• • Name: F.700

    Reference: F.711 - F740

    Version: 1992

    Sponsoring body: CCITT

    Status: To be ratified at March 1993 CCITT Plenary.

    Brief description: Audiographic, Videotelephony and Videoconference service standards.

    Detailed description: The individual recommendations are as follows:

    F.711 Audiographic Conference Teleservice for ISDN

    F.720 Videotelephony Services General

    F.721 Videotelephony Teleservices for ISDN

    F.722 Videotelephony Services General

    F.730 Videoconference Service General

    F.732 Broadband Videoconference Services

    F.740 Audiovisual Interactive Services (AVIS)
     

    Date of entry: 19 January 1993
     

    Name: G.711

    Reference: G.711

    Version: B (1988)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: Pulse Code Modulation (PCM) of voice frequencies

    Detailed description: 64 kbit/s 8kHz 8-bit PCM audio encoding.

    Date of entry: 15 December 1992
     

    Name: G.721

    Reference: G.721

    Version: B (1988)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: 32 kbit/s adaptive differential pulse code modulation (ADPCM) for audio
    encoding.

    Date of entry: 15 December 1992
     

    Name: G.722

    Reference: G.722

    Version: B (1988)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: 7 KHz audio encoding within 64 kbit/s

    Date of entry: 15 December 1992
     

    Name: G.725

    Reference: G.725

    Version: B (1988)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: System Aspects of the use of 7 kHz audio codec within 64 kbit/s

    Date of entry: 15 December 1992
     

    Name: H.221

    Reference: H.221

    Version: R1 (12/90)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices.
    Detailed description: Defines a frame structure for audiovisual teleservices in single or multiple
    B or H0 channels or a single H11 or H12 channel which makes the best use of the characteristics and properties of the audio and video encoding algorithms, of the transmission frame structure and of the existing recommendations. It offers several advantages:
    It takes into account Recommendations G.704, X.301/I.461, etc. It may allow the use of existing hardware and software.
    Closely related to H.261 & H.242. Supersedes H.220

    Products: Codecs from BT, GPT, Picturetel, Videotel & others

    Date of entry: 10 December 1992
     

    Name: H.242

    Reference: H.242

    Version: N (12/90)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: Audiovisual communication using digital channels up to 2 Mbit/s

    Detailed description: Recommendation H.242 should be associated with Recommendations
    G.725, H.221 and H.230.

    A number of applications utilising narrow (3 kHz) and wideband (7 kHz) speech together with
    video and/or data have been identified, including high quality telephony, audio and
    videoconferencing (with or without various kinds of telematic aids), audiographic conferencing
    and so on. More applications will undoubtedly emerge in the future.
     

    •         To provide these services, a scheme is recommended in which a channel accommodates speech,and optionally video and/or data at several rates, in a number of different modes. Signalling procedures are required to establish a compatible mode upon call set-up, to switch between modes during a call and to allow for call transfer.
    •         Some services will require only a single channel, which could according to the procedures in Recommendation H.242 be B (64 kbit/s), H0 (384 kbit/s), H11 (1536 kbit/s) or H12 (1920kbit/s). Other services will require the establishment of two or more connections providing B or H0 channels: in such cases the first established is called hereafter the initial channel while the others are called additional channels.

     

    •          All audio and audiovisual terminals using G.722 audio coding and/or G.711 speech coding or other standardised audio codings at lower bit rates should be compatible to permit connectio between any two terminals. This implied that a common mode of operation has to be established for the call. The initial mode might be the only one used during a call or, alternatively, switching to another mode can occur as needed depending on the capabilities of the terminals. Thus, for these terminals an in-channel procedure for dynamic mode switching is required.

     

    •          Recommendation H.242 develops these considerations and describes recommended in-channel procedures.

    Products: Codecs from BT, GPT, Picturetel, Videotel & others.

    Further information: Closely related to H.261 & H.221. Supersedes H.220

    Date of entry: 25 November 1992
     

    Name: H.261

    Reference: H.261

    Version: R1 (12/90)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: Video Codec for Audiovisual Services at p x 64 kbit/s

    Detailed description:

    • Recommendation H.261 describes the video coding and decoding methods
    • for the moving picture component of audiovisual services at the rate of p x 64 kbit/s, where p is  in the range 1 to 30. It describes the video source coder, the video multiplex coder and the transmission coder.

     

    •       This standard is intended for carrying video over ISDN - in particular for face-to-face videophone applications and for videoconferencing. Videophone is less demanding of image quality, and can be achieved for p=1 or 2. For videoconferencing applications (where there are more than one person in the field of view) higher picture quality is required and p must be at least 6.

