Network sharing was a Release 6+ feature in the 3GPP specifications. LTE R8+ allow sharing of the E-UTRAN among multiple PLMNs. EPC sharing is from day one and both does not make any sense.
One blog may be useful (http://lteworld.org/blog/network-sharing-lte), here is the content.
3GPP network sharing architecture allows different core network operators to connect to a shared radio access network. The operators do not only share the radio network elements, but may also share the radio resources themselves.
Network-sharing scenario allows operators without a UMTS/ LTE license to share the network and supply its customers with 3G/4G services. For example, a 2G operator may supply its subscribers with 3G/4G services using another operator’s allocated spectrum.
3GPP has identified two architectures for network sharing. In both architectures, the radio access network is shared.
In first architecture evolved packet core network element MME is also shared in addition of radio access network (E-UTRAN). This configuration is referred to as a Gateway Core Network (GWCN) configuration.
In second architecture only radio access network (E-UTRAN) is shared and is referred as the Multi-Operator Core Network (MOCN) configuration.
The UE behavior in both of these configurations is same. No information concerning the configuration of a shared network is indicated to the UE.
If the E-UTRAN is shared by multiple operators, the system information broadcasted in each shared cell contains the PLMN-id of each operator (up to 6) and a single tracking area code (TAC) valid within all the PLMNs sharing the radio access network resources.
Based on system broadcasts UE selects desired PLMN and reports it to eNB during RRC connection setup. eNB includes the selected PLMN is in the INITIAL UE MESSAGE message while sending it to MME. The MME indicates the selected core network operator PLMN-id to the UE in the GUTI during initial attach procedure.
