Patent Publication Number: US-2023164037-A1

Title: Network Access Method, Apparatus, and System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2021/107823, filed on Jul. 22, 2021, which claims priority to Chinese Patent Application No. 202010724017.7, filed on Jul. 24, 2020. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of communication technologies, and in particular, to a network access method, apparatus, and system. 
     BACKGROUND 
     In a process in which a user accesses a network of a communication system, a control plane (CP) device, a user plane (UP) device, and the like of the communication system need to provide a network service for the user. The communication system is usually provided with a plurality of UP devices, and a session of the user accesses the network through a UP device allocated to the user. 
     The UP device allocated by the communication system to the user is usually fixed, but network performance between a steering function SF device and the UP device changes. For example, a network delay between the UP device and the SF device changes with a bandwidth congestion status and the like. In this case, a network status between the UP device and the SF device cannot ensure that quality of the network service provided for the user meets a user requirement. 
     SUMMARY 
     Embodiments of this application provide a network access method and apparatus, which are used to ensure quality of a network service provided for a user. 
     According to a first aspect, an embodiment of this application provides a network access method. The method includes: A first device obtains first detection data of network performance between a steering function SF device and a first user plane UP device, where the first UP device is a UP device in a communication system in which a control plane CP is separated from a UP. Then, the first device configures the SF device and the first UP device based on the first detection data, to enable a first user to access a network through the SF device and the first UP device, where the first detection data meets a network performance requirement of the first user. 
     A UP device used by a user to access a network is dynamically adjusted according to the method, to ensure that detection data of network performance between an SF device and the UP device meets a network performance requirement of the user. Therefore, this helps ensure that quality of a network service provided for the user meets the network performance requirement of the user, and improves user experience. 
     Optionally, the first device is an SDN controller. The network access method in this case is specifically described below by using a first possible implementation to a seventh possible implementation of the first aspect. 
     In the first possible implementation of the first aspect, that the SDN controller configures the first UP device based on the first detection data includes: The SDN controller sends first information to a CP device in the communication system, where the first information is used to indicate to connect a session of the first user to the network through the first UP device. The SDN controller may indicate, by sending the first information to the CP device, the CP device to configure the first UP device, and this helps the first user access the network through the SF device and the first UP device. 
     In a second possible implementation of the first aspect, after the SDN controller sends the first information to the CP, and before the SDN controller configures the SF device based on the obtained detection data, the SDN controller receives response information sent by the CP device for the first information, where the response information is used to indicate that a session table of the first user has been delivered to the first UP device. In this way, the SDN controller may configure the SF device after completing configuration of the first UP device. This helps increase a rate of successfully accessing the network by the first user. 
     In a third possible implementation of the first aspect, that the SDN controller configures the SF device based on the first detection data includes: The SDN controller sends configuration information to the SF device, where the configuration information is used to indicate the SF to connect the session of the first user to the first UP device. 
     In a fourth possible implementation of the first aspect, before the SDN controller configures the SF device and the first UP device based on the first detection data, the SDN controller may obtain third information, where the third information is used to indicate that the first user is a user requesting to go online. 
     In a fifth possible implementation of the first aspect, after the SDN controller configures the SF device and the first UP device based on the first detection data, the SDN controller may obtain second detection data and third detection data, where the second detection data is detection data of the network performance between the SF device and the first UP device, the third detection data is detection data of network performance between the SF device and a second UP device, and the second UP device is a UP device in the communication system. If the second detection data does not meet the network performance requirement of the first user, but the third detection data meets the network performance requirement of the first user, the SDN controller configures the SF device and the second UP device based on the second detection data and the third detection data, to enable the first user to access the network through the SF device and the second UP device. This helps ensure quality of a network service of the user that has accessed the network. 
     In a sixth possible implementation of the first aspect, the network performance requirement of the first user is determined by the first device according to a service level agreement SLA of the first user. 
     In the seventh possible implementation of the first aspect, the network performance includes at least one of a network delay, a network jitter, and a network packet loss rate. 
     Optionally, the first device is a CP device. The network access method in this case is specifically described below by using an eighth possible implementation to a tenth possible implementation of the first aspect. 
     In the eighth possible implementation of the first aspect, that the CP device configures the SF device based on the first detection data includes: The CP device sends second information to an SDN controller, where the second information is used to indicate the SDN controller to send configuration information to the SF device, and the configuration information is used to indicate the SF device to connect a session of the first user to the first UP device. 
     In a ninth possible implementation of the first aspect, the first detection data is sent by the SDN controller. Optionally, the SDN controller may collect detection data of network performance between a UP device and the SF device, and report the collected detection data to the CP device. 
     In the tenth possible implementation of the first aspect, that the CP device configures the first UP device based on the first detection data includes: The CP device sends a session table of the first user to the first UP device. 
     Optionally, when the first device is the CP device, the network access method further includes another implementation. For the another implementation, refer to any one of the fifth to the seventh possible implementations of the first aspect for understanding. Details are not described herein again. 
     Optionally, the first device is a device other than the controller and the CP device. Optionally, the device is referred to as a UP steering function (USF) device as an example, and the USF device is a function node configured to formulate a steering policy. For the network access method in this case, refer to the foregoing implementations for understanding. For example, optionally, for a manner in which the USF device configures the first UP device based on the first detection data, refer to the first possible implementation of the first aspect for understanding. Optionally, for a manner in which the USF device configures the SF device based on the first detection data, refer to the eighth possible implementation of the first aspect for understanding. Optionally, when the first device is the USF device, the network access method further includes another implementation. For the another implementation, refer to any one of the second, the fourth, the fifth, the sixth, the seventh, or the ninth possible implementation of the first aspect for understanding. Details are not described herein again. 
