- manages multiple unicast and multicast sessions. Thus, there is no
need to have several instances of the tool running simultaneously.
- implements RTP, the
Real Time Transport Protocol .
- includes a signalling protocol to contact remote parties. For example,
use the "Call" button and type firstname.lastname@example.org to get in
touch with "person" at INRIA. The signalling protocol also notifies
of call acceptance or rejection.
- includes support for sampling rates ranging from 8 to 48 kHz. High
sampling rates such as 44 kHz and 48 kHz correspond to CD and DAT quality
audio, respectively. Note that different participants in a multicast group
might use different sampling rates in a transparent fashion.
- includes a redundancy mechanism for packet
reconstruction. The basis for using such a mechanism is described in
. The specific mechanism used
in Free Phone has been shown to provide much increased audio quality especially
when the packet loss rate is high (see 
and listen to this ).
The amount of redundancy included in each packet can be chosen in a manual,
semi-automatic, or automatic fashion. In automatic mode, Free Phone automatically
selects the amount of redundancy needed to keep the loss rate after reconstruction
between some watermarks specified by the user .
- supports the redundancy mechanism and the different sampling rates
using special RTP payload types .
- includes the usual assortment of codecs, including PCMU, VADPCM (ADPCM-DVI),
ADPCM at 6, 5, 4,
3, and 2 bits, GSM,
- is compatible with other MBone tools. It is of
course compatible with RAT
since both were developed
within the MERCI
It is compatible with vat when
it does not use the redundancy or the high quality audio features.
NeVoT will achieve
compatibility with fphone soon.
- uses Tcl/Tk8.0.
New features being added to Free Phone include 3D/spatial rendition
of sound, a TCP-friendly rate control, and an "optimal" redundancy control
You can subscribe to the fphone mailing list by sending an e-mail to
with the subject line `subscribe'.
A screendump of the main Free Phone window is shown below
The main window of Free Phone
If you want to see some other windows of Free Phone, please click here .