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LTE Protocols&
Specifications
8/22/2019 LTE Protocols & Specifications
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Introduction In LTE architecture, core network includes Mobility Management Entity (MME), Serving
Gateway (SGW), Packet Data Network Gateway (PDN GW) where as E-UTRAN has E-
UTRAN NodeB (eNB). With increased data rates, improved spectrum efficiency and
packet-optimized system, LTE technology is set to drive machine to machine technology
and data intensive applications.
The figures shown below provide mapping of protocols to
corresponding specifications. To find 3GPP LTE specification, click at the correspondingprotocol in the images below.
Protocol structure of control plane in between UE & MME is shown below.
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This figure below shows protocol structure in between UE & P-GW user plane. GPRS
Tunnelling Protocol for the user plane (GTP-U) tunnels user data between eNodeB and
the S-GW as well as between the S-GW and the P-GW in the backbone network.
The X2 interface is defined between two
neighbour eNBs.
This figure shows the control & user
plane protocol stack of the X2 interface.
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Non-Access-Stratum (NAS) Protocol
The non-access stratum (NAS) is highest stratum of the control plane between UE and
MME at the radio interface. Main functions of the protocols that are part of the NAS arethe support of mobility of the user equipment (UE) and the support of session
management procedures to establish and maintain IP connectivity between the UE and
a packet data network gateway (PDN GW).
NAS control protocol performs followings:
EPS bearer management;
Authentication;
ECM-IDLE mobility handling;
Paging origination in ECM-IDLE;
Security control.
Protocol specification
3GPP TS 24.301 - Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS);
Stage 3
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Radio Resource Control (RRC)
protocol layer exists in UE & eNodeb, It is part of LTE air interface control plane. The
main services and functions of the RRC sublayer include: Broadcast of System Information related to the non-access stratum (NAS);
Broadcast of System Information related to the access stratum (AS);
Paging;
Establishment, maintenance and release of an RRC connection between the UE and E-
UTRAN Security functions including key management;
Establishment, configuration, maintenance and release of point to point Radio Bearers;
Mobility functions
QoS management functions;
UE measurement reporting and control of the reporting;
NAS direct message transfer to/from NAS from/to UE.
Protocol specification
3GPP TS 36.331 - Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
Control (RRC)
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Packet Data Convergence Protocol (PDCP)
PDCP protocol layer exists in UE & eNodeb, It is part of LTE air interface control and userplanes.
The main services and functions of the PDCP sublayer for the user plane include:
Header compression and decompression: ROHC only;
Transfer of user data;
In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLCAM;
Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM; Retransmission of PDCP SDUs at handover for RLC AM;
Ciphering and deciphering;
Timer-based SDU discard in uplink.
The main services and functions of the PDCP for the control plane include:
Ciphering and Integrity Protection; Transfer of control plane data.
Protocol specification
3GPP TS 36.323 - Evolved Universal Terrestrial Radio Access (E-UTRA); Packet DataConvergence Protocol (PDCP) specification
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Radio Link Control (RLC)
RLC protocol layer exists in UE & eNodeb, It is part of LTE air interface control and user
planes. The main services and functions of the RLC sublayer include:
Transfer of upper layer PDUs;
Error Correction through ARQ (only for AM data transfer);
Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data
transfer); Re-segmentation of RLC data PDUs (only for AM data transfer);
In sequence delivery of upper layer PDUs (only for UM and AM data transfer);
Duplicate detection (only for UM and AM data transfer);
Protocol error detection and recovery;
RLC SDU discard (only for UM and AM data transfer);
RLC re-establishment.
Protocol specification
3GPP TS 36.322 - Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control
(RLC) protocol specification
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Medium Access Control (MAC)
MAC protocol layer exists in UE & eNodeb, It is part of LTE air interface control and user
planes.The main services and functions of the MAC sublayer include:
Mapping between logical channels and transport channels;
Multiplexing/demultiplexing of MAC SDUs belonging to one or different logical channels
into/from transport blocks (TB) delivered to/from the physical layer on transport
channels;
scheduling information reporting;
Error correction through HARQ;
Priority handling between logical channels of one UE;
Priority handling between UEs by means of dynamic scheduling;
Transport format selection; Padding.
Protocol specification
3GPP TS 36.321 - Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access
Control (MAC) protocol specification
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Air Interface Physical LayerThe LTE air interface physical layer offers data transport services to higher layers. The access to these services is
through the use of a transport channel via the MAC sub-layer. The physical layer is expected to perform thefollowing functions in order to provide the data transport service:
Error detection on the transport channel and indication to higher layers FEC encoding/decoding of the transport channel
Hybrid ARQ soft-combining
Rate matching of the coded transport channel to physical channels
Mapping of the coded transport channel onto physical channels
Power weighting of physical channels
Modulation and demodulation of physical channels Frequency and time synchronisation
Radio characteristics measurements and indication to higher layers
Multiple Input Multiple Output (MIMO) antenna processing
Transmit Diversity (TX diversity)
Beam forming
RF processing
Protocol specification
3GPP TS 36.201 - Evolved Universal Terrestrial Radio Access (E-UTRA); LTE physical layer; General description
3GPP TS 36.211 - Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation
3GPP TS 36.212 - Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding
3GPP TS 36.213 - Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures
3GPP TS 36.214 - Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements
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S1 Signalling Transport
S1 signalling bearer provides the following functions:
Provision of reliable transfer of S1-AP message over S1-MME interface.
