VAT(1)                    User Commands                    VAT(1)



NAME
     vat - X11-based audio teleconferencing tool

SYNOPSIS
     vat [ -aAcdEjJklLMnnsSv ] [ -F device ] [ -f audiofmt ]
     [ -g geometry ] [ [ -m host/port[/fmt] ] [ -N sessionname ]
     [ -C conferencename ] [ -K key ] [ -P priority ] [ -t ttl ]
     [ -U socket ] [ -u script ] [ dest ]

DESCRIPTION
     Vat allows users to conduct host-to-host or multihost  audio
     teleconferences  over  an  internet  (multihost  conferences
     require that the kernel  support  IP  multicast).   On  most
     architectures,  no  hardware  other  than  a  microphone  is
     required - sound I/O is via the built-in audio hardware.  On
     DEC systems, an AudioFile server must be running.

OPTIONS
     (Note that all the parameters set by the following flags can
     also  be  controlled by X resources (which all have `reason-
     able' defaults) so one should not need to give vat any flags
     in  the  usual  case.   The  flags only exist to temporarily
     override some resource.)

     -a    Enable automatic gain control on the output (speaker).

     -A    Enable automatic gain control on the input (mike).

     -c    Start up in `conference mode' (see description below).
          (This flag is the opposite of -l.)

     -C    Use conference as the title of this vat window.  If no
          - C flag is given, the destination address and port are
          used as the window title.

     -d    Start up with the VU  meters  disabled  (this  can  be
          changed using the `Disable Meters' checkbox on the aux-
          iliary controls panel.

     -E    Include a checkbox in the auxiliary controls panel for
          specifying  that  echo  cancellation is being performed
          externally (i.e., in hardware).  This option  can  also
          be    effected    by    setting    the    X    resource
          Vat.externalEchoCanel to ``true''.

     -f    Sets the output audio packet format to fmt. (Note that
          it  not necessary to set an input format since vat will
          accept any packet format it  knows  about.)   Currently
          available audio formats are:
               pcm  78Kb/s 8-bit mu-law encoded 8KHz PCM (20ms frames)
               pcm2 71Kb/s 8-bit mu-law encoded 8KHz PCM (40ms frames)
               pcm4 68Kb/s 8-bit mu-law encoded 8KHz PCM (80ms frames)



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               idvi 46Kb/s Intel DVI ADPCM (20ms frames)
               dvi2 39Kb/s Intel DVI ADPCM (40ms frames)
               dvi4 36Kb/s Intel DVI ADPCM (80ms frames)
               gsm  17Kb/s GSM (80ms frames)
               lpc4 9Kb/s Linear Predictive Coder (80ms frames)
          (The idvi encoding was contributed by  Jack  Jansen  of
          CWI.  The  _g_s_m coder was contributed by Carsten Bormann
          of the Technische Universitaet Berlin.  The  lpc  coder
          was contributed by Ron Frederick of Xerox PARC.)
          The default audio format can be set with the  audioFor-
          mat X resource.  It defaults to pcm.

     -g    Override the default window  geometry  with  geometry,
          which should be a standard X geometry string.

     -j    Start up with audio output to the external audio jack.
          This  flag  can  be defaulted by setting the X resource
          Vat.speaker to false.

     -J    Start up with audio output muted.

     -k    Keep all sites in the `Conference Hosts' panel.   Nor-
          mally sites that exit are deleted from the panel.  With
          -k, sites that exit are grayed-out but not deleted.

     -K    Use key as the encryption key for this vat session.

     -l    Start up in `lecture mode'  (see  description  below).
          This  flag  can  be defaulted by setting the X resource
          Vat.lectureMode to true.

