Some advice regarding reliable multicast!!

Hi to all,

I need some advice with regard to a networking program of mine. I
wanted to know how we can ensure reliability when sending multicast
traffic to a group of computers. Since I'm sending UDP traffic as
multicast, how can I ensure that each computer belonging to that group
received it? I can add reliability by adding sequence numbers to the UDP packets. but that will only work for unicast UDP connections. What about UDP multicast traffic?

Any help will be much appreciated..
Thanking you in advance..

Warm regards,
Visham

UDP traffic is not reliable...
so you will need to implement the retransmission mechanism that is already provided by TCP, why not to use the suitable protocol is you need this feature?

That is right..but what I'm uncertain of is that how do I keep track of which PC in the multicast group received all the packets and which didnt. Is there a way to keep track of it. As for the protocol to use, well, since I have to use Multicast, I have but the choice to use UDP.

Tell me what u think about wat I wrote..

MAny thx for the reply..

Regards,
Visham

You can't do this without a lot of work. Here are the problems you need to overcome in order to do reliable multicast:
- How does the sender know when someone joins the group?
- When a group member fails to receive a packet, how do you retransmit it (over multicast or out of band)?
- What happens if the link to one receiver is slower than the rest. Do you slow the transmission to all receivers so the slow link can keep up?

Multicast is not the best transport protocol to use if you need reliability. This is why multicast is usually used for real-time data where a packet loss is not crucial to the system.

I wrote a multicast file transfer protocol a few years back. You can find a description of the protocol and the source here.