2/5/13 Telecom Tutorials by Samir Amberkar: LTE - end-to-end UE initial attach
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LTE - end-to-end UE initial attach
LTE - end-to-end UE initial attach [Under LTE]» E-UTRA and E-UTRAN overall description - 36.300, Rel 8 « » E-UTRAN access - 23.401, Rel 8 « » EMM and ESM - 24.301, Rel 8 « » GTPv2-C - 29.274, Rel 8 « » S1AP - 36.413, Rel 8 « » NAS overall - 24.007/8, Rel 8 « » RRC - 36.331, Rel 8 « » Numbering - 23.003, Rel 8 « » SAE Security architecture - 33.401, Rel 8 « » 3G Security - 33.102, Rel 8 « » USIM Application - 31.102, Rel 8 «
In SAE/EPS article, we looked at LTE network architecture; in this article, we will look at end-to-end initial UE attach signaling.
What is different with LTE UE initial attach ? In LTE, initial attach is combined with (default) PDN (IP) connectivity. You can call this default PDN (IP)connectivity as default (or basic or initial) PDP context activation. This default connectivity is always of non-guaranted bit rate type (basically somethingwhich handles mostly bursty internet traffic). This default connectivity is called "default bearer". LTE no more use NAS terminology of "Sessions". By the way, LTE NAS consists only of Mobility Management (EMM) and Session Management (ESM). Additional PDP Contexts or Sessions (withdifferent QoSs than default bearers) are called "dedicated bearers". Yes, it is misleading to call it "dedicated" !
Just like "Secondary PDP Context" in GPRS/UMTS, dedicated bearer has same PDN (IP) address as default bearer and specific QoS. Yes, Template) is utilised here (UE and PGW) too ! QoS is defined differently in LTE (check out 3GPP TS 36.300 section 13 and 23.401, section 4.7.3).
Below is a end-to-end signaling diagram for UE initial attach. I have included lot of specification references to dig in further.
USIM UE eNB MME SGW PGW
UICC
E-UTRA N Uu
S1
S1 1
S5 /S8
S6 a
UE pow er s on .
Sy n ch r on isa t ion a n d
cell select ion
pr ocedu r es in it ia ted.
MM/RR/PLMN da ta
ta ken fr om USIM
a pplica t ion .
To sta r t a t ta ch
pr ocedu r e, EMM
r equ est RRC
Con n ect ion .
In it ia l a t ta ch
2 3 .4 01 :5 .3 .2 .1
RRC in it ia t ion
3 6 .3 3 1 :5 .3 .3 .2
RRC Con n ect ion
Requ est (Ca u se,
Iden tity - S-TMSI or
r a n dom ).
eNB in v okes RRM
a n d RRC pr ocedu r es.
RRC Con n ect ion Setu p
(Ra dio con fig s -
RLC/PDCP/MA C/PHY
r ela ted to SRB1 )
RRC in it ia t ion
3 6 .3 3 1 :5 .3 .3 .2
RRC Con n ect ion Setu p
Com plete
(PLMN iden tity , NA S
PDU) NA S PDU
con ta in EMM A tta ch
Requ est (old GUTI or
IMSI, ESM PDN
Con n ect iv ity
Requ est).
RRC in it ia t ion
3 6 .3 3 1 :5 .3 .3 .2
EMM A tta ch
2 4 .3 01 :5 .5 .1 .2
ESM PDN
2/5/13 Telecom Tutorials by Samir Amberkar: LTE - end-to-end UE initial attach
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ESM PDN
Con n ect iv ity
2 4 .3 01 :6 .5 .1 .2
GUTI 2 3 .003 :2 .8
S1 A P - In it ia l UE
Messa g e
(UE S1 A P ID, NA S
PDU, RRC ca u se)
3 6 .4 1 3 In it ia l
UE:8 .6 .2 .1
MME m a y tr ig g er
a u th en tica t ion ,
secu r ity & ciph er in g
pr ocedu r es.
