5G Interview Questions Answers 17-26

Q17. What’s are the Deployment option’s of RAN’s implementation available in 5G NR.

Ans. These are the possible deployment options are available in 5g ran offered by 3gpp:

Q18. What is CU, DU use in 5G NR?

Ans. CU stands for Central Unit and DU stands for Distributed Unit. Main jobs of CU and DU are define below:
A gNB may consist of a gNB-CU and one or more gNB-DU(s). A gNB-CU and a gNB-DU is connected via F1 interface.
One gNB-DU is connected to only one gNB-CU.
NG, Xn and F1 are logical interfaces. Please refer below image:

the Functionality of CU-CP and CU-UP is defined below:
- A gNB may consist of a gNB-CU-CP, multiple gNB-CU-UPs and multiple gNB-DUs;
- One gNB-CU-CP is connected to only one gNB-DU through the F1-C interface;
- One gNB-CU-CP is connected to only one gNB-CU-UP through the E1 interface;
- The gNB-CU-UP is connected to the one or more gNB-DU through the F1-U interface;
- One gNB-DU can be connected to multiple gNB-CU-UPs under the control of the same gNB-CU-CP;
- One gNB-CU-UP can be connected to multiple DUs under the control of the same gNB-CU-CP;
Please refer below image for more clarity:

Reference:

TS 38.401 3GPP

Q19. Name of Interface use between CU and DU?

Ans. it’s F1 interface use between CU and DU.

Q20. What is CU-CP and CU-UP?

Ans. CU-CP stands for Central Unit-Control Plane and CU-UP stands for Central Unit-User Plane both are the sub-part of Central Unit present in gNB.
Some main function are given below:
-- The connectivity between a gNB-CU-UP and a gNB-DU is established by the gNB-CU-CP using Bearer Context Management functions.
-- The gNB-CU-CP selects the appropriate gNB-CU-UP(s) for the requested services for the UE. In case of multiple CU-UPs they belong to same security domain as defined in TS 33.210 [18].
-- Data forwarding between gNB-CU-UPs during intra-gNB-CU-CP handover within a gNB may be
supported by Xn-U.
For more details refer Que. No. 20 Answer.

Q21. Name of Interface use in CU-CP and CU-UP?

Ans. That is E1 interface present between CU-CP and CU-UP.
- it’s inter-connection of a gNB-CU-CP and a gNB-CU-UP supplied by different manufacturers.
E1 interface function are below:
-- The error indication function.
-- The reset function.
-- The E1 setup function.
-- The gNB-CU-CP and gNB-CU-UP Configuration Update functions.
-- The E1 setup and gNB-CU-UP Configuration Update functions.
Reference:
TS 38.460 3GPP

Q22. What do you mean by Class 1 and Class 2 messages?

Ans. The class 1 messages are those message which are two sided, for example RRCSetupRequest sent by UE to Network and Network should reply back with RRCSetup if it’s pass, else RRCReject if it’s failed.

Class 2 messages are only single sided messages means sender doesn’t require the acknowledgement.

Note: In different-2 protocols have different-2 Class 1 and Class 2 messages.

Q23. Please tell me the Class 1 and Class 2 messages that’s are use in F1AP protocol?

Ans.

Q24. Explain the protocol structure of 5G NR?

Ans. To learn 5G protocol structure briefly please click on this link:

Control Plane: protocol structure of 5G NR

User Plane: protocol structure of 5G NR

Q25. Please tell me the name of protocol use between UE and R(AN) in 5G NR?

Ans. It’s NR-Uu protocol. Also called air interface protocol of 5G. Refer Q24 Ans image.

Q26. What is AMF? What is the essential function of AMF in 5G NR?

Ans. Below are the main functions of AMF in 5G.
NAS signalling termination;
NAS signalling security;
AS Security manipulate;
Inter CN node signalling for mobility among 3GPP access networks;
Idle mode UE Reachability (including manage and execution of paging retransmission);
Registration Area management;
Support of intra-machine and inter-system mobility;
Access Authentication;
Access Authorization including take a look at of roaming rights;
Mobility management manage (subscription and policies);
Support of Network Slicing;
SMF selection.