Attach flow & srb

Attach – Call Flow
13 Feb 2016

2015 © Samsung Electronics 2
Network Identities

 GUTI – Globally Unique Temporary UE Identity - is assigned only by the MME during
initial attach of a UE to the E-UTRAN – masks the true identity of the subscriber
 GUTI provides an unambiguous identification of the UE that does not revel the UE’s
permanent identity. It also allows identification of the MME and Network to which
UE attaches
 GUTI has to main components - GUMMEI Globally Unique Mobility management
Entity Identifier and the M –TMSI that uniquely identifies the UE within the MME
 For paging, the mobile is paged with the S-TMSI which is a shorter version of GUTI
 On the S1 Interface, the IMSI is typically not seen just like the GUTI. Exceptions are
initial attach when no old GUTI is stored on the USIM card or in paging procedure
Identities Used in LTE - GUTI
MCC and
MNC are 3
DIGITS

 RNTI – Radio Network Temporary Identifier
 RNTI is signaled in the MAC Layer. When MAC uses the PDCCH to indicate radio
resource allocation, the RNTI is mapped on the PDCCH depends on the logical channel
type -
 C- RNTI : Temporary Cell Radio Network Temporary Identifier for Dedicated Control Channel
(DCCH and DTCH). It defines which data sent in DL belongs to a particular subscriber – all RRC
messages are marked with same C RNTI for a subscriber
 P- RNTI : Paging Radio Network Temporary Identifier for Paging Control Channel (PCCH) is
derived from IMSI. It does not refer to a particular UE but to a group of UEs.
 RA- RNTI : Random Access Radio Network Temporary Identifier for Random Access Response
(RAR) on DL-SCH – assigned to particular UE and is contained in the response from eNode B
for PRACH. The UE then uses this RA- RNTI to send RRC Connection Request
 Temporary C-RNTI for Common Control Channel (CCCH) during random access procedure
 SI- RNTI : System Information Radio Network Temporary Identifier for Broadcast Control
Channel (BCCH) – sent on PDCCH - it signals to all UEs where SIBs are found on PDSCH
Identities Used in LTE - RNTI
RNTI Values

LTE Identities

Bearers

LTE Identifiers

UE Temporary ID’s at different interfaces

S1AP Interface
 In between eNB and MME, the User can be identified using the S1AP ID’s.
 eNB-UE-S1AP ID is the S1AP ID terminating at the eNB side
 MME-UE-S1AP ID is the S1AP ID terminating at the MME Side.

GTP Teid’s
 GTP-C Teid’s (S11 MME GTPC Teid and S11/S4 SGW GTPC Teid) are used as the control
plane teid’s at MME and GW respectively.
 GTP-U Teid’s(S1-U eNB GTPU Teid and S1-U SGW GTPU Teid) are used as the user
plane teid’s at eNB and GW respectively.

Diameter Session ID
 Gx Diameter Session Id can be used to identify the diameter packets related to a
particular subscriber session.
 Gx diameter session Id will be created when the session is created for the subscriber
and will stay till the session is available.

Attach Procedure

Attach Procedure
T300 stops in UE
T300 starts in UE (200ms)
Timer starts in eNB :
RRC_CONNECTION_SETUP (1000 ms)
Timer stops in eNB :
RRC_CONNECTION_SETUP
Timer Stops at UE :
S1_INITIAL_CONTEXT_SETUP
Timer Starts at UE :
S1_INITIAL_CONTEXT_SETUP =
10000 ms

Attach Procedure
RRC Connection Reconfiguration message including EPS Radio Bearer Identity and Attach
Accept message; UE sends Uplink Information Transfer message to the eNodeB which
includes the Attach Complete message

Attach Procedure
RRC_CONNECTION_RECONFIG = 1500 ms
RRC_SECURITY_MODE_COMMAND = 2000
ms
RRC_SECURITY_MODE_COMMAND
RRC_UE_CAPABILITY_ENQUIRY[ms] = 2000

RACH
rrcConnection
Request
rrcConnection
Setup
rrcConnection
Setup Complete
EPS mobility management

RACH Trigger (Two Examples)

RRC Connection Request (UpLink) (Two Examples)

RRC Connection Setup (Down Link)

