LTE System Structure and Signalling

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Course 502

LTE Long Term EvolutionArchitecture and Connection Processing

LTE Long Term EvolutionArchitecture and Connection Processing

August, 2010 Page 1Course 502 v1.1 (c)2010 Scott Baxter


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Course Outline

LTE Network Architecture and Networking Components

Standard Interfaces and key protocol stacks

Radio System Identifiers

Tunnels, Connections and Bearers

System Acquisition and Synchronization

Idle Mode and Pa in

UE Attach to the Network (Registration procedures)

Connected Mode and UE States

Mobility, Interoperability and Handover Management

Lets setup and process various LTE call flows and scenarios


Review, Summary and conclusion


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LTE Network Architecture

LTE Network Architecture

August, 2010 Page 3Course 502 (c)2010 Scott Baxter


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1. LTE Network Architecture

and Networking Components

1-1 Quick Review of the Air Interface

-

(EPC) overview 1-3 Networking Functional Elements (eNB; MME; SGW; PGW;

Remarks



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The LTE Air InterfaceThe LTE Air Interface



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The LTE Downlink and Uplink Signals

The LTE signal uses variations of Orthogonal Frequency DivisionMulti lexin on both its u link and downlin

The LTE downlink signal uses dozens to even thousands of thincarriers spaced 15 kHz, covering the operators licensed spectrum

carriers, using dynamic scheduling to maintain QoS

the Operator sets the number of carriers to fit in its spectrum

QPSK to even 64QAM in response to instantaneous conditions

The LTE uplink signal of each user is dynamically assigned to usea small or lar e fraction of the u link s ectrum to meet oS oals

OFDMs spectral efficiency is higher than CDMA or HSPA

Multiple antenna techniques can be used on both uplink and



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Advanced Technologies of LTE

OFDM OFDM, OFDMAOrthogonal Frequency Division Multiplexing;Ortho onal Fre uenc Division Muli le Accesser

The signal consists of many (from dozens tothousands) of thin carriers carrying symbols

In OFDMA the s mbols are for multi le users

Frequency

Pow

OFDM provides dense spectral efficiency androbust resistance to fading, with great flexibilityof use

MIMO MIMOMultiple Input Multiple Output

,exploitation of multiple antennas at the basestation and the mobile to effectively multiplythe throu h ut for the base station and users



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The LTE Downlink Uses OFDMA

In generic OFDM, users are assigned fractions of the total,

OFDMA means Orthogonal Frequency Division Multiple Access

OFDMA uses dynamic scheduling to package each users data

immediate needs

This assures effective utilization of the total capacity of the



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The LTE Uplink Signal

The uplink uses SC-FDMA with some dynamic multiple of 4 15-khzsubcarriers to carrier the information

Modulation can be QPSK, 16QAM or 64QAM for conditions


SC-FDMA has a low Peak-to-Average Power Ratio (PAPR)

which provides more transmit power and longer battery life


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Type 1 Forward Link Frames:

For Frequency Division Duplex (FDD)

In Frequency Division Duplex, separate identical blocks of

(UE) to transmit independently at the same time

This frequency division duplex mode is used virtually everywherein North America and is the most revalent mode in the rest of the

world In FDD mode, LTE radio frames are 10 ms long


Each subframe is composed of two slots, each 0.5 ms long


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Type 2 - TDD

In some cases, governments assign a wireless operator a single

block of frequencies to use for an LTE system In this case, transmitting and receiving must alternate with

each other, like one lane traffic in a construction site

The forward link is transmitted discontinuously, alternating with the

reverse n on e same requencyThis arrangement allows effective LTE operation in a small amount

of spectrum, but does limit the capacity of the system


e gure s ows e su vs on o me n o up n an own nperiods, with the additional requirement of guard periods between


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The Building Blocks of the Downlink Signal:

Elements and Blocks

Its what one subcarrier can do in just one modulation symbol

One Resource Block is the smallest usable piece of the signal

s w a su carrers can o urng a w o e s o , . ms

In one slot, a subcarrier normally carries 7 symbolsAugust, 2010 Page 12Course 502 v1.1 (c)2010 Scott Baxter


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Downlink Physical Resources and Mapping



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Example of Downlink Control Signal Mapping

This figure shows a typicalma in of downlink controlsignals to the timeslots whichcarry them

Notice the T1, T2, T3, and T4information which occupies afixed pattern. By observing

these streams the mobile is-antenna configuration of thebase station (eNB) withoutrequiring long layer-3

messages



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Generic Frame Sequences

Each OFDM s mbol be ins with a c clic refix of duration below:



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Uplink Physical Resources and Mapping



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Uplink Format PUCCH 0 or 1



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UL SC-FDMA Subcarrier Options

On the reverse link, there are two ways to assign subcarrier frequencies to

One is Localized Subcarriers, which gives one user a single block ofadjacent carriers

as critical The other is Distributed Subcarriers

this provides superior protection against selective fading


this requires very precise frequency control to avoid interference


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LTE Physical Signals



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LTE Physical Channels



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SISO, MISO, SIMO, MIMO

Single-Input Single-Output is thedefault mode for radio links over theears and the baseline for further

comparisons.

Multiple-Input Single Output providestransmit diversity (recall CDMA2000

.power required, but does not increasedata rate. Its also a delicious

Japanese soup. Single-Input Multiple Output is receive

diversity. It reduces the necessarySNR but does not increase data rate.Close but no relation to Dr. Ernest

Simo, wireless communications expert Multiple-Input Multiple Output is highly

effective, using the differences in path


dimension to hold additional signals

and increase the total data speed.


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SU-MIMO, MU-MIMO, Co-MIMO

Single-User MIMO allowsthe sin le user to ainthroughput by havingmultiple essentiallyindependent paths for data

Multi-User MIMO allowsmultiple users on the

reverse link to transmit ,increasing system capacity

Cooperative MIMO allows auser to receive its si nal

from multiple eNBs incombination, increasingreliability and throughput



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The Evolved Packet System (EPS)

and Evolved Packet Core (EPC)

The Evolved Packet System (EPS)

and Evolved Packet Core (EPC)OverviewOverview



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The Evolved Packet System and theEvolved Packet Core

eNB

E-UTRAN

Inter-cell RMM

RB Contro l

Connection Mobility Ctrl

EPC

Radio Admission Ctrl.

eNB Measurement

Config. & Provision

NAS Security

Idle State Mobility

Dynamic ResourceAl locat ion (scheduler)

RRC

Handling

EPS BearerControl

S-GW P-GWPDCPRLC

MAC

MobilityAnchor ing

UE IP AddressAl locat ion Internet


PHY Packet FilteringS1


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Networking Functional ElementsNetworking Functional Elements



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Networking Functional Elements(eNB; MME; Anchors/Gateways, PCRF; HSS)

Legacy GSM radio Networks

GERAN Gb

GPRS COREUTRAN

SGSN PCRF

S7Iu Rx+

WCDMA /HSPA radio Networks

Mobility Management Entity

User Plane Entit y

Home Subscriber Server

Super HLR

HSS

S5a

S6aS5b

Ref Pt.

