Lte Call Flow Guide

7/13/2019 Lte Call Flow Guide

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ATT Best Practices: LTE Performance & Optimization


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LTE Call Flows

Rethink Possible


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[email protected]


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Abstract:

Main purpose of this document is to discuss LTE basic call flows.

It also introduces LTE network architecture, Nodes, their functionality as well as interfaces that

connect these network nodes.

A brief description of UE states is also i!en.

Contents:

"ocument consists of followin sections#

Network Architecture

Network Interfaces

UE States Transitions

LTE Call Flows

Revision:

Version Date Update

V1.0 July 12, 2011 LT !all Flo"s


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Networ Arc!itect"re:

E!ol!ed $acket %ystem &E$%' contains followin network elements#

EPS Architecture


#E: The User E(uipment.

Evolve$ #TRAN %eNo$eB: The eNode) supports the LTE air interface and includes followin functions#

*unctions for +adio +esource Manaement# +adio )earer ontrol, +adio Admission ontrol, onnectionMobility ontrol, "ynamic allocation of resources to UEs in both uplink and downlink &schedulin'-%election of an MME at UE attachment when no routin to an MME can be determined from the information

pro!ided by the UE-

+outin of User $lane data towards %er!in ateway-

%chedulin and transmission of pain messaes &oriinated from the MME'-

%chedulin and transmission of broadcast information &oriinated from the MME or /0M'-Measurement and measurement reportin confiuration for mobility and schedulin.


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'obilit( 'ana)ement Entit( %''E: The MME manaes mobility, UE identities and security parameters. It includesfollowin functions#

Non Access %tratum &NA%' sinalin and security-

Idle mode UE reachability &includin control and e1ecution of pain retransmission'-

Trackin Area list manaement &for UE in idle and acti!e mode'-

$"N 2 and %er!in 2 selection-

MME selection for hando!ers with MME chane-

+oamin- &terminatin %3a towards home 4%%'

Authentication

)earer manaement functions includin dedicated bearer establishment.

*ervin) +atewa( %*+,: The %er!in ateway is the node that terminates the interface towards EUT+AN. *or eachUEassociated with the E$%, at a i!en point of time, there is one sinle %er!in ateway. *unctions include#

$acket +outin and *orwardin


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The local Mobility Anchor point for inter5eN) hando!er-

E5UT+AN idle mode downlink packet bufferin and initiation of network triered ser!ice re(uestprocedure-

E5UT+AN idle mode downlink packet bufferin and initiation of network triered ser!ice re(uestprocedure-

Accountin on user and 6o% lass Identifier &6I' ranularity for inter5operator charin-UL and "L charin per UE, $"N, and 6I.

End marker handlin$acket *ilterin with T*T

P-N +atewa( %P+,: The $2 is the node that terminates the %i interface towards the $"N. If a UE is accessin

multiple $"Ns, there may be more than one $2 for that UE. The $2 pro!ides connecti!ity to the UE to e1ternalpacket data networks by bein the point of e1it and entry of traffic for the UE. The $2 performs policy

enforcement, packet filterin for each user, charin support, lawful Interception and packet screenin.

$"N 2 functions include#

Mobility anchor for mobility between 7$$ access systems and non57$$ access systems. This is sometimesreferred to as the %AE Anchor function.

$olicy enforcement &atin and rate enforcement'

$er5user based packet filterin &by e.. deep packetinspection' harin support

Lawful Interception &out of scope for phase8' UE I$ address allocation

$acket screenin

Transport le!el packet markin in the downlink-

"L rate enforcement based on A$N Areate Ma1imum )it +ate &A$N5AM)+'

PCRF# $+* is the policy and charin control element. $+* functions include#

$olicy &6o% and atin'control harin control


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In non5roamin scenario, there is only a sinle $+* in the 4$LMN associated with one UE9s I$5ANsession. The $+* terminates the 1, 1c and 1a interfaces.

Networ .nterfaces:


*/0C# +eference point for the control plane protocol between E5UT+AN and MME.

*/0## +eference point between E5UT+AN and %er!in 2 for the per bearer user plane tunnellin and intereNode)path switchin durin hando!er.

*1# It pro!ides user plane tunnellin and tunnel manaement between %er!in 2 and $"N 2. It is used for%er!in2 relocation due to UE mobility and if the %er!in 2 needs to connect to a non5collocated $"N 2 forthe re(uired $"N connecti!ity.

*2a# It enables transfer of subscription and authentication data for authenticatin:authori;in user access to the e!ol!edsystem &AAA interface' between MME and 4%%.

+3# It pro!ides transfer of &6o%' policy and charin rules from $+* to $olicy and harin Enforcement*unction&$E*' in the $"N 2. The interface is based on the 1 interface.


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+3a It pro!ides transfer of &6o%' policy information from $+* to the Trusted Non57$$ accesses.