2 3 .4 01
Ov er a ll:5 .3 .2 .1
Dia m eter -
A u th en tica t ion In fo
Requ est
(IMSI, PLMN ID)
S6 a
in ter fa ce/Dia m eter
a u th en tica t ion
2 9 .2 7 2 :5 .2 .3
Dia m eter -
A u th en tica t ion In fo
A n sw er
(A u th In fo - RA ND,
A UTN, SRES, KASME)
S1 A P - DL NA S
Tr a n spor t
(NA S PDU - EMM
A u th en tica t ion
Requ est {RA ND,
A UTN} )
3 6 .4 1 3 In it ia l
UE:8 .6 .2 .2
UE-EPC
a u th en tica t ion
3 3 .4 01 :6 .1
EMM a u th en tica t ion
2 4 .3 01 :5 .4 .2
RRC DL In for m a tion
Tr a n sfer
(NA S EMM PDU)
RRC DL In fo:5 .6 .1
UICC - A u th en tica te
UE w ou ld ex ecu te
A UTHENTICA TE
com m a n d in USIM
a pplica t ion to g et
SRES a n d CK
(Cih per in g Key ).
USIM A u th en tica te
3 1 .1 02 :5 .2 .1
RRC UL In for m a tion
Tr a n sfer
(NA S PDU - EMM
A u th en tica t ion
Respon se {SRES} )
RRC UL In fo:5 .6 .2
S1 A P - UL NA S
Tr a n spor t
(NA S EMM PDU)
3 6 .4 1 3 In it ia l
UE:8 .6 .2 .3
MME com pa r es SRES
(r eceiv ed fr om UE
a n d HSS).
3 3 .1 02
A u th en tica t ion :6 .3
MME tr ig g er s NA S
secu r ity pr ocedu r e.
NA S en cr y pt ion a n d
in teg r ir y key s
(KN ASenc a n d KN ASi nt
r espect iv ely ) w ill be
der iv ed fr om KASME
r eceiv ed fr om HSS.
3 3 .4 01 Secu r ity
key s:6 .2
UE NA S w ou ld sta r t
ciph er in g a n d
in teg r ity pr otect ion
(sta r t in g fr om n ex t
Secu r ity Mode
Com plete m esssa g e).
UE w ou ld der iv e
KASME fr om CK
r eceiv ed fr om USIM
(a s pa r t of
A u th en tica te
com m a n d. UE w ou ld
th en der iv e NA S
EMM - Secu r ity Mode
Com m a n d over
RRC/S1AP transport
(UE Secu r ity
ca pa bilit ies,
Ciph er in g a lg or ith m ,
In teg r ity a lg or ith m )
3 3 .4 01 NA S
secu r ity :7 .2 .4 .4
2 4 .3 01 EMM
Secu r ity :5 .4 .3 .2
2/5/13 Telecom Tutorials by Samir Amberkar: LTE - end-to-end UE initial attach
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th en der iv e NA S
en cr y pt ion a n d
in teg r ir y key s (i.e.
KN ASenc a n d KN ASi nt
r espect iv ely ).
EMM - Secu r ity Mode
Com plete over
RRC/S1AP transport
Dia m eter - Upda te
Loca t ion Requ est
(IMSI, V isited PLMN
ID, RA T ty pe)
S6 a
in ter fa ce/Dia m eter
a u th en tica t ion
2 9 .2 7 2 :5 .2 .1 .1
MME does th e SGW
(a n d PGW ?)
select ion .
2 3 .4 01 SGW
select ion :4 .3 .8 .2
Dia m eter - Upda te
Loca t ion A n sw er
(Su bscr ipt ion da ta )
GTP-C - Cr ea te Session
Requ est
(IMSI, A PN, PGW
S5 /S8 a ddr ess/F-TEID,
PDN ty pe, EPS Bea r er
ID, Defa u lt EPS QoS,
A g g r eg a te Ma x im u m
Bit Ra te, PDN a ddr ess
(fix ed?), PCO)
2 9 .2 7 4 Cr ea te
Session :7 .2 .1
GTP-C - Cr ea te Session
Requ est
(IMSI, A PN, SGW User
pla n e TEID, PDN ty pe,
EPS Bea r er ID, Defa u lt
EPS QoS, A g g r eg a te
Ma x im u m Bit Ra te,
PDN a ddr ess (fix ed?),
PCO)
2 9 .2 7 4 Cr ea te
Session :7 .2 .1
PGW u ses QoS policy
(loca l or r eceiv ed
fr om PCRF) to com e
ou t w ith a list of
bea r er s (defa u lt +
option a l dedica ted
bea r es).
