LTE Interfaces and Protocols
The main interfaces in LTE are Uu, S1-MME, X2, S1-U, S11 and S5. LTE Uu: - This is the air interface between UE and eNB. LTE layer 1 is dealt with later. RRC is the protocol that is used for communication between UE and eNB. Above RRC there is a NAS layer in UE. This NAS layer terminates at MME and eNB shall silently pass the NAS messages to MME. LTE S1-MME: - eNB and MME communicate using this IP interface. S1-AP is application layer interface. The transport protocols used here is SCTP. (Stream control transmission protocol) LTE X2: - This interface is used by a eNB to communicate to other eNB. This again is a IP interface with SCTP as transport. X2-AP is the application protocol used by eNB’s to communicate. LTE S11: - An IP interface between MME and SGW! GTPv2 is the protocols used at the application layer. GTPv2 runs on UDP transport. This interface must and should run GTPv2. LTE S5: - This is the interface between SGW and PGW. This again is an IP int...