+3c It pro!ides transfer of &6o%' policy information from $+* to the %er!in ateway

*4: It pro!ides transfer of &6o%' policy and charin control information between the 4ome $+* and the


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?EMM &E!ol!ed Mobility Manaement' is a NA% le!el protocol and is used for UE authentication


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LTE Call Flows:

*ollowin call flows ha!e been discussed in the document#

Initial Call Setup

UE Initiated Detach

MME Initiated Detach

Active to Idle Transition

Network Initiated Idle to Active Transition

UE Initiated Service Request

S1 ased Inter eN !andover

"# ased Inter eN !andover


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.nitial Call *et"p

UE


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MME SGW

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S!

st

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"an#

o$Access"es%onse

""CConnection"e&uest


)a

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""CConnectionSetu%Co$%lete

Attach "e&uest

I#entit! "e&uest

I#entit!"e&uest 'IMSI(

Authentication) Securit!

Initial Conte*t Setu% "e&uest

'Attach Acce%t(

Securit!Mo#eCo$$an#

Securit

!Mo#eCo$%lete

UECa%a+ilit! In&uir!

UECa%a+ilit!Infor$ation

UE Ca%a+ilit! Info In#ication

""CConnection"econfi,uration

""C

Con

ne

In

UL

'A

UL

'A

++ to perorm

@es

U%#ateLocation"e&uest

U%#ate

Location

Answer

CreateSession"e&uest

CreateSession"es%onse

Mo#if!-earer"e&uest

Mo#i

f!-earer"es%

on


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$ -


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Brief -escription:

*(stem Ac9"isition: UE performs fre(uency synchroni;ation and reads MI):%I)s from $)4 to ac(uire systeminformation. It then camps on the most suitable cell.

RRC Connection *et"p: The UE and eNode) e1chane sinalin to set up an ++ connection. The UEthensends ++ onnection %etup omplete messae to the eNode).

Attac! Re9"est: The UE includes in the ATTA4 +E6UE%T messae a !alid UTI toether with the last!isited reistered TAI, if a!ailable. If there is no !alid UTI a!ailable, the UE shall include the IM%I in theATTA4 +E6UE%T messae.

eNode) forwards the Attach +e(uest messae &includin# Messae Type, eN) UE I", TAI, I etc.' to theMME.

.$entit( Proce$"re: In the case of the first Attach, MME sends an Identity +e(uest to the UE. Identity procedureis re(uired only if attach re(uest contains UTI:last5TAI and the TAI is not local to MME

The UE responds with Identity +esponse includin Mobile Identity that is set to IM%I.

A"t!entication*ec"rit(: In case of initial attach when there is no UE conte1t on the network, authentication

isperformed. The MME sends an Authentication Information +e(uest to the 4%% and recei!es an

Authentication Information Answer which is used to send Authentication +e(uest to the UE. Authentication

procedure is optional. UE then sends an Authentication +esponse to the MME

#p$ate Location Re9"est: The MME sends the Update Location +e(uest includin the IM%I. The 4%%replieswith Update Location Answer. %ubscription "ata shall be present when the +esult is %uccess.

Create *ession Re9"est: The MME sends a reate %ession +e(uest to %2 which is followed by confirmation.

.nitial Conte3t *et"p Re9"estAttac! Accept: Attach Accept is sent as NA% $"U in the Initial onte1t %etup

&Messae Type, E5+A) I", 6o% parameters, Transport Layer Address, NA%5$"U, UE %ecurity apabilities,%ecurity key' from MME to eNode).

Attach Accept messae contains new UTI if the attach re(uest contained IM%I or forein:non5local UTI. Thiscompletes Attach +e(uest.

%ecurity procedure and UE apability e1chane is then performed.

RRC Connection Re0confi)"ration: The eNode) sends the ++ onnection +econfiuration messaeincludin the E$% +adio )earer Identity to the UE, and the Attach Accept messae to the UE. The A$N ispro!ided to the UE for which the acti!ated default bearer is associated.

.nitial Conte3t *et"p Response: The eNode) sends Initial onte1t %etup +esponse to the MME

#plin .nformation Transfer: The UE sends an Uplink Information Transfer messae. This messae includesthe Attach omplete messae for MME

Attac! Complete: eNode) encapsulates the Attach omplete messae and transfers it to MME.

'o$if( Bearer 'essa)e: /ne recei!in both onte1t %etup +esponse and Attach omplete, the MME sends aModify )earer +e(uest to %2. %2 sends the response and starts sendin the "L packets.


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#E .nitiate$ -etac!