     -m    Serve as a `mixer' for host host which is listening on
          port port optionally using audio packet format fmt. The
          mix function allows vat  to  function  as  `application
          level gateway'. There are three uses for this function:
          Bandwidth Adaptation 
          Say you want to participate in  a  conference  at  work
          that  is  using  64Kb/s  PCM  but  you to join over the
          9.6Kb/s line to your  home.   If  there  is  a  machine
          "work"  at  work that can proxy for your machine "home"
          at home, this could be set up as:
               At work:  vat -m home/5678/lpc4
               At home:  vat work/5678/lpc4
          Concentration
          If a conference has two communities connected by a  low
          speed  link,  it's  desirable to mix multiple conversa-
          tions into a single data stream  rather  than  shipping
          them  over  the link individually. If, say, the gateway
          machines were "foo" and "bar" and the  conference  were
          on  the default multicast address, this would be set up
          as:
               On foo:  vat -m bar/5678



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               On bar:  vat -m foo/5678
          (Note that the port used by the mixers has to  be  dif-
          ferent than the port used by the conference.)
          Format Conversion
          Say organization A uses Etherphone audio packet  format
          for  internal  conferencing  but  wants to have a joint
          conference with organization B that uses  G.278  packet
          format.  If  a  machine  AtoB  at  A  can  be  used  to
          convert/concentrate traffic to B via a peer  BtoA,  the
          two conferences can be combined with:
               on A's AtoB:  vat -m BtoA/5678/pcm Aaddr/Aport/etherphone
               on B's BtoA:  vat -m BtoA/5678/pcm Baddr/Bport/g278
          Note that the two  conference  environments  need  have
          nothing in common --- they can use different audio for-
          mats, addresses and/or ports. The only agreement needed
          is over the peer-to-peer communication between AtoB and
          BtoA.

     -M    Start up with audio input unmuted.

     -n    Force `native' vat packet format and default  address.
          (This flag is the opposite of -v.)

     -N    Use session, in lieu of your user name and local host,
          to identify you to other sites. If no -N flag is given,
          the X resource Vat.sessionName is used.

     -P    Use priority as this vat window's priority for obtain-
          ing  the audio device.  All vat windows have a priority
          which   is   typically   set   by   the   X    resource
          Vat.defaultPriority  (defaults  to 100) but this can be
          overridden by a -P flag.   If  a  window  requests  the
          audio (because new network data arrived or the mike has
          been unmuted) and  the  window  currently  holding  the
          audio is either lower priority or hasn't used audio for
          Vat.idleHoldTime seconds, the audio holder  immediately
          gives  it  up.   Otherwise  the new window's request is
          ignored.   (Vat.idleHoldTime  provides  hysteresis   to
          prevent  `thrashing'  when two conferences go active at
          about the same time; the priority  provides  a  way  to
          distiguish  `background'  windows,  say a radio station
          broadcast or a `directory' window of  people  reachable
          via  vat,  from `foreground' activity like a particular
          audio conference so vat can make  better  decisions  on
          what should get the audio.)

     -s    Start up with audio output to  the  internal  speaker.
          (This flag is the opposite of -j.)

     -S    Make new sites come up  `suppressed'  (the  check  box
          next  to the sitename will be checked and you will have
          to click on it to hear the site speak).  This  flag  is



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          intended  for something like meeting audiocasts where a
          moderator wants to have control over  who  is  able  to
          speak.    This   flag   can   also   be   set   by  the
          Vat.muteNewSites X resource.

     -t    Set the multicast ttl (time-to-live) to ttl. (The  ttl
          is ignored if the destination address is not an IP mul-
          ticast address.)  If no -t flag is given, the value  of
          the X resource Vat.defaultTTL is used.

     -U    Use the unix-domain stream socket specified by  socket
          for  audio I/O.  Some process should bind to and listen
          on this socket before vat is run.  The data is raw 8khz
          mulaw samples.

     -u    Use scrip as the tcl program to build the user inter-
          face,  rather  than  the built-in script.  You can also
          override vat's built-in tcl script with  your  own  tcl
          code in $HOME/.vat.tcl.

     -v    Use a packet format and default multicast address that
          is  compatible  with  ISI's  vt (voice teleconferencing
          tool). Vat and vt can interoperate but vt does not par-
          ticipate  in  vat's  `session' protocol so the names of
          conference participants running vt will not show up  in
          the  vat `Conference Hosts' window (IP addresses for vt
          participants appear instead).
          In vt compatibility mode, the default destination  host
          or  multicast  group  is  controlled  by the X resource
	  Vat.defaultVTHost rather than Vat.defaultHost. The   -v
          flag  can be defaulted by setting the X resource VTMode
          to true.

     Note:  In addition to invoking the ``quit''  button,  typing
     `q',  `Q', ctrl-C or ctrl-D anywhere in the window will ter-
     minate vat.