RRC Connection Setup Complete (Uplink)
Attach Request

• The UE initiates the Attach procedure by sending the Attach Request message to the eNodeB
with following identities.
• IMSI or GUTI
• TAI (if available)
• UE Capabilities - indicates supported NAS and AS security algorithms by UE
• Attach Type - indicates EPS or combined EPS/IMSI
• ESM Message Container
• RRC Parameters
• The ESM Message Container contains the following identities.
• Request Type
• PDN Type - indicates requested IP version (IPv4, IPv6 or IPv4v6)
• Protocol Configuration Options (PCO) - included by UE and sent transparently to MME to
indicate Address allocation preference of UE (eg. after establishing default bearer using DHCP)
• Ciphered Options Transfer flag - must be set if PCO or APN or both are to be sent by UE
• KSIASME (if valid EPS security parameters available)
• NAS Sequence number (if valid EPS security parameters available)
• NAS-MAC (if valid EPS security parameters available)
• additional GUTI
• P-TMSI
• The RRC parameters indicate the Selected Network and old GUMMEI.
Attach Request

Attach Request

• UE-AMBR and APN-AMBR
• APN-AMBR
The APN-AMBR defines the total bit rate that is allowed for all non-GBR bearers associated with a
specific APN. The APN-AMBR limits the total non-GBR traffic for an APN, independent of the
number of PDN connections and non-GBR bearers that are opened for that APN. For example, if an
operator provides an APN for Internet, the operator may then limit the total bandwidth for that
APN.
UE-AMBR
• The UE-AMBR is defined per subscriber and defines the total bit rate allowed to be consumed for
all non-GBR bearers of a UE. The subscription profile contains the UE-AMBR. The eNodeB enforces
the UE-AMBR.
• There are different AMBR values for uplink and downlink directions - UL APN-AMBR, DL APN-
AMBR, and UL UE-AMBR, DL UE-AMBR.
AMBR

29
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RJIL Initial Attach Request (APN=jionet)
SAE GW
UE eNB MME
S-GW P-GW
HSS PCRF SPR
Power on
RRC Connection Setup
1. Attach Request(PDN Connectivity Request)
3. UE IP allocation
LTE Authentication
NAS Security Setup
2. Create Session Request
IMSI, MSISDN, APN=jionet, PCO, Bearer Context (Bearer ID, Bearer QoS – QCI:9, GBR: 0, MBR: 0)
4. CCR(Indication of IP-CAN Session establishment)
Initial Request, Subscription-Id(e.g., IMSI), UE-IP, APN, Event-
Report, QoS Info(APN-AMBR(UL/DL)), EPS Bearer QoS(QCI, ARP)
5. Profile Request
6. Profile Response
User Profile = internet
7. Policy Decision
8. CCA(Acknowledge of IP-CAN Session Establishment)
PCC Rule for Default bearer(QCI=9, ARP=1, APN-
AMBR(UL/DL)=50Mbps/100Mbps, Offline, TFT(UL/DL))
IMSI, Initial Request, APN=jionet
11. Attach Accept(Activate Default EPS bearer Context Request)
APN=jionet, UE-IP, Default Bearer QoS(QCI=9, ARP=1, UE-AMBR(ULAPN-
AMBR(UL)=50Mbps, TFT(UL)=(UE IP, *, SIP, *, UDP), PCO, GUTI, TAI-list
12. Policy Enforcement
13. Attach Complete(Activate Default Bearer Context Accept)
14. Modify Bearer Request
15. Modify Bearer Response
Default Bearer(QCI=9)
Bearer ID
Location Update
9. Policy Enforcement
10. Create Session Response
UE-IP, Default bearer QoS(QCI=9, ARP=1, APN-AMBR(UL)=50Mbps, TFT(UL)=(UE IP, *, SIP, *, UDP)
OCS
9.1 CCR (Indication of Session, APN=JioNet)
9.2 CCA (Ack of session, APN=JioNet)
Steps after Attach Request are :
1. Authentication
2. Security Mode
3. Identity Check
4. Update Location
5. Create Session
6. Attach Accept
7. UE capability
8. Modify Bearer
ASIUCAUM

30
Samsung Confidential and Proprietary Information. All Contents Copyright ⓒ 2011 Samsung Electronics Co., Ltd.
RJIL PDN Connectivity Request (APN=ims)
OCS
4.1 CCR & CCA to/from PCRF, APN=ims)
PCRF
4.2 CCR & CCA to/from OCS, APN=ims)
PCO : Protocol
Configuration Option is
used to allocate the PCSCF
domain name /IP address
DNS : Domain Name
Server translates
hostname into IP address
PCO option is used
by UE during PDP
context activation
to request for
P_CSCF address,
DNS server details
etc
Steps after
Modify
Bearer are :
1. PDN
Request
2. Create
Session
3. Activate
Bearer
4. Modify
Bearer
Modify Bearer Request
Modify Bearer Response
Not
configured
PCAM

