INBULLETS I

215

LONG TERM EVOLIJTION (LTE)

23.L RRC CONNECTION ESTABLISHMENTRRC conncction establishment is used 1tr make the transilion from RRC ldle mode to RRC Connecled mode. UE mustmake the lransition 1() RRC Connecled mode before transfening any applicalion dat4 or oompieting any signallingprocedures

The RRC conncction cstablishment procedure is always initiatod by thc UE but ca.r be- tliggcrcd bf either the UE or the

-19!_gork. For example, the Ulr triggers RRC conncction establishment ifthe end-user starts an application to browse theintemct, or to send an email. SimiJarly" the iJE triggers RI{C connection establishment ilthe IJE movcs into a nerv'fracking Area and has 10 completc the-l'racking Area Update signalling procedure. 'l'hc nctwork triggers thc RRCconnection cstabljshment procedure by sending a Paging messagc. This could be used to allow the delivcry ofan incomingSMS or notillcation of an incoming voice call

RRC corLnection eslablishmcnt for LTE is rclalively simple compared to RRC connection cstablishmenl for UM'I-S. TheIJM l'S procedurc rcquires NBAP and ALCAP signalling across the Iub interlace betwecn the Node B and RNC. Thcsesignaliing protocols are used to setup a radio link and new transport connection. I he flat network architccture for LIEremoves the requirement for liesc signalling procedures

In the casc of LTII, the initial Non-Access Stratum (NAS) message is transferred as part ofthe RRC conncctionestablishmcnt proccdure. In the case of LIMTS, thc initial NAS mcssage is transferrcd after the RRC conncctioncstablishment procedure. Thc approach uscd by L l'E hclps to rcduce connection establishment delay

RRC conncction establishment configures Signalling Radio Bearer (SRB) I and allows subsequent signalling 10 use theDedicated Control Channel (DCCIJ) ralher than the Common Conlrol Channcl (CCCIJ) used by SRB 0

The signalling 1br RRC connection establishmcnl is shown in Figure 107. the entirc procedurc is compleled using oniyRltC signalling. A 3-way handshakc is used 10 move thc IJE into RRC connected node

eNode B

liigure 107 Signalling for RRC connection establishmcnt

The RRC Conncction Request message is sent as part oflhc Random Access procedure. It con'esponds to thc jnitial Laycr3 message shown in Figure 84 (section 2l.l). It is transferred using SRB 0 on the Common Control Channcl (CCCH)because neither SRB 1 nor a Dedicated Control Channel (l)CCl l) havc bcan setup at this point. 'Ihe uplink Resource Blockallocation 1br the R.RC Conneclion Rcquest message is signalled within the l{andom Access l{esponsc mossage

The content ofthc RRC Connection Request message is shown in l'ablc 130. It includcs a UE identity and ancstablishmcnt cause. There is no scope for the LIE to report any measurcments wilhin the RRC Conncclion Requcstmessage. The [,MTS version ofthc RRC Connection Requcst messagc allows thc UD to reporl CPICH measurementswhich can subsequently be used lor downlink open loop power conhol oalculations

The LJE identit), is signailed using tho SAE Temporary Mobile Subscriber ldentity (S-TMSI) ifthc LIIJ is rcgistered u ith .^thc l'racking Area 1o whioh thc cuncnl ccll belongs. Othcrwise, the UE selects a rirndom numbcr in thc range from l)to 2o'- I to represent the IJH identity. ]'he S-|MSI is described in scction 26.3.3

UEsi

Er

I

&RRC Connection Request / SRB 0 / CCCH / UL-SCH / PUSCH

RRC Connection Setup / SRB 0 / CCCH / DL,SCH / PDSCH

/SRB 1 / DCCH / UL.SCH / PUSCH

216

IN BULLETS

Trblc 130 - Content of RRC Connection Request mes$age

l'he eslablishnenl causc wilhin thc RRC.Connection Request message is dctermined by thc Non-Acccss Straturn (NAS)procedure for which thc connection is being cstablished. lhc relationship bctween eslatiishmenr causc and NAS proccjureis specified by 3 GPP 'f S 24.3 01 . lh is relationship is presentcd in I'able l 3 L ln all caies. ihc RRC establ ishrn ent causc issct 1(] 'll.igh Jtioi ty A qr,gss' if thc UE use s Acce ss class (AC) r I to I 5. The I ist of establishment causes is significantlyshorter thlur the list used by UMTS

Informarior) lilem€nts

UE Idenlily cltotcEs-'r'Msl

Random Value

iistablishmenl Cause CiIOICE

Em€rgcncy

High Priority Acccss

Mobile Terminating Access

Mobile Originating Data

NAS l,rocedure RRC llstablishment Cause

Attach Mobile Originating SignaltingDctach

Tracking Area Updalc

Sen ic,l] Requcst Uscr plane radio resources request Mobile Originating Data

Uplink signalling resourc€s request

Paging.csponse for PS core n€twork domain Mobilc Terminating Access

Extendcd Serviolj Requcst

i '. I.l , 'r.;.t t..1

Mobile origiDali4g CS fallbaok Mobile Originating Data

Mobil€ terminating CS fallback Mobile Tgrmjnating Access

Mobile originatjng CS fallback emergency cali hmcrgency

,.1t

Tablc l3l - Relationship betwcen higher layer establishment cause and RRC establishment caxse

The I JE starls thc T300 timer aller transmitting the RRC Conncction Roquest messagc. l'he value of T300 is broadcastwjthin SIB 2 [.lM'l'S uscs T300 in,combination with N300 to manage re-transmissions of the RRC Connection l{equestmessage. l-Tll does not have an N300 paramcter and the IIRC Conncction Request message is sent only once p€reslablishment procedure. l-TE uses the T300 timer 1o define how long the UE waits for a iesponse to the I{RC ConnectionRcquest lnessage. 1 hc cstab)ishment procedure fails if T300 cxpires beforc receiving an RRC Connectjon Sctup messagc.The procedure aiso fails iflhe UE completes a cell re-selectjon prior lo rcceiving the RRC Connection Setup rnessage

Random access contcntion can occur afler scnding the RRC Conncction Request message. Seotion 2l .l explains thatconlention occurs when multjple liE select the same subframe and preamble scquence for pRACH transmtsston.contention requircs the UF to repeat lraosmission ofthc PRACII preamble and ihe subsequent RRC Connection Requeslmcssage. This increases the delay associated with connection €stabjjshment but docs not cause the ovcrall procedure to lailunlcss the maximum number ofprcamble lransmissions has br:en reached

Assuming that.andom access contentio-n does not occur, the UII proceeds to wait for an RRC Conneclion Setup mcssagefrom the eNodc B.'l-he UE has successfully compieted the random access procedurc so has been allocated a C-RNII(signalied within thc random aocess response mcssage). l'he tJl.l monilors the PDCCIJ for a downljni allocation addrcsscdto i1s (l-RNll lhc PDCCII sp(jcifies the set ofPDSCII Resource Blocks used to transfer the ]lllc Conncction Setupmessagc. The IIRC Connection Sctup message is transferred using SRB 0 on thc CCCH

Thc RIIC Conneclion Setup messagc conlains configuralion information for,sll] | 'fhis allows subsequenl signaljing touse the DCCH logical channel SRB 2 is always configurcd after security activation st, the RRC Connectjon selupmessage does not include any inlbrmation regarding SRB 2. l he cNodc B can inslruct thc UL to appiy a defaultconfiguration for SRB 1, or it can instruct thc IJE to apply a specific configuration.

LONG TERM EVOI,UTION (I-TE)

The delault configuralion for SRB I is pr€scnlcd in l able 132. This dcfault configuration has been specified by 3GPPwithin TS 36.331. tJsing the dclauil configuralion heips to reduce thc signalling requirement. The defauil oonfiguntion lorSIiB 2 is also presented in Table 132 lbr information. SRB 2 has a lower prior;ry than SRB l- i.e. a value of3 represents a

lowcr priority than a valuc of I . Both SRll I and 2 always use acknowledged modc Rl.C

SRB I SRB 2

RLCConfiguration

Uplink Poll Rctransmission I imer 45

Poll PDU Infinity Infinitv

Poll B)4o lnfinity Infinity

Max Rctransmission l'hreshold 4 4

Downiink R€-ordering Timer 35 35

Status Prohibit Tim€r 0 0

Logical ChannelConfiguration

Priority 3

Prioritised Bit Rale lnfinity lnfinity

Bucket Size Duration N/A N/A

Logical Channel Group 0 0

'l'able 132 - Default configurations for SRB I and SRB 2

'I he RRC Connection Setup mcssage can also define configuration information for the PDSCH, I'tJCCH and Pt.lSCHphysical channels. I1 can also include informalion regarding uplinJ< power control, CQI reporting, the Sounding Relcrence

Signal, antenna configuration and scheduling requests

Upon recelving ar RllC Conncction Setup message, the UE stops the T300 timer and makes the transilion 10 Rli.CConnected mode. The UE thcn proceeds to complete the procedure by sending ar RRC Connectjon Setup Completcmessage.'lhe conlent ofthc RRC Connection Setup Complete message is shown in'lable 133

Information Elements

RRC Transaction ldenti{ier (01o 3)

Selecicd PLMN ldcnfiry (1 to 6)

Registered MMU PLI\4.1 ldontity

MMEG]

MMEC

l)edicated NdS J nformation

'fable 133 - Confcnt ofRRC Connection Setup Complete message

Thc l'ransaction Idcntifier, combined with the message type, identifics thc RRC procedure with thc UE

Thc Sclected PLMN Identity defines a pointcr to a PLMN listed within SIB l. i.e. UE. sclect thc PLMN to which they wantto connect when a cell belongs to more than a single PLMN

The llegistered MME inlormaljon is optional, and is included when available. It becomes available after a UII has

regisrered *ith an MME. Thc MMll is identilicd by its Globaily Unique MME ldentity (Gt.lMMUl) which is aconcatcnarion of the PLMN idenrity, MME Group Idcnrity (MMDGI) and MME Codc (MMEC). Thc MMEC identifies the

MME u,ithin its group

The llll also includes its initial Non-n ccess Stratum (NAS) mcssage wilhin the RRC Connection Setup Complcte message.

