The table contains the list of CSG groups indexed by the
CSG group name.
A pair of CSG instances works with the QS together,
to achieve CSG redundancy. But only one of them is active,
performing the packet forwarding functionality at any time.
User information is replicated from the active to the standby.
The pair appears as one virtual CSG to the rest of the network
by using a virtual IP address on both of them. This virtual
address is the address to be used for the CSG.