LTE Attach Procedure Interview Questions 21-30

Q21. Who generate IP address for UE? In which message UE get this IP address?

Ans. Packet Gateway (P-Gw) generate the IP address for ue in lte network. UE get the ip address in RrcReconfiguration (attach accept) message during attach procedure.

Q22. How many maximum IP addresses a UE can have in lte?

Ans. If UE connect with 1 P-Gw than UE have 1 IP Address, if UE connect with 2 P-Gw than UE have 2 IP address.
Note: if UE is IMS compatible and at UE location there is IMS service present, then UE will do combine attach and UE get 2 IP addresses. because IMS is separate PDN, and Internet is separate PDN, so UE have 2 IP Address (1 for Internet, 1 for IMS)

Q23. How MME select S-Gw and P-Gw in LTE?

Ans. MME send update location request message along with subscriber info request message to HSS. A HSS reply back with update location answer along with subcsriber info answer to MME. In that messages HSS give the s-gw location based on network topology (geographical present) and p-gw information behalf of user info saved on HSS respectively. So based on these information’s MME select S-Gw and P-Gw in LTE.

Q24. How MME get the PDN address of a specific UE in attach procedure?

Ans. In subscriber info answer a mme knows about PDN info based on user subscription. reference TS 3GPP 23.401.

Q25. What are the Information Element present in Create Session Request?

Ans.

Q26. What are the causes of Authentication Failure?

Ans. Authentication response carry the authentication failure message:
Message type: AUTHENTICATION AND CIPHERING FAILURE 

Significance: dual
Direction: UE to network
failure cause: AUTN Token, RAND value, Timer 3302, XRES, KASME etc.

Q27. What are the causes of Security Mode Command Failure?

Ans. Ciphering failure or integrity protection failure are main causes for more refer to TS 24.301, Table no. 9.9.3.9.

Q28. What is Service Request?

Ans. After complete attach procedure ue sent the rrc connection request again according to testcase body. So the rrc connection request (with C-RNTI) sent by ue in 2nd time is called service request.

Q29. What is the difference between Service Request and Extended Service Request?

Ans. Service request i explain the Q28 answer. Now the extended service request sent by ue at time of when ue want to perform MO, MT call (CSFB procedure) time.

Q30. The RRC-Connection Re-configuration message receive by UE and send by UE in Attach procedure in Which Signalling Radio Bearer(SRB)?

Ans. In attach procedure ue receive RrrcConnectionReconfiguration message on SRB1. The Reconfiguration message response sent on SRB1 also. But point to be note here the attach complete message sent by ue on SRB2.