Question

I have a certain application running on my computer. The same application can run on many computers on a LAN or different places in the world. I want to communicate between them. So I basically want a p2p system. But I will always know which computers(specific IP address) will be peers. I just want peers to have join and leave functionality. The single most important aim will be communication speed and time required. I assume simple UDP multicast (if anything like that exists) between peers will be fastest possible solution. I dont want to retransmit messages even if lost. Should I use an existing p2p library e.g. libjingle,etc. or just create some basic framework from scratch as my needs are pretty basic?

Answer 1

I think you’re missing the point of UDP. It’s not saving any time in a sense that a message gets faster to the destination, it’s just you’re posting the message and don’t care if it arrives safely to the other side. On WAN – it will probably not arrive on the other side. UDP accross networks is problematic, as it can be thrown out by any router on the way which is tight on bandwidth – there’s no guarantee of delivery for it.

I wouldn’t suggest using UDP out of the topology under your control.

As to P2P vs directed sockets – the question is what it is that you need to move around. Do you need bi/multidirectional communication between all the peers, or you’re talking to a single server from all the nodes?

You mentioned multicast – that would mean that you have some centralized source of data that transmits information and all the rest listen – in this case there’s no benefit for P2P, and multicast, as a UDP protocol, may not work well accross multiple networks. But you can use TCP connections to each of the nodes, and “multicast” on your own, and not through IGMP. You can (and should) use threading and non-blocking sockets if you’re concerned about sending blocking you, and of course you can use the QoS settings to “ask” routers to rush your sockets through.