SFECHO(1)

NAME
sfecho - Speak Freely remote echo server

SYNOPSIS
sfecho [ -du ] [ -pport ]
[ -vtimeout ] [ -zdrop%,shuffle%,depth ]

DESCRIPTION
sfecho is a server program which receives sound from remote 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 different 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 number instead of the default port specified by ``INTERNET_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 compression 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.

-zdrop%,shuffle%,depth
    sfecho will simulate an imperfect Internet connection by randomly dropping (discarding) drop% percent of the packets it receives, then shuffling in order shuffle% percent of the remaining packets with a maximum reordering of depth packets. This option should never be used on a production echo server; it is intended to simulate bad connections to permit testing various error-tolerant algorithms to cope with them.

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

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 nonstandard 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.