     According to a second aspect, an embodiment of this application provides a network access method. The method includes: A CP device in a communication system in which a control plane CP is separated from a user plane UP receives first information sent by a first device, where the first information is used to indicate that a first user corresponds to a first UP device in the communication system, and detection data of network performance between a steering function SF device and the first UP device meets a network performance requirement of the first user. The CP device sends a session table of the first user to the first UP device. This helps the first user access a network through the SF device and the first UP device, and helps ensure quality of a network service provided for the first user. 
     Optionally, the first device is the USF device or the SDN controller that is used as an execution body in the method described in the first aspect. 
     Optionally, after the CP device sends the session table of the first user to the first UP device, the CP device sends response information for the first information to the first device, where the response information is used to indicate that the session table of the first user has been delivered to the first UP device. In this way, the first device may perform other configuration after completing configuration of the first UP device, for example, configure the SF device. This helps increase a rate of successfully accessing the network by the first user. 
     Optionally, before the CP device receives the first information sent by the first device, the CP device receives a go-online request packet of the first user, and then sends third information to the first device, where the third information is used to indicate that the first user is a user requesting to go online. This helps ensure that a user accesses, when going online in a session establishment process, a network through a UP device that meets a requirement, and improves network use experience of the user. 
     According to a third aspect, an embodiment of this application provides a network access method. The method includes: A software designed network SDN controller may receive second information sent by a first device, where the second information is used to indicate that a first user corresponds to a first user plane UP device, the first UP device is a UP device in a communication system in which a control plane CP is separated from a UP, and detection data of network performance between a steering function SF device and the first UP meets a network performance requirement of the first user. Then, the SDN controller sends configuration information to the SF device, where the configuration information is used to indicate the SF to connect a session of the first user to the first UP device. Because the detection data of the network performance between the SF device and the first UP meets the network performance requirement of the first user, the SDN controller sends the configuration information to the SF device. This helps the first user access a network through the SF device and the first UP device, and helps ensure quality of a network service provided for the first user. 
     Optionally, the first device is the USF device or the CP device that is used as an execution body in the method described in the first aspect. 
     Optionally, before the SDN controller receives the second information sent by the first device, the SDN controller sends the detection data of the network performance between the SF device and the first UP device to the first device. This helps the first device select, for the first user, a UP device that meets the requirement of the first user. 
     According to a fourth aspect, an embodiment of this application provides a network access method. The method includes: A software designed network SDN controller sends first detection data of network performance between a steering function SF device and a first user plane UP device to a first device, where the first UP device is a UP device in a communication system in which a control plane CP is separated from a UP, the first detection data is used to indicate the first device to configure the SF device and the first UP device, and the first detection data meets a network performance requirement of the first user. This helps the first device select, for the first user, a UP device that meets the requirement of the first user, helps the first user access a network through the SF device and the first UP device, and ensures quality of a network service provided for the first user. 
     Optionally, after the SDN controller sends the first detection data of the network performance between the SF device and the first UP device to the first device, the SDN controller receives second information sent by the first device, where the second information is used to indicate that the first user corresponds to the first user plane UP device. Then, the SDN controller sends configuration information to the SF device, where the configuration information is used to indicate the SF to connect a session of the first user to the first UP device. Because the detection data of the network performance between the SF device and the first UP meets the network performance requirement of the first user, the SDN controller sends the configuration information to the SF device. This helps the first user access the network through the SF device and the first UP device, and helps ensure the quality of the network service provided for the first user. 
     According to a fifth aspect, an embodiment of this application provides a network apparatus. The apparatus may be a network device, may be an apparatus in the network device, or may be an apparatus that can be used together with the network device. In a design, the apparatus may include modules that are in one-to-one correspondence with the methods/operations/steps/actions described in the first aspect, the second aspect, the third aspect, or the fourth aspect. The modules may be implemented by a hardware circuit, software, or a combination of a hardware circuit and software. 
     According to a sixth aspect, an embodiment of this application provides a network apparatus. The apparatus includes a processor and a memory. The memory is configured to store instructions. The memory is coupled to the processor. When executing the instructions stored in the memory, the processor may implement the method described in the first aspect, the second aspect, the third aspect, or the fourth aspect. The communication apparatus may further include a communication interface. The communication interface is used by the apparatus to communicate with another device. For example, the communication interface may be a transceiver, a circuit, a bus, a module, a pin, or another type of communication interface. The another device may be a terminal device. 
     According to a seventh aspect, an embodiment of this application provides a chip system. The chip system includes a processor, and may further include a memory. The chip system is configured to implement the method described in the first aspect, the second aspect, the third aspect, or the fourth aspect. The chip system may include a chip, or may include a chip and another discrete component. 
     According to an eighth aspect, an embodiment of this application provides a computer-readable storage medium. The computer-readable storage medium includes instructions. When the instructions are run on a computer, the computer is enabled to perform the method according to any possible implementation of the first aspect, the second aspect, the third aspect, or the fourth aspect in embodiments of this application. 