VoLTE - UE Attachment and IMS Registration message
UAR : User Authorization Request, UAA : User Authorization Answer
MAR : Multimedia Authorization Request, MAA : Multimedia Authorization
Answer
UDR : Update Data Request, UDA : Update Data Answer
SAR : Server Authorization Request, SAA : Server Authorization Answer
Auth Challenge
Steps after Modify
Bearer are :
1. REGISTER
2. Authorization
3. 401
Unauthorized
4. REGISTER
5. Authorization
6. 200 OK
RA4RA2

 "Signalling Radio Bearers" (SRBs) are defined as Radio Bearers (RB) that are used only
for the transmission of RRC and NAS messages. More specifically, the following three
SRBs are defined:
 SRB0 is for RRC messages using the CCCH logical channel;
 SRB1 is for RRC messages (which may include a piggybacked NAS message) as well as for
NAS messages prior to the establishment of SRB2, all using DCCH logical channel;
 SRB2 is for RRC messages which include logged measurement information as well as for
NAS messages, all using DCCH logical channel. SRB2 has a lower-priority than SRB1 and is
always configured by E-UTRAN after security activation.
 Once security is activated, all RRC messages on SRB1 and SRB2, including those
containing NAS or non-3GPP messages, are integrity protected and ciphered by PDCP.
NAS independently applies integrity protection and ciphering to the NAS messages
SRB

LTE SRB Type Direction RRC message RLC Mode
LTE SRB0 (CCCH)
Downlink
RRC Connection Setup
RRC Connection Reject
RRC Connection Re-establishment
RRC Connection Re-establishment reject Transparent
Uplink
RRC Connection Request
RRC Connection Re-esblishment Request
LTE SRB1(DCCH)
Downlink
RRC Connection Reconfiguration
RRC Connection Release
Security Mode Command
UE Capability Enquiry
DL information transfer(if no SRB-2)
Mobility from EUTRA Command
Handover from EUTRA preparation request
CS Fallback parameter response CDMA2000
Counter Check
Acknowledged
Uplink
RRC Connection Setup Complete
Security Mode Complete
Security Mode Failure
RRC Connection Reconfiguration Complete
RRC Connection Re-establishment Complete
Measurement report
UE Capability information
UL Information Transfer(if no SRB2)
UL handover preparation transfer
CS fallback parameters request CDMA2000
Counter Check response
LTE SRB2 (DCCH)
Downlink DL Information Transfer
Uplink UL Information Transfer
SRB

Message RB Lo CH
LoCH
No
LCID
MIB - BCCH 0 -
SIB 1 - BCCH 1 -
SIB 2 - BCCH 1 -
RRC : PRACH Preamble - - - -
RRC : RACH Response - - - -
RRC : RRC Connection Request SRB0 UL CCCH 0 0
RRC : RRC Connection Setup SRB0 DL CCCH 0 0
RRC : RRC Connection Setup Complete + NAS : Attach Request + ESM : PDN Connectivity Request SRB1 UL DCCH 0 1
RRC : DL Information Transfer + NAS : Authentication Request SRB1 DL DCCH 0 1
RRC : UL Information Transfer + NAS : Authentication Response SRB1 UL DCCH 0 1
RRC : DL Information Transfer + NAS : Security Mode Command SRB1 DL DCCH 0 1
RRC : UL Information Transfer + NAS : Security Mode Complete SRB1 UL DCCH 0 1
RRC : Security Mode Command SRB1 DL DCCH 0 1
RRC : Security Mode Complete SRB1 UL DCCH 0 1
RRC : RRC Connection Reconfiguration SRB1 DL DCCH 0 1
RRC : RRC Connection Reconfiguration Complete SRB1 UL DCCH 0 1
RRC : UL InformationTransfer + NAS : Attach Complete + NAS : Activate Default EPS Bearer SRB2 UL DCCH 1 2
RRC : UL Information Transfer + ESM : PDN Connectivity Request SRB2 UL DCCH 1 2
Control Channel Mapping
DRB (user) Data Radio Bearer
SRB Signalling Radio Bearer

