
                               Netfone
                Voice Communication Over Data Networks

                            by John Walker
                 Release 5.1  --  2nd September 1995

The  phone  company  never gives you a break!  You pay a fortune for a
leased line connection to the Internet, and you *still*  have  to  pay
every  time  you  want  to chat with somebody, even though you're both
sitting in front of Sun SPARCStations  or  Silicon  Graphics  machines
with  digital  audio  capability,  linked by a high-bandwidth network.
Netfone can intercommunicate with Speak Freely for Windows,  available
from my Web site listed at the end.

Netfone   uses  the  workstation  audio  chip  and  network  to  allow
bidirectional conversations right over the network.   Workstations  on
local  area  networks  can  generally communicate with excellent audio
quality and response.  A software implementation (developed  by  Jutta
Degener  and  Carsten  Bormann, Technische Universitaet Berlin) of the
compression algorithm used in GSM digital cellular  telephones  allows
operation  over Internet links of very modest bandwidth.  By using GSM
compression in conjunction with sample interpolation,  the  data  rate
can  be  reduced  to about 9600 baud.  Users with CPUs too slow or two
heavily  loaded  to  perform GSM compression and decompression in real
time may select less compact but  quicker  to  execute  ADPCM  coding,
using  an  implementation  developed  by Jack Jansen of the Centre for
Mathematics and Computer Science, Amsterdam, The Netherlands.

Sound  can be encrypted either with a one-time pad supplied in a file,
DES and/or  IDEA  with  given  key(s).   The  DES  implementation  was
developed  by  Phil  Karn,  KA9Q.  The IDEA algorithm was developed by
Xuejia Lai and James L. Massey, of  ETH  Zurich.   The  implementation
used  in  Netfone  was  modified  and  derived  from  original  C code
developed by Xuejia  Lai  and  optimized  for  speed  by  Colin  Plumb
<colin@nsq.gts.org>.    The  IDEA[tm]  block  cipher  is  patented  by
Ascom-Tech AG. The Swiss patent number is PCT/CH91/00117, the European
patent  number  is  EP  0  482  154  B1, and the U.S. patent number is
US005214703.  IDEA[tm] is a trademark of Ascom-Tech AG.  There  is  no
license  fee  required  for  noncommercial  use.  Commercial users may
obtain  licensing  details  from  Dr. Dieter  Profos,  Ascom-Tech  AG,
Solothurn  Lab,  Postfach 151, CH-4502 Solothurn, Switzerland, Tel +41
65 242 885, Fax +41 65 235 761.

The  Silicon  Graphics  audio drivers are based on the stand-alone SGI
Netfone  developed  by  Paul  Schurman  (schurman@frs.fi)  of   Espoo,
Finland.

Key generation for IDEA and DES encryption uses an  implementation  of
MD5  message-digest algorithm based on a public domain version written
by Colin Plumb in 1993.  The algorithm is due to Ron Rivest.

Complete instructions for building, installing, and using NetFone  are
given  in the manual page, netfone.1.  You can view the manual page on
your screen with the command:

    make manpage

All  files in the Netfone root directory are in the public domain: "Do
what thou wilt shall  be  the  whole  of  the  law".   I'd  appreciate
receiving any bug fixes and/or enhancements, which I'll incorporate in
future versions of the program.  Please leave the original attribution
information   intact   so  that  credit  and  blame  may  be  properly
apportioned.

Please see the readme and/or copyright files in the adpcm,  des,  gsm,
and idea subdirectories for information regarding the distribution and
conditions of use of those components.

AUTHOR
            John Walker
            E-mail: kelvin@fourmilab.ch
            WWW:    http://www.fourmilab.ch/