     The vat window is divided into two parts: the right has con-
     trols  for the local audio and the left has a status display
     of the hosts participating in the current  conference.   The
     audio  controls consist of two sliders that control the mike
     and playback gain, a button to  toggle  output  between  the
     built   in  speaker  and  the  headphone  jack,  buttons  to
     mute/unmute either the mike or speaker, and buttons to  con-
     trol  acquistion of the audio hardware.  To adjust the slid-
     ers, either click at the desired position or click and  drag
     the  slide button to the desired position.  Just to the left
     of each slider is a VU meter.  A rule of thumb is to  adjust
     the  mike  and  speaker gain sliders so the peak readings on
     the meter are about 80% of full scale.





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     To change the audio output line (i.e.,  speaker,  headphone,
     lineout,  etc.)  click on the speaker icon (it should change
     to a headphone icon).  Additional  clicks  will  round-robin
     among the available lines.  If there is only one option, the
     button will be disabled.  Similarly, click on the mike  icon
     to  select  among  the  input lines.  To toggle mike/speaker
     muting, click on the appropriate mute  button.   The  button
     will be highlighted when muting.

     The Conference Hosts window lists every site currently  par-
     ticipating  in  the conference, with your site always listed
     first.  The participant name is displayed in a box  that  is
     highlighted whenever that site is speaking and grayed-out if
     a `session'  message  message  from  the  site  hasn't  been
     received  for  at least 30 seconds (each vat sends `session'
     message every 6 seconds) - this usually indicates  that  the
     site  has  lost connectivity or that vat has been aborted or
     stopped.  There is a checkbox to the left of  each  partici-
     pant  name.  Clicking  on the box will cause audio from that
     participant to be discarded instead of played (for  example,
     this  might  be  used  to suppress a site that is generating
     echoes). Names, by default, appear in  the  form  user@host,
     but  can be arbitrarily specified by each participant (i.e.,
     with -N).

Multiple VAT Windows
     One host can be running an arbitrary number of vat  sessions
     (presumably with different destination addresses).  However,
     since most workstations have only one set of audio hardware,
     only  one  of those sessions will be able to access the mike
     and speaker.  For the  most  part,  the  vat  sessions  will
     automatically  follow the action.  If you unmute the mike or
     press the ``Keep'' button, the audio device will be acquired
     by  that  session  and  the session that previously held the
     audio will relinquish it.  Vat displays it's title bar in an
     oblique font when the audio is not being held.

     A vat session will also acquire the audio if there is  input
     from  the  network.  But to prevent a background vat session
     from stealing the audio from the foreground session, you can
     toggle  the  ``Keep''  button.   When the ``Keep'' button is
     highlighted, vat will reliquish the audio only if there is a
     user  demand  in  another window (i.e., unmuting the mike or
     selecting the Keep button).

     The audio can be explicitly  released  by  clicking  on  the
     ``Release''  button.  Note however that if no other vats are
     active and there is input from  the  net  with  idleHoldTime
     seconds,  the  vat session that just released the audio will
     re-acquire it.





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     Participants in a multi-site conference often want  to  have
     `side  conversations'  that  don't  bother  the  rest of the
     conference participants. Vat has some support for establish-
     ing  side conversations:  If you middle-click on the name of
     some site in the conference hosts window, a new  vat  window
     will  be  created  that  talks  only to that participant (it
     sends unicast datagrams rather  than  multicast).   If  that
     other  participant  also middle-clicks on your site, you can
     have a private conversation  between  just  your  two  sites
     using  the newly created vat windows.  Note:  due to a `bug'
     in the way most systems implement multicast, if you create a
     new  window  aimed  at  a  particular  participant  but they
     haven't created a window aimed at you, they  will  hear  you
     speaking  in  the main conference window and may not realize
     that your audio is being sent only to them  and  not  multi-
     cast.   One can view this either as a feature (it provides a
     semi-private channel you can use to ask someone to set up  a
     side  conversation)  or  a  bug  (it often leads to strange,
     one-sided conversations where one side  multicasts  and  the
     other doesn't).

     Note that a site that's running as a `mixer' (-m  flag)  for
     some  other  site  should not run multiple vat windows:  The
     audio hardware is needed to provide the timing for the  mix-
     ing  function  and  the  window  doing the mix will cease to
     function if it loses control of the audio hardware.