LTE radio

Networks

IASA

MMEUPE

3GPPAnchor

SAEAnchor

EvolvedRAN: eNB

IP Services

Inter Access System Anchor

S1 SGi

Ref Pt.

-

vo ve ac e oreS2a

UuS2b,c

August, 2010 Page 26Course S2K 5000 v1.5 (c)2010 Scott Baxter

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EV-DO networks IP access

IP access


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Functions of Key Network Elements

Legacy GSM radio Networks

GERANNAS signalingMobility between 3GPP AnsIdle mode UE connectivit Mobil it Anchor

UE IP Address allocationPacket Screenin &

GPRS COREUTRAN

SGSN PCRF

S7

IuRx+S12

P-GW and S-GW selection

SGSN selection at HOAuthent icationBearer Establishment

Packet RoutingIdle Mode packet buffering& DL initiationLegal Interception

FilteringPolicy Enforcement$Charging SupportLegal Interception

WCDMA /HSPA radio Networks

Mobility Management Entity

User Plane Entit y

Server Super HLR

HSSS11

S6aS8a

LTE radio

Networks

IASA

MMEUPE

ServingGateway

PDNGateway

EvolvedRAN: eNB

Inter Access

System Anchor

SGiS1-MMEIP Services

S10

-

vo ve ac e oreS2a

UuS2b,c

S1-U

August, 2010 Page 27Course S2K 5000 v1.5 (c)2010 Scott Baxter

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EV-DO networks IP access

IP access


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LTE Standard Interfaces andLTE Standard Interfaces and



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2. Standard Interfaces andKey Protocol Stacks

2-1 Interfaces (Uu, X2, S1, S5, S8, S11)

- , , , , ,

Layers)



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Key Network Interfaces (1)

Uu The LTE physical layer interface connecting the UE with theeNodeB on both uplink and downlink directions (GTP-U Protocol)

- e on ro ane comman an con ro connec on

from the eNB to the MME managing user mobility (GTP) S1-U The User Plane (traffic-carrying) connection from the eNB

S2a PDN link to trusted non-3GPP networks (CDMA EVDO)

(based on proxy mobile IP, can use client mobile IP FA mode) n o servng ga eway or an un rus e ne wor(based on proxy mobile IP)

S2c PDN link to trusted non-3GPP network (CDMA, EVDO) GTP-

S3 Connection between 2G/3G SGSN and SAE MME (GTP)

S4 -- Provides user plane connection and mobility support

point defined between SGSN and GGSN) (GTP protocol)



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S5 Provides user plane tunneling and tunnel managementbetween SGW and PDN GW. Handles S GW relocation for UEmobility if the S GW must connect to a non-collocated PDN GW.

S5 is the intra PLMN variant of S8.

S6a Carries subscription and authentication data between theMME and the HSS (often called a super HLR)

S7 Carries policy and charging rules information between the

PDN gateway and the PCRF S8 Inter-PLMN reference point providing user and control plane

between the Serving GW in the VPLMN and the PDN GW in theHPLMN. S8 is the inter PLMN variant of S5.

- rans ers o po cy an c argng con ro n orma onbetween Home/Visited PCRF to support local breakout function.

S10 -- Reference point between MMEs for MME relocation and



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S11 -- Reference point between MME and Serving GW

Direct Tunnel. Based on Iu-u/Gn-u ref. point and GTP-U protocolSGSN-to-UTRAN or SGSN-to-GGSN. Optional by Operator.

SGi -- Reference point between PDN GW and packet datanetwork. Packet data network can be external public, private, or

intra-o erator acket data network, e. . for rovision of IMS.Corresponds to Gi interface for 3GPP accesses.

Rx -- The Rx reference point resides between the AF and thePCRF in the TS 23.203 [6].

Wn* The reference point between the Untrusted Non-3GPP IPAccess and the ePDG. Traffic on this interface for a UE initiatedtunnel must be forced towards the ePDG.



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X2 -- The X2 interface can provide

-

support of continuation between eNBs of the E-UTRANservices offered via the S1 interface;

Transport Network functionality to facilitate introduction offuture technology.

-message delivery and control functions



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Radio Control Plane Protocol Stack

UE eNB MME

NAS

RRC

PDCP

RRC

PDCP

NASNon-Access Stratum

Radio Resource Control

Packet Data Conver ence Protocol

Layers

RLC

MACPHY

RLC

MACPHY

Radio Link Control

Media Access ControlPhysical

The NAS protocol is used for network attach, authentication,setting up bearers, and mobility management

, ,system information, controls UE measurements, assigns cell-leveltemporary identifiers to UEs, transfers UE contexts in handovers

The RLC formats and transports traffic between UE and eNB

The MAC layer implements HARQ

e PHY ayer uses a aptve mo uaton an co ng to protectdata from errors and keep rates optimally high



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Radio User Plane Protocol Stack

eNodeB

PDCP

UE

PDCP

User Plane

Packet Data Convergence Protocol

Layers

MAC

PHY

MAC

PHY

Media Access Control

Physical

e compresses ecompresses ea ers an oesciphering

The RLC formats and transports traffic between UE and eNB, and

The MAC layer implements HARQ

The PHY layer uses adaptive modulation and coding to protect



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Layer-2 Structure for Downlink



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Layer-2 Structure for Uplink



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The S1 User Plane

The S1 User Plane Interface (S1-U) connectsbetween the eNB and the S-GW. It rovides:

S1 InterfaceUser Plane

Guaranteed delivery of user plane PDUsff

The transport network layer is built on IP transport-

User PlanePDUs

-

user plane PDUs between the eNB and the S-GW

GTP-U

UDP

IP

Data Link Layer

Physical Layer



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The S1 Control Plane

The S1 control plane interface (S1-MME) isdefined between the eNB and the MME

S1 Interface

Control Plane(eNBMME)

The transport network layer is built on IPtransport, like the user plane

User Plane

PDUs

,messages SCTP is added on top of IP

The application layer signaling protocol is called

S1-AP (S1 A lication Protocol)

SCTP

Data Link Layer

Physical Layer



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S1 Interface Signaling Procedures

E-RAB signaling: Setup, Modification, Release, Release Indication

Handover signaling: Preparation, Resource Allocation, Completion,

Transfers: eNB Status, MME Status Paging procedures

.,

LPPa Transport: UE and Non-UE Assoc. UL/DL transport

Error Indication procedure: eNB initiated, MME initiated

,

Initial Context Setup; UE Context Modification

S1 Setup procedure;

