SIP uses the high availability features in WebSphere Application Server to offer a comprehensive high availability (HA) solution.
A core group is a set of processes which establish a high-availability domain to monitor and replicate state to one another. Each core group member communicates with one another through DCS. DCS handles elections, quorums, and heartbeats (virtual or TCP keepalive). DCS communicates with its peers via either Multicast/TCP or Reliable Multicast/UDP.
For more information on core groups, see Core groups (high availability domains)