NAS messagcs are specilied within 3GPP l S 24.301. As jndicatcd within Table l3l, thc NAS message could be an

Attach, Detach, 'l'racking Arca Update, Scrvice Request or Exlended Service Request mcssage

'l he cNodc B cxtracts thc NAS message from the IIRC Connection Sctup Complete message and forwards il to an MMIlusing thc Sl Application Protocol (Sl -AP) Initial UE Message. Forwarding this message does not form pad ofthe RRCcstablishment procedurc but is described within this soction for complctcncss

The contenl ofthe S1-AP Initial UE Mcssage is shown in Tablc 134. The eNodc B scnds this mcssage to the approprialeMMII based upon i1s NAS Node Selection Funclion (NNSF). In thc case of a Service Request, the S- I MSI includod with jn

218

$lI1'

I

&

Figurc 108 - Signalling for rejccted RRC connection establishmcnt

* The contenl ofthe RRC connection Rciect message is presented in l-ablc 135. The message only includes a wait time.This is in contrast to the equivalenl UMTS messagc which also jncludcs a rejection cause- although the UMTS rejectioncausc can onJy be dcfincd as congestion or unspecified The UM I'S messagc can also include redireclion information todirect the ULI towards another RF carrier, or Radio Access 'l'echnology (RA'l')

lJpon recciving an IIRCI Connecljon Re.iecl mcssage, the UE starts the T302 limer with its value set equal to the wait 1ime.Access Class barring for mobilc originating caiJs, mobiic originating signalling and mobile terminating access is applieduntil T302 expircs, i.e. the tJE is no1 allo\.vcd to send another RRC Conncction Roquest for thosc conniction types, and tothe same cell, until T302 expires. '1302 is stopped ifthc tJE completes ccll reselcction. In that casc. the UIi is p;rmjlted toscnd an I{RC Connection I{eques110 the ncw cell

ln conlrast 10 UM I S. L fE rcquires thr; higher iayers to initiate a new connectjon estabiishmcnl proccdure after the UErcccives an RRC Conneclion l{eject messagc. UMI S allows the llRC Conneclion Requcst message to bc repeated fromthc RI{C laycr, based upon 1he value ofN300

RRC Conneclron Request / SRB 0 / CCCH / UL,SCH / PUSCH

IN BULLET

the RRC Connection Requcst is used to identiry the appropriate MME (S- I MSI jncludes the MMEC). In the case ol anAltach or Tracking Area ljpdalc" the cNodc B uses thc GUMMEI included within the I{RC Connection Sctup Completemessage. Thc eNode B is lree 10 selcct an MME u,hen the UE does nol have an S-TMSI nor GUMMlll

Information lllements Pres€flc€

€Node B UE S l-AP ldentity Mandatory

NAS PDIJ Mardatory'lracking Area Identity (TAI) Mandatory

E-tJ I'RAN Ccll Global Jdenriry (CGI) Mandalorv

S.TMSI Optional

CSG Identity Optional

RRC Dstablishment Cause Mandalory

Globally Unique MME ld€ntity (cUMMEI) Optional

Tebt€ t34 - Content ofSl ApplicatioD protocot (Sl_Ap) Initial Utr] Message

Thc cNode B allocatcs thc cNode B UE Sl-A? Identity to allow the eNode B 10 identifr the tJE wilhin SI signallingprocedures. l'hc MME UE Sl-AP Identity (not included within ths Initial UE Message) allows the MME ro idendtthcUE within Sl signalling procedures

Figure 108 illustrates the signalling associated with the RRC connoction cstablishment proccdure when the cNode Brejects thc RRC Connection Requesl. The reject mcssage is rctumed to thc UE using SRB 0 on ihe CCCI I logical channei.l hc eNode B may reject the connection eslablishment request as a rcsuh ofcongestion

eNode B

lnformation Elements

Wail lime (0 to 16 seconds)

Table 135 - Content of RRC Connection Reiect messag€

UE

{p

RRC Connection Reject / SRB 0 / CCCH / Dt -SCH / PDSCH

I,ONG TERM EVOLUTION (I,TE)

23.2 ATTACH AND DE,FAULT BEARER ESTABLISHMENT

* Thc attach procedure is uscd to registcr with the Evolled I'acket (lore (EPC). This allows thc subsequent uso ofpacketservices within the Evolved Packct System (llPS). ]'he IJD can also usc thc a11ach procedurc to regisler for non-EPS

services, e.g. thc speech service based upon CS faliback

* 'Ihc atlach procedure also involves establishing a default bearer betwccn the IJE and PDN Gateway. This provides always-

on corlnectiviry for thc UE. In addition, the attach procedurc can lrigger thc cslablishment of dcdicated bearers

* The signalling associated with thc a11ach and delault bearer establishment procedure is illustrated in Figurc 109. Somc

signalling messages are nested wilhin othcr messages, e.g. rhe PDN Connectivity Rcqucsl message is scnt within an Attach

Request message, which is sent within an RRC Conncclion Sotup Complete mcssage

MI\,4E

w'Serving

GatewaywPDN

Gateway

w@

RRC Connection Reconfiguration /

lnitial Context Setup Requesl /Attach Accept /

Activate Default EPS BearerContext Request

Create Session Response

Attach Accept /Aclivate Default EPS Bearer

Context Request

RRC Connection

Uplink lnforma|on Transfer /Atiach C.omplete /Activate Default EPS BearerConlextAccept

Uplink NAS Transport /Attach Complele /Activate Default EPS B€arerContext Accept

Figur€ 109 Signalling for the attach and default bearer establishmcnt procedur€

The atlach procedurc slarts with the RRC connectjon cstablishment proccdure which takes the UD from RRC ldlc mode to

RRC connected mode. Thc Altach Requcst messagc is included as the 'Dedicatcd NAS Information' within thc RRC Sctup

Complctc mcssage . Thc full contcnt of the RRC Selup Complete mcssage is presented in Table 1 33 within section 23. I .

The Atlach Roqucst is a Non-Access Stratum (NAS) message so its contcnt is spccified by 3GPP TS 24.301. This cortenlis presented in 'l able 136

The firs1 3 information elements within the Attach Rcquest messagc rcpresent the message hcadcr. fhe Protocol

Discriminator indicatcs that the subsequenl message is an EPS mobility managcmcnt message. lts vaiue is specified within3GPP 24.007. 'fhc Sccurjty Ileader Type jndicates whcther or not the Nn S message is integib, prolected aId ciphered.

The Atlach Request Messagc ldentity indicates that thc mcssage itself is an Attach Request

i Attach Reouest/I PDN Connec{ivity Request

Reconflguraton Complete

IN BULLETS

* The main contenl 01'the Attach Request mcssage stads with the EPS Anach 1'ype \\'hich can be configurcd with yaiues of'EPS Altach' or 'Combined EPS/IMSI Altach'. Thcsc valucs corrcspond to registering for only EPS packel scn,iccs, andregistering for both EI'S packet scrvices and non-EPS scrviocs. Thc mosl common non-EPS service is likely to be the CSspeech service

lnformalion Elements Presence

Protocol Discrtminatur Murulutory

Secatily Headel Type Mandalory

Attach ReqtEsl Messdge ldentity

EPS Attach Typc Mandatorv

NAS Key Set ldcntifier Mandalory

Oid CiUTI or IMSI Mafldatory

UE Nehvork Capability Mandatory

ESM Mcssagc Containcr Mandalory

Oid P-TMSI Signature Optional

Additional GUl l Optional

l,iut Visited Registcred TAl Optional

DRX Parameter Optional

MS Netrvork Capability C)ptional

Old Localion Are, Idenlificalion Optional

TMSI Status Optional

Mobile Station Classmark 2 Optional

Mobile Station Classmark 3 Ontjonal

Supported Codecs Optional

Table 136 - Cont€nl ofAttach Request message

* The NAS Key Se1 Identifier (KSI) is used 10 idcntily thc sccurity panmeters for aulhenlication. integrity proteclion andciphering. Security is not activated at this poinl in tjmc when scnding the Attach Request mcssage within an RRCConncction Sclup Complclc mcssage so the KSI information element is nol rclcvant

* Ihc Old Clobaliy Unique Tcmporary IJE ldenliry (GUl'l) or IMSI inlormation clement provides the nctwork with anidentity for thc UE. Tbe GUTI can be dcrived lrom a previous P--I MSI and the associated RAI iflhcy are avaiJable. TheIMSI is oniy sent if a GUTI js not available

* ['hc UL Nctwork Capability provides information regarding the encryption and integrily proteclion algorithms supporledby thc Ull. It also signals whethcr or no1 the lJIi has a prelerence for thc dcfauit alphabel over the Universal Chamcter Set(UCS) 2. Support lor Single Radio Vojce Call Continuity (SRVCC) is also indicaled

* The trSM Mcssage Container is used 10 include a PDN Connectivity Requost message. Ihe PI)N Connectivity Requesl is

another NAS mcssagc, so one NAS message is transf-erred within another NAS mcssage. The contenl olthc PI)NConnectivity R(-quest message is shown in Table 137

* The llrst 4 information elements within the PDN Conncctivity Requesl message represcnl the message header. 1heProlocol Djscriminalor;ndicates thal the subsequent rrcssagc is an DPS session managcment message

* The main content ofthe I']DN Connectivity Requcst message starts with the Requesl Type which can bc configurerJ wilhvalues of'lnilial Rcqucsl' or 'llandover'. The 'Handover' value can be used lor an incoming inter-system transition fromanother lechnology

* The PDN Type indicates the IP capability oflhc LIE. It can be signalled using valucs oflPv4, IPv6 or lPv4v6. The IPv4v6value indicates that thc Ull suppods the dual stack configuration which uscs both lPv4 and lPv6 address allocations

-ONG TERM EVOLUTiON (LTE)