 Diameter is an authentication, authorization, and accounting protocol for computer
networks. It evolved from and replaces the much less capable RADIUS protocol that
preceded it.
 The main features provided by Diameter but lacking in RADIUS are:
 Support for SCTP
 Capability negotiation
 Application layer acknowledgements, Diameter defines failover methods and state machines
(RFC 3539)
 Extensibility; new commands can be defined
 Aligned on 32-bit boundaries
 A Diameter Application is not a software application but is a protocol based on the
Diameter base protocol defined in RFC 6733 (Obsoletes: RFC 3588).
 Each application is defined by an application identifier and can add new command codes
and/or new mandatory AVPs (Attribute-Value Pair). Adding a new optional AVP does not
require a new application.
Diameter

LTE Attach Messages
FromeNB to MME
UE Capabilities for E-UTRAN
IMS PS Voice preferred and
CS voice as secondary

Message Details in brief (UE messages shown in Red Font)
Attach Request – UE to MME over 102 VLAN (RRC Connection Set Up); contains
S1AP ID allocated from eNB, Contains PDN connectivity request for Jionet APN, with
IMS Voice as preferred and CS Voice as secondary
1. Authentication – MME to DRA to HSS using Diameter ID for S6a, contains IMSI,
HSS replies using same Diameter Session ID with Authentication Vectors , MME
sends Authentication Request (EPS Challenge Request) to UE using same S1AP
ID received from eNB during Attach Request and allocates the MME end S1AP
ID. Now both S1AP ID allocated (eNB side and MME side). UE then sends
Authentication Response computed by it using the same S1AP IDs.
2. Security Mode – MME to UE over S1AP interface; MME sends Security Mode
Command to UE using the same S1AP ID, UE replies with Security Mode
Response which also includes IMEI.
3. Identity Check – MME to DRA to EIR over S13 interface; MME sends IMSI &
IMEI to EIR for Identity Check through Diameter. New Diameter ID created. EIR
replies stating IMEI as “white listed”
4. Update Location – MME to HSS over S6a; In case MME does not have context
information of UE, Update Location is sent to HSS which then sends Cancel
Location Message to old MME. HSS sends Update Location Answer to new MME
using same Diameter Session ID as contained in the request – this reply contains
APN details (Jionet and IMS) and three PDN types IPv4, IPv6 and IPv4/IPv6

5. Create Session: MME to SAEGW over S11 interface; This is first GTP C message
for the subscriber. GPTC TeID from MME side added. SAEGW sends CCR-I
request over Gx interface to PCRF. CCA-I is received from PCRF containing the
charging rules & the triggers for CCR-U towards PCRF. SAEGW sends CCR-I
towards OCS over Gy interface with details of session related information. OCS
replies with CCA-I. After receiving reply from both PCRF and OCS, SAEGW sends
Create Session Response to MME and adds the GTPC TeID for the S11 interface
(now both ends TeID created for GTPC over S11) and IPv4 and IPv6 Address
allocated to UE for Jionet APN, indicates the AMBR values, adds the GTPU
TeID for eNB for S1-U interface
6. Attach Accept: MME to UE using the same S1AP ID created earlier. Contains
GTPU TeID for S1-U interface received from SAEGW, contains GUTI & S-TMSI.
7. UE capability: eNB to MME using already existing S1AP ID; sends UE capability
for UTRAN and GERAN; eNB sends Initial Context Set Up Response to UE
(Activate Default EPS Bearer Context Request) which includes the GTPU TeID
for S1-U interface towards SAEGW; UE sends Attach Complete Message
towards MME
8. Modify Bearer: MME sends Modify Bearer Request towards SAEGW which
contains the GTPU TeID received from eNB (Now both ends TeID of GTPU are
with SAEGW); SAEGW acknowledges by sending Modify Bearer Response to
MME

IMS Attach Messages
IMS Registration Messages

eNB S1AP ID which was allocated by eNB for this UE
NAS-PDU content received from UE.
InitialUEMessage, Attach Request (1/2) S1AP/NAS message from UE
S1AP message from eNB
Message in Hex
Attach Request from UE to MME
VLAN 102

Attach Request – Voice Preference (2/2)
FromUE to MME
IMS PS Voice preferred and
CS voice as secondary
VLAN 102

Authentication Information Request from MME to HSS
AIR message from
MME DRA HSS
Diameter session ID for S6a Interface
IMSI
Authentication Request from MME to HSS

Authentication Vectors
Authentication Information Answer from HSS to MME
AIA message from
HSS  DRA MME
Same
session ID

