So I'm assuming we have a 20 node cluster, and every node sends 25KBytes/sec (25 KBytes == 200KBits). When using UDP, every node sends 1 multicast packet, to be received by every other node. So you scenario above (15x15) doesn't apply. When using TCP, every node sends a message N-1 (19) times, so your scenario *does* apply in this case. With respect to network bandwidth, sending is not the issue because every node has a full duplex line to the switch. However, when receiving, a line from the switch to a node has to be shared between 19 (N-1) instances. In other words, every node can receive concurrent traffic from the 19 other nodes. So if you have a 1GB switch, then the effective rate / node is 1000MBits/19 = 52MBits = 52'000KBits = 6'500KBytes /sec. That 260 times more that you need ! So this is peanuts traffic-wise. The bottleneck might lie somewhere else, namely in the data: when everyone replicates its date to everybody else, every node has to store DATA * 20 on average. So if every node has data of 1MB, then the avg data size on a node is 20MB. This is fine, but of course not scalable if (1) your avg data size increases or (2) your cluster size increases. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4240771#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...