Informatioo Elements

P rol oc o I D i scr im ifial o tEPS Bealer ldentllY

P / oce(lue Tr ansacli on I de n I i ry

Prescnce

Mandatory

Mandatory

Mandatorl,

PDN CotlnectNitj Reguest Message ldenliry

I{ccuest l"vPe

PDN Typc

ESM Information Transfer Flag

Acc€ss Point Name

Protocol Confi guration L)Ptlons

Mandatory

Mandalorv

Mandatory

()ptional

Optional

Oplional

'l'abl€ 137 Content ofPDN Connectivity Requcst messagc

iil';r:il,;i#;;;,i"q*;i.;;"".d";; rhisproccdirrcallowsthcuFro-rrovidcanApN":.t:l] ^__i:v,l]:::":]::ffi;Hil'"nffi'.';;T;ili;;;;;;ie""iii"s r""1'" ESM Inrormation *":.""'^'.ll:-":1i':-':.',1"J"":11.',t11: l3;l*iH"iffiil:;:ue"i*ril'n ir-.,iilNa3 rru,.'rpo.t-'nessases between thc MME and eNode B, and wirhin RRC

inlormaliion transler messages bet\Yeen the cNode B and IJB

TheoptionalF,sMlnlormationlransferFiagisincludcilif'thet]Ijhasprotoco]configuralionoptionsthalnecdtobefanstbrred securily protected. ot ,r the t.ll ,iishes to provide an Access Point Name (APN) for the PDN conneclion to be

establishcd during the attach prn""au-.;ii. optio.al Acccss point Namc infomralion clemcnt is always excludcd u'hen

the pDN Conncctivity Requcsr messlle i i""rl,a.a wilh,in an Atlach Rcqucsr messaFL" i.c. thc Al'N is translerred during a

subsequcnt DSM Infonnarion n"q";;i;;;;;; Transler olthis information is deiaved to allou its transfer alier securily

has been cnabied. i.e. to allow ciphering ofthe content

'l.heUEstartstimerl.34l0allelsendjngtheAttachRequcslmessage.3Gl,Phasstaldardisedafixedva]ueofl5slorthc

T3410 timer. tf T3410 expires prior Lo ire ll E recciving a rcsponse from the MME. then the currenl attach atlempt is

aboltgdaldtheattachattcmptcountisincrementct]uyr.rleunstaltstimerT34llifthergsultantattachancm|tcountiSless than 5. 3Gpp has standaraiseo a itxea value of 1d s for the T34l I timer. The UFI re-lransnlits the Attach Rcquest

message once'f3411 has cxPired

If the atlach attempt count reaches 5, thc tlll starts timer'f34!2, ard deletes its GUTI. TAI and list ofequivalent PI-MN'

3Gpp has standardised a aefautt vatr]e oi i2 minutes for the T3402 timer. The network can signd a differenl value lor.13402 within thc Attach Accept anJi racking Area Update Accept messages. A value signal)cd by the nctrvork is only

"ppli*or.'*irlri, arr","t ur"rrign"a i.u"tin! ar."r. i'he default-valu^e,is re-acloptcd ifthc UE recejves an Attach Acocpt

or Tracking Arca lJpau," a"".prn-'"rru!-" *rt-i.t ao", not specify a l'3402 value The atlach procedure can be rc-iniliatcd

once T3402 expircs

IoncelheeNod€BroceiveslhcRRCConnectionSefupCompletemcssage'theAttachRequestmessageisexfactcdandplaced within an S I Application protocol (S l -AP) Iniiial t.lE Message. ',l:he content of this message is presented in ]'able

t j/t t6t wjtbtnsecrion 2j.I . Th. .N;i"";;;;l"dc; iniomdtion rcga-rdirg thc rracking Ar€a ld€ntity OAI) and ccll Global

Idenlity (ccl). The S-TMSI can also ue included.'t hc cNode B procieds to forward the lnitial uE Messago 1o thc MMF

once the MME has receivcd thc Attach Reque st message. it dclermines the IMSI belonging to the UE The IMSI may have

bcen included expJicitly within tle airach Rcqucst mes-sag1 HoI*-"l: if rhe uE included an old GUl l inslead of an IMSI

thcn thc MME uses the old ctJ I L" iJ""ttri rir. address -olthc

old MMr (or sGSN) to which the uE.was previously

registcrerl. l-he MMll then ,"na, unia.niity ncluesr messagc to the.otd MN4E @r SGSN) asking for the IMSI. If the MME

cannot delermine the IMSI using this a;priaoh, an taentiry i.equest is sent to the UIr asking for its IMS1 The signalling

uscd to determine the IMSI is not shown in Figurc 109

l.heMMLcanthcncompleteauthenticationandNASSeculitysefup'AuthenticationiscompletedusinganEquipmentii""ilry n"girr* rEIR) whioh can be connected to the MME using thc S13 interface. security setup is used to enable

integrity protcction ana "ipt

ering to-, a;f ruur.qu"nt rigno'ing. fhc sigalling used lor authentication and N A S securitl

setup is no1 shown in Figure 109

If the uE included the rsM Informalion 'l'ransfer I.lag within the PDN connecliviry Requcst mcssage, thelMMFl-inilialcs

IN BULLETS

UE

s "N"d"B ql

5FI

llll(,1 Cenne(lroi Se1!p Coilpl.i{e / l

/\liaah il.]llLesi l

P0N Conneciivliy ReqLregl

Downlink NAS Transpod /ESM lnformation Request

i Crea{e S-.sercfl Reques{ i

Figure ll0 Additional signalling for the fiSM Information Requcst procedure

Th(r content o f lhc IISM Infbrmation Request and ESM Infbrmation Rcsponse messages is prescntcd in I'ablc 1 3 8. 'l hercquesl nlessage scrvcs as a simple prompt which triggers the IJE lo rclum a responsc. The response mcssage can incluclean Acccss Point Name (At'N) and a set of Protocol Configuration Options. 'l'he protocol configumtion options can definethe uscrname and password lor the AI)N

ESM lnltrrmahon Rcsponsc

I nforrnation Elenents Presence

Pralocal Discrimnalor ,Vandalary

EPS Bedrer ldentitv Mandgtory

P r oc e du re 7i an sac t i on ! de nt i^, Mdndalory

ESM lnformalion Respo se Mess(tge \denti4) Mandalory

Acccss Point Name Optional

Protocol Configuration Options Oplional

Table 138 Clontcnt of ESM Information Request and ESM Infornation Rcsponse mcssagcs-i

he dcf'ault AI'N can bc uscd ilthe tJL did not inciudc thc ESM lnformation 'Iransfcr Flag within the pDN ConnectivityRequesl message. Oncc thc MME has linalised the APN to be used, it scnds a Creatc Session Requesl message to lhcScrving Gatcway. This message beiongs to the Cl'P control planc protocol (GTPv2-C) ard is specificd within 3Gpp TS

Tbe Serving Galeway creates an en1ry within its EPS Bearer table and forwards the Create Session Request mcssage to thcPDN Gatcway. 1-he PDN Gateway creates a new entry wilhin its I]PS llearer Contexl lablc and gcnerates a chargingidentiry. 'Ihc new context allo\a,s the PDN Gateway 10 slart rouling user plane data between the Packct Data Nctwork(l'DN) and the Serving Galc\\,ay, and to start charging

'l he PDN Gateway relurns a Crcatc Session Responsc mcssage to the Scrving Gateway. This mcssagc includes the lPaddrcss that has been allocalcd to the UD by the PDN Gatervay, i.e. thc PDN Gatcway is responsible for managing thcallooation of lP addresscs

The Serving Gateway foru'ards the Crcate Session Rcspons€ messagc to the N4MD, rvhich then proceeds to initiate thc S l-AP injtial context setup proccdure. This is done by sendjng an lnitial Contoxl Setup Request message to thc eNode Il. Thecontent ()1'the lnitial Context Setup Rcquest mcssage is prcsented in l'ablc 139. It allows the cNode Il to confisure itselffor the new E-I{AR

[,,IME

q@Se.ving

Galeway

Wi'PDN

Galeway

s#*"'

ESM lnformatjon Request

Information Elements Presencc

Plolocol DBcriminalor Manda/try;

EPS Bealer ldehlit,, Mandatory

P r oce dure Transact i an lde n I i l| Mandalory

ESM lnformation Request i4essage ]dentitr- Mandalon,

fr-rN cuIrrL c,i!,lr F ,q e5i

Uplink lnformation l€nsfer /ESM lnformation Response Upllnk NAS Transport /

ESM lnformation Response

I,ONG TERM EVOLUTION (LTE)

lnformalion Elements

Message Type

MME UE S|AP ]D

eNB UE S|AP ID

UE Aggrcgate Maximum llit Rate

E-RAB to be Setup List E-RAB to be Setup E-RAB ID

F-IIAB Level QoS Parameters

Tra{Nport Layer Address

GTP TEID

NAS PDI]

UE Security Capabilities

Security Key

Trac€ Activation

Handover Restriction List

UE Radio CapabilitY

Subscriber Profile ID for RAT/Irequency Priority

Cs Fallback lndicator

SRVCC Operation Possible

Table 139 - Content oflnitial Contexl Sefup Requesi message

The llE Aggegate Maximum Bit Rate (UE-AMBR) defineslhe maximum aliow€d throughput for a [lE ba-sed upon the

sum ofalliti non-GBR bearers. This parametcr forms part ofthe QoS profile described in seclion 2.9. It can be configured

with values between 0 and 10 000 Mbps, and can be specified independently for the uplint and downlink

The E-RAB Level QoS Parameters include:

o QoS Class ldentifier (QCI)

o Allocation and Retention Priority (ARP)

o Guaranteed Bit Rates (GBR)

o Maximum Bit Rates (MBR)

These paramcters form part ofthe QoS profile descdbed in section 2.9. The relationship between QCI and its associated

eoS pirameters is presented in Table 5. QCI values of 8 and 9 are intended for the default bearer. QCI 8 can be used for

premium subscribers, whereas QCI 9 can be used for basic subscribers. The GBR and MBR paramete$ are only applicable

to GBR bearers

'I'he transporl layer address defines an IP address which can subsequently be used for tmnsferring user plane data from the

eNode B to the Serving Gateway

The GTp Tunnel Endpoint Identifier (TEID) defines the GTP-U tunnel for the user plane data. Multiple tunnels will share

the same transport layer address

The Non-Access Stmtum CNAS) PDU is used to tuansler the Attach Accept message which acknowledges the original

Attach Request message.

