Shulou(Shulou.com)11/24 Report--

The signaling process reflects how the network elements cooperate with each other when using 5G services. But do the intricate flowcharts disinterest you at all? Although the signaling flow chart listed in the protocol is comprehensive, it is inevitable that it is redundant and not vivid.

Therefore, in the process explanation of this series, we will follow Li Hua into the process and see how Li Hua deals with the service staff in the core network.

On the weekend, after the bleary-eyed Li Hua turned on the phone, the first thing he did was to open Weibo to have a look at the hot search.

At this moment, the "service staff" of 5G service company made great efforts to open up the communication channel between Li Hua and the data network.

This time, in addition to the reception staff (AMF), HR (UDM) and administrative staff (PCF), two professionals are required to put into service:

Correction: the first table in the article, SMF, the full name of the network element is "Session Management function", and the function is "session management function"; UPF, the full name of the network element is "User plane function", and the function is "user-side function". So what kind of service does the "service staff" provide for him? Let's take a look.

Li Hua's application 1. UE (Li Hua) came to the company gate, through the wireless base station (gNB) to take the initiative to submit a visit card to the reception staff (AMF), said: "Hello, I want to access the data network, please handle the business for me."

Message name: PDU Session Establishment

Request, the key information in the message includes:

two。 The receptionist (AMF) hurriedly found the planner (SMF) and asked him to handle the conversation business for UE.

Message name: Nsmf_PDUSession_CreateSMContext Request

After receiving the instruction, the planner's work planner (SMF) immediately began his own work to put on record Li Hua's conversation business. He dialed the number HR (UDM).

3. Planner (SMF): "Hello, HR, this is Xiao S, the planner. Now I will receive UE. Please register!"

Message name: Nudm_UECM_Registration request

4. HR (UDM) replied hurriedly: "all right".

Message name: Nudm_UECM_Registration response

5. Planner (SMF): "Don't hang up, you have to send me Li Hua's signing information about the conversation."

Message name: Nudm_SDM_Get Request

6. HR (UDM) promised again and again and told him the information the salesman wanted.

Message name: Nudm_SDM_Get Response

7. Planner (SMF): "besides, if his signing information about the conversation changes, you have to let me know!"

Message name: Nudm_SDM_Subscribe Request

8. HR (UDM) also agreed.

Message name: Nudm_SDM_Subscribe Response

9. The planner (SMF) told the receptionist (AMF) that I had established the basic information of the user's session.

Message name: Nsmf_PDUSession_CreateSMContext Response.

But the planner's work is not over yet.

10. The planner (SMF) went to the executive (PCF) and said, "what conversation restrictions does Li Hua have in our company?"

Message name: Npcf_SMPolicyControl_Create Request

11. The company's administrative staff (PCF) summed up the relevant restriction strategies about Li Hua and told the planner (SMF).

Message name: Npcf_SMPolicyControl_Create Response

After the work of the planner is handed over to the planner (SMF), he needs to hand over the information he has collected. He first found the salesman (UPF).

twelve。 The planner (SMF) said: "this is the rule that Li Hua needs to abide by in the course of conversation. Please implement it well."

Message name: PFCP Session_Establishment request

13. The salesman (UPF) said, "all right."

Message name: PFCP Session_Establishment response

Then, the planner (SMF) found the receptionist (AMF) and gave him a job of running errands.

14. The planner (SMF) said to the receptionist (AMF): "I have two couriers here. Don't open them. Please submit them to gNB and UE respectively for me."

Message name: Namf_Communication_N1N2Message

Transfer request, the contents of the message:

15. The receptionist (AMF) said, "copy that and make sure the job is done!"

Message name: Namf_Communication_N1N2Message

Transfer response

The job of running errands 16. The receptionist (AMF) handed over the N2 information submitted by the salesman to the base station and requested the base station to further submit N1 information to UE.

Message name: PDUSessionResourceSetup request, the content contained in the message:

17. After the base station completes the errand mission (message name: PDU session establish accept), tell the receptionist: "I have completed the task you sent, this is my IP address, please tell the salesman if you want to contact me in the future, please contact me through this address." Message name: PDUSessionResourceSetup response

At this point, Li Hua has been able to tell the data network that he wants to use Weibo, but the data network is not clear where to send the data that Li Hua wants to view.

Upload and release the clean-up work 18. The receptionist (AMF) told the planner (SMF) (message name: Nsmf_PDUSession_UpdateSMContext Request) about the IP address reported by the base station, and the planner (SMF) further told the IP address to the salesman (UPF) (message name: PFCP Session Modification request). Now the salesman (UPF) finally knows where Li Hua is and where the data needs to be sent!

At this point, Li Hua can search through the 5G network.

Through this story, it is not difficult to find that planners (SMF) and salespeople (UPF) play a very key role. These two different network elements also reflect the important characteristics of the C / U separation of the 5G core network-SMF is only responsible for issuing rules, while the real implementation of the rules is UPF. Seeing here, does your understanding of C / U separation become a little clearer?

PS: attach a large picture of the customized session establishment process signaling process:

This article comes from the official account of Wechat: ZTE document (ID:ztedoc), author: ZTE document

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