Provision of networking and routeing function
Provision of redundancy in the signalling network
Support for flow control and congestion control
L2 - Data link layer
Support of any suitable data link layer protocol, e.g. PPP, Ethernet
IP layer
The eNB and MME support IPv6 and/or IPv4
The IP layer of S1-MME only supports point-to-point transmission for delivering S1-AP message.
The eNB and MME support the Diffserv Code Point marking
Transport layer
SCTP is supported as the transport layer of S1-MME signalling bearer.
SCTP refers to the Stream Control Transmission Protocol developed by the Sigtran working group of
the IETF for the purpose of transporting various signalling protocols over IP network.
There is only one SCTP association established between one MME and eNB pair.
The eNB establishes the SCTP association. The SCTP Destination Port number value assigned by IANA
to be used for S1AP is 36412.
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S1 Signalling Transport
Protocol specification
3GPP TS 36.410 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 general
aspects and principles
3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1
3GPP TS 36.412 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 signalling
transport
IETF RFC 2460: "Internet Protocol, Version 6 (IPv6) Specification"
IETF RFC 791 (September,1981): "Internet Protocol"
IETF RFC 2474 (December 1998): "Definition of the Differentiated Services Field (DS Field) in the IPv4and IPv6 Headers
S1 layer 1
The main functions of S1 interface layer 1 are as following:
Interface to physical medium;
Frame delineation;
Line clock extraction capability;
Layer 1 alarms extraction and generation;
Transmission quality control.
Protocol specification
3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 11Telcomz
http://www.3gpp.org/ftp/Specs/html-info/36410.htmhttp://www.3gpp.org/ftp/Specs/html-info/36411.htmhttp://www.3gpp.org/ftp/Specs/html-info/36412.htmhttp://www.ietf.org/rfc/rfc2460.txthttp://www.ietf.org/rfc/rfc791.txthttp://www.ietf.org/rfc/rfc2474.txthttp://www.3gpp.org/ftp/Specs/html-info/36411.htmhttp://www.3gpp.org/ftp/Specs/html-info/36411.htmhttp://www.ietf.org/rfc/rfc2474.txthttp://www.ietf.org/rfc/rfc791.txthttp://www.ietf.org/rfc/rfc2460.txthttp://www.3gpp.org/ftp/Specs/html-info/36412.htmhttp://www.3gpp.org/ftp/Specs/html-info/36411.htmhttp://www.3gpp.org/ftp/Specs/html-info/36410.htm8/22/2019 LTE Protocols & Specifications
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S1 Application Protocol (S1AP)
S1AP provides the signalling service between E-UTRAN and the evolved packet core (EPC)and has following functions:
E-RAB management function
Initial Context Transfer function
UE Capability Info Indication function
Mobility Functions
S1 interface management functions
NAS Signalling transport function
S1 UE context Release function
UE Context Modification function
Status Transfer
Trace function
Location Reporting
S1 CDMA2000 Tunneling function
Warning message transmission function
RAN Information Management (RIM) function
Configuration Transfer function
Protocol specification
3GPP TS 36.413 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1
Application Protocol (S1AP) 12Telcomz
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GTP-U Transport
The transport layer for data streams over S1, X2, S4, S5 and S8 is an IP based Transport. TheGTP-U protocol over UDP over IP is supported as the transport for data streams on the userdata interfaces.
Any data link protocol that fulfils the requirements toward the upper layer may be used.
UDP/IP The UDP port number for GTP-U is as defined in 3GPP TS 29.281.
The eNB and the EPC support fragmentation and assembly of GTP packets at the IP layer.
The eNB and the EPC support IPv6 and/or IPv4.
Protocol specification
3GPP TS 36.410 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1
general aspects and principles 3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1
3GPP TS 36.414 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 datatransport
3GPP TS 36.420 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 generalaspects and principles
3GPP TS 36.421 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 layer 1
3GPP TS 36.424 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 datatransport
IETF RFC 2460: "Internet Protocol, Version 6 (IPv6) Specification"
IETF RFC 791 (September,1981): "Internet Protocol"
IETF RFC 2474 (December 1998): "Definition of the Differentiated Services Field (DS Field) in the
IPv4 and IPv6 Headers 13Telcomz
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GPRS Tunnelling Protocol User Plane (GTP-U)
GTP-U protocol is used over S1-U, X2, S4, S5 and S8 interfaces of the Evolved Packet
System (EPS). GTP-U Tunnels are used to carry encapsulated T-PDUs and signalling
messages between a given pair of GTP-U Tunnel Endpoints. The Tunnel Endpoint ID (TEID)which is present in the GTP header indicates which tunnel a particular T-PDU belongs to.
The transport bearer is identified by the GTP-U TEID and the IP address (source TEID,
destination TEID, source IP address, destination IP address).
Protocol specification
3GPP TS 29.281 - General Packet Radio System (GPRS) Tunnelling Protocol User Plane
(GTPv1-U)
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X2 Application Protocol (X2AP)
The X2AP protocol is used to handle the UE mobility within E-UTRAN and provides the
following functions:
Mobility Management Load Management
Reporting of General Error Situations
Resetting the X2
Setting up the X2
eNB Configuration UpdateProtocol specification
3GPP TS 36.423 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2
Application Protocol (X2AP)
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--Thank You--
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