The Veritas Cluster Server provides the communication, configuration, and membership services required to create a cluster. VCS is the first component installed and configured to set up a cluster file system.
GAB and LLT are VCS-specific protocols implemented directly on an Ethernet data link or on a Fibre Channel fabric. Both GAB and LLT run over redundant data links that connect all the servers in a cluster. VCS requires redundant cluster communication links to minimize the possibility of cluster failure due to the failure of a single communication link.