EPS Challenge towards UE
Authentication Request
Same eNB S1AP ID as
received in Attach Request
MME sends
the Allocated
MME S1AP
ID
Authentication Request from MME to UE
Now both UE S1AP
Ids are created from
eNB side and MME
side

eNB and MME S1AP ID’s
Response calculated by UE
Authentication Response
Authentication Response from UE to MME
Same UE S1AP Ids
created from eNB
side and MME side
are used

Security Mode Command
Security Capability related
From MME to UE

Security Mode Complete
FromUE to MME
Contains IMEI

IMEI Check
MME  DRA  EIR
ME Identity Check Request
Diameter Session
ID for S 13
IMSI
IMEI
ME Identity from MME to EIR

IMEI Check Response
EIR -> DRA -> MME
ME Identity Check Answer
White Listed
ME Identity Response from EIR to MME
Same Session
ID

ULR message from
MME -> DRA -> HSS
Update Location Request
Update Location Request is sent
when MME does not have the
context information for the UE
Diameter Session
ID for S6a
Update Location Request from MME to HSS
IMSI

CLR to Old MME to delete the UE Context
HSS-> DRA -> Old MME
Cancel Location Request to old MME

ULA message with subscription data
HSS -> DRA -> new MME
Update Location Answer to new MME
APN Information is
sent
Same Diameter
Session ID for S6a as
contained in request

APN Profile in Update Location Answer
Jionet
IMS APN
Three PDN types IpV4,
IpV6 and IPv4v6

S11 MME GTP-C Teid
Create Session Request
First GTP-C message for this subscriber, so GW GTP-C Teid is ‘0’
From MME to Gateway (SAEGW)
IMSI
Can contain - Three PDN
types IpV4, IpV6 and
IPv4v6

CCR-I
SAEGW(PCEF) -> DRA -> PCRF
Credit Control Request –Gx(CCR - I)
From PGW to PCRF over Gx
Diameter Gx Session ID
Subscription ID contains
IMSI

CCA-I
PCRF -> DRA -> SAEGW(PCEF)
Credit Control Answer – Gx(CCA-I)
Event Triggers for CCR-U towards PCRF
Charging Rule Names
Trigger for ECGI
change can be
added
Same Session ID

CCR –I (Gy)
SAEGW -> DRA -> OCS
Credit Control Request – Gy(CCR-I)
Session Related Info Sent to OCS
Gy Interface
Diameter Session ID for Gy Interface

CCA-I (Gy)
OCS -> DRA -> SAEGW
Credit Control Answer – Gy(CCA-I)

IPv4 and IPv6 Address allocated to UE
Create Session Response
SGW GTP-c Teid
SGW GTP-U Teid
From SAEGW to MME after receipt of CCA from OCS
TeID already received by SAEGW
SAEGW adds its GTP C TeID
GTP C both ends
TeID complete
SAEGW adds its GTP U TeID to eNB
Aggregate MBR values for
Jionet APN

S1AP Attach Accept
S1AP Attach Accept
MME -> eNB
GUTI Value Allocated
To UE
GW GTP U TeID
S-TMSI
Allocated =
MME Code + M-
TMSI

UE Capability Info Indication
FromeNB to MME
UE Capabilities for E-UTRAN
UE Capabilities for geran-cs
UE Capabilities for geran-ps

eNB GTP-U Teid
S1AP Initial Context Setup Response
Initial Context Seutp Response
eNB -> MME

S1AP Attach Complete
From UE to MME

CCA-I (Gy)
OCS -> DRA -> SAEGW
Gtpv2 Modify Bearer Request
GTP-C Teid of GW
S1-U eNB GTP-U Teid
From MME to SAEGW for Default Bearer

S1U SGW GTP-U Teid
Gtpv2 Modify Bearer Response
GTP-C Teid of MME
From SAEGW to MME for Default Bearer