,

Location Reporting: Reporting Control, Report, Report Failure Indication

Overload: Start, Stop, Write Replace Warning procedures

rec n orma on rans er: e on gura on, on gura on

S1 CDMA2000 Tunneling: DL S1 CDMA2000, UL S1 CDMA2000



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The X2 Interface

eNodeB

X2AP

SCTP

IP

eNodeB

GTP-U

UDP

IP

eNodeB

X2AP

SCTP

IP

eNodeB

GTP-U

UDP

IP

L2

L1

L2

L1

L2

L1

L2

L1

X2 Control Plane X2 User Plane

Usually routed via the same transport connection used by S1

used only for control plane data but during handover it can be used

tem oraril for user data forwardin X2 control plane uses SCTP (Stream Control Transmission Protocol)

for reliable delivery of control data between eNBs

X2 user plane is sufficiently reliable using ordinary UDP

X2AP (X2 Application Protocol) functions are

Management of Intra-LTE mobility (HO msg. over X2 interface)

Load management for inter-cell interference coordination by sharingresource, load, and traffic details

Setting up and resetting the X2 interface



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X2 Protocol Stack

The transport layer over X2 is IP based. Transportnetwork layer for

-streams on the X2 interface. There may be zero orone UL data stream and zero or one DL data streamper E-RAB at the X2 interface.

data streamsover X2

The DL stream is used for DL data forwardingfrom the source eNB to the target eNB.

The UL stream is used for UL data forwardinfrom the source eNB to the target eNB.

Each data stream is carried on a dedicatedtransport bearer.

The identity of a transport bearer signaled in theRNL control plane consists of the IP address andthe TEID of the corresponding GTP tunnel,

.



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GTP-U Protocol over X2 Interface

The UDP path protocol is used

The GTP-U UDP user-plane port number is 2152

eNBs over the X2 interface can support fragmentation and

assembly of GTP packets at the IP layer An eNB will support IPv6 and/or IPv4.

A pair of eNBs may use one or several IP addresses

A source eNB sends packets of a given E-RAB to the target eNB

IP address (received in X2AP)This address corresponds to the DL transport bearer of that

particular E-RAB.

The Trans ort La er Address in X2AP messa es is a bit strin of

a) 32 bits in case of IPv4 address b) 128 bits in case of IPv6 address


X2 Control Plane Procedures


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X2 Control Plane Procedures


H dli f A li i P l Id i i


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Handling of Application Protocol Identities

An Application Protocol Identity (AP ID) is allocated when a newUE-associated lo ical connection is created in an eNB or an MME.

An AP ID uniquely identifies a logical connection for the UEover the S1 or X2 interface within a node (eNB or MME).

sending node, the receiving node stores the AP ID of thesending node for as long as the logical connection lasts

The receivin node assi ns the AP ID to be used to identif thelogical connection for the UE and include it as well as thepreviously received new AP ID from the sending node, in thefirst returned message to the sending node

n a su sequen messages o an rom sen ng no e, sof both sending node and receiving node are included


UE A i t d S1 X2 C ti


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UE-Associated S1 or X2 Connections

Control plane messages (S1AP, X2AP) associated with the UE aresenton the lo ical S1 or X2 connection.

This connection is set up at the first S1/X2AP exchangebetween peer nodes.

exchanged.

The UE-associated logical S1-connection uses the identities

MME UE S1AP ID and eNB UE S1AP ID.The UE-associated logical X2-connection uses the identities

Old eNB UE X2AP ID and New eNB UE X2AP ID. When anMME or eNB receives a UE associated S1/X2AP message itre reves e assoc a e ase on .

UE-associated signaling is an exchange of S1/X2-AP messagesfor one UE over the UE-associated logical S1/X2-connection.

NOTE: The UE-associated logical S1/X2-connection may existbefore the eNB UE context is setup in eNB.


S1 d X2 A li ti P t l Id titi


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S1 and X2 Application Protocol Identities

An eNB UE S1AP ID uniquely identifies a UE over the S1 interface within an eNB logical node.When an MME receives an eNB UE S1AP ID it stores it for the duration of the UE-associatedlo ical S1- connection for this UE. Once known to an MME this IE is included in all UEassociated S1-AP signaling.

An MME UE S1AP ID uniquely identifies a UE over the S1 interface within the MME logicalnode. When an eNB receives MME UE S1AP ID it stores it for the duration of the UE-associated logical S1- connection for this UE. Once known to an eNB this IE is included in all

- .

An Old eNB UE X2AP ID uniquely identifies a UE over the X2 interface within a source eNBlogical node. When a target eNB receives an Old eNB UE X2AP ID it stores it for the durationof the logical X2-connection of this UE. Once known to a target eNB this ID is included in all

UE assoc. X2-AP signaling. A New eNB UE X2AP ID uniquely identifies a UE over the X2 interface within a target eNB.

When a source eNB receives a New eNB UE X2AP ID it stores it for the duration of the UE-associated logical X2-connection for this UE. Once known to source eNB this IE is included inall UE associated X2-AP signaling. The New eNB UE X2AP ID is unique within the eNB logicalnode.

An eNB1 Measurement ID identifies the measurement configuration over the X2 interfacewithin the eNB requesting measurement. The eNB1 Measurement ID is unique within the eNBlogical node.

An eNB2 Measurement ID uniquely identifies the measurement configuration over the X2.

within the eNB logical node.



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Radio System Identifiers andRadio System Identifiers and


3 Radio System Identifiers and Parameters


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3. Radio System Identifiers and Parameters

UE Identifiers (IMSI, TMSI, GUTI )

Random Access Radio NetworkTemporary Identifier (RA-RNTI)

C-RNTI (Cell Radio Network TemporaryIdentifier)

PCI Physical Cell Identifier

contained in the MA sub-header of each random access

response LCID Logical channel identifier

I o lass Identi ie

RNTI Radio Network TemporaryIdentifier

S stemInformationBlockT e9 contains RRC layer in the Enb allocates cell-

level temporary identifiers

S-TMSI SAE Temporary Mobile

Station Identifier

a home eNB identifier (HNBID);

eNB Identifier (eNB ID): used to identifyeNBs within a PLMN.

UTRAN and EPC Identifiers

ECGI E-UTRAN Cell GlobalIdentifier

' '

identify tracking areas

NAS UE identifier

NAS (EPC/UE) level AKA procedure

given cell CSG identity: broadcast by cells in a

CSG to allow authorized CSG

identifier (KSIASME). MME includes a session identifier

SI-RNTI System Information RNTI


CID Context Identifie

E UTRAN Network Identities


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E-UTRAN Network Identities

PLMN Identity

A Public Land Mobile Network is uni uel identified b its PLMN Identit .

