5.1.2 Specification phase and achievements

Architecture

The E-UTRAN overall architecture is described in TS 36.300 and TS 36.401.

The E-UTRAN consists of eNBs which are interconnected with each other by the X2 interface. Each eNB is connected to the Evolved Packet Core (EPC) network by the S1 interface. On the User Plane the S1 interface terminates the Serving Gateway (S-GW), on the Signalling Plane the S1 interface terminates the Mobility Management Entity (MME).The eNBs are terminating points for Control- and User Plane towards the UEs in the Evolved UTRA.

Overall Architecture

 eNB Functions

The eNB hosts the following functions:

• Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling)

• IP header compression and encryption of user data stream

• Selection of an MME at UE attachment when no routing to an MME can be determined from the information provided by the UE

• Routing of User Plane data towards Serving Gateway

• Scheduling and transmission of paging messages (originated from the MME)

• Scheduling and transmission of broadcast information (originated from the MME or O&M

• Measurement and measurement reporting configuration for mobility and scheduling

Functional Split between e-utran and epc

 

General principles of the E-UTRAN Architecture (see TS 36.401)

The general principles guiding the definition of E-UTRAN Architecture as well as the E-UTRAN interfaces are the following:

• Logical separation of signalling and data transport networks

• E-UTRAN and EPC functions are fully separated from transport functions. Addressing scheme used in E-UTRAN and EPC shall not be tied to the addressing schemes of transport functions. The fact that some E-UTRAN or EPC functions reside in the same equipment as some transport functions does not make the transport functions part of the E-UTRAN or the EPC.

• Mobility for RRC connection is fully controlled by the E-UTRAN.

• When defining the E-UTRAN interfaces the following principles were followed: the functional division across the interfaces shall have as few options as possible.

• Interfaces should be based on a logical model of the entity controlled through this interface.

• One physical network element can implement multiple logical nodes.

5.1.3 Radio Interface

The figure below shows the protocol stack for the user-plane, where PDCP, RLC and MAC sublayers (terminated in eNB on the network side) perform header compression, ciphering, scheduling, ARQ and HARQ.

User-plane protocol stack

The figure below shows the protocol stack for the control-plane. The NAS control protocol is mentioned for information only and is part of UE -EPC communication. The PDCP sublayer performs e.g. ciphering and integrity protection, RLC and MAC sublayers perform the same functions as for the user plane. The RRC performs broadcast, paging, RRC connection management, Radio Bearer control, Mobility functions, UE measurement reporting and control.