RAN sharing is also known as E-UTRAN sharing in LTE network. 3GPP has defined two approaches for E-UTRAN sharing i.e. Multi Operator Core Network (MOCN) and Gateway Core Network (GWCN). In MOCN approach, multiple operator core network have connection with shared e-UTRAN. Shared eNodeB have S1 connection with each operator MME and SGW. That is also known as S1-flex. Using S1-flex, eNodeB does load balancing.
In another approach, shared e-UTRAN shall have S1-flex with shared MMEs and each shared MME will have connection with each of the core network.
RAN sharing is a good solution where number of users are less like rural area but for urban area this solution may not be best suited since number of users within a coverage area shall be more and also they will use different different types of services which require more bandwidth. And requirement of more bandwidth may result radio congestion. In MOCN approach, shared e-NodeB shall broadcast PLMN of each core network. There is a limitation on number of broadcasting PLMNs i.e. 6.
There are challenges like maintaining End-to-End QoS in shared e-UTRAN environment.