GTP-C - Cr ea te Session
Respon se
(PDN a ddr ess,
A g g r eg a te Ma x im u m
Bit Ra te, PCO,
Defa u lt/Dedica ted
bea r er con tex ts {EPS
bea r er ID, PGW User
pla n e TEID, QoS} )
2 9 .2 7 4 Cr ea te
Session :7 .2 .2
User DL da ta (if a n y )
th r u GTP tu n n el
(ov er S5 /S8
in ter fa ce).
MME h a s n ow
ev er y th in g in pla ce
to in str u ct eNB to
sta r t In it ia l Con tex t
Setu p pr ocedu r es.
S1 UE con tex t {S1 A P
ID, Bea r er ID, TEIDs}
w ou ld be cr ea ted.
KeN B is der iv ed fr om
KASME.
3 3 .4 01 Secu r ity
key s:6 .2
GTP-C - Cr ea te Session
Respon se
(PDN a ddr ess,
A g g r eg a te Ma x im u m
Bit Ra te, PCO,
Defa u lt/Dedica ted
bea r er con tex ts, SGW
User pla n e TEID)
2 9 .2 7 4 Cr ea te
Session :7 .2 .2
RRM pr ocedu r es
w ou ld "a dm it" EPS
bea r er , cr ea te S1 UE
con tex t {S1 A P ID,
Bea r er ID, TEIDs} ,
in for m GTP-U a bou t
Bea r er ID-Tu n n el ID
m a ppin g a n d
in it ia te fu r th er RRC
pr ocedu r es. Fir st
pr ocedu r e w ou ld be
A S Secu r ity
pr ocedu r e to sta r t
Ciph er in g a n d
S1 A P - In it ia l Con tex t
Setu p Requ est
(UE S1 A P ID,
A g g r eg a te Ma x im u m
Bit Ra te,
defa u lt/dedica ted
bea r er {E-RA B IDs,
QoS, SGW GTP TEID,
NA S PDU, EPC
Tr a n spor t a ddr ess} ,
UE Secu r ity
Ca pa bilit ies, Secu r ity
key KeN B)
3 6 .4 1 3 In it ia l
Con tex t Setu p:8 .3 .1
2/5/13 Telecom Tutorials by Samir Amberkar: LTE - end-to-end UE initial attach
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Ciph er in g a n d
In teg r ity pr otect ion .
eNB w ou ld der iv e
User da ta
en cr y pt ion a n d RRC
en cr y pt ion &
in teg r ity key s fr om
KeN B. Th ese key s
r esepect iv ely a r e
KU Penc , KRRCi nt , a n d
KRRCenc .
3 3 .4 01 Secu r ity
key s:6 .2
A lon g w ith
Secu r ity , RRC
Recon fig pr ocedu r e
ca n be sta r ted.
Con tex t Setu p:8 .3 .1
Tr a n spor t a ddr ess is
EPC IP a ddr ess to
w h ich u ser (UL) IP
pa ckets a r e to be
for w a r ded.
3 6 .4 1 4 Tr a n spor t
a ddr ess:5 .3
NA S PDU con ta in EMM
A tta ch A ccept (GUTI,
ESM m essa g e). ESM
m essa g e w ou ld be
A ct iv a te Defa u lt EPS
Bea r er Con tex t
Requ est (EPS bea r er
ID, QoS no ARP, PDN
A ddr ess, A PN)
2 4 .3 01 EMM A tta ch
A ccept:5 .5 .1 .2 .4
2 4 .3 01 ESM Defa u lt
Bea r er
r equ est :6 .4 .1 .2
RRC A S Secu r ity Mode
Com m a n d
(Ciph er in g a lg or ith m ,
In teg r ity a lg or ith m )
3 3 .4 01 A S
Secu r ity :7 .2 .4 .5
3 6 .3 3 1 RRC
Secu r ity :5 .3 .4
Sim ila r to eNB, UE
der iv es KU Penc ,
KRRCi nt , a n d KRRCenc
fr om KeNB to sta r t
Ciph er in g a n d
In teg r ity pr otect ion .