1. PDN Connectivity Request for IMS APN – UE to MME; uses the same S1 AP
ID already created ; indicates PDN connectivity type as IPv4 or IPv6 or
IPV4/IPv6; requests details of P CSCF and DNS Server;
2. Create Session: MME to SAEGW using the GTPC TeID already defined; This
contains the GTPC TeID from MME; SAEGW sends CCR U message to PCRF
over Gx interface; New Diameter Session ID created for IMS APN; This message
contains details of IMSI & MSISDN and the IPv4 & IPv6 address allotted to IMS
APN; PCRF replies with CCA I which contains charging rule and event triggers
to sent CCR U; SAEGW then sends Create Session Response to MME with
GTPC TeID of SGW & PGW for QCI 5 and the Primary & Secondary IPv4 &
IPv6 address of P-CSCF and the IP Address of DNS and the IPv4 & IPv6
address allocated to IMS APN and the SAEGW TeIDs for S1-U traffic
3. Attach Accept: MME to ENB ; MME sends S1 ERAB Set Up Request to eNB
and Activate Default Bearer Context Request to UE; Message also contains
the the IP address for IMS APN for UE and AMBR values for IMS APN. The eNB
sends ERAB Set Up Response containing the GTPU TeIDs for S1 U for QCI 5;
Now both ends of GTPU TeID defined for QCI 5; UE sends Activate Default
Bearer Context Accept.
4. Modify Bearer: MME to SAEGW; MME sends Modify Bearer Request which
contains details of the eNB GTP TeID for S1 U for QCI 5; SAEGW sends Modify
Bearer Accept. Now QCI 5 bearer is established and data can start flowing.

S1AP PDN Connectivity Request [1/2]
Same
MME- UE-S1AP-ID
Same
ENB- UE-S1AP-ID
S1AP PDN Connectivity Request for IMS APN
UE to MME

S1AP PDN Connectivity Request [2/2]
S1AP PDN Connectivity Request for IMS APN
APN: IMS
Requesting Details of DNS
and P-CSCF Address
UE to MME
Three PDN types IpV4,
IpV6 and IPv4v6

Create Session Request for IMS APN
GTPv2 Create Session Request
APN: IMS
IMSI: same
GTP-C Teid of MME
GW GTP-C Teid
allocated before
MME to SAEGW

CCR-I for IMS Session on Gx Interface
CCR-I for IMS Apn on Gx Interface
SAEGW(PCEF)  DRA  PCRF
Subscription ID contains IMSI
and MSISDN
Diameter Gx Session ID
for IMS APN
IPv4 and V6 Address
allocated to IMS APN
This is new Diameter Session ID
allocated for IMS. This is not the same
ID which has been used for Jionet
SAEGW to PCRF

CCA-I for IMS Session on Gx Interface
CCA-I for IMS Apn in Gx Interface
PCRF  DRA  PCEF(SAEGW)
Charging
Rule Name
Event Triggers about
when to send CCR-U
Same IMS Diameter Session ID of Gx Interface
used in Request message(CCR-I)

Create Session Response for IMS APN [1/3]
GTPv2 Create Session Response
Bearer ID for IMS
EBI - 6
GTP-C Teid of SGW and
PGW
MME GTP-C Teid
allocated before
SAEGW to MME
EBI 5 is allocated to Jionet and EBI 6 for IMS
based on availability

Primary and Secondary IPV4 P-
CSCF Address (since only IPv4
configured)
IPv4 and IPv6 Address
allocated for IMS APN
If available, IPv6 P-CSCF
address can also be given
by SAEGW
SAEGW to MME
UE is allocated two sets of IP Addresses – one for Jionet APN and second for IMS APN
The UE would be allocated IPv4 or IPv6 or IPv4v6 based on initial request,
configuration in HSS and PGW. Final decision on allocation by PGW . For usage
Ipv6 would be preferred if available on both UE and Network side
DNS IP which UE has
to Use

S1-U SGW and S5/S8 PGW GTP-
U Teid’s for User Plane Packet's
QOS for EBI-6 bearer
QCI -5
SAEGW to MME

S1AP E-RAB Setup, Activate default EPS… [1/3]
S1AP E-RAB Setup Request
S1AP E-RAB Setup Request which
contains
EBI-6
QOS details
One message contains
S1AP E-RAB Setup Request &
NAS Activate default EPS bearer Context Request
MME to eNode B

S1AP E-RAB Setup, Activate default EPS… [2/2]
NAS Activate default EPS bearer Context Request
NAS PDU
towards UE
QCI -5
EBI-6
Only last 64 bits of IPv6
Address and IPv4 Address
Aggregate MBR values for
IMS APN
MME to UE

S1AP E-RAB Setup Response
S1AP E-RAB Setup Response
S1AP Message from eNB
EBI-6
GTP-U Fteid details of eNB
eNode B to MME

S1AP/NAS Activate default EPS bearer context accept
Activate Default EPS bearer context accept
NAS Message from UE
Accept message from UE
UE to MME

Gtpv2 Modify Bearer Request for Ebi-6
Modify Bearer Request
GTP-U Fteid of eNB
MME to SAEGW

Gtpv2 Modify Bearer Response for Ebi-6
Modify Bearer Response
GTP-U Fteid of SGW
Request Accepted
Now the GTP-U teid’s of eNB and
GW are known at both sides.
User data transfer can flow now.
SAEGW to MME

TCP 3-Way Handshake
A three-way-handshake is a method used in a TCP/IP network to create a Reliable Connection
between a client and server. It is a three-step method that requires both client and server to
exchange SYN and ACK (acknowledgment) packets before actual data communication begins.
A three-way-handshake is also known as a TCP handshake.

