I have Started working with JBoss Cluster, I have a few basic questions

What is the use of HAPartation (Besides we have cluster services, what is the difference).

We have JGroups Channels for configuring the Protocal stack which says how to do the intra cluster communication . Now what are the scenerios that may cause to modify the Jgroups protocal stack to implement a custom one.

Thanks in advance for all the information provided :-)