Globally Unique MME Identif ier (GUMMEI)

The Globally Unique MME Identifier consists of a PLMN Identity, a MME GroupIdentity and a MME Code

,GUMMEI uniquely identifies an MME logical node.

Global eNB ID

The Global eNB ID is used to globally identify an eNB E-UTRAN Cell Global Identifier (ECGI)

The ECGI is used to globally identify a cell.

Tracking Area Identity (TAI)

ac rac ng rea a e ne group o oca ce s as an ass gne

E-RAB ID

An E-RAB uniquely identifies the combination of an S1 bearer and thecorresponding Data Radio Bearer. Under an E-RAB, there is a one-to-onemapping between this E-RAB and an EPS bearer of the Non Access Stratum.


E UTRAN UE Identifiers (1)


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E-UTRAN UE Identifiers (1)

RNTI

identifiers within E-UTRAN and in signaling messages between

UE and E-UTRAN. Some types of RNTI exist:

-

The C-RNTI provides a unique UE identification at the celllevel identifying RRC Connection

- -

The RA-RNTI is used during some transient states, the UEis temporarily identified with a random value for contentionresolution ur oses

S-TMSI S-Temporary Mobile Subscriber Identity (S-TMSI) The S-TMSI is a temporary UE identity in order to support

-allocated by MME.


E UTRAN UE Identifiers (2)


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E-UTRAN UE Identifiers (2)

Transport Layer Addresses

The transport layer address parameter is sent in radio signaling.

The transport layer address parameter is not interpreted in theradio network application protocols

held by the eNB.

The block contains

s a e n orma on, secur y n orma on, capa yinformation, identities of the UEs logical S1-connection

An eNB UE context is established when the transition to

completion of handover resource allocation duringhandover preparation.

RRC layer in the eNB allocates cell-level temporary identifiers



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Tunnels, Connections andTunnels, Connections and


4 Tunnels Connections and Bearers


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4. Tunnels, Connections and Bearers

4-1 Default Bearers, Dedicated Bearers

- u xy

4-3 Tunnel parameters (TEID; F-TEID )


LTE Bearers


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LTE Bearers

In LTE data lane traffic travels over virtual connections calledservice data flows (SDFs).

SDFs travel over bearers: Virtual containers with unique QoScharacteristics.

A bearer is a datapath between UE and PDN, in three segments:

Radio bearer between UE and eNodeB

Data bearer between SGW and PGW (S5 bearer)


Basics of GTP-U ProtocolG l T li P t l


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General Tunneling Protocol

GPRS Tunneling Protocol (GTP) is a group ofIP-basedcommunications rotocols used in wireless networks.

GTP includes variant protocols, GTP-C, GTP-U and GTP'.

GTP-C is used within the GPRS core network for signaling

GPRS Support Nodes (SGSN).

GTP-U is used for carrying user data within the GPRS Core

Network and between the Radio Access Network and the corenetwork. The user data transported can be packets in any ofIPv4,IPv6, or PPP formats. It is used in the LTE EPC network.

GTP' (GTP prime) uses the same message structure as GTP-Can - , u can e use or carryng c argng a a rom e

Charging Data Function (CDF) of the GSM or UMTS network tothe Charging Gateway Function (CGF).

.on UDP.


GTP-U Tunneling Protocol


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GTP U Tunneling Protocol

GTP-U is an IP-based tunneling protocol allowing many tunnelsbetween each setof end oints.

Each tunnel has TEID (Tunnel Endpoint Identifier) in the GTP-U

messages, derived from a dynamically generated random number.- -

control plane (setup, teardown and modification of the user plane'sparameters mainly).

GTP-C is ust the control rotocol used to set u the user tunnels. Actually GTP-C gets allocated its own TEID by both ends of the

connection so it is a tunnel on its own. It is possible use different IPaddresses for GTP-U and GTP-C.

Both use UDP and fixed port numbers (2123 for GTP-C and 2152for GTP-U). User's are separated based on the TEID (which isunique per direction).


Basics of Proxy Mobile IP


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as cs o o y ob e

Proxy Mobile IP (or PMIP, or Proxy Mobile IPv6) is a newstandard under the InternetEn ineerin Task Force IETF .

Also called Network-based mobility management, it is

somewhat like Mobile IP, but does not require modifications to themobile host's network stack, as mobility is handled by the network.

How Proxy Mobile IP works

Two network entities are involved:

in a Proxy Mobile IP domain.

Mobile Access Gateway (MAG) is a function on an access routerthat mana es the mobilit related si nallin for a mobile host that

is attached to its access link.


Operation of Proxy Mobile IP


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p y

The protocol works as follows:

A Mobile Access Gateway on that link checks hostauthorization

A Mobile Access Gateway updates a Local Mobility Anchorabout the current location of a host

o an crea e a - rec ona unne


Default and Dedicated Bearers


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When a UE connects to the network it gets an IP address. This iscalled "Default EPS Bearer Activation and it has no oS.

Its also possible to do a "Dedicated EPS Bearer Activation"

which offers QoS and other beneficial features , , ,

depend on QoS policies on the air interface

A dedicated bearer is connected to a Traffic Flow Template (TFT),

a list of IP addresses and TCP/UDP ort combinationsThe TFT is forwarded to the mobile during the dedicated

bearer activation and it guides the protocol stack to move theIP packets to or from a specific TCP/UDP port and/or IPa resses n o a spec a o queue or e er rea men

No extra IP address is needed, as the protocol stack uses theTraffic Flow Template information to decide what to do with each

.


Tunnel parameters (TEID; F-TEID )Default Bearer (2)


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Default Bearer (2)

The call flow is straightforward. Notice the fields TEID and FTEID.

- .

FTEID is Fully Qualified Tunnel End Point Identifier. This IE isused to send TEID/GRE Key and IP info of the sending entity.

.

The S-FTEID is the senders FTEID.

The MME sends this field with a TEID value, say 0x111 and itsa ress o - .

From this message the S-GW learns the IP address of the MMEand the TEID field to be used in the response.

- sen s rea e ess on esponse message w

value 0x111 and S-FTEID which contains the TEID value, say0x222, for use by MME and IP address of the S-GW.

-and S-GW uses TEID 0x111 to send control plane info to MME.




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Default Bearer (1)

LTE : Tunnel Identif iers (GTPv2)

.identified? Lets follow LTE call flow where two activities are

running on mobile phone, one is using default bearer and other isusing dedicated bearer.

The key detail is the TEID and FTEID fields.