Auxiliary Controls
     Clicking on the ``Menu'' label at the bottom of the vat win-
     dow will cause a panel of auxiliary controls to open.

     The Audio Tests buttons will enable some audio  test  modes.
     These  should not be selected during a conference. The loop-
     back mike button will cause input from the mike to  be  sent
     to  the local speaker/jack.  This might be useful for check-
     ing levels and debugging cable problems but the  20ms  delay
     from  input  to  output  makes  talking  in this mode almost
     impossible.  The three tone buttons  will  generate  one  of
     three reference tones through the local speaker.  Level set-
     ting should generally be done with the -6dBm tone.

     The Output Mode buttons control what vat will  do  to  avoid
     feedback/echo  from  the mike to the speaker.  In mike mutes
     net mode, vat will mute the speaker whenever it thinks  that
     you are talking, while in net mutes mike mode, vat will mute
     the mike whenever input from the network arrives.   In  full
     duplex  mode, vat will assume that feedback can't happen and
     do nothing to avoid  it.  In  echo  cancel  mode,  vat  will
     attempt  to eliminate echoes by doing some fancy signal pro-
     cessing.  (EchoCancel requires the BSD sound driver - it  is
     disabled  when  running  vat  under  Sun  OS because the Sun
     driver does not provide  any  mechanism  to  time  correlate



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     audio  output  and input.)  The internal speaker should only
     be used in `speakerphone' or `echo cancel' mode -  selecting
     `headphone' mode for it will result in your site injecting a
     lot of unpleasant echoes into the conference.  The headphone
     jack  should  be  set to `FullDuplex' mode if you have head-
     phones plugged into it and  `MikeMutesNet'  or  `EchoCancel'
     mode  if  you  have an external amp and speaker plugged into
     it.

     There are two type-in boxes (see below) at the bottom of the
     Auxiliary  Controls  panel.   The  one labeled `Name' can be
     used to change the session name announced  to  other  sites.
     The  one labelled `Key' can be used to specify an encryption
     key (see next section).

Encryption
     Since vat conversations are typically conducted over open IP
     networks  there is no way to prevent eavesdropping, particu-
     larly for multicast conferences.  To  add  some  measure  of
     privacy,  vat  allows  the  audio  packet  streams to be DES
     encrypted.  Presumably only sites sharing the same key (and,
     of  course,  the  NSA) will be able to decrypt and listen to
     the encrypted audio.

     Encryption is enabled by entering an arbitrary string in the
     key  box  (this string is the previously agreed upon encryp-
     tion key for the conference -  note  that  key  distribution
     should  be  done  by  mechanisms totally separate from vat).
     Encryption can be turned off by entering a null string (just
     a  carriage  return  or any string starting with a blank) in
     the key box.

X Resources
     The  following  are  the  names  and  default  values  of  X
     resources used by vat. This list is incomplete.  Consult the
     tcl code in vat.tcl for the complete set.

          Vat.defaultHost:          224.2.0.1
          Vat.defaultVTHost:        224.1.0.200
          Vat.defaultPort:          3456
          Vat.defaultTTL:           127
          Vat.audioFormat:          pcm
          Vat.vtMode:               false
          Vat.lectureMode:          false
          Vat.inputPort:            Mike
          Vat.outputPort:           Speaker
          Vat.speakerMode:          Speakerphone
          Vat.jackMode:             Headphone
          Vat.mikeGain:             32
          Vat.speakerGain:          180
          Vat.jackGain:             180
          Vat.mikeAGC:              false



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          Vat.mikeAGCLevel:         32
          Vat.speakerAGC:           false
          Vat.speakerAGCLevel:      32
          Vat.maxPlayout:           6
          Vat.defaultPriority:      100
          Vat.idleHoldTime:         10
          Vat.idleDropTime:         0
          Vat.autoRaise:            true
          Vat.pushToTalk:           false
          Vat.keepSites:            false
          Vat.key:
          Vat.muteNewSites:         false
          Vat.siteDropTime:         30
          ! fonts
          Vat.titleFont:            -*-helvetica-bold-r-normal--*-140-75-75-*-*-*-*
          Vat.audioFont:            -*-helvetica-medium-r-normal--*-100-75-75-*-*-*-*
          Vat.helpFont:             -*-times-medium-r-normal--*-140-75-75-*-*-*-*
          Vat.ctrlFont:             -*-helvetica-bold-r-normal--*-100-75-75-*-*-*-*
          Vat.ctrlTitleFont:        -*-helvetica-bold-r-normal--*-120-75-75-*-*-*-*
          Vat.entryFont:            -*-helvetica-medium-r-normal--*-100-75-75-*-*-*-*

