ETSI TS 136 401 V19.0.0 (2025-10)

LTE; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Architecture description (3GPP TS 36.401 version 19.0.0 Release 19)

RTS/TSGR-0336401vj00

General Information

• Status: Not Published
• Technical Committee: 3GPP RAN 3 - lub specification, lur specification, lu specification and UTRAN & O&M
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 08-Oct-2025

Standards Content (Sample)

TECHNICAL SPECIFICATION
LTE;
Evolved Universal Terrestrial
Radio Access Network (E-UTRAN);
Architecture description
(3GPP TS 36.401 version 19.0.0 Release 19)

3GPP TS 36.401 version 19.0.0 Release 19 1 ETSI TS 136 401 V19.0.0 (2025-10)

Reference
RTS/TSGR-0336401vj00
Keywords
LTE
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3GPP TS 36.401 version 19.0.0 Release 19 2 ETSI TS 136 401 V19.0.0 (2025-10)
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3GPP TS 36.401 version 19.0.0 Release 19 3 ETSI TS 136 401 V19.0.0 (2025-10)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 General principles . 8
5 General architecture . 9
5.1 General . 9
5.2 User plane . 9
5.3 Control plane . 10
6 E-UTRAN architecture. 10
6.1 Overview . 10
6.1.1 Overall architecture for CP/UP separation of an eNB . 11
6.2 E-UTRAN identifiers . 11
6.2.1 Principle of handling Application Protocol Identities . 11
6.2.2 PLMN Identity . 13
6.2.3 Globally Unique MME Identifier (GUMMEI) . 13
6.2.4 Global eNB ID . 13
6.2.5 E-UTRAN Cell Global Identifier (ECGI) . 13
6.2.6 Tracking Area Identity . 13
6.2.7 E-RAB ID . 13
6.2.8 UE Identifiers . 13
6.2.8.1 Radio Network Temporary Identifiers (RNTI) . 13
6.2.8.2 S-Temporary Mobile Subscriber Identity (S-TMSI) . 13
6.3 Transport addresses . 14
6.4 UE associations in eNB . 14
7 E-UTRAN functions description . . 15
7.1 List of functions . 15
7.2 Functions description . 15
7.2.1 Transfer of user data . 15
7.2.2 Radio channel ciphering and deciphering . 15
7.2.3 Integrity protection . 16
7.2.4 Header compression . 16
7.2.5 Mobility control functions . 16
7.2.5.1 Handover . 16
7.2.5.2 void . 16
7.2.5.3 void . 16
7.2.5.4 Dual Connectivity . 16
7.2.6 Inter-cell interference coordination . 16
7.2.7 Connection set-up and release . 16
7.2.8 Load balancing . 16
7.2.9 Distribution function for NAS messages . 17
7.2.10 NAS node selection function . 17
7.2.11 Synchronization . 17
7.2.12 Radio Access Network (RAN) sharing . 17
7.2.13 MBMS function . 17
7.2.14 Subscriber and equipment trace . 17
7.2.15 RAN Information Management (RIM) . 17
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7.2.16 Paging . 18
7.2.17 Positioning . 18
7.2.18 Delivery of warning messages . 18
8 Mobility management. 18
8.1 Signalling connection . 18
8.2 Consequences for mobility handling . 18
9 Synchronization . 19
9.1 eNB Synchronization . 19
9.2 eNB and MME Synchronization . 20
10 void . 20
11 E-UTRAN interfaces . 20
11.1 General protocol model for E-UTRAN interfaces . 20
11.1.1 Radio Network Layer (RNL) and Transport Network Layer (TNL) . 20
11.1.2 Control plane . 20
11.1.3 User plane . 21
11.2 Iuant interface - general principles . 21
Annex A (informative): Change history . 22
History . 23