     According to a ninth aspect, an embodiment of this application provides a computer program product. The computer program product includes instructions. When the instructions are run on a computer, the computer is enabled to perform the method according to any possible implementation of the first aspect, the second aspect, the third aspect, or the fourth aspect in embodiments of this application. 
     According to a tenth aspect, an embodiment of this application provides a communication system. The communication system includes the first device in the method described in the first aspect, the CP device in any one of the second aspect or the possible implementations of the second aspect, and the SDN controller in any one of the third aspect or the possible implementations of the third aspect or any one of the fourth aspect or the possible implementations of the fourth aspect. Alternatively, the communication system includes the SDN controller used as the first device in the possible implementations of the first aspect and the CP device in any one of the second aspect or the possible implementations of the second aspect. Alternatively, the communication system includes the CP device used as the first device in the possible implementations of the first aspect, and the SDN controller in any one of the third aspect or the possible implementations of the third aspect or any one of the fourth aspect or the possible implementations of the fourth aspect. Alternatively, the communication system includes the USF device used as the first device in the possible implementations of the first aspect, the CP device in any one of the second aspect or the possible implementations of the second aspect, and the SDN controller in any one of the third aspect or the possible implementations of the third aspect or any one of the fourth aspect or the possible implementations of the fourth aspect. Alternatively, the communication system includes a steering function SF device, a user plane UP device, and the first device described in the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a structure of a CU separation communication system according to an embodiment of this application; 
         FIG.  2    to  FIG.  6    are flowcharts of network access methods according to embodiments of this application; 
         FIG.  7    to  FIG.  12    are schematic diagrams of structures of network apparatuses according to embodiments of this application; and 
         FIG.  13    is a schematic diagram of a structure of a chip according to an embodiment of this application. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Embodiments of this application provide a network access method and apparatus. Embodiments of this application are described below with reference to accompanying drawings. 
     A broadband remote access server (BRAS) is a new access gateway oriented to a broadband network application, and is also referred to as a broadband network gateway (broadband network gateway, BNG) or a virtual BNG (VBNG). Usually, the BRAS is deployed in a manner in which a CP device is separated from a UP device (CU separation for short). In the BRAS deployed in the CU separation manner, a plurality of UP devices are deployed in a distributed manner. Each UP device serves as a user plane of the BRAS, and is configured to forward a user packet based on a user entry delivered by the CP device and implement a traffic policy based on technologies such as quality of service (QoS) and an access control list (ACL). The CP device may be implemented by using a cloudification technology and deployed in a centralized manner. As a control plane of the BRAS, the CP device is configured to control and manage a user and manage the plurality of UP devices in a unified manner. For example, the CP device is mainly responsible for managing a go-online process of the user, configuration and user entry delivery, and the like. The UP device may also be referred to as a forwarding plane device. Therefore, the CU separation may also be referred to as forwarding and control separation, namely, forwarding-control separation. A system deployed in the CU separation manner is also referred to as a CU separation communication system or a forwarding-control separation communication system. 
       FIG.  1    is a schematic diagram of a structure of a CU separation communication system according to an embodiment of this application. As shown in  FIG.  1   , an example in which the CU separation communication system includes one CP device  1  and three UP devices (a UP device  21 , a UP device  22 , and a UP device  23 ) is used for illustration. The UP device  21 , the UP device  22 , and the UP device  23  each may establish a communication connection to at least one user through an access node (AN)  3 , and exchange data with the at least one user. In  FIG.  1   , a user  4  is used as an example for illustration. The user  4  may access a network through the UP device  21 , the UP device  22 , or the UP device  23 . 
     The CP device  1  is responsible for control and management of the user  4 . The CP device  1  may be connected to each UP device in  FIG.  1    through a service interface, a management interface, and a control interface. The service interface is usually a virtual extensible local area network (VXLAN) interface. After receiving packets (for example, an access protocol packet and a service packet) sent by the user  4 , any UP device in  FIG.  1    may send, through the service interface, the packets to the CP device  1  for processing. The management interface is usually a network configuration protocol (NETCONF) interface. The CP device  1  may deliver a configuration to each UP device in  FIG.  1    through the management interface, and each UP device in  FIG.  1    may report a running status to the CP device  1  through the management interface. The control interface is usually a forwarding-control separation protocol (control plane and user plane separation protocol, CUSP) interface. After completing processing of the access protocol packet sent by the user  4  and completing management of a go-online process of the user  4 , the CP device  1  may deliver a user session table (or referred to as a user entry) to a corresponding UP device through the control interface. The user entry usually includes information such as a routing table and quality of service (QoS) of the user  4 . 
