UDP prototype¶

Goals¶

• Make a program which will listen for multicast message.
• It must be work between sub-networks (vlan).
• It should be also able to send. User can type a message and all other peers will print it when it is sent.
• Test it with some computers.

Qt and UDP multicast¶

There is no support to UDP multicast in QT4.5 according this bug issue : http://www.qtsoftware.com/developer/task-tracker/index_html?method=entry&id=57952.

Maybe it can be possible to use setsockopt() with QAbstractSocket::socketDescriptor(). See http://linux.die.net/man/7/ip and options for multicast like IP_ADD_MEMBERSHIP.

Broadcast¶

An alternative is to use a broadcast address with QHostAddress::Broadcast. It will only work with IPv4.

It's possible to use UDP multicast only with the low-level API. This solution is OS dependent and will not be accepted.

For the moment the broadcast alternative will be used.

References¶

• http://en.wikipedia.org/wiki/Multicast
• (fr) http://www.ibiblio.org/pub/Linux/docs/HOWTO/translations/fr/html-1page/Multicast-HOWTO.html