The MME slarts timer T3450 afler sending the Attach Accept message. 3GPP has standardised a fixed value of 6 s for the

T3450 timer. IfT3450 expires prior to the MME r€ceiving a response from the UE, then the Attach Accapt message is re-

sent. The Attach Accept message can be re-sent four times. The overall attach procedure is aborted ifT3450 expires a fifthtime

The content ofthe Atlach Accept message is shown in Table 140. The first 3 inlormation elements within the Attach

Accept mcssage represent the mcssage header. The Protocol Discriminator indicates that the subsequent message is an EPS

mobility management message. lts value is specified within 3GPP 24.007. The Security Header 'l ype indicates whether or

not the NAS message is integrily protectsd and ciphered. The Attach Accept Message ldentity indicates that the message

itselfis an Attach Accept

IN BULLETS

Information E €melts Paesence

Protoco I Di scr iminal or Mandator-v

Seartq lleader Type Mandatory

Attach Accept Message ldediy) Mandatolv

EPS Attach Result Mardalory

T3412Vafue Mandatory

TAJ List Ma.dalory

ESM Message Container Mandatorv

GUTI Optional

Location Area Idefl tifi cation Optional

MS ldentitv Optional

EMM Cause Optional

T3402 Value Optional

T3423 Yaluc Optional

Equivalent PLMN Optional

Emergency Numb€r List Optional

EPS Network Feature Support Optional

Table 140 - Content ofAttach Accept message

* The main content ofthe Atlach Accept message starts with the EPS Attach Result which can be configured with values of'EPS only' or'Combined EPS/IMSI Attach'. These values correspond to EPS Attach Type specified within the requestmessagg

* T3412 defines the periodic Tracking Area Update (TAU) timer. UE lriggcr a periodic TAU procedure when this timerexpires. It can be configured with a value up to 186 minutes

* The Tracking Area Identity (TAI) list defines the set ofallocated tracking areas, i.e. the tracking areas with which the UEis registered within. The TAI list can include tracking areas belonging to more than a single PLMN when a shared networkis being used. Tracking Area Updates are subsequently higgered ifthe UE moves into a tracking area which is notincluded within the TAI list

* The ESM Message Container is used to transfer the Activate Defauil EPS Bearer Context Request message whichrepresents a response to the PDN Connectivity Request message. The conlent ofthe PDN Connectivity Riqucst message isshown in Table 141

* The first 4 information elements within the Activate Default EPS Bearer Context Request message represent the messageheader. The Prolocol Discriminator indicates that the subsequent message is an EPS session manigement message

'* The EPS QoS parameter defines:

o QoS Class Identifier (QCI)

o Guaranteed Bit Rates (GBR)

o Maximum Bit Rates (MBR)

These parameters form part ofthe QoS profile descdbed in section 2.9. The relationship between eCI and its associatedQoS parameters is presented in l-able 5. The GBR and MBR parameters are only appliiable to GBi bearers. TheAllocation and Retention Priority (ARP) has been signalled to the eNode B but is not signalled to the UE, i.e. ARp valuesare used by the network rather than by the UE

* The Access Point Name (APN) inlorms the UE ofthe APN to which the default bearer is connected

* The PDN Address allocates the UE with an IP address

* The eNode B exhacts the Attach Accept message from within the Initial Context Sctup Requesl., and packages it within anRRC Connection Reconfiguration message. The RRC Corurectioo Reconfiguration is iransferred to the Ulr across the air-interface. This message provides the UE with all ofthe information necessary to establish the default bearer

':?t

LONG TERM IVOLUTION (LTE)

Table 141 - Contcnt ofActivate Default EPS Bear€r Context Rcquesf message

The IJE responds to the eNode B using the RRC Conneclr'on Reco_nfiguration completc messagc.'lhis message is a simple

acknowledjement without any inlormllion contcnt. lt does not oiler the ability to tnnsfer NAS messagcs so thc llll has to

send the Aiach Complete within a subsequcnt Uplink Information Transfer message

l.he eNodc B completes the S I -AI' Iniliai Contcxt Setup proccdure by forwarding an lnitial Conlext Sctup ResPonse

mcssage to the MME. The content ofthis message is shown in Table 142. It acknou'ledgcs that thc FI-RAB for th(r dcfault

bearerlias been successfully sclup. A transport iayer address is provided in lenns of an lP address for downiink data

transfer from the Scrving Gateway to the eilodc B. A GTP Tunnel Endpoint ldentitier ('lElD) is also provided to define

the GTp_u tunnej for thi user plaae data. A failure cause is specified if the E-RAts setup failed

Information lilem€nts

Protocol Discrihi alor

EPS Bearer ldentilY

Prccedwe Transact ion ldenlilY

Acl ate DeJauh EPS Bearet Conlext Request Message ldentity

EPS QoS

Presenc€

llantlorory

Mandalorf

Mandatorv

Access Point Name Mandatory

PDN Addr€ss Mandatory

Transaction Identifier Optional

Negotiated QoS Optional

Negotiated LLC SA?l Optional

Radio Priority

Packel FIow Identificr

Optional

Optional

APN-AMBR Optional

FsM Cause Optional

Protocol Confi guration OPtlons Optronal

Informalion Elemgftts

Message Tjpe

MME T]E SIAP ]I)

eNB UE Sl)P ID

E-RAB Sclup List E-RAB Sctup Ilem E-RAB ID'I ransport Layer Addr€ss

(iTP 'I'EID

E-RAB Failed to SetupList

E-RAB I"ist E-RAts ID

Cau,se

Crilical ity Diagnostics

Information Elements Prssenca

P r o lo c o I D i s cr im i nator Mandatory

Securtly Header TyPe Mandatory

Anach Complete Messdge ldentilY Mand.ttory

ESM Mcssagc Clontainer Mandatory

'Iehle 142 - Coot€nt oflnitial Contcxt Setup Response message

l he content olthe A11ach complsle messagc is shown in Table 143. lt is a simple acknowledgement but also coniains an

FlpS Session Management (ESM) NAS meisage. The IrSM NAS message is an ActiYate I)efault EPS Bearcr Contcxt

Accept mcssage

'l'able 143 - Content ofAttach Complete message

The content ofthe Activate Dcfault Eps Bearer cont€xl Accept mcssage is shown in Table I44.acknowledgement but may aiso contain some protocol config;ration options

IN BULLETS

It is another simple

lnfornratriQn Elements Presence

Pr o I ocol Discrimi nat or MaadatoryEPS Bearer ldentig Mqndatory

P roce dure Transacuon I de nt t ty Mandatorv

Actiyale Defdult EPS Bealer Coktext Accept Message (dentity

Protocol Configuration Options Optional

Tabte 144 _ Content of Activat€ Default EpS Bearer Cohtext A"lT,rgT"g"After receiving both the Initial Context Rcsponse and Attach Accept messages, the.l ;de.b,ends u Modily BearerReqlestmessag€ to thc Serving Gateway. This message belongs tothe GTicont.ot plane protoJ 1cin.,nz-c;. lt prou;0.,the Serving Gateway with the downlink transport layer address and the associated Gip rBro, Both ofthese are taken liomlhe S l-AP lnitial Conlexl Setup Response message

The Serving Gateway completes the procedure by sending a Modify Bearer Response message to the MML..l.his messagcis a simple acknowledgement

3GPP References: TS 24.301,T5 23.401, TS 36.413. TS 29.274

LONG TERM EVOLUTION (LTE)

23.3 DEDICATED BEARER ESTABLISHMENT

* A dedicated bearer is required if tbe end-user requires a different Quality ofService (QoS) to thal offered by the default

bearer, or ilthe end-useirequires connectivity to a different Packet Data Network (PDN) to that provided by the default

bearer. Dedicated bearers are configured to run in parallel to the existing default bealel

>t The dedicated bearer establishment procedure is initiated by the network but may be requested by the l lE- The UE can

request a dedicat€d bearer by sending a Non-Access Stratum (NAS) Bearer Resource Allocation Request to the MME. The

UE shrts the T3480 timer when sending a Bearer R€sourcc Allocation Request message, The message is re-transmitted iiT3480 expires prior to the UE recciving a response from the MME. 3GPP have specifi€d a fixed value of 8 s for the T3480

timer. The Beaier Resource Allocation Request messagc can be re-transmitted a maximum of4 times before the overall

procedure is abofted

* The signalling associated with dcdicated bearer establishment is shown in Figure I I I

[llI

wRRC Connection Reconllguration /

Activate Dedicated EPS BearerConiext Request

RRC Connection Reconfiguration

E-RAB Setup Response

Figure I l1- Signalling for the dedicated bearer establishment procedure

The pDN Gateway starts by sending a Create Bearer Request message to the Serving Gateway. This message belongs to

the GTpv2-C protocol so is specified within 3GPP TS 29.274. It includes a definition ofthe dedicated bearer QoS

requirernents, i.e. eoS Class ldentifier (QCI), Allocation and Retention Priority (ARP), Guaranteed Bit Rate (GBR) and

Maximum Bit Rate (MBR). It also specifies the uplink GTP-U tunnel endpoint address at the PDN Gateway. This Tunnel

Endpoint Idsntity (TEID) defines the GTP-U tunnel to be used by the Serving Gateway when forwarding user plane data to

th. iDN Gut"*iy. The Create Bearer Requcst also includes the identiry ofthe default bearer so the dedicated bearer and

default bearer can be linked. Protocol configuration options can be included to transler application layer parameters

between the PDN and UE. These paramet€rs are sent transparently through the Serving Gateway and MME

The Serving Gateway generates its own version ofthe Create Bearer Request message. The content is similar to that

received from the PDN Gateway but the Serving Gateway replaces the uplink GTP-U TEID at the PDN Galeway with an

uplink GTP-U TEID at the Servjng Gateway. The MME is responsible for forwarding this TEID to the €Node B to allow

the eNode B to forward uplink user plane data to the appropriate address within the s€rving Gatevr'ay

The MME generates an E-RAB Setup Request message which encapsulates an Activate Dedicated EPS Bearer Context

Request meisage. The E-RAB Serup Request bclongs to the Sl Application Protocol (Sl-AP) so is specified within 3GPP

TS 36.413. The Activale Dedjcated EPS Bearer Context Request belongs to the session management component ofth€Non-Access Stratum Q.qAS) protocol so is specified within 3GPP TS 24.301. The content ofthe E-RAB Setup Request is

shown in l'able 145

PDNGateway

SPServing

Gateway

qpe1

MME

qp"UE

{gCreate Bearer

E-RAB Setup Request /Activate Dedicated EPS Bearer

Context Reqirest

Create Bearer Request

Uplink lnformation TEnsfer /Activate Dedicated EPS BearerContext Accept Uplink NAS Transport / )