Th is w ou ld be
a ckn ow ledg ed to
n etw or k.
RRC Con n ect ion
Recon fig u r a ion
[EPS bea r er ID, DRB
ID, Ra dio con fig s -
RLC/PDCP/MA C/PHY,
NA S pdu ]
RRC 3 6 .3 3 1 :5 .3 .5
RRC Secu r ity Mode
Com plete
RRC 3 6 .3 3 1 :5 .3 .4 .1
RRC/L2 /PHY w ou ld be
con fig u r ed for SRB2
a n d DRB. RRC w ou ld
a ckn ow ledg e th is is to
eNB a n d pa ss on NA S
PDU to EMM.
RRC Con n ect ion
Recon fig u r a t ion
Com plete
RRC 3 6 .3 3 1 :5 .3 .5
UE NA S w ou ld
con str u ct EMM
A tta ch Com plete
m essa g e w h ich
w ou ld con ta in ESM
r eply a s w ell.
S1 A P - In it ia l Con ex t
Setu p Respon se
(UE S1 A P IDs, E-RA Bs
setu p {E-RA B ID, eNB
GTP-U TEID, eNB
Tr a n spor t a ddr ess})
3 6 .4 1 3 In it ia l Con ex t
Setu p:8 .3 .1 .2
EMM - A tta ch
Com plete over
RRC/S1AP transport
(ESM PDU)
ESM PDU w ou ld
con ta in ESM A ct iv a te
defa u lt EPS bea r er
Con tex t A ccept
m essa g e (PCO).
2 4 .3 01 EMM
A tta ch :5 .5 .1 .2 .4
2 4 .3 01 ESM Defa u lt
bea r er
a ct iv a t ion :6 .4 .1 .3
MME w ou ld tr ig g er
GTP-C pr ocedu r e
tow a r ds SGW to
in for m eNB r ela ted
deta ils to SGW.
GTP-C - Modify Bea r er
Requ est
(EPS bea r er IDs, eNB
F-TEID)
2 9 .2 7 4 Modify Bea r er
Requ est :7 .2 .7
For h a n dov er
scen a r ios, SGW w ill
h a v e to tr ig g er GTP
m odify bea r er
pr ocedu r e tow a r ds
PGW ov er S8
in ter fa ce.
GTP-C - Modify Bea r er
Respon se
2 9 .2 7 4 Modify Bea r er
Respon se:7 .2 .8
User UL da ta
2/5/13 Telecom Tutorials by Samir Amberkar: LTE - end-to-end UE initial attach
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User UL da ta
th r ou g h DRB
User UL da ta
th r ou g h GTP tu n n el
(S1 1 in ter fa ce)
User UL da ta
th r ou g h GTP tu n n el
(S5 /S8 in ter fa ce)
User DL da ta (if a n y
bu ffer ed ea r lier )
th r ou g h GTP tu n n el
(S1 1 in ter fa ce)
User DL da ta
th r ou g h DRB
Th is com plete LTE
in it ia l a t ta ch
pr ocedu r e. UE is
a tta ch ed, defa u lt
bea r er a ct iv e. RRC-
Con n ected, EMM-
Reg ister ed, ECM-
Con n ected sta te.
In next article, we will look at end-to-end signaling for dedicated bearer setup.
References: 3G Evolution: HSPA and LTE by Dahlman, Parkvall, Sköld, and Beming, LTE - From Theory to Practice, Edited by Sesia, Toufik, and Bakerand SAE and the Evolved Packet Core: Driving the Mobile Broadband Revolution by Olsson, Sultana, Rommer, Frid, and Mulligan.
Copyright © Samir Amberkar 2010-11
LTE - QoS « LTE Index » LTE - dedicated bearer setup
Posted on Tu esday, October 25, 2011