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Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
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1 Scope
The present document describes the overall architecture of the E-UTRAN, including internal interfaces and assumptions
on the radio, S1, X2 and E1 interfaces.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) Overall description Stage 2".
[3] 3GPP TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) access".
[4] 3GPP TS 36.414: "Evolved Universal Terrestrial Access Network (E-UTRAN); S1 data transport".
[5] 3GPP TS 36.424: "Evolved Universal Terrestrial Access Network (E-UTRAN); X2 data
transport".
[6] 3GPP TS 36.440: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); General
aspects and principles for interfaces supporting Multimedia Broadcast Multicast Service (MBMS)
within E-UTRAN".
[7] ITU-T Recommendation G.823 (2000-03): "The control of jitter and wander within digital
networks which are based on the 2048 kbit/s hierarchy".
[8] ITU-T Recommendation G.824 (2000-03): "The control of jitter and wander within digital
networks which are based on the 1544 kbit/s hierarchy".
[9] ITU-T Recommendation G.825 (2001-08): "The control of jitter and wander within digital
networks which are based on the synchronous digital hierarchy (SDH)".
[10] ITU-T Recommendation G.8261/Y.1361 (2008-04): "Timing and Synchronization aspects in
Packet networks".
[11] 3GPP TS 23.003: "Numbering, addressing and identification".
[12] 3GPP TR 44.901: "External Network Assisted Cell Change (NACC)".
[13] 3GPP TS 48.018: "General Packet Radio Service (GPRS); Base Station System (BSS) - Serving
GPRS Support Node (SGSN); BSS GPRS Protocol (BSSGP)".
[14] 3GPP TS 23.251: "Network Sharing; Architecture and functional description".
[15] 3GPP TS 22.268: "Public Warning System (PWS) requirements".
[16] 3GPP TS 33.401: "3GPP System Architecture Evolution (SAE); Security architecture".
[17] 3GPP TS 32.421: "Telecommunication management; Subscriber and equipment trace; Trace
concepts and requirements".
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[18] 3GPP TS 32.422: "Telecommunication management; Subscriber and equipment trace; Trace
control and configuration management".
[19] 3GPP TS 32.423: "Telecommunication management; Subscriber and equipment trace; Trace data
definition and management".
[20] 3GPP TS 32.441: "Telecommunication management; Trace Management Integration Reference
Point (IRP); Requirements".
[21] 3GPP TS 32.442: "Telecommunication management; Trace Management Integration Reference
Point (IRP); Information Service (IS)".
[22] 3GPP TS 32.446: "Telecommunication management; Trace Management Integration Reference
Point (IRP); Solution Set (SS) definitions".
[23] 3GPP TS 25.411: "UTRAN Iu interface layer 1".
[24] 3GPP TS 23.682: "Architecture enhancements to facilitate communications with packet data
networks and applications".
[25] 3GPP TS 38.401: "NG-RAN; Architecture Description".
[26] 3GPP TS 38.425: “NG-RAN; NR user plane protocol”.
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply.
A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
Dual Connectivity: Defined in TS 36.300 [2].
eNB-Control Plane (eNB-CP): a logical node hosting the RRC/ RLC/MAC/PHY and the control plane part of the
PDCP protocol for an eNB. The eNB-CP terminates the UP interface for E-UTRA or NR PDCP PDUs with the eNB-
UP.
eNB-User Plane (eNB-UP): a logical node hosting the user plane part of the PDCP protocol for an eNB. The eNB-UP
terminates the UP interface for E-UTRA or NR PDCP PDUs with the eNB-CP.
E-RAB: An E-RAB uniquely identifies the concatenation of an S1 Bearer and the corresponding Data Radio Bearer.
When an E-RAB exists, there is a one-to-one mapping between this E-RAB and an EPS bearer of the Non Access
Stratum (NAS) as defined in TS 23.401 [3].
S1: logical interface between an eNB and an EPC, providing an interconnection point between the E-UTRAN and the
EPC. It is also considered as a reference point.
X2: logical interface between two eNBs. Whilst logically representing a point-to-point link between eNBs, the physical
realization need not be a point-to-point link.
3.2 Abbreviations
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply.
A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
AP Application Protocol
AS Access Stratum
CGI Cell Global Identifier
CIoT Cellular IoT
CMAS Commercial Mobile Alert Service
C-RNTI Cell RNTI
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ECGI E-UTRAN Cell Global Identifier
ECM EPS Connection Management
EEC Ethernet Equipment Clock
eNB E-UTRAN Node B
EMM EPS Mobility Management
E-RAB E-UTRAN Radio Access Bearer
ESM EPS Session Management
E-SMLC Evolved Serving Mobile Location Centre
ETWS Earthquake and Tsunami Warning System
EPC Evolved Packet Core
EPS Evolved Packet System
E-UTRA Evolved UTRA
E-UTRAN Evolved UTRAN
FDD Frequency Division Duplex
GUMMEI Globally Unique MME Identifier
ID Identity
IP Internet Protocol
LTE Long Term Evolution
MBMS Multimedia Broadcast Multicast Service
MBSFN Multimedia Broadcast multicast service Single Frequency Network
MeNB Master eNB
NDS Network Domain Security
MME Mobility Management Entity
NAS Non-Access Stratum
OTDOA Observed Time Difference Of Arrival (positioning method)
PLMN Public Land Mobile Network
PWS Public Warning System
RA-RNTI Random Access RNTI
RET Remote Electrical Tilting
RIM RAN Information Management
RNL Radio Network Layer
RNTI Radio Network Temporary Identifier
RRC Radio Resource Control
RTP Real-time Transport Protocol
QoS Quality of Service
SFN System Frame Number
S-GW Serving Gateway
SAP Service Access Point
SCG Secondary Cell Group
SeNB Secondary eNB
SON Self Organizing Networks
S-TMSI S-Temporary Mobile Subscriber Identity
TCP Transmission Control Protocol
TDD Time Division Duplex
TDM Time Division Multiplexing
TMA Tower Mounted Amplifier
TNL Transport Network Layer
UDP User Datagram Protocol
UE User Equipment
UMTS Universal Mobile Telecommunication System
UTDOA Uplink Time Difference of Arrival
4 General principles
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.
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- 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 General architecture
5.1 General
The protocols over Uu and S1 interfaces are divided into two structures:
- User plane protocols
These are the protocols implementing the actual E-RAB service, i.e. carrying user data through the access
stratum.
- Control plane protocols
These are the protocols for controlling the E-RABs and the connection between the UE and the network from
different aspects (including requesting the service, controlling different transmission resources, handover etc.).
Also a mechanism for transparent transfer of NAS messages is included.
5.2 User plane
The E-RAB service is offered from SAP to SAP by the Access Stratum. Figure 5.2-1 shows the protocols on the Uu and
S1 interfaces that linked together provide this E-RAB service.
Non-Access Stratum
Radio
Radio S1
S1
proto-
proto proto
proto-
cols
cols cols
cols
(1)
(1)
(2) (2)
Access Stratum
EPC
UE
EUTRAN
Radio
S1
(Uu)
Note 1: The radio interface protocols are defined in 3GPP TS 36.2xx and TS 36.3xx.
Note 2: The S1 interface protocols are defined in 3GPP TS 36.41x.