Activate Dedicated EPS Beal€rContext Accept

228

IN BULLETS

lnformation Elemenls

Message Iype

MME I]E SIAP ID

eNB tJE SI AP JD

UL Aggrcgate Maximum Bjt Ratc

E-RAB 10 be Sctup List j IiRAB to be Setup E.RAB 1D

E-R B Ler'el QoS Parameters

'f ransport Layer Add.ess

GTP TElI)

NAS PI]U

Tablc 145 Content of Ii-RAB Sctup Request messag€

1'he UE Aggregate Ma:rimum Bit Rate is used to update thc value currently appiied by lhc eNode Il. This paramctcrdefines a maxirnum total throughput for all non-GBR bearers bclonging to the UE. 'I'he FI-R-AB QoS parameters arc basedupon thosc originating lrom thc PDN Gateway. Thc GTI'l FllD conesponds 1(] the uplink tunnel specilied by thc ScrvingGateway. 1he transpofi Iayer address idenlifics thc Serving Gateway itscll

The NAS PDtl within the E-RAB S€tup Itequest corresponds to thc Activate Dcdicated BPS Bearer Context Request. Thismessagc is directed 1tl the UE mther than the eNode B so thc cNode l3 is rcsponsible lor forwarding it across the air-interface. 'l he content oflhe Aclivate Dedicatcd EPS Bearcr Context Rcquest is shown in'l'ablc 146

InfoImation ElemenLs Presence

P r o I oc o I D tsc r im i1a ! or Mandaton,

liP:i Bearer ldcntt) Mdndato.t^

Prcced re 'l run\action ldentitv Mandotorv

Activdle Dedrcaled tJ'S ]ledrer Conlett Re(luast Message ldentily Mandalory

Linked FPS Bcarcr ldenlitv Mandatory

FPS QoS Mandatory

1'FT Mandatory

lraflsaclion Idenlificr Optional

Negotiated QoS Optional

Ncoolialcd 1.1 .C SAPI Optional

Radio Priorily Optional

Packet Irlow ldcnlilicr Optional

Protoool CooliSuralion C)plions Optional

'l'ahlc 146 - (lontent ofActivate Dcdicat€d [pS Bearer Context Request message

The linked EI'S bearcr id€nlificr is used to link thc dedicated bearer to fre dclauil bcarer. The QoS irlformation wilhin theActivalc l)cdicated EPS Bcarcr Context liequest js similar to that within th(r E-ltAB Setup Request bu1 jt excludes thcAllocation and Iletcntjon Priority (ARP) informalion. ARP is used b), the nctwork rilther than the llll so is not sent to thetJlr. Thc Traffic Flou'Tcmplatc (TF]-) defines a sat ofpackct filtels for thc IJE to app)y in the uplink direction. I'hescfil1crs can bc bascd upon various criteria. including source and destination porl ranges. lype of servicc. remole addresslypes and protocol identifien

Thc cNode B uscs the Ir-l{AB Setup Ilequest to oonfigurc itself for the dedjcatcd bearer. It also exlracts thc ActivaleDedicated FIPS Bearer Conlext llequest and packages it within an RRC Connectjon Rcconiiguralion ntessagc belorelorwarding to the UIl. l'hc RRC Conncction Reconfiguration mcssa€ge belongs to thc RRC protocol s6 is specifiecl within3GPPTS36.331. Ihis message providcs the L]E with all ofthc information nccessary ibr ir to oonfigurc itself for thededicated RA-B. It is lranslerred across thc air-interface using SRB I and acknowledgcci modc RLC

The []E acknowlcdges rcception ol the RIIC Connection Reconfiguration message using the RRC ConnecljonI{econfiguration Complete mcssalte. 'l'his nrcssage also acknorvlcdges that the LJFlhas applied the configuration for the

Informalion El9me nts

Message Type

MME UL SI/lP JD

eNB UE SIAP ID

E-RAB Sctup List I E-R-AB S€tuP II.RAB ID

Transport Layer Address

GTP TEII)

Criticality Diagnostics

Table 147 - Content ofE-RAB Sctup Response message

* 'l'he UE gcnerates an Activate Dedicated EPS Bearer Contcxt Accept message to respond to the Activate Dedicated EPS

Bearer C-ontext Request from the MME. This message belongs to the NAS protocol so is specificd within 3GPP TS 24.301.

Its content is shown in Table 148. The UE packages the NAS message within an Uplirk Information Transfcr message

before sending it to the eNode Il. The eNode B cxtracts the NAS messagc and packages it within an Sl-AP LJplink NAS

Transport mcssage before sending it to the MME

lnformation El{]ments Presenc€

Ptotocol [)6cri inator Mandatory

EPS Bearer ldentitY Mondalory

P roce dwe Trarsaction I de nli lY Mdndalory

ActNate Dedicated EPS Bearer Conrext Aclapt Me\sa}e ldenfily Mandatom

Protocol Configuration OPlions Optional

LONG TERM EVOLUTION (LTE)

dedicated bcarer. The RRC Connection Rcconfiguration completc messagc is a simple acknowledgcmenl and is not able

to transfer any NAS signalling. This means that ihc response lor the Actiyate Dcdicated IPS Bearer Conlext Rcquest bas

lo bc scnt in a seParale messagc

* Oncc the cNode B has received the llRC Connection Reconfiguration mcssage, i1 responds to th€ E-RAB Setup Request

from the MME using an E-RAB Setup Response. l-he content of this mcssage is shown in'l able 147. It provides the MMts

with a transport layei address and GTP-U Tunnel En<lpoint ldentib' (TEID) for the downlink user plane data

Table I48 - Contellt ofAclivate Dcdicated EPS Bearer Context Accept messag€

The MMD then uses the GTpv2-C protocoi to respond 10 the Serving Gateway by sending a Create Bearer Response. This

message provides thc Serving Gateway wilh thc G fP-U tunnel identity fbr the downlink uscr plane data, i.e it allowsthe

S".uirig Gut"*uy to forward"rlownljnk data to tbe eNodc B. l-he eNode B providcd the MME with this information within

the E-RAB Sctup Response

The Serving Gateway compJetes the proccdure by sending its own version ofthe Create Bearel Responsc to the PDN

Gateway. ihis u"rrion includcs the downlink GTP-tl tunnel identity at the Serving Gateway so allows th€ PDN Gateway

to transfer downlink data 1o the Serving Gateway

3GPP References: l S 24.301, TS 23.401. 'fS 36.413' TS 29.274. TS 36 33 1

2?O

IN BULLETS

23.4 TRACKING AREA UPDATE

].Iacking Area Updales (TAIJ) become applicabie afler the UE has complet€d the Attacb procedure and moved into theEI'S MobiJity Management (EMM) I{EGIS'I ERED state. They can be triggered ir eithcr RRC ldle mode or RRCConnected mode, but the UE must be in RRC Connecled mode to aclualiy complcte thc procedure

* The l'Atj procedure is used for:

o

o

normal TAU due to mobility. j.e. when the UE entcrs a hacking area which is not included wilhin thc li$ oltrackingareas with which the UE is rcgislcred

periodic TAU alter the T3412 timer expires. The vaiue of T3412 is initialised during the Attach procedurc within thoAtlach Acccpt message shown in Table 140. Periodic TA{J confim to thc network that the UE is still present

rcgislering with thc CS domain for non-EPS services when the UD is already atlached for EPS services. This invoivescomplcting an IMSI attach as part of the I AU procedure

registering wil.h the EPS after an incoming inler-system change, e.g. reselecting the LTE network after being campedon the lJMl'S network

re-registering with the EPS aflcr a CS fallback connsction has been completed

MME load balancing. The UE initiates a TAU proccdure ifthe eNode B releases its RRC cornection using a causevalue of'Load Baiancing TAU Rcquired'

updating the UE specific DRX cycle. UE tlre allowod to select their own DRX cyclc and signal it to the MME. Theselected DItX cycle can be specified within thc Tracking Area IJpdate Requesl messago

o indioating that a IJE has sclccted a Closed Subscriber Group (CSG) cell whose CSG ldcntity is not included withinthe I lll's allowed CSG lisl

The TAU procedure may involvc a change ofScrving Gateway and/or a change of MME

The signalling associated with the TAU procedurc is illustrated in Figure 1 12. -fhis

exampie includes a change of MMI;bu1 mainlains the same Serving Gatcway. The example assunres that the UFI starts in RRC ldle mode so the Tracking AreaUpdale Request is sent wilhin an RRC Connection Setup Complete message. lfthc U[ is already in RRC Connectcd modewhen thlr TAU procedure is triggercd, thc'l'racking Area Update Request is scnl within an lJplink Inlormation Transferin0ssage

l'he Utl s1ar1s timer'I'3430 afler sending thc Tracking Area Update Requcst mcssage. 3GPP has standardised a fixed valueof I5 s for the T3430 timcr. IfT3430 expires prior to the UE receiving a response from thc MME, th€n the curent TAUattcmpt is abortcd and the TAU attempt count is incrcmenlcd by l. The UE starts timer T34l I ifthe resultant atlemptoount is lcss than 5. 3GPP has slandardised a fixed value ol l0 s for the T341 I timer. The UE re-transmits the TrackingArea Update Request message oncc T34l I has expired

If the TAU attempt count reachcs 5. the UE slarts timcr T3402. and deletes i1s lis1 of equivalcnt PLMN. 3GPP hasstandardised a default value of I2 minutcs for thc 'l'3402 limer. The network can signal a dillcrent value lor T3402 withinthe Aflach Accept and Tracking Area Update Accept messages. A value signallcd by the network is onJy applicable withinthc sct ofassigned Tracking Areas. lhe default value is re-adopted jfthe UE receives an Attach Accept or'l racking AreaUpdate Accept message which docs not specify a T3402 valuc. The IAU procedure can bc re-initiated once f3402 cxpires

231

I,ONG TERM EVOI,UI'ION (LTE)

UE

€

"r"... 1[ffi

NewM[,1Ew'

ordI\.4ME

W!tr'