     Vat.maxPlayout is the maximum `play out' delay, in  seconds,
     that  can  be  tolerated.   I.e.,  vat dynamically adapts to
     delays introduced in the network by delaying the play out of
     a  remote  site's audio packets.  The range of adaptation is
     limited by the size of a buffer in vat  and  this  parameter
     essentially  sets the size of that buffer.  Setting maxPlay-
     out larger than 10 seconds will probably result poor vat and
     system behavior due to excessive paging activity.

     Vat has two different modes of adapting the  playout  delay,
     one more suitable for an interactive, multi-party discussion
     or conference and the other more suitable for listening to a
     speech  or lecture. The two modes differ in how quickly they
     `forget' the delay vat introduces to adapt to transient net-
     work  congestion:  In Conference mode vat attempts to minim-
     ize the delay (since large delays make interactive conversa-
     tions difficult) but this usually results in more lost pack-
     ets when the delay becomes too short handle the next conges-
     tion  event.   In Lecture mode vat attempts to minimize lost
     packets by reducing delays very slowly. This results in  the
     clearest playback but interactivity may suffer.

     Conference mode is the default when vat starts up unless the
      - l  flag  is given or the X resource lectureMode is set to
     true.  There are radio buttons in the network section of the
     Auxiliary  Controls  panel  to switch between Conference and
     Lecture modes.  The switch can be made at any time and takes
     effect immediately.

Type-in Boxes
     Since there's no standard for X keyboard  input  we  had  to



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     roll  our own and vat's type-in boxes need some explanation:
     To enter something new in a type-in box, position the  mouse
     in  the  box  and  click  to insert a cursor.  To modify the
     existing contents of the box, click with the left mouse but-
     ton  where you want to append (or click-and-drag if you want
     to replace) then start to type.  If you hit carriage return,
     your  new input will be acted on.  If you hit escape or bell
     (^G) your new input will be discarded.

     If the string is too long for all of it to be  visible,  the
     right  mouse  button  can be used to drag invisible portions
     into view.  Hold down the  button  and  drag  the  text  the
     direction you want it to move.

     While typing, a tiny subset of emacs-like line editing  com-
     mands  are available: ^H or DEL (delete previous character),
     ^D (delete  character),  ^F  (forward  char),  ^B  (backward
     char),  ^A (beginning of line), ^E (end of line), ^W (delete
     previous word), ^U (delete everything).

Statistics
     Clicking on a name with the left mouse button will bring  up
     a  window  with packet statistics for that site.  The window
     will remain mapped as  long  as  the  button  is  depressed.
     There  are  three of numbers.  The last column is the aggre-
     gate statistics since vat started, and the first  column  is
     the  difference between the last update time and the current
     time.  The middle column is a smoothed average of the  first
     column  with  units  depend on the statistic.  The smoothing
     filter  is  a  exponentially  weighted  average  with   gain
     Vat.statTimeConst.   All of the averages (except total pack-
     ets) are displayed as a percent of number  of  packets  sent
     (which  is actually an estimate based on the number of pack-
     ets received plus those estimated to be missing).

     The statistics are updated every second or so while the win-
     dow  is  mapped.   If  you  hold down the shift-key when you
     bring up the statistics window, it  will  be  mapped  perma-
     mently  and  will  include stripchart.  The stripchart plots
     the selected statistic against time.

