LTE UE Attach Interview Que Ans 1-10

Q01. Which layer carry Attach Request Message in uplink direction?

Ans. RRC layer piggyback attach request message (a NAS message) in uplink direction, because NAS layer not present in EnodeB. Once enodeb received this message it forward this message to MME.

Q02. What are the information elements are presents in attach request message?

Ans.

Q03. How UE get PDN connectivity request?

Ans. UE get default PDN connectivity information from Access Point Name, yes APN have default PDN information. For eg internet (internet also a part of PDN types)

Q04. What is the timer of Attach message? And it duration?

Ans. When UE send attach request it’s start timer T3410 and it’s duration is 15s.

Q05. What is the meaning of EPS Mobility Management (EMM) and what kind of information it carry?

Ans. EMM is a sublayer of nas layer and provides the mobility management to user equipment. EMM have 3 procedures:-

(1) EMM common procedure, (2) EMM specific procedure, (3) EMM connection management procedure

**Note: All EMM procedure are describes in NAS layer interview que ans page.

Q06. In which case UE carry IMSI or GUTI? Elloborate them?

Ans. GUTI always generate by MME and allocated to ue in Attach Accept message.

When a user brought a new sim-card from market, at that time ue don’t have any GUTI or S-TMSI. So we send attach request to mme with IMSI only for 1^st time. Once ue received Attach accept and mme allocate GUTI then next time we send attach request with GUTI and S-TMSI.

Q07. What are the Information Element are present in Authentication Request Message?

Ans. Authentication Request message is transferred my MME 2 times, 1^st time mme send auth. Request ot HSS side and 2^nd time it send to UE side.

Q08. What are the Information Element are present in Security Mode Command?

Ans.

Q09. Suppose IMSI and GUTI both are not available, then what UE will do?

Ans. In this case UE use IMEI to send attach request to MME.

Q10. How UE calculate Authentication Token and Random Value?

Ans. When MME send Authentication information request to HSS it send SN ID (serving identity means PLMN Id). The authn. Token drive from k key present in hss. After that hss sent back it to mme inside authen. token SN ID also present and mme stored this information. And do same procedure in UE side also. Once ue sent back response mme validate them.

Random value also present in HSS and USIM both and applied EPS AKA Algorithm and drive XRES in hss and RES in UE.