ServlngGaleway

sw.HSS

@RRC Connectlon Setup Complete / i

'I rack nq Area Updaie Request lnrtial UE Message /'I racking Area UPdate Requesl

Downlink lnformation Transfer /Trackinq Area uPdate Accept

Downlink MS Transpod /Tracking Area UPdate Accept

Uplink lnformation Transfer /tlollnK lnrormallolr r rirrrsrcr /

Trackrnq Area Update Co'nplete Uplrnk NAS Transpon /Trackrng Area UPdate ComPrele i

I i Update Location Acknowledge

llll

Modify Bearer Request

I,igurc l l2 - Signalling for thc 'I'rackiDg Area'Ilpdstc (TAtJ) procedure (with changc of MMII)

The contcnt ofthe Tracking Arca Update Request mcssage is shown in Table 149

.l"he lirst 3 inlormaljon elcments within the Tracking Area Update Requesl message rcpresent the message header. The

protocol Discriminator indicales that the subsequent mossage is an EPS mobility managemcnt message .lts value is

.p""ifi"d *i,hin 3GPP 24.007. Ihc Securiry Header'l ype iidicates whcther or not thc NAS mcssage is integrily protccted

-a lipn"r"a. .l he Tracking Area Updatc l{equest Mcssagc Idcntily indicates that the message ilself is an 'l racking Arca

Updatc Request

The main content ofthc l'racking Area update Requcst message starts with the EPS Update Type rvhich can bc configurcd

with values of .I A Updating'. 'C--omt incr] tA,rla iJpdating', 'Combincd TAn-A Updating with 1MSI Atlach' and

.ttrio,lic Up,lating'. i'tr" 'rx Updating' valuc is ussd ifthi UE is only rcgislercd with thc I,PS' i e onll'rcgistered 1br PS

scr.,iccs. l.he ,coirbined TA/I-A Updaiing' value is usctl ifthe tJE is registcred for both EPS and non-EPS scn iccs, I c

borh CS and pS senices. The .Cn.bin"d:l,q"rt.a tJpdating with IMSI Attach' value is used ifthc U!) is rcgistercd for EPS

seniccs but wishes to also register lor non-EPS servjces. Thc 'Pcriodic Updating' value is used whcn thc T3412 timcr

expircs

The NAS Key Sct Idenlilier (KSI) is used to identjly thc security parameters for authcntication, inlegrity protcction and

ciphcring. Sccurity is not activaled at thjs pojnl in time whcn sending the 'l racking Area Update Rcquest mcssagc within

un nnCi:onn""tinn Setup Complete message so the KSI inlbtmation elemcnl is no1 relevant

'fhe old Globally unique lemporary tJE Identjly (GUTI) inlormation elemenl provjdcs thc nelwolk with an identity for

the UE. l he GUil can bs derivcd lrom a previous P-TMSI and thc associatcd RAI ifthey are availablc

Once the eNode B receives the I{RC Connection Setup Complele mcssage, the Trucking Area Updatc Requcst message is

cxtracredandolacedrvithinan5lApplicarionProiocul {\l-Al') lnrlial Ul \4e:sats( lheconl'"nt ol thismes'ageis

;;;;J;;;';;"-J;6. iir' in ,..,ton'z:. t . Thc e Nodc B includes jnformalion regarding thc ne w liacking Area ldentitv

(TAI) and Ccll clobal Identity (ccl). r'rre S- IMSI can also be inciu6ed. Thc eNode B proceeds to forward thc Initial tlE

Message to tire new MME (this examplcs assumcs the TAIJ procedurc involves a change of MME)

, Context Response i

IN BUI,LETS

Info.mation ElemenG Pr€senca

Protocol Disctimirnlor MandatoO,

Securit! Header Type Mandatory

'frachng Area Updale Reqlast Message ldentity Mamiato4',

EPS Update ]'ype Mandatory

NAS Kcy Sct Identifiel Mandalory

OId GIJ'II Mandalory

\('n-( urrcnl Nati\ e Nn S kc) sct ldcntil'cr Oplional

CPRS Ciphcring Key Sequence Numbcr Optional

Old P-TMSI Signature Optional

Additional (iUl'J Optional

Nonce I lF Optional

Ull Netrork Capability Optional

Lasl Visjted Registered TA.1 Optional

f)RX Parametor Optional

UJ.l Radio Capabilily Inlormalion Update Needed Optional

FPS Bcarer Contcxt Status Optionrl

MS Nelwork Capability Optional

Old Location AJca ldcntification Oplional

TMSI Status Optional

Mobile Stalion ClassmaJk 2 (lnli(lnal

Mohile Station Classmark 3 Optional

Supported Codeos Optional

'Irhlc 149 - Content ofTratking Area Update Rcqucst mcssagc

'i he new MME uscs rhe old GUTI inlomation ftom $'i1hin the'Imckjng Area Updatc Rcqucst to dcrjvc the addrcss o1'1he

old MME. Thc ncu' MME then scnds a Conlcxl R€quest mcssage 10 the old MME. This mcssagc bcJongs to thc GTP

conlrol plane prolocol (Cill,v2-C) and is specilled within 3GPP 1'S 29.274. lt is used to request user inlbmration liom thc

old MMt.i

Thc ncu MMFI responds u ith c (-ontcxl Rcsponse message which includes thc re qucslcd tJE infolmation. l he new MMBiinaliscs thc 3-u,ay handshakc b,v sending a Context Acknowledgc mcssagc to thc old MMI1. l'his triggers the old MMI'i tomark its galcway and lJomc Subscriber Scrver (l ISS) inlormalion fbr thc UII as jnvalid. I'he context ilseifis mainlained

and is no1 deletcd at this stage

The nerv MMI sends a Modili Bearer Requcst ncssage to the Serving (iatcway. This message also belongs to thc GTPcontroi plane proroool (C;l l,v2-C). I1 inlorms thc Scrving Gateway thal the MME a-ssociatcd with the existing PDNoonneclion has changcd. Addilional Modilj,Bearer Rcqucst mcssages are sent ifthe IJE has multiple I'jDN conneclions.

l he Serving Galeway acknowlcdgcs the ncw informalion using the Modiiy Bearcr Rcsponse m(jssage

'I'he neu, MMI1 thcn proceeds to send an [Jpdale Location Rcquesl message 1() the l lSS. 1'bis message belon€]s to the

l)iameter protocol and js specified wjthin 3GI'l' TS 29.2'12. Thc MMI'. is connecled 1() the IISS using the S6a inlerface.

Thc Updatc l.ocation Request identifjcs the LIE by its IMSI and informs the I ISS that the UE has n]oved to the new MME.'fhe I ISS contacts thc old MME usjng the Cancc] Location mcssage which also uses thc Diameter prolocol. The old MIr4E

thcn deleres the context lor the IIE and responds with a Canccl Location Acknowledge. Finally, the HSS uses the tjpdat€l,ocation Acknowledge message to confinn to the new MME thal is has updated its records for the L/Fl

'l he new MMll then progressos the'I'AIJ proccdurc by scnding a Tracking Arca Update Accept message to the UE. Thismessage is transferred across the Sl intcrlace using an SIAP: Dorvnlink NAS I ransporl message. 'l he conlenl oflhelracking Area LJpdalc Accepl messagc is shown in Tablc I50

LONG TI]RM EVOI,UTION (LTE)

lnlolmatlon I lcmcnlt I

D.^'^,,) Div rlntn.tlor IMawlatory

\"-,,t" Hr"d", ftr. I

h,.rAing Area L)pJare Acctpr Vctsrqr ld?nlth I

EPS Updat€ Result

'I3412 Valuc

GTJTI

TAI Lisl

I.IPS Bearer Context Status

l.ocatioo Area ldentifi calion

MS IdentitY

EMM Cause

'f3402 Value

T1423 Value

Iiquivalen( PLMN

EmergencY Number l'ist

IIPS Network Ircature Supporl

Mandat.try

Mandatory

Optional

Optional

OIlronal

Optiondl

Optional

Oplional

Optional

Optional

Optional

Optional

Optional

Ontional

Table 150 - Content of-lracking Area Update Accept message

.l.hc firs1 3 information clements within the Tracking Arca Updatc A-cc^epr messagc refresenl the mcssa!e hcader' 'fhc

prolocor Discrim jnuto, ina;.ut", t jt tnJ';;;;;;.;*ce.is an EpS mobiliq manage me nt message lls valuc is

specjfied wirhin 3cpp 2.1.007. .,n"il;;;;;,1- lype iidicates whether or not the NAS message is integrity protected

and ciphered. .fhc Tracking Arca ,ff#;;";il";i# io"",iry indioatcs that the message itse ll is an Tracking Area

Update AccaPl

The Et,s update l{esul1 can be allocatcd values of 'TA Upilatcd', 'combincd l A/l.A tlpdatcd" "fA updated and lsR

Acrivaled, and ,combined .'.A/LA ;;;;;;; isR Actirateil'. ldle rnode signalling Reduction (lsR) is applicable to E-

tlTRAN UE which ruppo.t cnnai'ii)- ui*N uai"$sarcductionof the signalling beiu'een the Ui-' and the

;;il;, ;;":;ii;; "

""'ou"rinn

of the signalling within the netlvork

l.heMMEStartslimcrT3450allerscnciingthe.I.rackingArgau.pdateAuceFtmessage'3GPPhasStandardiscdafiXcd\aluror hslorthe 1.1450,it., fr f iqio""toirt'lrioi r'-' rhc,MM re ceiving a responsc lit'm lhc UL rhcnthe lraclinp

ArcalpJdleA!cepImcs5agc,.,.-*n,.lhc'lracl'ingAreal'pdaleAcceptrn-es.age(anb(.r(-'enlfuurlitlL...lhctlreralliau plu..aur. rs ahuned ii'l 1450 expires a fillh t ime

t.he eNodc B cxtracts the Tracking Area updatc Accept.tiom within the slAP message and packages i1 u'iihin an I{RC:

