SFECHO(1)                                               SFECHO(1)


NAME
       sfecho - Speak Freely remote echo server

SYNOPSIS
       sfecho [ -du ] [ -pport ] [ -vtimeout ]

DESCRIPTION
       sfecho  is  a server program which receives sound from re­
       mote hosts in the same manner as sfspeaker, but instead of
       playing  sound  on the workstation's audio output, buffers
       it in memory for ten seconds and then  retransmits  it  to
       the  sending  host.   This allows remote users, even those
       with half-duplex audio hardware, to experiment  with  dif­
       ferent  compression  and encryption modes to optimise end-
       to-end performance without tying up a person on the  other
       end of the connection.

       sfecho  can echo sound in RTP and VAT protocols as well as
       Speak Freely's native protocol.  To permit this,  messages
       on  both  the  specified port and the next higher numbered
       port are monitored, queued, and retransmitted.

       An echo server can invite connections  by  publishing  its
       existence  on  one  or  more  directory  servers.  See the
       ``Look Who's Listening'' section in the  sfspeaker  manual
       page  for details on how to set the environment variables.

OPTIONS
       -d     Enables debug output from sfecho.

       -pport Causes sfecho to listen on the specified port  num­
              ber  instead of the default port specified by ``IN­
              TERNET_PORT'' in the Makefile.  To comply with  the
              RTP  standard,  the  port  specified should have an
              even number; the next higher numbered port is  used
              for RTCP control messages.

       -u     Prints how-to-call information.

       -vtimeout
              When sfecho receives a packet from a host it hasn't
              heard from in timeout seconds, it will  attempt  to
              find  the host name and print a message on standard
              error noting the new connection and  what  compres­
              sion mode is being used.  If the host name can't be
              found, the numeric  IP  address  is  given.   After
              timeout  seconds  of inactivity a message is issued
              indicating the host is  idle.   If  no  timeout  is
              specified, 180 seconds is used.

BUGS
       If  sfecho runs out of memory to buffer sound awaiting re­
       transmission, packets are discarded without warning.




                            8 APR 1996                          1





SFECHO(1)                                               SFECHO(1)


       By default, sfecho listens on Internet port  number  2074,
       the  same  as  sfspeaker, and hence cannot run at the same
       time on the same machine as sfspeaker.  You can specify  a
       different  port  for  sfecho  with the -p option, but many
       users have difficulty connecting to servers with  nonstan­
       dard  port numbers, so this isn't a terribly good idea for
       public servers.  If your server is intended  primarily  to
       echo  messages  in  RTP  protocol, you may want to specify
       port 5004, the default  port  for  RTP  specified  in  RFC
       1890.     Many VAT compatible applications default to port
       3456.

ACKNOWLEDGEMENTS
       The implementation  of  MD5  message-digest  algorithm  is
       based on a public domain version written by Colin Plumb in
       1993.  The algorithm is due to Ron Rivest.  The  algorithm
       is described in Internet RFC 1321.

SEE ALSO
       sfspeaker(1)

AUTHOR
            John Walker
            WWW: http://www.fourmilab.ch/

       All  modules  of  Speak  Freely developed by me are in the
       public domain.  See the readme and/or copyright  files  in
       the  idea directory for conditions of use and distribution
       of that component.  This software is  provided  ``as  is''
       without express or implied warranty.



























                            8 APR 1996                          2