TCP SYN
When Client wants to initiate a connection with Server, Client sends a segment with
SYN(Synchronize Sequence Number). This segment will inform the Server that Client would like
to start a communication with Server and informs that with what sequence number it will
start its segments with.
Note: Sequence Numbers are mainly used to keep data in order.

TCP SYN –ACK
Now Server will respond to Client with "Acknowledgment" (ACK) and SYN bits set.
Here Servers ACK segment does two things; they are as below
1. It acknowledges Client’s SYN segment.
2. It informs Client that what sequence number it will start its data with.

TCP ACK
Now finally Client Acknowledges Server’s initial sequence Number and in its ACK signal.
And then Client will start the actual data transfer.
Note: Initial Sequence Numbers are randomly selected while initiating connections between
two machines.

IMS REGISTRATION using
QCI 5 Bearer already created
A different subscriber taken as example
CCR: Credit Control Request , CCA: Credit Control Answer
UAR : User Authorization Request, UAA : User Authorization Answer
MAR : Multimedia Authorization Request, MAA : Multimedia Authorization Answer
UDR : Update Data Request, UDA : Update Data Answer
SAR : Server Authorization Request, SAA : Server Authorization Answer

Message Details in brief(UE messages shown in Red Font)
1. REGISTER: UE to P CSCF; contains the IP Address allocated for IMS APN to UE and IP
address of P CSCF received via PCO Options and the SIP Call ID used for Registration;
P CSCF sends REGISTER Message to ICSCF : contains the Public User Identity which
generally starts with sip: or tel:
2. Authorization: ICSCF sends UAR message to HSS; HSS replies with UAA to I CSCF; I-
CSCF forwards the SIP Register message to the S-CSCF address received from HSS; S
CSCF then sends MAR to HSS requesting Authentication Vectors for Multimedia
session from HSS. HSS replies with MAA;
3. 401 Unauthorized: From S CSCF to P CSCF to SAEGW to UE; Contains SIP
Authorization parameters received from HSS and uses the same Call ID as received in
the REGISTER Message;
4. REGISTER: UE sends second REGISTER to SAEGW to P CSCF to S CSCF using same
Call ID; This contains the Authentication Response based on the keys received in 401
Unauthorized
5. Authorization: S-CSCF Sends the REGISTER Message to I CSCF; I-CSCF (SCFX in NSN)
sends UAA to HSS and again asks HSS about which S CSCF (S-CFX) to use; HSS replies
with UAA to I CSCF; I-CSCF forwards the SIP Register message to the S-CSCF address
received from HSS; S CSCF sends SAR to HSS and Updates HSS that the user is
authenticated and asks to provide the subscription Information; S-CSCF request HSS
to map the subscriber to the mentioned S-CSCF server name; HSS replies with SAA
which contains charging information and identities present in HSS for the subscriber;
6. 200 OK: S- CSCF to P CSSF to SAEGW to UE; uses the same Call ID; After this
message is received we can see the two Horizontal BARS symbols for IMS in UE

SIP REGISTER (Unprotected)
SIP Register(Unprotected)
SIP Call ID used for Registration
process
P-CSCF Address received i
PCO options
IPv6 Address allocated to
IMS APN
SIP “Via” header contains Transport,
Last SIP hop and transaction ID
Expiry Value for SIP Transaction
Private Identity of the user
Used in Authentication Request
A different subscriber taken as example
UE to P CSCF

SIP REGISTER (Unprotected) from P-CSCF to I-CSCF
SIP Register(Unprotected)
REGISTER message
One more “Via” header
added about p-cscf route
Content of the Message will not
be modified, rather new
headers like Via and IMS related
will be added.
From: contains the Public User Identity
Generally starts with sip: or tel:

User Authorization Request (I-CSCF to HSS)
User Authorization Request
SCFX  DRA  HSS
New Diameter Session ID allocated by
I-CSCF
User Name Contains IMSI