Downlink Inlormation T'ansttr messall "ili;t

t"ttug" it rttcn scnt to the LJII across the air-interface

The UE completes the ovcrall procedure by sending a Tracking ArealJpclate Complelc messrge to the M Mll This

mcssase is translerr"a u"ru.r,r," uil]iir!;ilil;'RRa, tiplink IniormaLiot' iran'fer me'sage The rontcnt of the

ir"Jnft^i-, upoale Complere mcssage is shown in Table 151

* The'fracking Arca llpdate Complcte mcssage is a simple acknow.ledgement rvhich

pro,"""LUl.iriminator, Security HeaiJer trpe and Messagc ldentity

* The eNode B extracts the Tracking Area Update Cr)mplelc lrum \ ithin the RRC messagc and packages

Uplink NAS I ransonn rntt'uf Fli' '*t'og" i' thcn scrt tu thc oc\\' MMD across the Sl interfacc

only includes header inlormation, ic'

iiacLing Ated Ufuate Complete Message ldently

l'abl€ 151 - Content ofl racking Area []pdatc Complcte message

234

ir wilhin an SIAP:

IN BULLETS

23.5 INTRA-SYSTEM HANDOVERThc intra-system handover procedure is applicable to tJE in the ECM-(IONNEC'I'ED state. UE trigger handovers as th€ymove from one cell to another. Handovcrs are IJE assisted but network controlled, i.e. LJIi provide mcasurements whichhclp thc eNodc B to makc handover decisions

l,TE does no1 support sofl handover so all handovers are hard handovers. Data is forwarded from the sourcc eNode B tothc targel eNode B during the handover procedure to ensure that handovers are lossless

The intra-system handover proccdurc may involvc a changc of cNode B and/or a change of Serving Gateway

The signalling associated with the intra-system handover procedurc is jllustrated in F'igure I 13. This examplc includes achange of eNode B but maintains thc same Serving Gatervay. lt is refencd 10 as an X2-based handover because it uscs theX2 interlace between neighbouring eNode B for both control plane signalling and user plane data lransfer

RRC Connection Reconfiguration

HandoverPreparation

ryse

UE

€'

!|r

wMIME

wServing

Gatewayw

HandoverExecution

HandoverCoftpletion

and Downlink U$er Plane Data

Uplink and Dowrlirk Use..Plane Da{a

User Piane Dala

Uplink and Downlink User Plane Dsia

Modify gaarer Raspons€fath Switch RequestAck

Uf Cofllext Rel$se

Figure I lJ - Signalling for th€ intra-syst€m handovcr proccdurc (with changc ofeNodc B)

SN Status Transfer

FoMa.d Use( Plane Data

RRC Connection Reconf,glration Cornplete

l-,.@

LONG TERM EVOLTJTION (LTE)

* The overall handover procedure is divided into 3 phases: hardovtr pre.paratio":.n""dol:':1-::^"jton and handover

compterion. "^"0.,.,

nripi. u,,; ;;; ;;; i;".; ;^ ecur,on inrol.e onll rhe radiu accerr rrcr\\ork llando\cr complflion

involle: both thc core nerqorl anLl radlo acccs\ nelworK

)kHandoverpleparatiot]StartswithconfigulingthelJEtosendMeasuremcntRepoflmessages.TheUEcanbeconfigurcdtosend these periodically, or based upon onc or morc mcasurcment rcpofiing events The RRC Connection Reconfiguration

message is u."o rn .onttgui"-ii; u'E'i; ,;;; M""Suremcnr Reporr mcssages. l'his messagc, re places the Measurement

control messagc used biuMl'S. Intra-fiequcncy measuremcnt rcporting events are dcscribed in seclion 19 'l'hey include:

o evenl Al scrving cell becomes better than an absoir;te threshold

o event ,42 - serving cell becomes worsc than an absolutc thrcshold

o event A3 neighbouring cell becomes x dB better than thc serving cell

o event ,A4 - neighbouring cell becomes betlcr than an absolute threshold

oevent45_servingcellbecomeswolsethanthresholdlarrclneighbouringcellbgcomesbctlelthanthreshold2

Events 43 and A5 are the most likely to bc used for triggering inlra-frequency handovers

*TheUEsendsaMeasurementRgporttotheeNodeBwheloneofilsrepoftingeventsiStggered'orwhenlheperiodicrcporting timer cxpir", iffp"ioli.i *p.rting has been configured. The compleie conlent ofa Measurement Report is shown

in l.ablc 152. U_y ,Lt ""it".r r* ip,i*'"r and in practici, only a subsct ofthe content is included

:

i4

.i

)i

:!.i

'l

,li' ";sa

S€rving C€ll Measur€ment R€sults

E-UTRA Result ListNeighbouring CellMcasurcment Resulls CGI Informalion

UTRA Rcsult t,ist

CGI Information

GERAN R€sult List

CDMA2000 Resuits

Teblc 152 - Contcnt ofMeasurcment Report messagc

236

IN BULLETS IThc Measurement I{eport identifies ils triggering mechanism using the Mcasuremcnt ldentity. I'his identily links thcmcssagc content to the configuration inlormation rvithin the lll{C Connection Ileconfiguration message. lt docs Dotexplicitly indicatc the triggcring nechanism. For cxamplc. thc Measuren'rent Idcntit) could bc signalled as '4' and thenmeasurement idenlity '4' within thc RRC (lonnection Rcconfiguralion mcssage refcrcnces event A3

Serving cell measurements are always included within the Measurement Report. These measurcments allow thc eNode B10 evaluate the coverage provided by the existing serving ce1l, and lo comparc it against the coveragc reported lor each ofthe neighbouring cclls

In the case of inlra-frequency handovers. the Measuremenl Report includes thc ll-UTRA iist of measurement results butcxoludes the inter-systcm ljsts ofmcasurcmcnt results, j.e. the LlTItA, GERAN and ClDM 2000 measuremcnt rcsults arecxcluded

'l hc E-U]'RA list ofmcasurcmcnt resulls identifies each ncighbouring cell by ;ts I'hysical l-aycr Cell Identib, (PCI). TheCell Global Idcntiry (CGI) inforrnation is tl,pical11, cxcludcd al this stage. This information is only included whenspccifically requested by the eNodc B. lt is not includcd by defbult bccause the UFI ha-s lo dccode the MIB and SIII 10

extracl the CGI. Thjs makes it relatively processor lntensive compared to jusl rqoording I{eference Signal measurcments.The eNode B may rcquest the CGI in a separate Measurement Reporl ifthe Automatic Neighbour l{elation (ANR)procedure described in section 25.2 is triggcrcd. The CGI information is not rcquircd ifthe ncighbouring celi is aheadyincluded wilhin the eNode B database 01'neighbours. i.e. the eNode [] can identiry thc ncighbouring cel1 using its PCI

RSIiI and/or RSITQ measurements fiom the ncighbouring cclls are reported to allow the eNodc B to evaluate thcircoverage. lfthc eNode B can identiry a caodidate ncighbouring cell from its PCI, and iflhe coverage conditions indicatethat a handover should bc completed, the eNode B initiates the handovcr procedure bv sending an X2-AP HandoverI{equcsl mcssagc to thc targct c'Node B. I'he conlent of this mcssagc is prcsented in 'l'able I 53

lnformation Elemenls Presence

Message Type

Old eNode B UIi X2AI' ID Mandatory

Cause Mandalorv

'l'srget Cell Idenlity Mandatory

GT]MMEI Maodalory

IJE Conlext lnli)rmalion MME U[ SIAP ID Mandatory

UE Securiry Capabilities Mandalory

AS Sccuritv Inlormation Mandatory

Ul Aggr€gatd Maximum Bit Rate Mandatory

Subscriber Profile ld lor RA'f/l,r€quency Priorilr Optional

E-RAB Selup I-ist E-R {B Idcnlily Mandatory

EJI B t,evel QoS Paramclcrs Mandatory

Downlink Forwarding Oplional

Uplinl G IP I'unnci Endpoirlt Mandatory

RR('('ontext Mandatorv

Haidovcr Rcstriction Lisl Optional

Location Rcporting lnformation Oplional

tiE Historv lniormation Mandalory

Tracc Activation Optional

SRVCC Operation Possible Optional

l'ablc 153 Contenl of thc X2-Al' llandover Request mcssag€

The Cause value wilhin thc X2-AP Ilandover Ilequest is t-vpically configured as 'l landovcr Dcsirable for Radio Rcasons'l1 can also be configured as 'Tjme Critical I Iandover', 'Resource Optimisalion Ilandovcr' or 'il{educe l-oad in ScrvingCell'. Thc lime critical cause indicates that the conncction is likell to drop if a handovcr is no1 completed. I'he resourceoptimisation causc indicales {hat the serving cNode B is allen1ptinEl to balancc the notwork load bctrvccn itsclf and itsncighbours

I,ONG TERM EVOLLTTION (LTE)

rnessage is Presenled in Table 154

II

IIl

.l.he,l.argetCellldenlityissignalledastheE-t]TItAn\CCil.ThjsinfornralioniSextraclcdftomtheeNcldct]databaseol

ncishbours using the pcl u, u,","r"i.".'i:t"",t,,tomatic NeJghbour.Relation (ANR) procedure is triggercd ifthe PCll and

the-corresponding CGI cannot be fou'ii *;ti;,r^ifrc au,ut^" iassuming the network supports the ANR proccdure)

The Globally Unique MME Identity (GUMMEI) is included to inlbnn the tarset eNode B of which MME hosts the UE

connection- l.his alJows thc target cNtoiliii,o "ia."r.,fr" S1-AP 'Path Swilc;Requesl' message to the approprialc MME

during a later stage ofthe handover proccdure

t]I]ConlextlnlbrmationinfomsthctalgetcNodcBofrvhichbearcrsneedtobecstablishcdtosupporttheincominghandover request The se1 of E-RA; ;;;s;;;;; ;c' i I a1c.sn'cc ;;f alonA with their Qualitv of Sen'ice (QoS)

rcouiremenrs. lhe uplink aTp 1"";.;';;;;;i'nr'i. utrn i,,.tua.u to allo* thJ turg''t eNodc B to send uplink tr:er planc datr

;H:r il;'ti ,;;.'t;. i"" "ttrt

it't opp'op'i''t ternt inarion point at t he serr ing ( iateu a1

l.hetargeteNodgBapp]iesilsadmissioncontrolalgorithmaftelreceivingtheX2-APilandoverRequest.ASSumingapositivc outcome, the targel eNode ;;","r".t * XZ:af, gandover Reques-1 Ackrowledge message Thc conlenl ofthis