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Default Bearer (3)

Once the control plane is set traffic has to flow. Modify BearerRe uest is used to indicate the S1-U interface of eNB. So S-FTEID(S1-U eNB FTEID) value is set to say 0x0a + IP address and sent

to S-GW. S-GW replies with its S1-U interface FTEID. At this stagethe TEID for the user plane are set. User plane traffic will flow' .

bearer.


Tunnel parameters (TEID; F-TEID )Dedicated Bearer (1)


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Dedicated Bearer (1)


Tunnel parameters (TEID; F-TEID )Dedicated Bearer (2)


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Dedicated Bearer (2)

A Bearer Resource Command is used by MME to request adedicated bearer.

Receiving the bearer resource command, the S-GW initiates a

Create Bearer request. .

In create bearer request S-GW includes S1-U SGW F-TEID foruser plane traffic.

-eNB FTEID.

Now the dedicated bearer is created and the user plane traffictunnel is ne otiated. Dedicated bearer user lane traffic flowsusing the exchanged TEIDs

The interface is S11. This interface is mapped to S5/S8 and S1-MME interfaces. TEID are used to identify and map the tunnels invarious interfaces.



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System AcquisitionSystem Acquisition


System Acquisit ion


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earc ng n meearc ng n requency

At power-up, the UE notes its LTE band class capabilities and beginsexploring the frequencies used for the SCH in each band

The UE first looks for the primary synchronization signal (P-SCH) in the

in each radio frame. It reads symbol timing, and learns which of three cellidentities is being transmitted, and locks its freqencies to the eNB.

The UE next searches for the (S-SCH) secondary synchronization signal,an earns w c o ce en es s eng ransm e . rom s

decodes the PCI, physical cell identity, and the frame boundaries The UE next finds the RS sequence and learns antenna port configuration

-reselection criteria


The Downlink Reference Signal


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The downlink reference signals consist of known reference symbolsinserted in the first and third last OFDM symbol of each slot.

There is one reference signal transmitted per downlink antenna port.

The number of downlink antenna ports equals 1, 2, or 4. Fre uenc ho in can be a lied to the downlink reference si nals. The

hopping pattern period is one frame (10 ms). Each frequency hoppingpattern corresponds to one cell identity group.

The downlink MBSFN reference signals consist of known reference

- ,symbol of sub-frame in case of 15kHz sub-carrier spacing and extendedcyclic prefix


Example of RS Sequences for 4 Antennas


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How The UE GetsEssential System Information


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y

After the cell-search, the UE can decode the Physical BroadcastChannel PBCH and read the Master Information Block MIB

The PBCH is in the first four OFDM symbols of the second time

slot of the first subframe. Thats every 40 ms, so the MIB istransmitted every fourth radio frame.

The PBCH is scrambled by a sequence based on the cells cell IDN. Its carried by the 72 reserved subcarriers, QPSK-modulated

The MIB carries the most essential s stem information:

transmission bandwidth i.e., # of available resource blocks.

configuration ofPhysical HARQ Indicator Channel (PHICH)

The number of transmission antennas used on the eNB side This is derived from the sequence in which one of the CRC

.


Types of System Information Blocks


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S Cell Selection and Reselection criteria


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After finding a cell, the UE may or may not be permitted to use it,based on various si nal ualit criteria broadcastb the eNB.

Here are two procedures for cell qualification:

In the initial cell selection procedure, no knowledge about RF- .

In that case the UE scans the supported E-UTRAfrequency bands to find a suitable cell. Only the cell with

the stron est si nal er carrier will be selected b the UE.The second procedure relies on information about carrier

frequencies and optionally cell parameters received and storedfrom previously-detected cells.

If no suitable cell is found using the stored information theUE starts with the initial cell selection procedure.

S is the criterion defined to decide if the cell is still suitable . Thiscriterion is fulfilled when the cell selection receive level is Srxlev >0. Srxlev is computed based on the following Equation:


S Cell Selection and Reselection criteria


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Srxlev = Qrxlevmeas (Qrxlevmin + Qrxlevminoffset) PcompensationWhere Pcompensation = max (PEMAX PUMAX, 0)

All in db

Qrxlevmeas is the UE-measured receive level value for this cell, i.e.the Reference Signal Received Power (RSRP

Qrxlevmin is the minimum required receive level in this cell, in dBm.

Qrxlevminoffset is an offset to Qrxlevmin that is only taken into

account as a result of a periodic search for a higher priority PLMNwhile camped normally in a Visitor PLMN (VPLMN).

PCompensation is a maximum function. PEMAX is maximum powerallowed for a UE in this cell. PUMAX is maximum for power class

A UE may discover cells from different network operators.

First the UE will look for the strongest cell per carrier,

Then the PLMN identit from the SIB T e 1 to see if suitable,

Then it will compute the S criterion and decide if suitable


Cell Search Measurements


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An LTE UE measures reference signal RSRP (Reference Signal ReceivedPower) and RSRQ (Reference Signal Received Quality).

RSRP is a RSSI type of measurement. It measures the average received

power over the resource elements that carry cell-specific reference signalswithin certain frequency bandwidth.

s a ype o measuremen an n ca es e qua y o ereceived reference signal, defined as (N*RSRP)/(E-UTRA Carrier RSSI),

N ensures the nominator and denominator are measured over the

same fre uenc bandwidth; carrier RSSI measures the average total received power observed

only in OFDM symbols containing reference symbols for antenna port0 in the measurement bandwidth over N resource blocks. The total

.

RSRP is applicable in both RRC_idle and RRC_connected modes, whileRSRQ is only applicable in RRC_connected mode.

In the rocedure of cell selection and cell reselection in idle mode RSRPis used. In the procedure of handover, the LTE specification provides theflexibility of using RSRP, RSRQ, or both.


Physical Layer Measurements Definition


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The physical layer measurements to support mobility are classifiedas:

within E-UTRAN (intra-frequency, inter-frequency);

between E-UTRAN and GERAN/UTRAN (inter-RAT);

- -system mobility).

For measurements within E-UTRAN at least two basic UE

Reference symbol received power (RSRP);

E-UTRA carrier received signal strength indicator (RSSI).