     Still refer to  FIG.  1   . In this embodiment of this application, the CU separation communication system further includes a software-defined networking (SDN) controller  6  and a steering function (SF) device  5 . In some application scenarios, the SDN controller  6  in this embodiment of this application may also be replaced with a network control engine (NCE). The SF device  5  is disposed between the AN  3  and the UP devices in  FIG.  1   . The SDN controller  6  is connected to the SF device  5 , and the SDN controller  6  creates layer  2  tunnels between the SF device  5  and the UP devices in  FIG.  1   . Specifically, the SDN controller  6  separately creates a layer  2  tunnel T 1  between the SF device  5  and the UP device  21 , a layer  2  tunnel T 2  between the SF device  5  and the UP device  22 , and a layer  2  tunnel T 3  between the SF device  5  and the UP device  23 . The SF device  5  may send a packet (including a packet header of the layer  2  tunnel) from the user  4  to a corresponding UP device (the UP device  21 , the UP device  22 , or the UP device  23 ) through one of the layer  2  tunnels (T 1 , T 2 , or T 3 ), to further send the packet to the CP device  1  or a core network. The layer  2  tunnel may be a virtual local area network (VLAN), a virtual leased line (VLL), a virtual private local area network service (VPLS), a virtual extensible local area network (virtual extensible LAN, VXLAN), or an SRv6. SRv6 is a network forwarding technology that combines a segment routing (segment routing, SR) technology and an internet protocol version  6  (IPv6) technology. Optionally, the SDN controller  6  is connected to the CP device  1 , and is configured to communicate with the CP device  1 . It should be noted that the “connection” mentioned in this embodiment of this application is not limited to a direct connection, provided that two connected parties can communicate with each other. 
     Optionally, with reference to  FIG.  1   , the communication system further includes an authentication server  7 , and the authentication server  7  may be a remote authentication dial-in user service (RADIUS) server. The authentication server  7  stores a service level of the user  4 , and supports an authentication, authorization, and accounting (AAA) protocol. The authentication server  7  is connected to the CP device  1 . After completing exchange of the access protocol packet with the user  4  through the UP device, the CP device  1  may send an authentication request for the user  4  to the authentication server  7 . The authentication server  7  may perform authentication on the user  4 , and send SLA information of the user  4  to the CP device  1 . The SLA information includes the service level of the user  4 . 
     Optionally, as shown in  FIG.  1   , the communication system further includes a UP steering function (USF) device  8 . The USF device  8  is separately connected to the SDN controller  6  and the CP device  1 . The USF device  8  may be a function node configured to formulate a steering policy. 
     In this embodiment of this application, optionally, the CP device  1  may include a plurality of virtual machines (VMs) deployed on a physical server. The UP device  21 , the UP device  22 , and the UP device  23  may be physical UP (pUP) devices, or may be virtual UP (vUP) devices. For example, the UP device  21 , the UP device  22 , and the UP device  23  may be VMs deployed on the physical server. The SF device  5  may be a physical device independent of the AN  3 , for example, may be a router or a switch independent of the AN  3 . Alternatively, the SF device  5  may be a software component disposed in the AN  3 . The user  4  may also be referred to as a client device or user equipment, and may be a mobile phone or a computer device such as a notebook computer or a desktop computer. The AN  3  may be a switch (SW), an optical line terminal (OLT), a digital subscriber line access multiplexer (DSLAM), or the like. The AN  3  may encapsulate an outer virtual local area network (VLAN) into a packet used to indicate a location of the user  4 . 
     The foregoing describes an example of a communication system in embodiments of this application with reference to  FIG.  1   . The following describes network access methods in embodiments of this application.  FIG.  2    is a flowchart of a network access method according to an embodiment of this application. The method in the embodiment corresponding to  FIG.  2    may be applied to the communication system shown in  FIG.  1   , or may be applied to another communication system. This is not limited in this embodiment of this application. Optionally, an execution body (namely, a first device) of the network access method shown in  FIG.  2    is the SDN controller  6 , the CP device  1 , or the USF device  8  in  FIG.  1   . Refer to  FIG.  2   . The network access method in this embodiment of this application includes step  201  and step  202 . 
       201 : The first device obtains first detection data of network performance between a steering function SF device and a first UP device. 
     The first UP device is a UP device in a CU separation communication system. For example, the first UP device is a UP device in the communication system shown in  FIG.  1   . 
     In an optional manner, the UP device in the CU separation communication system may collect detection data of network performance between the UP device and the SF device, and the first device may obtain the detection data collected by the UP device. 
     Optionally, the detection data is detection data of network performance of a layer  2  tunnel between the UP device and the SF device. For example, the network performance in this embodiment of this application includes at least one of a network delay, a network jitter, and a network packet loss rate. 
       202 : The first device configures the SF device and the first UP device based on the first detection data, to enable a first user to access a network through the SF device and the first UP device. 
     After the first device obtains the detection data (namely, the first detection data) of the network performance between the SF device and the first UP device, based on a fact that the first detection data meets a network performance requirement of the first user, the first device configures the SF device and the first UP device based on the first detection data, to enable the first user to access the network through the SF device and the first UP device. 
     Because the first detection data meets the network performance requirement of the first user, the first user accesses the network through the SF device and the first UP device. This helps obtain a network service that meets the requirement, and improves network experience of the first user. 
     Optionally, step  201  and step  202  may be applied to a session establishment process of the first user, and/or applied to an established session of the first user. An example in which step  201  and step  202  are applied to the session establishment process of the first user is used. In an optional manner, refer to a dashed line part in  FIG.  2   . After step  202 , the method in this embodiment of this application further includes step  203  and step  204 , and step  203  and step  204  are applied to the established session of the first user. 
       203 : The first device obtains second detection data and third detection data. 
     The first UP device and a second UP device are two UP devices in the CU separation communication system. For example, the first UP device and the second UP device are respectively the UP device  21  and the UP device  22  in the communication system shown in  FIG.  1   . 
     After the session of the first user is established, the first device obtains the second detection data of the network performance between the SF device and the first UP device, and obtains the third detection data of network performance between the SF device and the second UP device. 