     

    •          H.261 defines two picture formats: CIF (Common Intermediate Format) has 288 lines by 360 pixels/line of luminance information and 144 x 180 of chrominance information; and QCIF(Quarter Common Intermediate Format) which is 144 lines by 180 pixels/line of luminance and 72 x 90 of chrominance. The choice of CIF or QCIF depends on available channel capacity - eg  QCIF is normally used if p<3.

     

    •         The actual encoding algorithm is similar to (but incompatible with) that of MPEG. Another difference is that H.261 needs substantially less CPU power for real-time encoding than MPEG.  The algorithm includes a mechanism which optimises bandwidth usage by trading picture quality against motion, so that a quickly-changing picture will have a lower quality than a relatively static picture. H.261 used in this way is thus a constant-bit-rate encoding rather than a constant-quality, variable-bit-rate encoding.

    Products: H.261 codecs have been implemented in VLSI and are now built in to commercially
    available codec equipment.

    Further information: Document available on line on:

    src.doc.ic.ac.uk:/doc/ccitt-standards/ccitt/1992/h
     

    Date of entry: 15 December 1992
     

    Name: H.320

    Reference: H.320

    Version: N (12/90)

    Sponsoring body: CCITT

    Status: Recommendation currently in force

    Brief description: Narrow Band Visual Telephone systems and terminal equipment
     

    •             Detailed description: Recommendation H.320 covers the technical requirements for narrow-band visual telephone services defined in H.200/AV.120-Series Recommendations,  where channel rates do not exceed 1920 kbit/s.

     

    •            Note - It is anticipated that Recommendation H.320 will be extended to a number of  Recommendations each of which would cover a single videoconferencing or videophone service (narrow-band, broadband, etc.). However, large parts of these Recommendations would have identical wording, while in the points of divergence the actual choices between alternatives have not yet been made; for the time being, therefore, it is convenient to treat all the text in a single Recommendation.

     

    •          The service requirements for visual telephone services are presented in Recommendation  H.200/AV.120-Series; video and audio coding systems and other technical set aspects common to audiovisual services are covered in other Recommendations in the H.200/AV.200-Series.

    Date of entry: 15 December 1992
     
     

    Name: JPEG

    Reference:

    Version:

    Sponsoring body: CCITT | ISO (JTC1/SC2/WG10)

    Status: Committee Draft

    Brief description: Compression Standard for continuous-tone still images
     

    •           Detailed description: JPEG is a standardised image compression mechanism. JPEG stands for Joint Photographic Experts Group, the original name of the committee that wrote the standard. JPEG is designed for compressing either full-colour (24 bit) or gray-scale digital images of "natural" (real-world) scenes. JPEG does not handle black-and-white (one bit/pixel) images, nor does it handle motion picture compression.

     

    •           JPEG is "lossy", meaning that the image you get out of decompression isn't quite identical to what you originally put in. The algorithm achieves much of its compression by exploiting known limitation of the human eye, notably the fact that small colour details aren't perceived as well as small details of light-and-dark. Thus, JPEG is intended for compressing images that will be looked at by humans. If you plan to machine-analyse your images, the small errors introduced by JPEG may well be a problem for you, even if they are invisible to the eye.

     

    •              A useful property of JPEG is that the degree of lossiness can be varied by adjusting compression parameters. This means that the image maker can trade off file size against output image quality. You can make extremely small files if you don't mind poor quality; this is useful for indexing image archives, making thumbnail views or icons, etc etc. Conversely, if you aren't happy with the output quality at the default compression setting, you can jack up the quality until you are satisfied, and accept lesser compression.

     

    •            Although it handles colour files well, it is limited in handling black-and-white and files with sharp edges (files come out very large). The processing costs, even on up-to-date computers, is also high.

    Products: Many products now use this algorithm. There is free JPEG source code available
    from the Independent JPEG group, at many FTP sites.

    Further information: Independent JPEG group at jpeg-info@uunet.uu.net. JPEG software
    and file specifications are available from several FTP sites, including
    ftp.uu.net:/graphics/jpeg.
     

    Date of entry: 21 December 1992
     

    Name: MPEG

    Reference: ISO 11172

    Version: MPEG I

    Sponsoring body: ISO (JTC1/SC2/WG11)

    Status: Committee Draft

    Brief description: Standard for compressed video and audio

    Detailed description:
     

    •         MPEG (Moving Pictures Expert Group) is the name of the ISO committee
    • which is working on digital colour video and audio compression, and by extension the name of the standard they have produced.

     

    • MPEG defines a bit-stream representation for synchronised digital video and audio, compressed to fit into a bandwidth of 1.5 Mbit/sec. This corresponds to the data retrieval speed from CD ROM and DAT, and a major application of MPEG is the storage of audio visual information on this media. MPEG is also gaining ground on the Internet as an interchange standard for video clips.

