LTE Attach in Bullet Points

UE switched ON - Cell selection

UE > eNB - RRC connection request

eNB > UE - RRC connection set-up

UE > eNB - RRC Connection complete+ Attach request + PDN conn request

eNB > MME - Initial UE message + NAS-PDU ( Attach request + PDN conn request )

MME > HSS - Authentication request ( Acquisition of Authentication vector )

HSS > MME - Authentication information Answer ( RAND, AUTN, XRES, Kasme )

MME > UE -  Authentication request ( RAND, AUTN )

UE - UE generates Auth response from the information received and uses the same algorithm HSS used to generate AV

UE > MME - Authentication response ( RES )

MME - Authenticates UE if RES = XRES (  UE authenticated )

MME - Generates Security keys 

MME > UE -  Security Mode  command

UE - Generates NAS keys

UE > MME - Security mode Complete. 

MME > HSS - Location update request

HSS - Registers UE IMSI , MME ID.

HSS > MME -  Update location answer  ( Subscriber profile + APN + P-GW + QoS )

MME - MME stores APN & subscriber profile 

MME - Assigns EPS bearer ID & P-GW selection by HSS or MME

MME > S-GW - Create session request 

S-GW > P-GW - Create session request

P-GW - Assigns IP address to UE 

P-GW > PCRF -  Notification of EPS session set-up

PCRF - Determines PCC ( Policy charging & control ) policies for the EPS session to established

PCRF > P-GW - Acknowledging EPS Session Establishment

P-GW - Policy Enforcement (Install Policy Rule)

P-GW > S-GW - Create session response

S-GW > MME - Create session Response

MME - Generates Various parameters ( UE AMBR  )

MME - eNB - Initial context set-up request ( Attach accept in NAS-PDU )

eNB - Receives S-GW address and generates keys 

eNB > UE -  Security mode command

UE - UE generates Kenb and AS keys

UE > eNB - Security mode complete

eNB > UE - RRC connection reconfiguration + Attach Accept

UE - DRB is created between UE and eNB

UE > MME - Attach complete ( via eNB )

eNB > MME - Initial context set-up response

MME > S-GW -  - Modify bearer request + eNB address + EPS bearer ID

S-GW > MME -  Modify bearer response

S1 bearer is established between eNB and S-GW. EPS default bearer is UP and user can exchange data.

Mohiuddin Syed

The Motive of the blog is to share the resources and Knowledge about the latest technologies and work practices evolving in the field of Telecommunications.

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