In SA2 of 3GPP, the 23.501 protocol defines the system architecture of 5G, as shown in Figure 13. Future 5G is based on a service-oriented architecture, and the functions it needs to support include separation of CP and UP, network slicing, capability opening, and local routing. and other functions.
The adoption of this service-based architecture as a unified infrastructure means that the 5G network is truly open, service-oriented, and software-based.
direction, which is conducive to realizing the integrated development of 5G and vertical industries. This “service”-based architectural design method makes the 5G network truly cloud-oriented design and has many advantages, such as facilitating rapid network upgrades, improving network resource utilization, and accelerating Introduction of new network capabilities and opening them to third parties under authorization. The functions defined mainly include: user plane function (UPF), session management function (SMF) and other network element modules, At the same time, corresponding interfaces are also defined between each module. The interface situation is shown in Figure 14, from Nl to N15, as shown in Figure 14.
The functions to be completed by this architecture are very complex, including functions such as: registration management, connection management, session management, service quality management, user plane management, etc. Among them, the functions supporting edge computing are specifically listed in Section 5.13 of the literature [7] Write, the content of edge computing defined by it is as follows:
Edge computing allows operators and third-party services to be deployed close to UE access points. Therefore, this can achieve more efficient service delivery and shorten end-to-end delays, while also reducing the load on the transmission network. 5G core network selection A UPF is close to the UE and performs traffic direction at the same time, from the UPF to the local data network (via the N6 interface). This may be based on the UE’s subscription data, UE location, policy or other related traffic rules. This actually defines traffic diversion, A key function of edge computing is to direct traffic locally.
Since 5G is a service-oriented architecture and the edge computing platform needs to be open to third-party APPs, the core network needs to open up some network capabilities, which is also an important part of building an edge computing ecosystem. Whether APPs are allowed to directly interact with control plane network functions The interaction depends on the operator’s deployment.
The following are the edge computing functions that 5G will support as defined in the protocol: Local routing. The 5G core network selects UPF to route user traffic to the local data network.
Traffic steering. The 5G core network selects traffic to be routed to the APP (in the local data network).
3. Session and service continuity to support UE and APP mobility. 4. User plane selection and reselection, such as input based on APP functions. An APP function may affect the traffic grooming of the UPF plane and the selection of UPF.
Network exposure function (NEF). It mainly includes the corresponding functions of the 5G core network and APP to provide information through NEF.
⑦Quality of service and billing. The policy and control function (PCF) provides rules for quality of service control, while billing the traffic forwarded by the local data network.
Support local data network. The 5G core network provides support for connecting local data network (LADN) in specific areas.
Detailed system processes and details, as well as steps related to session establishment, can refer to the 23.502 protocol, but some detailed processes are still in the process of being formulated. In addition, some system processes are basically consistent with the existing LTE processes and have not been significantly changed. Details The analysis also requires subsequent updates to the protocol version.
In the literature [15], some offloading solutions based on the core network side are also introduced, which also support the corresponding functions of data offloading and can provide reference. LoRa gateway
3.3 Business continuity plan analysis
In 23.501, a business continuity solution is defined, which is closely related to edge computing. In edge computing, business continuity needs to be ensured. Currently, three business continuity solutions are defined: SSC1, sSC2 and SSC3. This solution The uplink classifier and multi-homing content mentioned in Section 3.4 will be introduced in Traffic Grooming in Section 3.4.
Support for session and service continuity (in the 5G system) can meet different continuity requirements for different applications/services for UE. The 5G system supports different session and service continuity (service and session continuity, sSC). With A protocol data unit (PDU) session anchor associated with SSC mode will not change during the lifetime of the entire PDU session. There are three main types:
1) ssC Model. During the movement of the UE, no matter what access technology the UE adopts, the anchor point UPF when establishing the PDU session remains unchanged. This model is similar to the public data network (PDN) in the LTE network The anchor point does not change. The UEIP will not change at this time.
2) sSC Mode2. When the terminal leaves the service area of the current UPF, the network will trigger the release of the original PDU session, instructing the UE to immediately establish a new PDU session with the same data network. When establishing a new session, you can choose a new UPF As a PDU session Anchor UPF, it is necessary to ensure that the UEIP of the newly established session information is the same as that of the original session information.
3) sSC Mode3. When the terminal leaves the service area of the anchor UPF, it maintains the original PDU session and anchor UPF and communicates at the same time.
By selecting a new anchor UPF and establishing a new PDU session on the anchor UPF, the UE has PDU sessions to two anchor UPFs at the same time, and finally releases the original PDU session. In this process, the UEIP constant.
The SSC mode selection policy should be used to determine the session type and service continuity mode associated with the application or application group provided to the UE. The operator can provide the UESSC mode selection policy. This policy includes one or more An sSC mode selection policy rule can be used by the UE to determine the SSC mode type associated with an application or application group. This policy includes a default SSC mode selection policy rule that applies to all APPs of the UE.