Implementation process of 5G network
1. Introduction to the mobility management process of the 5G core network
1.5G registration process
The 5G registration process is mainly used for: the initial registration of the UE, the registration triggered by moving out of the registration area, and the periodic registration update between the UE and the network
There are four types of registration, and different registration processing processes can be realized by carrying different registration types
- Initial registration (similar to Attach in 4G)
- Mobility registration update (similar to TAU in 4G)
- Periodic registration update (similar to periodic TAU in 4G)
- emergency registration
The registration process is as follows:
In the first step, the terminal selectively sends a registration request message to the AMF network element according to the relevant field description, weight, and even slice information
In the second step, if this registration request is different from the last registration request, the new AMF (New AMF) will find a way to find the old AMF (Old AMF) to obtain user information. If the same can not be changed. If the 5G Old AMF can provide information to the New AMF, then the third step is not required
In the third step, AMF obtains user information from the user
In the fourth step, AMF will perform authentication after obtaining the information. AMF will find AUSF through SUCI, and AUSF will find UDM through SUCI to obtain the authentication vector and complete the authentication process.
The fifth step, after completing the authentication, the new AMF will notify the old AMF that the user has been registered to the new AMF
In the sixth step, the user's terminal equipment is authenticated, and the AMF acquires UE information. (This function is not enabled in China)
In the seventh step, AMF will authenticate the user UE through EIR (this function is not enabled in China)
The eighth step, a. Due to the change of AMF information, AMF will update its own information to UDM, b. AMF obtains user subscription information from UDM, c. AMF obtains subscriber information from UDM, d. UDM notifies the old AMF to delete the old dialogue
In the ninth step, AMF obtains information related to user mobility from PCF
Step 10: PCF subscribes to AMF for user-related location information
In the eleventh step, if the first registration message is only a session that needs to be awakened, AMF will select SMF (at this time, the ID information of SMF can be obtained from Old AMF)
The twelfth step, accepting this registration request, can issue a new 5G logo to the user. At the same time, if the user has brought the requested slice before, then in this step, the slice information allowed by the network slice can also be issued.
The thirteenth step, if there is a new 5G logo in the twelfth step, then send it again
Q: What are the similarities and differences between the registration process of 5GC and the attachment process of EPC?
Answer: (1) The difference is that the registration process of 5G does not include the bearer establishment process of the 4G attachment process (media plane channel establishment)
(2) Both the 5G registration process and the 4G attachment process include authentication and user location update processes at the same point
2. Session establishment process of 5G core network
The PDU session establishment process is used to create a new PDU session. After the PDU session is successfully established, the network will assign an IP address to the UE and establish a dedicated channel from the UE to the DN. The UE can use this IP address to access services located on the DN.
The PDU session establishment process can also be used for cross-system handover of sessions, or session handover with N3GPP (non-3GPP)
The session establishment process is as follows:
In the first step, the user initiates a session establishment request (NAS layer message)
In the second step, AMF selects and forwards to SMF, based on the parameter of 5G APN/DNN, or slice parameter selection
In the third step, SMF obtains session signing related parameters from UDM
The fourth step, SMF supports/does not support this call request, notify AMF
Step 5: SMF finds PCF to obtain user session-related policies, based on user SUPI, slice information, etc.
Step 6: Request related billing information, SMF will find CHF for interaction
The seventh step, SMF chooses UPF
In the eighth step, the SMF sends the IP address assigned to the user and the user plane network element information to the AMF, and the session completes the establishment of the user plane pipeline
In the ninth step, the AMF notifies the base station, and at the same time, responds to the user with the user's IP address
The tenth step, the user obtains the IP after receiving the message, at this time the 5G base station establishes an air interface connection with the user
In the eleventh step, the 5G base station transmits the user plane information to the AMF
In the twelfth step, AMF forwards the user plane information of the base station to UPF, requesting to establish a user plane channel
Step 13, SMF forwards the information to UPF again
The fourteenth step, if there is billing-related information that needs to be updated, SMF will update it interactively with CHF
Step 15, SMF responds to AMF
Step 16: SMF subscribes user-related information to AMF based on policy
Q: What are the similarities and differences between the session establishment process of 5GC and the connection establishment process of EPC?
Answer: The same point will assign IP to UE, establish PDU session, and establish dedicated channel
The difference is that the 5GC session establishment process includes slice information, and the 4G PDN connection establishment process has no slice concept
3. 5G Voice Solution
1.5G solution
Including the following types: VoLTE, EPS, VoeLTE, VoNR
The voice solution we chose evolved gradually based on the development of 5G. In the initial stage of 5G network construction, because 5G signals were not as complete as 4G, we still used 4G to carry 5G call tasks. In the middle of the evolution, we use EPS and VoeLTE to solve voice calls. Then, after 5G is fully mature, VoNR will be used to replace 4G calls.
2. The comparison between 5G calls and 4G calls.
Considering the cost, 5G has a relatively low bit bandwidth cost compared to 4G bandwidth, and 5G has obvious advantages over 4G. From the perspective of accessibility, with the gradual popularization of mobile phones for video calls and the gradual deployment of video intercommunication among operators, 5G will support various video call services, and the future will be brighter. From the perspective of business experience, Vo5G reduces coverage requirements and all aspects of data are stronger than 4G, and it has better applicability to support multi-faceted video calls.
3. Deploy 5G voice solutions based on EPC+
NSA option 3.3a.3X voice program
Fixed voice using VoLTE/CSFB
The principle of the voice solution: IMS APN is fixedly distributed to the LTE base station, and the user calls are directly processed by the LTE base station, using VoLTE/CSFB calls.
The principle of the SMS solution: the SMS of the VoLTE mobile phone goes through the IMS, and the SMS of the data card continues to go through the SGs interface.
4. Deploy 5G voice solutions based on 5GC
Solution 1: Do not activate VoNR, EPS Fallback to VoLTE
The principle of the voice solution: make a call, switch to 4G triggered by NG-RAN
Deployment premise: VoLTE is required as the basic network, 4G coverage includes 5G; EPC and 5GC, open N26 interface and enable 4/5G switching
Solution 2: Activate VoNR, use VoLTE without NR coverage
The principle of the voice solution: when a user makes a call under NR coverage, it is directly processed by the NR base station, and VoNR calls are used. If there is no NR coverage, use VoLTE.
Deployment prerequisites: 4G coverage is not required, including 5G; EPC and 5GC open N26 interface, and enable 4/5G switching.
Q: What are the voice solutions for 5GC networking?
Answer: There are two options. Solution 1: VoNR is not activated, EPS Fallback to VoLTE. Solution 2: VoNR is enabled, and NR coverage falls back to VOLTE.