
  mouse pointer on the presenter’s display using a projector. The
  presenter moves the pointer on the display using a regular or maybe a
  wireless mouse whose location can easily be captured by appropriate
  software running on the capturing computer.

  This document describes an RTP payload format to transmit the pointer
  coordinates captured in one of the ways described above using RTP.

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in RFC 2119 [3].

  2. Payload Format

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |V=2|P|X|  CC   |M|     PT      |       sequence number         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           timestamp                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           synchronization source (SSRC) identifier            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  :            contributing source (CSRC) identifiers             :
  +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
  |L| |      x coordinate         |R| |      y coordinate         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    MBZ                             MBZ
              Figure 1 - An RTP packet for Real-Time Pointer



Civanlar & Cash                                                 [Page 2]

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  Fig. 1 shows an RTP packet carrying real-time pointer coordinates.
  This payload format does not have a payload specific header.

  2.1. RTP Header Usage:

  Payload Type (PT): The assignment of an RTP payload type for this new
  packet format is outside the scope of this document, and will not be
  specified here. It is expected that the RTP profile for a particular
  class of applications will assign a payload type for this encoding, or
  if that is not done then a payload type in the dynamic range shall be
  chosen.

  Marker (M) bit: Set to one if the payload carries information about
  mouse buttons.

  Extension (X) bit: Defined by the RTP profile used.

  Sequence Number: Set as described in RFC1889 [1].

  Timestamp: The sampling time for the pointer location measured by a
  1KHz clock.

  SSRC: Set as described in RFC1889 [1].

  CC and CSRC fields are used as described in RFC 1889 [1].

  RTCP SHOULD be used as defined in RFC 1889 [1].

  2.2. Payload:

  The pointer's x and y coordinates are measured from the upper left
  corner of the associated display window in pixels. The associated
  window SHOULD be specified out-of-band. The coordinates are
  represented as 14 bit, unsigned integers.

  When the M bit is set to one, L (left) and/or R (right) bits are set
  to one if their respective mouse buttons are down at the sampling
  time.

  3. Security Considerations

  RTP packets using the payload format defined in this specification are
  subject to the security considerations discussed in the RTP
  specification [1].

  This payload type does not exhibit any significant non-uniformity in
  the receiver side computational complexity for packet processing  to
  cause a potential denial-of-service threat.



Civanlar & Cash                                                 [Page 3]

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  4. References

    [1] Schulzrinne, Casner, Frederick, Jacobson RTP: A
    Transport Protocol for Real Time Applications  RFC 1889,
    Internet Engineering Task Force, January 1996.

    [2] M. R. Civanlar, G. L. Cash, "Networked Viewgraphs - NetVG" Proceedings
    of The 9th Int. Workshop on Packet Video,
    http://www.reseach.att.com/~mrc/PacketVideo99.html.

    [3] S. Bradner, Key words for use in RFCs to Indicate
    Requirement Levels, RFC 2119, March 1997.


 7. Authors' Addresses

 M. Reha Civanlar
 AT&T Labs - Research
 100 Schultz Drive
 Room 3-213
 Red Bank, NJ 07701
 USA
 e-mail: civanlar@research.att.com

 Glenn L. Cash
 AT&T Labs - Research
 100 Schultz Drive
 Room 3-221
 Red Bank, NJ 07701
 USA
 e-mail: glenn@research.att.com




















Civanlar & Cash                                                 [Page 4]