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Idle Mode and PagingIdle Mode and Paging


Tracking Area Update


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Consider a UE in idle state (RRC idle and ECM idle)

This UE is free to travel and only do a Tracking Area Update

If data arrives for the UE, the system must page the UEthroughout the TA where it last registered

,location and re-establishing its connection to the network

When a mobile is switched on it always has at least a

A UE is in ECM-IDLE state when no NAS signaling connectionexists between the UE and the network

There is no UE context, no S1_MME and no S1_U connectionThe UE will perform the TA procedure when the TAI in the

The UE will then be in ECM-CONNECTED state again


Cell Reselection (Idle Mode Handover)


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The mobile is in power-conservation mode

,it detects entry into a new Tracking Area

UE-terminated calls are paged in the UEs last reported TA

Static non-overlapping TAs were used in earlier technologies

New techniques reduce ping-ponging, distribute TA updateoa more eveny across ce s, an re uce aggrega eupdate load

Mechanisms include overlapping TAs, multiple TAs, and-


UE UL Transmission in Idle State


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In Idle State, a UE must use the Random Access Procedure to bereco nized b the eNB without causin interference to other UEs

There are four variations in Random Access Procedure types

The parameters of each RAP type are designed to ensure that the ,

Existing noise and interference levels,

UE apparent timing as received at the UE

ee e re ransmss on co s ons occur


Contention-BasedRandom Access Procedures (1)


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The four steps of the contention based random accessprocedures are:

1 Random Access Preamble on RACH in u link:

There are two possible groups defined and one isoptional. If both groups are configured the size of

message 3 and the pathloss are used to determine whichgroup a preamble is selected from. The group to which a

message 3 and the radio conditions at the UE. Thepreamble group information along with the necessarythresholds are broadcast on system information.

2) Random Access Response generated by MAC on DL-SCH:

Semi-synchronous (within a flexible window of which thesize is one or more TTI) with message 1;

No HARQ;

Addressed to RA-RNTI on PDCCH;

Conveys at least RA-preamble identifier, TimingAlignment information, initial UL grant and assignment of

Temporary C-RNTI (which may or may not be madepermanent upon Contention Resolution);

Intended for a variable number of UEs in one DL-SCHmessage.




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3) First scheduled UL transmission on UL-SCH:

Uses HARQ;

conveyed in step 2 and is at least 80 bits.

For initial access:

Conveys the RRC Connection Request generated bythe RRC la er and transmitted via CCCH;

Conveys at least NAS UE identifier, no NAS message;

RLC TM: no segmentation;

For RRC Connection Re-establishment procedure:

-generated by RRC layer and transmitted via CCCH;

RLC TM: no segmentation;

Does not contain any NAS message.

After handover in the tar etcell:

Conveys the ciphered and integrity protected RRC

Handover Confirm generated by the RRC layer andtransmitted via DCCH;

Conveys the C-RNTI of the UE (which was allocated viae an over omman ;

Includes an uplink Buffer Status Report when possible.




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For other events:

Conveys at least the C-RNTI of the UE.

4) Contention Resolution on DL:

Early contention resolution shall be used i.e. eNB doesnot wait for NAS reply before resolving contention

Not synchronised with message 3; HARQ is supported;

Addressed to:

The Temporary C-RNTI on PDCCH for initialaccess and after radio link failure;

The C-RNTI on PDCCH for UE inRRC_CONNECTED;

HARQ feedback is transmitted only by the UE whichdetects its own UE identity, as provided in message 3,echoed in the Contention Resolution message;

-establishment procedure, no segmentation is used

(RLC-TM). The Temporary C-RNTI is promoted to C-RNTI for a UE

which detects RA success and does not already have a; s roppe y o ers. w c e ec s

success and already has a C-RNTI, resumes using its C-RNTI.


Non-Contention-BasedRandom Access Procedure


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Non-contention based random access procedures are:

0) Random Access Preamble assignment viadedicated signaling in DL:

eNB assigns UE a non-contention RandomAccess Preamble

signaled via:

.

PDCCH in case of DL data arrival or positioning.

1) Random Access Preamble on RACH in uplink:

UE transmits the assigned non-contention RAP.

2) Random Access Response on DL-SCH:

Semi-synchronous (within a flexible window); NoHARQ, Sent to RA-RNTI on PDCCH;

Timing Alignment info, initial UL grant for HO Timing Alignment info. for DL data arrival;

RA-preamble identifier.

Sent to one or more UEs in one DL-SCH msg.



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UE Attach to the NetworkUE Attach to the Network


7. UE Attach to the Network(Registration Procedure)


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7-1 Suitable MME, SGW and PGW selection

- ,

7-3 Default Bearer setup

7-3 Initial Attach process: A comprehensive Message-flow



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Connected Mode and UE StatesConnected Mode and UE States


8. Connected Mode and UE States


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8-1 RRC connection setup

-

8-3 QoS parameters and TFTs

8-4 Connected Mode: Incoming and outgoing call flows (end-to-


RRC Connection


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RRC Connection Setup procedure triggered by a request from UE NAS layer

UE origination, NAS signaling, or Paging Response

connec on s es a s e e ween an e an s se up

If overloaded, eNodeB sets access class barring parameters in SRB1 If UE has valid S-TMSI, UE includes it in RRC connection request message;

,

After successful RRC connection procedure, UE is in RRC-Connected state


QoS Parameters and TFTs (1)

A T ffi Fl T l t (TFT) i ll th k t filt i t d ith EPS b


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A Traffic Flow Template (TFT) is all the packet filters associated with an EPS bearer.

A packet filter may be associated with a protocol.

.

EBI+Packet filter ID gives us a "unique" packet filter Identifier. The following is the

TFT for FTP protocol.



Bearer level QoS is associated with a bearer and all traffic mapped


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Bearer level QoS is associated with a bearer and all traffic mappedto that will receive same bearer level packet forwarding treatment.

QoS parameter values of the default bearer are assigned by thenetwork based on the subscription data received from HSS.

In LTE the decision to establish or modify a dedicated bearer istaken by EPC and bearer level QoS parameters are assigned by. ese va ues are no mo e y u are orwar e

transparently to EUTRAN. However MME may reject theestablishment of dedicated bearer if there is any discrepancy.




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A default bearer may or may not be associated with a TFT. But adedicated bearer is alwa s associated with TFT.

So we have bearers, the QoS values for them and TFT which

indicate what type of application should run over them. Thisdefines the LTE QoS. We have Uplink TFT and Downlink TFTwhich are used by UE and PDN

The UE routes uplink packets to the different EPS bearers basedon uplink packet filters in the TFT's assigned to those EPS

earers. We have evaluation packet precedence index in packet filter

which is used by UE to search for a match (to map the.

Once the UE finds a match it uses that particular packet filter totransmit the data.

no TFT has been assigned.



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Network Performance EvaluationNetwork Performance Evaluation


9. Network Performance Evaluationand Optimization Issues


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9-1 Channel Quality reporting

- -

9-3 QoS revisited

9-4 Throughput calculations and optimization

9-5 Voice-over-IP support and voice capacity projections


Limiting measurement load at UE


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Introduction of E-UTRA implies co-existence of various UEca abilities. Each UE ma su ortdifferentcombinations of RATse.g., E-UTRA, UTRA, GSM, and non-3GPP RATs, and differentcombinations of frequency bands, e.g., 800 MHz, 1.7 GHz, 2 GHZ,etc. Despite such heterogeneous environment, the measurement

.and the associated control load:

E-UTRAN can configure the RATs to be measured by UE;

e num er o measuremen cr era even an pero creporting criteria) should be limited (as in TS 25.133 subclause8.3.2 [7]);

-measurement control, to prevent unnecessary waking up of themeasurement entity;

possible.