Figure 5.2-1: S1 and Uu user plane
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5.3 Control plane
Figure 5.3-1 shows the control plane (signalling) protocol stacks on S1 and Uu interfaces.
EMM,ESM (3) (3)
EMM,ESM
Non-Access Stratum
S1 S1
Radio
Radio
proto- proto
proto- proto
cols cols
cols cols
(1)
(1) (2) (2)
Access Stratum
EPC
UE
EUTRAN
Radio S1
(Uu)
Note 1: The radio interface protocols are defined in 3GPP TS 36.2xx and TS 36.3xx.
Note 2: The protocol is defined in 3GPP TS 36.41x. (Description of S1 interface).
Note 3: EMM, ESM: This exemplifies a set of NAS control protocols between UE and EPC. The evolution of the
protocol architecture for these protocols is outside the scope of the present document.

Figure 5.3-1: S1 and Uu control plane
NOTE: Both the Radio protocols and the S1 protocols contain a mechanism to transparently transfer NAS
messages.
6 E-UTRAN architecture
6.1 Overview
EPC
S1 S1
EUTRAN X2
eNB eNB
Figure 6.1-1 Overall architecture
The LTE architecture can be further described as follows:
The E-UTRAN consists of a set of eNBs connected to the EPC through the S1.
An eNB can support FDD mode, TDD mode or dual mode operation.
eNBs can be interconnected through the X2.
S1 and X2 are logical interfaces.
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The E-UTRAN is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL).
The E-UTRAN architecture, i.e. the E-UTRAN logical nodes and interfaces between them, is defined as part of the
RNL.
For each E-UTRAN interface (S1, X2) the related TNL protocol and the functionality are specified. The TNL provides
services for user plane transport, signalling transport.
In S1-Flex configuration, each eNB is connected to all EPC nodes within a pool area. The pool area is defined in
3GPP TS 23.401 [3].
If security protection for control plane and user plane data on TNL of E-UTRAN interfaces has to be supported,
NDS/IP as described in 3GPP TS 33.401 [16] shall be applied.
The eMBMS architecture is defined in 3GPP TS 36.440 [6].
6.1.1 Overall architecture for CP/UP separation of an eNB
The overall architecture for separation of eNB-CP and eNB-UP is depicted in Figure 6.1.1-1.

Figure 6.1.1-1. Overall architecture for separation of eNB-CP and eNB-UP
- An eNB may consist of an eNB-CP and multiple eNB-UPs;
- The eNB-UP is connected to the eNB-CP;
- One eNB-UP is connected to only one eNB-CP;
NOTE 1: For resiliency, an eNB-UP may be connected to multiple eNB-CPs by appropriate implementation.
- The eNB-CP and the eNB-UP terminates the UP interface used to convey E-UTRA or NR PDCP PDUs. NR user
plane protocol, as defined in TS 38.425 [26], is used for this interface;
6.2 E-UTRAN identifiers
This subclause shows those identifiers that are used in E-UTRAN.
6.2.1 Principle of handling Application Protocol Identities
An Application Protocol Identity (AP ID) is allocated when a new UE-associated logical connection is created in an
eNB, or an MME, or in a WT. An AP ID shall uniquely identify a logical connection associated to a UE over the S1
interface, or X2 interface, or Xw interface within a node (eNB, or MME, or WT). Upon receipt of a message that has a
new AP ID from the sending node, the receiving node shall store the AP ID of the sending node for the duration
...