     Altenatively, the stats for all the sites  can  be  sent  to
     standard  out by typeing 's' or 'S' anywhere in the vat win-
     dow.  The first entry is the total packets received from the
     site  since  starting  vat  and  since  the  last  time  you
     requested stats. E.g., `3515/62'  means  3515  packets  have
     been  received  from the site and 62 received since the last
     time you printed stats. The next four  entries  are  various
     error counters.  Each consists of two numbers separated by a
     slash.  The first number is a count of how  many  times  the
     error occurred since the last time you requested stats.  The
     second is the same info expressed as percentage  of  packets



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     received.   E.g.,  `9/3.0' in the `drop' column would mean 9
     packets or 3% of the packets received since the  last  stats
     output  had  been  dropped. The `lost' column counts packets
     that didn't make it (this is computed by  keeping  track  of
     gaps in the packet sequence number space). The `drop' column
     counts packets that arrived but  were  dropped  because  the
     current  playout  delay  was  too  short  to  resequence the
     packet. The `dup' column counts duplicate packets that  were
     discarded (you shouldn't see any of these unless the packets
     had the misfortune to traverse the T1 NSFNet backbone -- the
     worthless  IBM  token  ring  hardware  in  each NSS loves to
     duplicate packets). The `order' column counts  packets  that
     arrived out of order (this is not an error but it does indi-
     cate routing strangeness and will always increase the  play-
     out  delay).  Following the error stats is the current play-
     out delay for the site and the site name.

SEE ALSO
     audio(4)

AUTHORS
     Van   Jacobson   (van@ee.lbl.gov)   and    Steven    McCanne
     (mccanne@ee.lbl.gov),  both of Lawrence Berkeley Laboratory,
     University of California, Berkeley, CA.
     Jack Jansen (Jack.Jansen@cwi.nl) of  Stichting  Mathematisch
     Centrum,  Amsterdam,  the Netherlands, contributed the Intel
     DVI ADPCM codec.
     Ron Frederick (frederic@parc.xerox.com) of Xerox PARC,  Palo
     Alto,  CA,  contributed  the  LPC codec which is based on an
     implementation       done       by       Ron       Zuckerman
     (ronzu@isu.comm.mot.com) of Motorola which was posted to the
     Usenet group comp.dsp on 26 June 1992.
     Carsten Bormann  (cabo@cs.tu-berlin.de)  and  Jutta  Degener
     (jutta@cs.tu-berlin.de)  of the Communications and Operating
     Systems Research Group (KBS) at the Technische  Universitaet
     Berlin contributed the GSM codec.
     Steve Casner (casner@isi.edu) of ISI, Los Angeles,  CA,  and
     Steve  Deering  (deering@parc.xerox.com)  of Xerox PARC have
     invested tremendous effort in making vat work on a scale far
     beyond  the  authors'  wildest expectations and have contri-
     buted greatly to vat's development, both directly (via care-
     ful  analysis of bugs and useful suggestions) and indirectly
     (via setting up several  global  conferences  that  severely
     pushed the envelope of vat's capabilities).

BUGS
     Speakerphone mode is difficult to get right - use a  headset
     if  you  can  (or  run BSD instead of Sun-OS to get a kernel
     audio driver that can support echo  cancellation).   If  you
     have  to  use speakerphone mode, try to position the mike as
     far as possible from the speaker (the speaker in a sparcsta-
     tion  is  on bottom of the machine in the front right corner



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VAT(1)                    User Commands                    VAT(1)



     near the LED).  If there's a problem with  echo  (i.e.,  you
     transmit whenever other people start speaking), try reducing
     the mike gain or mute the mike when you're not speaking.

     In speakerphone mode vat assumes that if there is audio data
     from  the net being sent to the speaker at least part of the
     signal from the mike is pickup from the speaker.  So, unless
     the  mike  signal is `large' compared to the signal from the
     net, vat assumes it is echo and suppresses it.   This  means
     that  if  you  want to interrupt someone who is talking, you
     may have to talk a bit louder than usual at the  start  (you
     can  tell  if  you succeed because your site's name box will
     light and the speaker will mute).

     The internal architecture of vat allows for almost any audio
     encoding  and  packet format. We are working on U.S. Federal
     Standard 1016 4800bps CELP (a very low bandwidth codec  that
     could  be  run over 9600baud dial-up SLIP links) and hope to
     have it in the official release. We'd be very interested  if
     anyone   would   like   to   contribute   additional   audio
     encode/decode routines.

     Vat's LPC coder is low quality.  We plan to incorporate  the
     U.S. Federal Standard 1015 LPC-10 2400bps algorithm.































Sun Microsystems    Last change: 17 Feb 1992                   11