Measurement Limitations of UE


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LTE UE Field Measurements and KPIs


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RF Key Performance Indicators

Reference Signal Received

Power

Received Signal StrengthIndicator

Reference Signal Receive

Quality. Defined as N ,

the number of resourceblocks across which RSSIwas measured



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Mobility, Interoperability andMobility, Interoperability and


Introduction to Handover


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With the fast-changing mobile landscape and convergence in allas ects of telecommunications seamless handoveris im ortantfor any technology to succeed.

Operators and consumers both benefit from seamless handover interms of cost effectiveness, enhanced features, locationindependence and ease of use, not only within a Long TermEvolution (LTE) network but also between networks includingUMTS, GSM and CDMA.

n s c ap er we re y ouc upon e proce ures execu e ythe user equipment (UE) and the various network elements toprovide the handover services requested by the UE. We coverIntra-LTE and LTE to/from UMTS handovers.


Handover Procedures - Objectives

Obj ti f H d P d


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Objectives of Handover Procedures

,a handover, but during the handover as well.

Handover must not unduly drain the UE battery power. . .,

latency).

Seamless handoff is required to 3G / 2G / CDMA technology.

ere are wo ways a an o can e ec e : Network Evaluated: the network makes the handover decision

Mobile Evaluated: the UE makes the handoff decision andn orms e ne wor a ou .

In this instance, the final decision will be made by thenetwork based upon on the Radio Resource Management.


Handover Types

In 3G and LTE networks, a hybrid approach is used to decide on


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y ppthe handover.

e w ass s n e an o ec s on y measurng eneighboring cells and reporting the measurements to the

network

cell/node.

The parameters to measure and the thresholds for reporting

. In LTE there are three types of handovers:

Intra-LTE: Handover happens within the current LTE nodes- -

Inter-LTE: Handover happens toward the other LTE nodes(inter-MME and Inter-SGW)

-networks, for example GSM/UMTS and UMTS



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Flow Examples

Intra-LTE (Intra-MME / SGW)

Handover

Intra-LTE (Intra-MME / SGW)

HandoverUsing the X2 InterfaceUsing the X2 Interface


Case I. Intra-LTE (Intra-MME / SGW) HandoverUsing the X2 Interface

Consider Intra LTE handovers with X2AP signaling and S1AP


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Consider Intra-LTE handovers with X2AP signaling and S1APsi nalin first then Inte -RAT handovers in LTE i.e. handoverbetween LTE and UMTS).

Intra-LTE (Intra-MME / SGW) Handover Using the X2 Interface:

(S-eNB) to a target eNodeB (T-eNB) using the X2 interface whenthe Mobility Management Entity (MME) and Serving Gateway(SGW) are unchanged. It is possible only if direct connectivity

exs s e ween e source an arge e o e s w einterface.

The X2 handover procedure is performed without Evolved Packet, . .

exchanged between the S-eNB and T-eNB. The release of theresources at the source side during the handover completionphase is triggered by the T-eNB. The message flow is shown inFigure 1 followed by the description




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The Data call is already established between the UE, S-eNB and

network elements..




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The Network sends a MEASUREMENT CONTROL REQ message.

The UE is instructed to send measurement report when thresholdsare met.



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Optionally S-eNB issues RESOURCE STATUS REQUESTmessage to determine the load on T-eNB.

Based on received RESOURCE STATUS RESPONSE, the S-eNBcan decide whether to continue the handover procedure using theX2 interface.




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The S-eNB issues a HANDOVER REQUEST message to the T-eNB with UE and RB contexts to prepare handover at the target.




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T-eNB checks availability, reserves resources and sends back

message nc u ng atransparent container for the UE as an RRC message to performthe handover.

- - ,identifiers for the selected security algorithms, and may include a

dedicated RACH preamble and possibly some other parameters(i.e., access parameters, SIBs, etc.).




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The S-eNB generates the RRC message to perform the handover,

i.e, RRCCONNECTION RECONFIGURATION message includingthe mobility Control Information. The S-eNB performs thenecessary integrity protection and ciphering of the message and

.




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-T-eNB to convey the PDCP and HFN status of the E-RABs.




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The S-eNB starts forwarding the downlink data packets to the T-eNB for all the data bearers (which are being established in the T-eNB during the HANDOVER REQ message processing).




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In the meantime, the UE tries to access the T-eNB cell using thenon-contention-based Random Access Procedure.




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If it succeeds in accessing the target cell, it sends the RRC- .



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The MME sends a MODIFY BEARER REQUEST (eNodeBa ress an s or own n user pane or e accep ebearers) message to the SGW. If the PDN GW requested the UEslocation info, the MME also includes the User Location InformationIE in this messa e.




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to the S-eNB and then can release any user plane / TNL resources

toward the S-eNB.




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15. T e MME respon s to t e T-eNB wt a PATH SWITCH REQ

ACK message to notify the completion of the handover.




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User data packets now flow between the SGW and the UE.




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The T-eNB now requests the S-eNB to release the resources


. ,handover procedure is complete.


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Flow Examples

Intra-LTE (Intra-MME / SGW)Handover

Intra-LTE (Intra-MME / SGW)Handover

Using the S1 InterfaceUsing the S1 Interface


Case II. Intra-LTE (Intra-MME / SGW) HandoverUsing the S1 Interface

An S1-based handover procedure is used when the X2-basedhandover cannot be used


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no X2 connectivity to the target eNodeB;

by an error indication from the T-eNB after an unsuccessful X2-based handover

by dynamic information learned by the S-eNB using theSTATUS TRANSFER procedure.

The S-eNB initiates the handover by sending a Handover required

message over the S1-MME reference point. The EPC does notchange the decisions taken by the S-eNB.

The availability of a direct forwarding path is determined in the S-e ase on e connec v y w e -e an n ca eto the source MME.

If a direct forwarding path is not available, indirect forwarding. -

eNB to determine whether to apply indirect forwarding or not.



Based on the MEASUREMENT REPORT from the UE, the S-eNBdecides to Handover the UE to another eNodeB T-eNB . The


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dec des o a do e e U o a o e e ode e ehandover procedure in this section is very similar to that in theprevious section (Intra-LTE Handover Using the X2 Interface),

except the involvement of the MME in relaying the handover- - .

There are two differences here:

No need for the PATH SWITCH Procedure between the T-eNB

an , as s aware o e an over.The SGW is involved in the DL data forwarding if there is no

direct forwarding path available between the S-eNB and T-.

