Simplified Call Flow Signaling: Registration - The Attach Procedure

Simplified Call Flow Signaling: Registration - The Attach Procedure

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2G/3G/4G Network Architecture

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BSC

BTS

MSC

Voice (PSTN) Network

SGSN

Data (IP) Network

RNC

Node B eNodeB

MME

GGSN

Access Network

Core Network

Air Interface

MS UE UE

BSS RNS

S-GW

P-GW

2G 2.5G

3G 4G

EPC

Simplified Network Architecture

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AS

CS NAS


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

Registration

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• 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.


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AS

CS NAS


Data (IP) Network

Device / UE

Radio Access

Network

Core Network



PS NAS

Backhaul

AS


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AS

CS NAS


Data (IP) Network

Device / UE

Radio Access

Network

Core Network



PS NAS

Backhaul

AS

Identities

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• 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.

The Attach Procedure Signalling

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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)


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UE AN CS CN PS CN


PS CN broadcast information

CS CN broadcast information

System information messages


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UE AN CS CN PS CN





Hello, I am UE 1


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UE AN CS CN PS CN





Hello, I am UE 1

Hello UE1, please use this channel <…>

Thanks, I am all setup.


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UE AN CS CN PS CN



CS CN broadcast information System information messages

Hello, I am UE 1



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 <…>

HLR, HSS & AuC

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• 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


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UE AN CS CN PS CN





Hello, I am UE 1



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 <…>


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UE AN CS CN PS CN


I trust UE1, please establish security with it Establish Security using <…>

Thanks, all done.

Security Established


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UE AN CS CN PS CN



Thanks, all done.


Attach Accept. Please use this new temporary identity for now

Attach Complete.


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UE AN CS CN PS CN


UE1 is now connected to us


Thanks, all done.


Attach Accept. Please use this new temporary identity for now

Attach Complete.

Thank You

To learn more, visit:

3G4G Website – http://www.3g4g.co.uk/

3G4G Blog – http://blog.3g4g.co.uk/

3G4G Small Cells Blog – http://smallcells.3g4g.co.uk/

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Technology

Simplified Call Flow Signaling: Registration - The Attach Procedure