       204 : The first device configures the SF device and the second UP device based on the second detection data and the third detection data, to enable the first user to access the network through the SF device and the second UP device. 
     After the first device obtains the second detection data and the third detection data, the first device configures the SF device and the second UP device based on a fact that the second detection data does not meet the network performance requirement of the first user and the third detection data meets the network performance requirement of the first user, to enable the first user to access the network through the SF device and the second UP device. 
     After the first user accesses the network, because the second detection data does not meet the network performance requirement of the first user, and the third detection data meets the network performance requirement of the first user, the first device configures the SF device and the second UP device, to enable the first user to access the network through the SF device and the second UP device. This helps continue to obtain the network service that meets the requirement, and maintain good network experience of the first user. 
     In this embodiment of this application, in an optional manner, the first device may directly configure the SF device. Alternatively, in an optional manner, the first device may indicate another device to configure the SF device. Similarly, in an optional manner, the first device may directly configure the first UP device. Alternatively, in an optional manner, the first device may indicate another device to configure the first UP device. 
     The following separately describes network access methods in which the first device is an SDN controller, a CP device, and a USF device. 
     In an optional manner, the first device in the method shown in  FIG.  2    is an SDN controller. In this case, optionally, the first device may directly configure the SF device, and indicate a CP device to configure the first UP device. With reference to  FIG.  3   , the following describes a network access method in this case by using an example.  FIG.  3    is a schematic diagram of the network access method according to another embodiment of this application. The method shown in  FIG.  3    is an example of the method shown in  FIG.  2   . Therefore, for some explanations of the method shown in  FIG.  3   , refer to the descriptions of the method shown in  FIG.  2   . The method shown in  FIG.  3    includes steps  301  to  317 . For ease of description, an example in which the method shown in  FIG.  3    is applied to the communication system shown in  FIG.  1    is used for description. An SDN controller  6  is connected to a CP device  1 , and an example in which a first user is a user  4  is used for illustration. 
       301 : The SDN controller  6  obtains detection data a from a UP device  21 . 
       302 : The SDN controller  6  obtains detection data b from a UP device  22 . 
     In this embodiment of this application, it is assumed that an SF device  5  is currently configured to send a packet of the user  4  to the UP device  21 . For example, it is assumed that the SF device  5  establishes a layer  2  tunnel T 1  with an interface  1  (which is referred to as a UP interface  1 ) of the UP device  21  through an interface  1  (which is referred to as an SF interface  1 ) of the SF device  5 , the SF device  5  establishes a layer  2  tunnel T 2  with an interface  2  (which is referred to as a UP interface  2 ) of the UP device  22  through an interface  2  (which is referred to as an SF interface  2 ) of the SF device  5 , and the SF device  5  establishes a layer  2  tunnel T 3  with an interface  3  (which is referred to as a UP interface  3 ) of a UP device  23  through an interface  3  (which is referred to as an SF interface  3 ) of the SF device  5 . It is assumed that a VLAN of the user  4  is currently configured on the SF interface  1 . 
     The SDN controller  6  obtains the detection data a of network performance between the SF device  5  and the UP device  21 , and obtains the detection data b of network performance between the SF device  5  and the UP device  22 .  FIG.  3    is illustrated by using an example in which the detection data a and the detection data b are respectively from the UP device  21  and the UP device  22 . 
     Optionally, the detection data a is detection data of network performance of the layer  2  tunnel T 1  between the SF device  5  and the UP device  21 , and the detection data b is detection data of network performance of the layer  2  tunnel T 2  between the SF device  5  and the UP device  22 . Optionally, the SDN controller  6  obtains the detection data a and interface information (for example, information about the SF interface  1  and information about the UP interface  1 ) that correspond to the layer  2  tunnel T 1 , and the SDN controller  6  obtains the detection data b and interface information (for example, information about the SF interface  2  and information about the UP interface  2 ) that correspond to the layer  2  tunnel T 1 . 
     In an optional manner, the SDN controller  6  may further obtain detection data of the SF device  5  and another UP device in the CU separation communication system. For example, still refer to  FIG.  1   . The SDN controller  6  may further obtain detection data from the UP device  23 . The detection data is detection data of network performance of the layer  2  tunnel T 3  between the SF device  5  and the UP device  23 . 
       303 : The CP device  1  receives a go-online packet of the user  4 . 
     Because the SF device  5  is currently configured to send the packet of the user  4  to the UP device  21 , the go-online packet is sent to the CP device  1  through the SF device  5  and the UP device  21 . For example, the SF device  5  sends the go-online packet to the UP device  21  through the layer  2  tunnel T 1 , and then the UP device  21  sends the go-online packet to the CP device  1 . 
       304 : An authentication server  7  performs authentication on the user  4 . 
     After receiving the go-online packet of the user  4 , the CP device  1  sends an authentication request for the user  4  to the authentication server  7 . The authentication server  7  may perform authentication on the user  4 , and feed back an authentication result to the CP device  1 . 
     Optionally, the authentication server  7  may further send SLA information of the user  4  to the CP device  1 . The SLA information includes a service level of the user  4 . Optionally, if service levels of two users are different, the two users have different network performance requirements. For example, service levels of users may be classified into a gold user, a silver user, and a copper user. A network performance requirement of the gold user is higher than a network performance requirement of the silver user, and the network performance requirement of the silver user is higher than a network performance requirement of the copper user. 
       305 : The CP device  1  sends third information to the SDN controller  6 . 
