LTE NAS Layer Interviews Questions ans Answers

Q1 What is the full form of NAS Layer?

Ans NAS stands for Non Access Startum, and it lies in LTE L3 Layer?

Q2 How many EPS Services modes NAS Layer have in LTE? Describe them?

Ans The NAS procedures are grouped in two categories:

  • the EPS Mobility Management (EMM)

      1) EMM common procedures:
      An EMM common procedure can always be initiated whilst a NAS signalling connection exists.
      The procedures belonging to this type are: Initiated by the network:
          - GUTI reallocation;
          - authentication;
          - security mode control;
          - identification;
          - EMM information.
      2) EMM specific procedures:
      At any time only one UE initiated EMM specific procedure can be running. The procedures belonging to this type are:
          - attach and combined attach.
          - attach.
          - normal tracking area updating and combined tracking area                 updating (S1 mode only)
          - periodic tracking area updating (S1 mode only).
          - detach and combined detach.
      3) EMM connection management procedures (S1 mode only):
          - service request
          - paging procedure
          - transport of NAS messages;
          - generic transport of NAS messages.

  • the EPS Session Management (ESM).

        Two types of ESM procedures can be distinguished:
      1) Procedures related to EPS bearer contexts:
          These procedures are initiated by the network and are used for the manipulation of EPS bearer contexts:
          - default EPS bearer context activation;
          - dedicated EPS bearer context activation;
          - EPS bearer context modification;
          - EPS bearer context deactivation.
          This procedure is initiated by the network or by the UE and is used for the transport of user data via the control plane:
          - transport of user data via the control plane procedure.
    2) Transaction related procedures:
        These procedures are initiated by the UE to request for resources, i.e. a new PDN connection or dedicated bearer resources, or to release these resources:
             - PDN connectivity procedure;
             - PDN disconnect procedure;
             - bearer resource allocation procedure;
             - bearer resource modification procedure.

Q3 UE attached with which EPS Services mode?

Ans UE attached with both modes EMM and ESM. Each mode have own information.

Q4 Jio network work on which EPS mode?

Ans jio is pure ip based network means it don’t have legacy network ex:2G or 3G. So it work only PS Mode 1 and PS Mode 2.

Q5 If a UE configured to use SMS over SGs, but not configured to use CS Fallback shall operate in which mode? 

Ans Then UE will use CS/PS 1.

Q6 What is the reason if, UE in CS/PS mode1 of operation will be failure in CS domain?

Ans if UE send combined attach message to enb and registration is done with CS/PS Mode 2 then UE will fail in CS domain.

Q7 What are reasons of IMS voice not available  “refers the conditions”.

Ans if any geographical area there is no volte enable network is available then ue move PS to CS with a conditions that IMS voice services not available.