World Wide Conferencing Network

WWCN is a system that provides multimedia conferencing services on a world-wide scale. It has been optimized for realtime data delivery: music, voice, video, pictures, text, software updates, and so on. To cope with today's bandwidth scarcity, it implements a reliable "multicasting" technology (one to many data communication) over standard TCP (internet) connections.

Contents

HOME

WHAT IS WWCN?
   Introduction
   White papers

HOWTO...
   connect
   tune in
   build a network?

SOFTWARE
   multimedia players
   multimedia producers
   chat clients
   server software

MANUALS
   xmit
   recv
   fifo123



recv manual

The basic format of the 'recv' command is: 
recv host channel [options]
where [options] can be zero or more of the following:
  • -b turns of buffering. By default, recv will use a buffer to reduce the effects 'jitter': unexpected delays when transmitting data. If you are on the same physical network as the WWCN server, you can try to turn off buffering.
  • -f filename tells recv to store the received data in a file. By default, it will write to stdout.
  • -n nickname is the nickname that should be used on WWCN. This nickname does not need to be unique.
  • -p port identifies the port that the WWCN server is listening to. The default is 777.
  • -s tells recv not to wait for a 'Start of File' token; see below for some more details on this.
Below, the most non-trivial of these options are discussed in more detail.

Buffering

recv uses buffering by default. This means that before starting to write data to the player application (e.g. mpg123), it will buffer data first. For an mp3 file, this would take about 4-8 seconds. This buffer is used to prevent 'hickups' when temporarily less data arrives from the WWCN network than necessary to keep the audio running. If your connection to the WWCN server is sufficiently fast, then you probably don't need buffering.
If you are writing data to a file (-f option), then buffering does not make any sense, and you might want to disable it.

Start of File token

This token is normally transmitted at the start of each file, but if you want to listen to a continuous broadcast (e.g. a radio station) then you would like recv to not wait for a Start of File token.
On the other hand, if you want to receive a binary file then you do want recv to wait for the start of the file first before receiving data. So when using WWCN to multicast binary files, do not use the -s option.

Different senders on a channel

Recv is a bit dumb. It will get smarter in the next release, but the current version (1.0) is willing to receive any file from anybody. It picks the first sender that it receives data from, and from that point ignores the data transmitted by other senders. So if there are two (or more) active senders on a channel, then there is no way to tell recv to which one it should listen.
If the sender recv is listening to leaves the channel, then it picks a new one: again the first one it receives data from. If the '-s' option was not specified, then it will again wait for a Start of File first.

Examples

To play an mp3 stream using mpg123, type: 
# recv wwcn.server.com radio.classic4u -s | mpg123 -
The -s option tells recv not to wait for a Start of File token, but to start receiving right away. To receive and show a .jpg file using xview, type: 
# recv wwcn.server.com chat.with.friends -b | xv -
Here, the -b option tells recv to disable buffering of data. Buffering is only useful when receiving continuous media (music, voice, video). Note that xview allows you to save the picture.