     The third information is used to indicate that the user  4  is a user requesting to go online. Optionally, the third information carries identification information and the service level agreement (SLA) information of the user  4 . Optionally, the third information may further carry interface information (namely, the information about the UP interface  1 ) of the UP device  21 . The SLA information is used to determine the network performance requirement of the user. 
       306 : The SDN controller  6  sends first information to the CP device  1  based on the third information, the detection data a, and the detection data b. 
     After obtaining the third information, the SDN controller  6  may determine the network performance requirement of the user  4  based on the third information (for example, the SLA information of the user  4  in the third information). The SDN controller  6  selects one UP device (which is referred to as a first UP device) from the UP device  21  and the UP device  22  based on the detection data a and the detection data b. Detection data of the first UP device meets the network performance requirement of the user  4 . 
     The first information is used to indicate the CP device  1  to configure the first UP device, to connect a session of the user  4  to a network through the first UP device. 
     In  FIG.  3   , an example in which the first UP device is the UP device  22  is used for illustration. Optionally, the first information carries an identifier of the user  4  and interface information (namely, the information about the UP interface  2 ) of the UP device  22 . 
     To reduce system overheads caused by UP device switching, in an optional manner, if both the detection data a and the detection data b meet the network performance requirement of the user  4 , the SDN controller  6  may preferentially select the UP device  21  as the first UP device. Alternatively, if the detection data a does not meet the network performance requirement of the user  4 , but the detection data b meets the network performance requirement of the user  4 , the SDN controller  6  may select the UP device  22  as the first UP device. 
       307 : The CP device  1  sends a session table of the user  4  to the UP device  22 . 
     After receiving the first information, the CP device  1  may configure the UP device  22  according to an indication of the first information, for example, including but not limited to sending the session table of the user  4  to the UP device  22 . 
     In addition, optionally, the CP device  1  may further allocate an IP address to the user  4 , and the IP address is an IP address corresponding to the UP device  22 . 
       308 : The CP device  1  sends response information for the first information to the SDN controller  6 . 
     After completing configuration of the UP device  22  according to the indication of the first information, the CP device  1  may send the response information for the first information to the SDN controller  6 , to indicate that the CP device  1  has completed configuration of the UP device  22 , and specifically indicate that the session table of the user  4  has been delivered to the UP device  22 . 
       309 : The SDN controller  6  sends configuration information  1  to the SF device  5  based on the third information, the detection data a, and the detection data b. 
     Refer to step  306 . The SDN controller  6  may determine, based on the third information, the detection data a, and the detection data b, that detection data of the UP device  22  meets the network performance requirement of the user  4 . After the CP device  1  completes configuration of the UP device  22 , the SDN controller  6  may send the configuration information  1  to the SF device  5 . The configuration information  1  is used to indicate the SF to connect the session of the user  4  to the UP device  22 . The SF device  5  may perform configuration according to an indication of the configuration information  1 , to migrate the session of the user  4  to the UP device  22 . 
     For example, the configuration information  1  carries information about an original SF interface (namely, the information about the SF interface  1 ), information about an SF interface after steering (namely, the information about the SF interface  2 ), and the VLAN of the user  4 . After receiving the configuration information  1 , the SF device  5  may cancel configuration of the VLAN of the user  4  on the SF interface  1 , and configure the VLAN of the user  4  on the SF interface  2 , to send the packet of the user  4  to the UP device  22  through the layer  2  tunnel T 2 . 
       310 : The user  4  accesses the network through the SF device  5  and the UP device  22 . 
     After the SDN controller  6  completes configuration of the UP device  22  through the CP device  1  and completes configuration of the SF device  5 , the user  4  may access the network through the SF device  5  and the UP device  22 . Specifically, the packet of the user  4  is sent to the UP device  22  through the SF device  5 , and then the UP device  22  sends the packet to a core network or the CP device  1 . 
       311 : The SDN controller  6  obtains detection data c from the UP device  22 . 
       312 : The SDN controller  6  obtains detection data d from the UP device  23 . 
     Because detection data of network performance between the SF and a UP device may change, after step  310 , the SDN controller  6  may obtain the detection data c of the network performance between the SF device  5  and the UP device  22  and the detection data d of network performance between the SF device  5  and the UP device  23 . 
       FIG.  3    is illustrated by using an example in which the detection data c and the detection data d are respectively from the UP device  22  and the UP device  23 . During actual application, the SDN controller  6  may further obtain detection data of the network performance of the layer  2  tunnel T 1  between the SF device  5  and the UP device  21 . If the detection data meets the network performance requirement of the user  4 , the SDN controller  6  may select the UP device  21  as a second UP device. 
     For step  311  and step  312 , refer to step  301  and step  302  for understanding. For example, optionally, the SDN controller  6  obtains the detection data c and the interface information (for example, the information about the SF interface  2  and the information about the UP interface  2 ) that correspond to the layer  2  tunnel T 2 , and the SDN controller  6  obtains the detection data d and interface information (for example, information about the SF interface  3  and information about the UP interface  3 ) that correspond to the layer  2  tunnel T 3 . 
     In an optional manner, the SDN controller  6  may further obtain detection data of the SF device  5  and another UP device in the CU separation communication system. For example, the SDN controller  6  may further obtain detection data from the UP device  21 . The detection data is the detection data of the network performance of the layer  2  tunnel T 1  between the SF device  5  and the UP device  21 . 
