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  • LTE NAS Layer Interview Questions and Answers



    1. What is the full form of NAS Layer?
    2. How many EPS Services modes  NAS Layer have in LTE? Describe them?
    3. UE attached with which EPS Services mode?
    4. Jio network work on which EPS mode?
    5. If a UE configured to use SMS over SGs, but not configured to use CS Fallback shall operate in which mode?
    6. What is the reason if, UE in CS/PS mode1 of operation will be failure in CS domain?
    7. What are reasons of IMS voice not available  “refers the conditions”.
    8. What is the functionality of eKSI in Lte?
    9. What is the reason if eKSI parameter are changed, after that what UE will do?
    10. Key hierarchy and its Derivation
    11. Define EPS Mobility Management?
    12. EMM Common Procedure?
    13. EMM Specific Procedure?
    14. EMM Connection Management Procedure?
    15. EMM Sublayer States?
    16. What is GUTI? GUTI size? GUTI combination? Who allocate GUTI? When? Why?
    17. Why identity procedure require by network?
    18. What is the purpose of Authentication Request, why it require, which entities(nodes) are responsible for that? And Authn.  Timer?
    19. If MME send Authn reject message which cause value MME send?
    20. What is IMEIsv in Security Mode Command(SMC)?
    21. Attach and Combined attach difference? When UE trigger this message and which purpose? Timer of attach message and Information Elements (IEs) present in attach procedure?
    22. Which layer transmit the attach message?
    23. If a UE transmit the normal attach and after some time UE need to send a combined attach, which scenario UE will follow?
    24. What is the parameter responsible for allocation fresh key to UE, if it attach to the Network every time?
    25. Detach procedure in Lte?
    26. What is Tracking Area Update? It’s Timer? And RRC Establishment cause UE send to ENodeB to send TAU Request? And what are the conditions for TAU?
    27. What is paging? How UE know that its paging message? If ue don’t have DRX Cycle in idle state then ue receive the paging? What information paging message carry?
    28. What kind of information HSS reply back to MME in Authentication Information Answer message (AIA)?
    29. Information Elements (IEs) present in Security Mode Command?
    30. 1 ENodeB is connected to maximum 6 MME at a time then, How ENodeB know which MME (out of 6) need to forward initial UE message?
    31. MME connected many S-GW via S-11 interface then, How MME know which S-GW (out of 10) need to forward Create Session Request
    32. How MME find the P-GW address?
    33. How MME transmit the UE request to attach network to concern PDN?
    34. Difference between Initial UE Request and Initial UE context Setup Request?
    35. Difference between attach accept and attach complete?
    36. Why in attach procedure there are two times security mode commands are transmit by network?
    37. Who will sent default bearer request and in which message?
    38. Who generate dedicated bearer in Lte?
    39. Difference between Access Startum (AS) and Non-Access startum (NAS)?
    40. Which common Key present in USIM and HSS, behalf of that which keys are generated by USIM and HSS?


    Joni Tyagi

    Author & Editor

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