Charging gateway (CG):

CG collects, consolidates, and preprocesses CDRs generated by the SGSN or the
GGSN. It provides an interface to the billing center.CG is used to reduce the work load of the billing center
by consolidating and preprocessing the CDRs before sending them to the billing
center. With the CG in the network, the SGSN or the GGSN need not provide the
charging interface to the billing center