A simple yet explanative presentation on EPS Architecture & Attach Procedure

1. EVOLVED PACKET SYSTEM (EPS)
Architecture & Attach Procedure
By
Anirudh Yadav

2. WHAT IS EPS ?
• Release 8 of 3GPP
• E-UTRAN (Radio N/W) + EPC (Core N/W) = EPS
• Flow of EPS architecture.
User  Radio N/W  Core N/W  IP N/W
(UE, e-nodeB) (E-UTRAN) (EPC) (IMS)

3. EPS ARCHITECTURE

4. Continued…..
• UE: refers to the device controlled by user Eg.- mobile,
tablet, USB dongle etc.
• E-nodeB:
– formal name for cell tower.
– X2 interface with other e-nodeBs.
– WCDMA vs. EPS architecture.
• MME:
– Keeps track of user state whether ON or OFF
– Communicates with HSS for security keys & encrypted data
– User can be registered with 1 MME at a time.
– Primary responsibilities include EMM (user’s location & state?)
& ESM (create actual data session)

5. Continued….
• HSS:
– Similar to HLR
– Contains all encrypted data related to user.
– Acts as a database information storage node.
• S-GW:
– 1 UE can be served by 1 S-GW.
– MME tells it what P-GW to connect to.
– Handles user IP packets b/w e-nodeB & P-GW.
• PDN-GW:
– Known as PCEF, connected to PCRF, OCS (billing server)
– Controls amount of QoS dictating its services as a DICTATOR.
– Functionally an IP router.

6. CONTROL & USER PLANE

7. ATTACH PROCEDURE

8. Continued….
1. ATTACH REQUEST:
– UE wants to connect, sends an attach request to e-nodeB
– E-nodeB determines which MME to connect to.
2. AUTHENTICATION INFO REQUEST/RESPONSE
– MME queries the HSS for key information
– Pre-shared key concept
– MME asks e-nodeB what specific it wants to ask?
– Authentication successful.
3. UPDATE LOCATION REQUEST
– HSS declares specific MME for the UE
– In case of old MME it cancels it & update the location
register.

9. Continued….
4. UPDATE LOCATION ANSWER
– HSS forwards the UE’s subscription services, QoS networks &
information to the MME.
5. CREATE SESSION REQUEST
– MME figures out what P-GW can serve that external network
& what S-GW can serve what e-nodeB to which subscriber is
connecting on.
– Tunnels points/legs get created b/w e-nodeB & S-GW & b/w
S-GW & P-GW.
6. CREATE SESSION RESPONSE
– P-GW- Dictator, billing with OCS sever, controls QoS settings
– MME gets this response from P-GW through S-GW.

10. Continued….
7. ATTACH ACCEPT:
– MME sends IP in ATTACH ACCEPT to UE.
– Also include IP of S-GW for e-nodeB
– E-nodeB forwards ATTACH ACCEPT as part of RRC message.
8. ATTACH COMPLETE
– UE sends ATTACH COMPLETE to MME
– Connection b/w UE & e-nodeB & b/w S-GW & P-GW gets
created.
9. MODIFY BEARER REQUEST
– MME sends this request to S-GW
– Includes TEID of e-nodeB
– Connection b/w e-nodeB & S-GW gets completed
– UE is able to exchange data

11. HISTORICAL CONTEXT
GPRS
• MS (Mobile sation)
• nodeB
• RNC
• SGSN
• GGSN
• HLR
EPS
• UE
• E-nodeB
• E-nodeB
• S-GW & MME
• P-GW
• HSS