1.
Simplified Call Flow Signaling:
Registration - The Attach Procedure
@3g4gUK

2.
2G/3G/4G Network Architecture
©3G4G
BSC
BTS
MSC
Voice (PSTN)
Network
SGSN
Data (IP)
Network
RNC
Node BeNodeB
MME
GGSN
Access
Network
Core
Network
Air
Interface
MSUEUE
BSSRNS
S-GW
P-GW
2G 2.5G
3G 4G
EPC

3.
Simplified Network Architecture
©3G4G
AS
CS NAS
Voice (PSTN)
Network
Data (IP)
Network
Device / UE
Radio
Access
Network
Core
Network
Air
Interface NAS = Non Access Stratum
AS = Access Stratum
UE = User Equipment
PS NAS
Backhaul
AS

4.
Registration
©3G4G
• The device or UE needs to let the core network(s) know that it is
switched on and active.
• This procedure is known as registration
• The UE can register individually to the CS and PS core networks
• Most modern networks allow combined registration (or combined
attach) whereby the UE registers only to the PS network and the PS
network informs the CS network that the UE is active.

5.
Simplified Network Architecture
©3G4G
AS
CS NAS
Voice (PSTN)
Network
Data (IP)
Network
Device / UE
Radio
Access
Network
Core
Network
Air
Interface NAS = Non Access Stratum
AS = Access Stratum
UE = User Equipment
PS NAS
Backhaul
AS

6.
Simplified Network Architecture
©3G4G
AS
CS NAS
Voice (PSTN)
Network
Data (IP)
Network
Device / UE
Radio
Access
Network
Core
Network
Air
Interface NAS = Non Access Stratum
AS = Access Stratum
UE = User Equipment
PS NAS
Backhaul
AS

7.
Identities
©3G4G
• Each Mobile device contain IMEI (International Mobile
Equipment Identity)
• The SIM (Subscriber Identity Module) contains:
• IMSI – International Mobile Subscriber Identity
• MSISDN – Mobile Subscriber ISDN number
• Secret keys for Authentication with the network
• During operation, the mobile uses temporary identity
called TMSI so that no one can find the true identity of
a mobile.

8.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
Primary Synchronisation Channel / Signal
Secondary Synchronisation Channel / Signal
Other Downlink Reference Signals (4G / LTE Only)

9.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
PS CN broadcast information
CS CN broadcast information
System information messages

10.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
PS CN broadcast information
CS CN broadcast information
System information messages
Hello, I am UE 1

11.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
PS CN broadcast information
CS CN broadcast information
System information messages
Hello, I am UE 1
Hello UE1, please use this channel <…>
Thanks, I am all setup.

12.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
PS CN broadcast information
CS CN broadcast information
System information messages
Hello, I am UE 1
Hello UE1, please use this channel <…>
Thanks, I am all setup.
Hello, I am UE 1. Want to Attach and let you know that I am now active
Hello UE 1, please authenticate yourself against this vector <…>

13.
HLR, HSS & AuC
©3G4G
• HLR – Home Location Register
• HSS – Home Subscriber Server
• AuC – Authentication Center
4G PS Core
Network
2G/3G PS
Core Network
2G/3G CS
Core Network
HLR/HSS/AuC
DATA
Logic

14.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
PS CN broadcast information
CS CN broadcast information
System information messages
Hello, I am UE 1
Hello UE1, please use this channel <…>
Thanks, I am all setup.
Hello, I am UE 1. Want to Attach and let you know that I am now active
Hello UE 1, please authenticate yourself against this vector <…>
No problems, here is my authentication response <…>

15.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
I trust UE1, please establish security with it
Establish Security using <…>
Thanks, all done.
Security Established

16.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
I trust UE1, please establish security with it
Establish Security using <…>
Thanks, all done.
Security Established
Attach Accept. Please use this new temporary identity for now
Attach Complete.

17.
The Attach Procedure Signalling
©3G4G
UE AN CS CN PS CN
Access Network Core Network
UE1 is now connected to us
I trust UE1, please establish security with it
Establish Security using <…>
Thanks, all done.
Security Established
Attach Accept. Please use this new temporary identity for now
Attach Complete.

18.
Thank You
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©3G4G