Once the Handover is complete, the MME clears the logical S1connection with the S-eNB by initiating the UE CONTEXT




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The UE is sending and receiving user data on both the uplink anddownlink.




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The S-eNB sends an RRC: Measurement Control message to the

UE, instructing it to take certain measurements at specific intervalsan to report t e resuts w en spec c cr tera are met.

The UE sets to work taking the requested measurements andperforming comparisons against the specified criteria.




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The UE notices that measurements have satisfied the specified. :

Serving eNB.

The handover procedure in this section is very similar to that in the- ,

except the involvement of the MME in relaying the handoversignaling between the S-eNB and T-eNB.




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The serving eNB sends a Handover Required message to theMME




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sen s an over eques o arge e



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The MME sends a Handover Command to the serving eNB




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The Serving eNB sends an RRC Connection ReconfigurationRequest to the UE




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The Serving eNB sends an eNB Status Transfer message to theMME




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SGW by GTP protocol




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The MME sends an MME Status Transfer message to the TargeteNB




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The UE performs the Non-Contention RACH Process on theTarget eNB




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The SGW sends Forward User Data to the Target eNB




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The UE sends an RRC Connection Reconfiguration Completemessage to the Target eNB




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The Target eNB sends a Handover Notify message to the MME




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The MME sends a Modify Bearer Request message to the SGW




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User ata pac ets now ow etween t e UE an t e SGW.




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The T-eNB sends an S1AP UE Context Release Command to the

the S-eNB.




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The S-eNB confirms the requested UE context release by sending


.

Flow Examples


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Flow Examples

Inter-MME Handover (Intra-SGW)Inter-MME Handover (Intra-SGW)

no c ange n a ewayno c ange n a eway


Case III. Inter-MME Handover (Intra-SGW)(no change in Gateway)

In an inter-MME handover, two MMEs are involved in thehandover the source MME S-MME and tar etMME T-MME .

The S-MME controls the S-eNB and the T-MME controls the T-eNB; both MMEs are connected to the same SGW This handover


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eNB; both MMEs are connected to the same SGW. This handover

is triggered when the UE moves from one MME area to another.


Case III. Inter-MME Handover (Intra-SGW)

The UE is sending and receiving user data on both the uplink andd li k


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downlink.




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The Serving eNB sends a Handover Request to the Serving MME




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The Serving MME sends a Forward Relocation Request to the




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he Tar et MME sends a Handover Re uest to the Tar et eNB




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The Target eNB sends a Handover Request Acknowledgment tothe Target MME




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The Target MME sends a Forward Relocation Response to theServing MME




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The Serving MME sends a Handover Command to the Serving




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he Servin eNB sends a RRC Connection Reconfi uration

Request to the UE




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e ervng e sen s an e a us rans er o e ervngMME, which forwards it to the Target MME




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The Target MME sends an eNB Status Transfer to the Target eNB




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The Serving eNB sends Forward User data to the SGW by GTP




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e UE per orms t e Non-Contenton RACH proce ure on t eTarget eNB




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The UE sends RRC Connection Reconfiguration Complete to the

Target eNB




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The Target eNB sends a Handover Notify message to the Target

MME




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The Target MME sends a Modify Bearer Request to the SGW byGTP




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The SGW sends a Modify Bearer Response to the Target MME by




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The Target MME sends a Forward Relocation Complete message


o e ervng



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Acknowledgment to the Target MME



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User Packets now flow directly from UE to SGW in both directions



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The S-MME sends a UE Context Release Command to S-eNB



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The S-eNB responds with a UE Context Release Complete

Flow Examples


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Inter-MME / SGW HandoverInter-MME / SGW Handover

s ng e n er aces ng e n er ace


Case IV. Inter-MME / SGW HandoverUsing the S1 Interface

Inter-MME / SGW Handover Using the S1 Interface

being the Source and Target eNodeBs are served by differentMME / SGW nodes. Figure 4 depicts the procedures and is

f ll d b h l i


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followed by the explanation.


Case IV. Inter-MME / SGW HandoverUsing the S1 Interface

1 Based on the MEASUREMENT REPORT from the UE, the S-eNBdecides to handover the UE to another eNodeB (T-eNB). The procedure islike earlier ones except for involvement of two SGWs (S-SGW and T-SGW) to transfer data packets during handover.

2. After receiving GTP: FORWARD RELOCATION REQ from S-MME, T-


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-,using GTP: CREATE SESSION REQ message.

3. After creation of requested bearers, T-SGW responds back to MMEwith a GTP: CREATE SESSION RESPONSE message.

4. From here on, message flow is very similar to Inter-MME, Intra- SGWhandover except for these differences:

While processing the S1 HANDOVER NOTIFY message from the T-- - -,

SGW using GTP: MODIFY BEARER REQ.

After updating T-eNB information in the bearers T-SGW sends GTP:MODIFY BEARER RESPONSE message to the T-MME.

When Handover Complete, S-MME releases bearer resources with the S-SGW for this UE by GTP: DELETE SESSION procedure


Case IV. Inter-MME / SGW Handover

The UE is sending and receiving user data on both the uplink anddownlink.


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The S-eNB sends RRC Measurement Procedures to the UE

The UE erforms the re uested measurements


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The UE erforms the re uested measurementsThe S-eNB receives information when specified thresholds are

exceeded, triggering need for a handover



The Serving eNB sends a Handover Request to the serving MME


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The serving MME sends a Forward Relocation Request to the


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he Tar et MME sends a Create Session Re uest to the Tar et


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he Tar et MME sends a Create Session Re uest to the Tar etSGW by GTP



Th T t SGW d C t S i R t t th T t


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The Target SGW sends a Create Session Request to the TargetMME by GTP




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The Target MME sends a Handover Request to the Target eNB




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The Target eNB sends a handover Request Acknowledgment tothe Target MME




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The Target MME sends a Forward Relocation Request to theServing MME using GTP




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eNB




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e ervng e sen s an onnec on econ gura on

Request to the UE




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The Serving eNB sends an eNB Status Transfer to the TargetMME




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The Target MME sends an eNB Status Transfer to the Target eNB




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The Serving eNB sends Forward User Data to the Target eNB




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-Target eNB




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The UE sends an RRC Connection Reconfiguration Completemessage to the Target eNB




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The Target eNB sends a Handover Notify message to the TargetMME




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The Target MME sends a Modify Bearer Request to the TargetSGW using GTP




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The Target SGW sends a Modify Bearer Response to the TargetMME by GTP




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The Target MME sends a Forward Relocation Complete message




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The Serving MME sends a UE Context Release Command to theervng e




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acknowledgment to

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LTE System Structure and Signalling

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