Long Term Evolution (Advanced) - LTE(-A)
Network architecture

Network architecture of LTE is derived from the former GSM and UMTS architecture. Contrary, to both, the LTE is designed to support only packet-switched services. Circuit-switched services are no longer supported in network architecture since LTE. The network is composed of access network denoted as E-UTRAN (Evolved Universal Terrestrial Radio Access Network) and EPC (Evolved Packet Core) as shown in Figure 22.

Networks architecture of LTE

The access part, E-UTRAN, is composed of base stations denoted in LTE as eNodeBs (taken over from UMTS name NodeB, with "e" standing for "Evolved"). These eNodeBs are responsible for radio resource management and allocation of radio resources, mobility control, scheduling resources for both uplink and downlink, encryption of radio data transmission, or for connectivity to EPC. If femtocells are deployed, those are also a part of E-UTRAN. In this case, HeNB gateway (HeNB GW) can be included between HeNB and EPC to support large number of HeNBs.

The EPC is composed of several entities. The S-GW transfers all IP packets of all users in a network. It serves as a local mobility anchor for handover between eNodeBs. The S-GW routs and forwards packet to and from the users. This gateway accounts for inter-operator charging, e.g., in case of roaming. The second entity, the MME, controls and manages the signalling between UE and EPC including authentication, authorization, security control, establishment of connection between UE and network, roaming, and procedures related to the user's location management. Last, the P-GW is responsible for actions related to the quality of service and flow management. It means it filters user's packets, enforces QoS to guarantee required bit rates, or control service level in both downlink an uplink.

Besides these three entities, two logical functions are also a part of the LTE-A EPC architecture:

- PCRF (Policy Control and Charging Rules Function) defines rules for charging and policy control. It means, it defines actions and rules in case of problems of inconsistency between user's QoS profile and provided services.
- HSS (Home Subscriber Server) contains user's subscription information such as QoS profile or roaming profile. It also keeps information about user home MME (i.e., the MME to which the UE is connected to)