     

    • The MPEG standard is the three parts - video encoding, audio encoding, and "systems" which includes information about the synchronisation of the audio and video streams. The video stream takes about 1.15 Mbit/s, and the remaining bandwidth is used by the audio and system data streams.

     

    • MPEG video encoding starts with a fairly low-resolution (352 x 240 pixels x 30 frames/s in the US; 352 x 288 x 25 frames/s in Europe) video picture. RGB pixel information is converted to chrominance/luminance and a complex, lossy compression algorithm is applied. The algorithm takes the time axis as well as spatial axes into account, so a good compression ration is achieved when the picture is relatively unchanging (and vice versa). The compressed data contains three types of frames: I (intra) frames are coded as still images; P (predicted) frames are deltas from the most recent past I or P frame; and B (bidirectional) frames are interpolations between I and P frames. I frames are sent once every 10 or 12 frames. Reconstructing a B frame for display requires the preceding and following I and/or P frames, so these are sent out of time-order.

     

    • Substantial computing power is required to encode MPEG data in real time - perhaps several hundred MIPS to encode 25 frames/second. Decoding is not quite so demanding.

     

    • The quality of MPEG-encoded video has been compared to that of a VHS video recording.

     

    • MPEG II is under development. MPEG II is designed to offer higher quality at a bandwidth of between 4 and 10 Mbit/s. This is too fast for playback from CD using today's technology.

    Products:
     

    • Phillips have developed an MPEG decoder chip, which will go into their CD-I

    product range.
     

    • Xing Technology Corp (California, USA) offer video capture and encode/decode hardware and software for PCs which uses MPEG and JPEG.

     

    • Ingenieurbuero Gatz und Hartmann (Berlin, Germany) offer a PC video input board and an off-line MPEG encoding program. Maximum video clip length is 20s (limited by 32Mb of expanded memory in the PC).

     

    • Optibase Inc (California, USA) have board-level products for PCs, called MPG-1000 (codec), MPG-2000 and MPG-2100 (playback only)

    There are freeware MPEG software decoder/players for DOS, MS Windows and X windows -
    see FTP sites below for details.
     

    Anonymous FTP sites are:

    phoenix.oulu.fi:pub/mpeg

    toe.cs.berkley.edu:pub/multimedia/mpeg
     

    Date of entry: 30 November 1992
     
     

     

    Name: G.723

    Description: CCITT standard for conversion between G.711 and lower-speed channels.
     

    Name: G.726

    Description: Replaces G.721
     

    Name: G.727

    Description: Extension of G.726 for use over G.764
     

    Name: G.728

    Description: Coding of Speech at 16 kbit/s using Low-Delay Code Excited Linear Prediction
    (LD-CELP). Audio encoding for videoconferencing.
     

    Name: G.764

    Description: Packetised Voice Protocol
     

    Name: G.765

    Description: Associated with G.764
     

    Name: H.200

    Description: Audio compression standard (forthcoming).
     

    Name: H.241

    Description: Signalling for conferencing.
     

    Name: H.243

    Description: Multipoint Video Codec Standard. Probably a draft
     

    Name: T.120

    Description: T.121-T.124: Network-independent audio conferencing protocols.
     

    Name: IP Multicast

    Reference: RFC 1112

    Version: August 1992

    Sponsoring body: IETF Network Working Group

    Status: Internet standard

    Brief description: The extensions required to a host implementation of the Internet Protocol (IP)
    to support multicasting.

    Detailed description:

    • IP multicasting is the transmission of an IP datagram to a host group,
    • which is a set of zero or more hosts identified by a single IP destination address. A multicast datagram is delivered to all members of a destination host group. The membership of the host group is dynamic. A host group may be transient or permanent.

     

    • Multicasting of this nature is essential to optimise bandwidth usage for multiparty conferencing applications.

     

    • Internetwork forwarding of IP multicast datagrams is handled by multicast routers. The special routing requirements of multicast IP can be met in several different ways. There are extensions to the OSPF and BGP routing methods, and there is a new routing method (CBT - Core Based Trees). At the time of writing, it seems that CBT is likely to be adopted as the appropriate method of routing multicast IP.

    Products: vat, nv, ivs, NEVOT, sd and other remote conferencing tools use IP multicast.
    Multicast support is available as kernel patches for SunOS 4.x.x, and is built in to SunOS 5.

    Patches to various UNIX system kernels to provide multicast support are available from:

    gregorio.stanford.edu:/vmtp-ip.

    Date of entry: 15 December 1992
     

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