UE

""CConnection

.etach"e&uest


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MME

S

G

W

.elete Session "e&uest

.elete Session "es%onse

.etach Acce%t

Si,nalin,Connection"elease

UEcanbedetachedeithe

rfromIdleoronnectedm

ode.IfitisIdle,++connectionset

u

U


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UE

If the UEis I#le it$a! +e%a,e#

.etach "e&uest

.etach Acce%t

Si,nalin,Connection"elease

SGW

.e

.e


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Active to .$le Transition

UE

User Inacti/it!.etecte#

MME

UEConte*t"elease"e&uest

UEConte*t"eleaseCo$$an#

UEConte*t"eleaseCo$%lete

SGW

Mo#

if!-earer"e&uest

Mo#if!-earer"es%on

se


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""CConnection"elease

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.$le to ActiveTransition


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UE


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MME

SGW

.ownlink .ata Notification

.ownlink .ata Notification Ack

Pa,in,

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#E .nitiate$ *ervice Re9"est

UE


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MME

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S!ste$Infor$ation

"an#o$AccessPrea$+le

"an#o$Access"es%onse



""

CConnectionSetu%Co$%l

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Initial UE Messa,e

Authentication)Securit!

Initial Conte*t Setu% "e&uest

Securit!Mo#eCo$

$an#

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ecurit!Mo#eCo$%

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Initial Conte*t Setu% "es%onse

Mo#if! -earer "e&uest

Mo#if! -earer "es%onse

U

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*/ Base$ .nter eNo$eB

;an$over

UE

Source

eN- Tar,et eN-

UL).L Pa!loa# .ata

.ecision to %erfor$ han#o/er an#o/er"e&uire#

an#o/er "e&uest

an#o/er "e&uest Ack

In#irect .ata Forwar#0 Tunnel "e&uest

In#irect .ata Forwar#0 Tunnel "es%onse

an#o/er Co$$an#

""C Connection "econfi,uration

eN-StatusTransfer

MME Status Transfer

In#irectforwar#in

, of.L.ata

.L Forwar#e# .ata

""C "econfi,uration Co$%lete

.LFor

w

ar#


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e#.ata

UL Pa!loa# .ata

an#o/er Notif!

Mo#if! -earer "e&uest

En# Marker 'Switch .L .ata Path(

Mo#if! -earer "es%onse

.L Pa!loa# .ata

UE Conte*t "eleaseCo$$an#

UEConte*t"eleaseCo$%lete

.elete Session "e&uest

.elete Session "es%onse

#a$e 12


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Brief -escription:

)ased on UE reports, source eN) decides to initiate %5based hando!er to taret eN) if there is no =>connecti!ity to taret eN).

eN) sends 4ando!er +e(uired &hando!er type, taret Id, cause etc.' messae to MME.

MME !erifies that source %2 can continue to ser!e UE and sends 4ando!er +e(uest messae to taret eN).

Admission ontrol is performed by taret eN) and taret eN) confiured the re(uired resources accordin to therecei!ed E5+A) 6o% information.

Taret eN) sends 4ando!er +e(uest Acknowlede messae to MME.

If indirect forwardin applies MME sets up reate Indirect "ata *orwardin Tunnel +e(uest to %2. %2responds with confirmation.

MME sends 4/ command &4ando!er Type, E+A)s forwardin &optional' etc.' messae to source eN).

%ource eN) sends ++ onnection +econfiuration messae to UE with necessary parameters &taret eN)security alorithm, %I)s etc.'.

%ource eN) sends %tatus Transfer messae !ia MME to taret eN) reardin downlink and uplink transmitterstatus.

/nce UE successfully synchroni;es to the taret cell, it sends an ++ onnection +econfiuration omplete

messae to taret eN). "L packets forwarded from source eN) can be sent to the UE. Also uplink packets can be

sent from UE, which are forwarded to %2.

Taret eN) sends 4ando!er Notify messae to taret MME. MME starts a timer to super!ise when resources in%ource eN) and data forwardin resources in %2 shall be released.

MME sends Modify )earer +e(uest &)earers conte1ts to be remo!ed, bearers need to be deacti!ated etc' messaeto %2.

%2 sends Bend markerC packet to source eN) and then releases resources towards it. /nce Bend markerC

reaches taret eN), %2 can start sendin "L payload data comin from $2. It also sends Modify )earer

+esponse messae to MME.


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67 Base$ .nter eNo$eB ;an$over

UE Source eN- Tar,et eN- MME

S

G

W

.ecision to %erfor$ han#o/er

""CConnection"econfi,uration

UL Pa!loa# .ata


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UL).LPa!loa# .ata

an#o/er"e&uest

an#o/er"e&uestAck

SNStatusTransfer

.ataForwar#in,

""CConnection"econfi,0Co$%lete

.L Forwar#e# .ata

PathSwitch"e&ue

En# Marker 'Switch .L .ata P

Path Sw"e&uestAck

UE Conte*t "elease

En# Marker

%ource eN) uses => interface to

initiate hando!er with taret eN).

$rocess is somewhat similar to %

based hando!er with difference

t

h

a

t

4

a

n

d

o!er re(uest, data

forwardin, End

marker messaes etc.

are e1chaned o!er

=> interface directly

between %ource and

Taret eN)s.

#a$


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For uestions

Fraz Tajammul

[email protected]

Documents

Lte Call Flow Guide