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lte signaling flows
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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
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