LTE architecture :
The LTE architecture mainly consist following nodes and interfaces.
Nodes:
UE – User equipment
E-UTRAN (eNodeB) – Evolved EUTRAN
MME – Mobility management entity
SGSN – serving GPRS support node
HSS – Home Subscriber Server
SGW – Serving Gateway
PGW – PDN(Packet data network ) Gateway
PCRF – Policy and Charging Rules Function
Interfaces:
LTE-Uu – It is an air interface which is used to communicate between UE and eNodeB.
S1-MME – This interface is used to communicate between eNodeB and MME.
S1-U – This interface is used to communicate between eNodeB and SGW. It carries user plane data.
S5/S8 – This interface is used to communicate between SGW and PGW.
S10 – This interface is used to communicate between MME to another MME.
S11 – This interface is used to communicate between MME and SGW.
S6a – This interface is used to communicate between MME and HSS.
S3 – This interface is used to communicate between MME and SGSN.
X2 – This interface is used to communicate between eNodeB to another eNodeB.
Also there are many others interfaces used in LTE, each having their own purpose.
For more architectural details go through 3GPP specification 23.401.