The EPC also makes a clear separation
between the network control and user data planes, with many of the mobility
support features that we will study in Section 6.7 being implemented in the
control plane. The EPC allows multiple types of radio access networks,
including legacy 2G and 3G radio access networks, to attach to the core
network. Two very readable introductions to the EPC are [Motorola 2007;
Alcatel-Lucent 2009].