Table l5,l Content ofthe X2-AP llandoYer Request Acknortledge messagc

flre targct eNode B urc' the llandorer Rcquc:t {''lnurvlcd€tc mcssagc lo inlurm lhc tt'ulqc q\od'' B ol uhich l -RAll

harc hecn admincd. L; I t, tunnel endioins"are specifico ro a-llou rhe.uurcc cNod. B t0 toruarJ uplinL and 'lo$nlinL user

plane dara across rhc x2 inrcrfaca. iil';;;.il;. tj .un atro s1'.. iry anv IJ-RAB which have not been admifled

TheTargeteNodeBtosourcgeNodeBTransparenlContainerjncludcsallandoverCommandmessage'l.hcllandovercommand message encapsulates ariilic;;;;"i; Rcconfigurarion message which has bcen generated by the targct

eNode B. The RRC Connccrion R".;;i;;;;;;; ;rssagc is seint to the sourcJ eNodc B to be forwarded across the air-

interface to the uE. .t.his

message p"r"rw iall irr. ug *itrr-;"slruotions for complering thc handovcr onto the targct aell

.l.hcsourcceNodeBextlactsthcIIRC]Conneclionl].econfigurationmessagefromthcX2-AI)mcssagcandinitiatesthc

r'r".i"t"t n.""*.n phase by forwarding it across thc air-inteface to thc llE

.fhe RRC connection Rcconliguration message includes a scction which specifies mobiliq' control irformation This

section oflhc mcssage is presented in l able 155

'lhePhrsical tater( ell ld(nlil) rl'( l)i: speiificd todircctthc ll onlo the rppropriare ccll lhc uplink and dorrnlink tU-

earricr. are specified in ,.r^ ni,n.i,'t -t/i't{Ai-ARil N. thcchanncl oan.lr. iorir isal.ospccifiedincomhinationqith

any additional spectrum emission requirements

l'he T304 timer is specified using a value of50' 100' 150' 200' 500'.l000 or 2000 ms fhe UE stads this lirner upon

receiving thc mobiljly controj ;"rir"""ii"". ii'i::o+ "*pir",

p.io. to the UE successfully completing the random access

;;;:"';; ;;i;;geroetl' thc uH initiatcs the RRC Conncction Rc-establishment procedure

ThcUEisa]locatedancwC-RNTIbythetargeteNodcB..I.hisC-RNTIisusedtoaddresstheUDwitlrinthetalgctccll

l.he common l{adio Iicsourca confiEluration providcs inlormation rugarding various transport-and physical channets al the

;;;;;li. ii'; ;;"i-um ,plint t'unl'nii fo*t' ano uplink c-r clic prcfix length are also spccificd

Thedct]icatedRACHConfiguralionprovidcssupportforallouingrhclJEtocompl(jlethcnon-contentionbasedRandornAccess procedure.

.l.he uE is attocatJi "'jial."i!i pr.*rfrle stqLi'nce rathcr than aliowing it to seiecl a sequencc at

randon lrom thc pool ol commo" ."u."".'..1rt" thACll mask defines the subftame dur-ing u'hich the Ul'l is aliowed to

use the dcdicated pr"ulnbl" s"qu"n"-"'it i, opprou"r., l"tp, to impro\e the reliabilif- oflhc overall handovcr procedure

Old eNode B tJE X2AP lD

Ne:l, eNode B UE X2AP lD

E-RAB Admitled l-ist

Uptrnt CTP l unncl EndNint

Downlink GTP lunnel Endpoin{

|-RAB Not Admitted List

frJ.NocJr to source eNode B Transparent Container

Criticality Diagnostjcs

238

IN BULLETS

Target Physical Cell ldenhty

Uplink Carrier Frequency

Additional Spectrum Emission Requiremenls

Conmon Radio Resourcc Configuration

Dedicat€d RAC]:l Confi guralion

Random Ac{css PRAC}l Mask Index

'labl€ 155 - Contcnt of Mobilit) Control lnformation from within an RRC Connection Reconfiguratio mcssage

* The source eNode B proceeds to scnd an X2-AP Sequcnce Numbcr (SN) Status Transfer messagc to the targct eNode R.'l his message provides the target eNode B with uplink and downlink PDCP sequence number information lor E,RABusing acknowledged mode RLC. l'his helps to ensure that sequcnce numbering is prcscrved during the handover and thattbe handover is losslcss PDCP sequence numbers for unackno\yledged mode RLC are reset in the larget eNode B. Thecontent ofthe SN Status Transfer message is shown in 'Iablc I56

lnfonnatien Elemenls Prcsonce

Message Type Mahdarory

OhJ eNode B (lti X2AP ID Mandalorv

New eNotle B tlE X2AP ]D Mandalorr

EJIAB Subject to StatusTransfer [-ist

E RAB ld€ntiry Mandalory

Recei!e Status ofUplink PDCP SDU Optional

Uplink COUNT value Mandatory

Downlink COIiNT vahre Mandatorv

Tablc 156 Content of the X2-AI' SN Status 'l'ransf€r mcssage

The optional Rcccivc Status ofllplink PDCI' SDU inlbrmation dcfines a bitmap to indicate which uplink SDU havc beensuccessftlly received, and which have not been reccivcd

The tJplink COI-NT valuc defincs the PDCP sequencc number and Hyper Framc Number (HFN) ofthe first missingupiink SDIJ. 'l he Downlink COLIITIT value delines thc PDCP sequcnce number and HFN that the larget eNodc B shouldallocatc to the next downlink SDU that has not already bccn allocaled a sequencc number

The sourcc eNode B starts for$'arding uscr plane data across thc X2 interfacl] to the larget eNode ts after receiving the X2-AP llandovcr Request Acknowledgc message. Forwarding makes usc ofthe X2 upJink and downlink GTP l unnell-ndpoints specified within thc Handovcr Request Acknowledge message. At this point in time, the targel eNodq B buffersthe packets without lorwarding

239

LONG TDRM EVOLLTTION (LTIi)

lnfomalion Elements Presellce

Message Type I'lanlatory

eNode B IIE SIAP ID Mandatory

Fl-RA B to be Switched inDo.r'nlink List

tj-MB ldcntity Mandatory

Transport Layer Address N4andatory

GI'P-T]JID Mandatory

Source MME UE SlAl'lD Mandatory

ir-IITRAN CGI Mandatory

1'AI Mandatory

tlI Security Capabililies Mandaory

Thc uli proccccls to achievc air-interfacc synchronisation with the 1ar8.ct ccll using thc PIimaD'and Secondary

Synchronjsation Signals. The tJE thcn initiates the random access procedurc whiclr is non-contention based if the target

cNodc B included Dedicated l{ACI I Configuration informalion wilhin the Mobility Control section ollhe RRC

Conncction Rooonfiguration mcssage. The random acccss procedurc is contention bascd ilthe Dcdicaled ItA(lH

Confi guration jnlormation was cxcludcd

.l'hc Random Access Rcsponse (RAR) mcssage providcs the lJ[ rvith timing advancc inlormation for thc larget ccl]. lt also

providcs an uplink resource allocation for the injlial laycr 3 message. In this c:r.se, the jnitial layer 3 messagc is the RRC

bonncction Riconfiguration Complete mcssagc. The IJE compietcs the handover procedurc from the LJE pcrspective by

sending this mcssage

Both uplink and downlinl data can now be transferred betwecn the tJE and larget cNode B. This.epresents lhe start ofthe

Hanilover Completion phasc. t)ownlink data lrom the Sen'ing Gatewa)' continucs to be sent 10 the souroc eNode B' from

where it is forwardcd to thc larget cNode B across tha X2 intcrface. 'fhc target eNode ll car forward uplink dala to thc

SeNing Gatcway using the Sl uplink G1'P Tunnel Endpoint spccified within the X2-AP Ilandover Requcst messagc

Afler receiving the RRC Conneclion Rcconfigumtion Complete mcssage, thc target eNode ll initiales the procedure for

switching the iowniink GIP tunnel from the source eNode B to thc target cNode B. This is done by sending an S1-AI'

Path Swiich Rcquest 10 the MMFI. Thc conlcnl ofthis mcssage is presenled in l'able 157

Tablt 157 Content ofth€ SI-AP Path Switch Requcst message

Thc l,ath Su,itch liequcst specifies both the transport la),cr address and the GTP l unnel Endpoint ldentity ('I EID) $hich

arc to be used when ibrwarding downlink dala to thc targel cNode B. Thc MME is also informcd oflhe Tracking Area

ldenlit_v (T'Al) and Cell Global Identiry (CCI) belonging to the cell with $hich the l lE is no\l connccted

The MME decicles whcther or no1 the exisling Scrying Gatorvay can continue providing services to the UE. Thc examplc

shou,n in Figure I l3 assumcs therc is no rcquirement to changc Serving Galcrvay. lf the Scn'ing Gateway needs 10 he

changccl, the MME forwards a GTPv2-C Creale Session Request message to the new Serving Galervay. and the new

Sen,ing Gateway oonlacts the I'DN Galeway 10 requcst re-direction ofthe existing G IP tunncl

Assuming the Scrving Galeway rcmains unchangsd, the MME lorwards a G'l'l'v2-C Modil Ilearer Roquest message to

thc existi"ng Serving Gatcway. This message instructs the Serving Gateway to start fbr$'arding downlink data tt)u'ards thc

larget cNoie B. 'l'hi Scrving Galovay proceeds to switch thc downlink path, and a{ this poinl bolh uplink and downlink

dala is tanslerrccl betwccn the UE and Scn ing Gateway without any forwarding via the source eNodc B

The Sening Gateway acknowledges thc switch to the MMtr using a GTPv2-C Modii-.r Bearer Rcsponse message. The

MME rhen icknowledgcs rhe swjtch to thc targct cNode B using ar Sl-AP Palh Switch Rcquest Acknorv)edge message

'I he larget eNode B completes lhe handover procedlrre by scndin€l an X2-AP 1)ll Contcxt Release mcssage 1() thc source

cNode E. This message inlorms the souro!'eNode B that it can release i1s rcsources for thc LIE *hich has now moved

aoross to the target eNodc Il

3CPt' References: l S 36.300. TS 23.401, TS 36.331- 'fS 36.423, 'l'S 29 2'74

240