       313 : The SDN controller  6  sends fourth information to the CP device  1  based on the detection data c and the detection data d. 
     After the SDN controller  6  obtains the detection data c and the detection data d, the SDN controller  6  may select one UP device (which is referred to as the second UP device) from the UP device  22  and the UP device  23  based on the detection data c and the detection data d. Detection data of the second UP device meets the network performance requirement of the user  4 . The fourth information is used to indicate the CP device  1  to configure the second UP device, to connect the session of the user  4  to the network through the second UP device. 
       FIG.  3    is illustrated by using an example in which the second UP device is the UP device  23 . For example, the fourth information carries the identifier of the user  4  and interface information (namely, the information about the UP interface  3 ) of the UP device  23 . 
     To reduce system overheads caused by UP device switching, in an optional manner, if both the detection data c and the detection data d meet the network performance requirement of the user  4 , the SDN controller  6  may preferentially select the UP device  22  as the second UP device. Alternatively, if the detection data c does not meet the network performance requirement of the user  4 , but the detection data d meets the network performance requirement of the user  4 , the SDN controller  6  may select the UP device  23  as the second UP device. 
       314 : The CP device  1  sends the session table of the user  4  to the UP device  23 . 
     After receiving the fourth information, the CP device  1  may configure the UP device  23  according to an indication of the fourth information, for example, send the session table of the user  4  to the UP device  23 . 
       315 : The CP device  1  sends response information for the fourth information to the SDN controller  6 . 
     After completing configuration of the UP device  23  according to the indication of the fourth information, the CP device  1  may send the response information for the fourth information to the SDN controller  6 , to indicate that the CP device  1  has completed configuration of the UP device  23 , and specifically indicate that the session table of the user  4  has been delivered to the UP device  23 . 
       316 : The SDN sends configuration information  2  to the SF device  5  based on first detection data. 
     Refer to step  313 . The SDN controller  6  may determine, based on the detection data c and the detection data d, that detection data of the UP  23  meets the network performance requirement of the user  4 . After the CP device  1  completes configuration of the UP device  23 , the SDN controller  6  may send the configuration information  2  to the SF device  5 . The configuration information  2  is used to indicate the SF to connect the session of the user  4  to the UP device  23 . The SF device  5  may perform configuration according to an indication of the configuration information  2 , to migrate the session of the user  4  to the UP device  23 . 
     For example, the configuration information  2  carries information about an original SF interface (namely, the information about the SF interface  2 ), information about an SF interface after steering (namely, the information about the SF interface  3 ), and the VLAN of the user  4 . After receiving the configuration information  2 , the SF device  5  may cancel configuration of the VLAN of the user  4  on the SF interface  2 , and configure the VLAN of the user  4  on the SF interface  3 , to send the packet of the user  4  to the UP device  23  through the layer  2  tunnel T 3 . 
       317 : The user  4  accesses the network through the SF device  5  and the UP device  23 . 
     After the SDN controller  6  completes configuration of the UP device  23  through the CP device  1  and completes configuration of the SF device  5 , the user  4  may access the network through the SF device  5  and the UP device  23 . Specifically, the packet of the user  4  is sent to the UP device  23  through the SF device  5 , and then the UP device  23  sends the packet to the core network or the CP device  1 . 
     In the method shown in  FIG.  3   , an execution sequence of step  301  and step  302  is not limited, and an execution sequence of step  311  and step  312  is not limited. In the method shown in  FIG.  3   , step  301  and step  302  only need to be performed before step  306 . 
     In addition, because this embodiment of this application is intended to select, for the first user, a UP device whose network performance meets a requirement, the method shown in  FIG.  3    is not limited to step  301  and step  302 , provided that the SDN controller  6  obtains the detection data that meets the network performance requirement of the user  4 . For example, it is assumed that the detection data b meets the network performance requirement of the user  4 . In this case, before step  306 , the SDN controller  6  obtains only the detection data b, and may select the first UP device for the user  4  without obtaining the detection data a. 
     Step  301  to step  310  are used to select, for the user in a session establishment process, a UP device whose network performance meets the user requirement, to enable the user to access the network through the UP device. Step  305  is used to provide the identifier of the user  4  and the SLA information of the user  4  for the SDN controller  6 . Optionally, step  305  may not be performed in the method shown in  FIG.  3   , and the SDN controller  6  obtains the identifier and the SLA information of the user  4  in the session establishment process in another manner. 
     If the CP device  1  fails to configure the UP device  22 , configuring the SF device  5  by the SDN controller  6  easily results in that the user  4  cannot access the network. Step  308  is used to notify that the configuration of the UP device  22  is completed, and this helps increase a rate of successfully accessing the network by the user  4 . In the method shown in  FIG.  3   , step  308  is not necessarily limited to being performed. Similarly, step  315  is used to notify that the configuration of the UP device  23  is completed. In the method shown in  FIG.  3   , step  315  is not necessarily limited to being performed. 
     Step  311  to step  317  are used to select, for the user that has established the session, a UP device whose network performance meets the user requirement, to enable the user to access the network through the UP device. Information and the SLA information of the user may be obtained and saved by the SDN controller  6  by using step  305 . Optionally, the SDN controller  6   may obtain, in another manner, the identifier and the SLA information of the user that has established the session. 