User Authorization Answer (HSS to I-CSCF)
User Authorization Response
HSS  DRA  SCFX
S-CSCF address
Result as
Diameter Subsequent Registration
I-CSCF forwards the SIP
Register message to the S-CSCF
address received from HSS

Multimedia Auth Request (S-CSCF to HSS)
Requesting Authentication Vectors for Multimedia
session from HSS.
Requested Authentication Vectors : 5
New diameter Session ID allocated by S-CSCF

Multimedia Auth Answer (HSS to S-CSCF)
Received
SIP Auth Items : 1
Same diameter session ID used for MAR

SIP 401 Unauthorized (S-CSCF  P-CSCF  SAEGW UE)
SIP Auth parameters
Received from HSS
Same SIP Call ID used in
REGISTER message
“Via” header used for routing
purposes

SIP Register (2nd ) (UE -> SAEGW -> PCFX -> SCFX)
Same SIP
Call ID
Authentication Response based on the
keys received in 401 Unauthorized

User Authorization Request ( 2nd time)
New Diameter Session ID again
I-CSCF(SCFX in NSN) again asks
HSS about which S-CFX to use

User Authorization Answer(HSS  I-CSCF)
S-CSCF Server name
I-CSCF forwards the SIP
Register message to the S-CSCF
address received from HSS

Server Assignment Request (S-CSCF  DRA  HSS)
S-CSCF Server name
S-CSCF Updates HSS that user is authenticated and
asks to provide the subscription Information

Server Assignment Answer (HSS  DRA  S-CSCF)
Identities present in HSS for this
subscriber
S-CSCF request HSS to map the
subscriber to the mentioned
S-CSCF server name
Charging Information

200 Ok for SIP Register (S-CSCF  P-CSCF  SAEGW  UE)
SIP Call ID
Used for registration process
After this message is received
we can see the two Horizontal
BARS symbols for IMS in UE
Public Identity
for the user for next transactions

Modify bearer request *is initiated by MME/S4-SGSN and/or from S-GW to P-GW*
Here you are not adding or deleting any resources/bearers.
This message is used when there is no change on allocated bearers, Only the cause is
user is moving from one place to another. Basically Radio Part is changing. This
information MME should inform to all Core Network Elements (S-GW) and it helps
them to attain the resources and handovers case too. It will just modify the bearers.
After getting the response of Modify Bearer Request it indicates that User Plane is
ready to carry the user data as Control plane is done and now data can flow in between
E-UTRAN and S-GW.
Update Bearer Request: *is initiated by P-GW to S-GW and/or from S-GW to MME/S4-
SGSN*
I want to explain here with example. Suppose you are playing a online game in your
Mobile. It requires a promised speed to avoid the delay and you are subscribed for that
too. Now suddenly you got to know that you have to send a mail to your boss but you
don't want to close your game. For this purpose you need more resources.
Here Update Procedure will come.
You already have dedicated bearers with you. Your packet forwarding is happening
through P-GW but you need more resources. In this case P-GW will initiate the
message Update Bearer Request.

Attach Procedure

Attach Procedure
T300 stops in UE
T300 starts in UE (200ms)
RRC_CONNECTION_SETUP (1000 ms)
RRC_CONNECTION_SETUP
Timer Stops at UE :
S1_INITIAL_CONTEXT_SETUP
Timer Starts at UE :
S1_INITIAL_CONTEXT_SETUP =
10000 ms

Attach Procedure

Attach Procedure
RRC_SECURITY_MODE_COMMAND = 2000
ms
RRC_SECURITY_MODE_COMMAND
RRC_UE_CAPABILITY_ENQUIRY[ms] = 2000

Attach Request (RACH third Message)
ASIUCAUM
EPC ATTACH
PDN connectivity
Request for Jionet APN

Security
Attach Accept & Activate Default Bearer
ASIUCAUM
Attach Accept and Default EPS
Bearer Request QCI 9
EPC ATTACH
UE Capability Information
Authentication Request
Authentication Response

Attach
Complete /
Default EPS
Bearer QCI 9
accept
PDN
Connectivity
Request to IMS
Default Bearer
Accept QCI 5
PCAM
IMS ATTACH

REGISTER
401
Unauthorized
REGISTER
200 OK
RA4RA2
SUBSCRIBE
200 OK
NOTIFY
200 OK
IMS REGISTRATION
TCP SYNC
SIP MESSAGES WOULD START AFTER TCP SYN

INVITE
100 TRYING
183 Session in
Progress
PRACK
200 OK

Attach flow & srb

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