     The method shown in  FIG.  3    may be applied to the session establishment process of the user, and may be applied to the established session of the user. Optionally, the method shown in  FIG.  3    may be applied only to the session establishment process of the user. For example, in this case, step  311  to step  317  may not be performed. Alternatively, the method shown in  FIG.  3    may be applied only to the established session of the user. For example, in this case, step  301  to step  310  may not be performed. 
     In an optional manner, the first device in the method shown in  FIG.  2    is a CP device. In this case, optionally, the first device may directly configure the UP device, and indicate an SDN controller to configure the SF device. With reference to  FIG.  4   , the following describes a network access method in this case by using an example.  FIG.  4    is a schematic diagram of the network access method according to another embodiment of this application. The method shown in  FIG.  4    is an example of the method shown in  FIG.  2   . Therefore, for some explanations of the method shown in  FIG.  4   , refer to the descriptions of the method shown in  FIG.  2   . The method shown in  FIG.  4    includes steps  401  to  416 . For ease of description, an example in which the method shown in  FIG.  4    is applied to the communication system shown in  FIG.  1    is used for description. An SDN controller  6  is connected to a CP device  1 , and an example in which a first user is a user  4  is used for illustration. 
       401 : The SDN controller  6  obtains detection data a from a UP device  21 . 
       402 : The SDN controller  6  obtains detection data b from a UP device  22 . 
       403 : The CP device  1  obtains the detection data a and the detection data b from the SDN controller  6 . 
     The CP device  1  obtains the detection data a of network performance between an SF device  5  and the UP device  21 , and obtains the detection data b of network performance between the SF device  5  and the UP device  22 .  FIG.  4    is illustrated by using an example in which both the detection data a and the detection data b that are obtained by the CP device  1  are from the SDN controller  6 . 
     For descriptions of the detection data a and the detection data b, refer to related descriptions of step  301  and step  302 . Details are not described herein again. 
       404 : The CP device  1  receives a go-online packet of the user  4 . 
       405 : An authentication server  7  performs authentication on the user  4 . 
     For step  404  and step  405 , refer to related descriptions of step  303  and step  304  for understanding. Details are not described herein again. 
       406 : The CP device  1  sends a session table of the user  4  to the UP device  22  based on the detection data a and the detection data b. 
     The CP device  1  selects one UP device (which is referred to as a first UP device) from the UP device  21  and the UP device  22  based on the detection data a and the detection data b. Detection data of the first UP device meets a network performance requirement of the user  4 . The CP device  1  may configure the first UP device, for example, including but not limited to sending the session table of the user  4  to the first UP device. 
     In  FIG.  4   , an example in which the first UP device is the UP device  22  is used for illustration. 
     To reduce system overheads caused by UP device switching, in an optional manner, if both the detection data a and the detection data b meet the network performance requirement of the user  4 , the CP device  1  may preferentially select the UP device  21  as the first UP device. Alternatively, if the detection data a does not meet the network performance requirement of the user  4 , but the detection data b meets the network performance requirement of the user  4 , the CP device  1  may select the UP device  22  as the first UP device. 
       407 : The CP device  1  sends second information to the SDN controller  6  based on the detection data a and the detection data b. 
     Refer to step  406 . The CP device  1  may determine, based on the detection data a and the detection data b, that detection data of the UP device  22  meets the network performance requirement of the user  4 . After sending the session table of the user  4  to the UP device  22 , the CP device  1  indicates the SDN controller  6  to configure the SF device  5 . For example, the CP device  1  sends the second information to the SDN controller  6 . The second information is used to indicate the SDN controller to send configuration information to the SF device. The configuration information is used to indicate the SF device to connect a session of the first user to the UP device  22 . 
       408 : The SDN controller  6  sends configuration information  1  to the SF device  5  based on the second information. 
       409 : The user  4  accesses a network through the SF device  5  and the UP device  22 . 
     For step  408  and step  409 , refer to related descriptions of step  309  and step  310  for understanding. Details are not described herein again. 
       410 : The SDN controller  6  obtains detection data c from the UP device  21 . 
       411 : The SDN controller  6  obtains detection data d from the UP device  22 . 
       412 : The CP device  1  obtains the detection data c and the detection data d from the SDN controller  6 . 
     Because detection data of network performance between the SF and a UP device may change, after step  409 , the CP device  1  may obtain the detection data c of the network performance between the SF device  5  and the UP device  22  and the detection data d of network performance between the SF device  5  and the UP device  23 . 
     For descriptions of the detection data c and the detection data d, refer to related descriptions of step  311  and step  312 . Details are not described herein again. 
       413 : The CP device  1  sends the session table of the user  4  to the UP device  23  based on the detection data c and the detection data d. 
     After the SDN controller  6  obtains the detection data c and the detection data d, the SDN controller  6  may select one UP device (which is referred to as a second UP device) from the UP device  22  and the UP device  23  based on the detection data c and the detection data d. Detection data of the second UP device meets the network performance requirement of the user  4 . The CP device  1  may configure the second UP device, for example, including but not limited to sending the session table of the user  4  to the second UP device. 
       FIG.  4    is illustrated by using an example in which the second UP device is the UP device  23 . During actual application, the CP device  1  may further obtain detection data of network performance of a layer  2  tunnel T 1  between the SF device  5  and the UP device  21 . If the detection data meets the network performance requirement of the user  4 , the CP device  1  may select the UP device  21  as the second UP device. 
     To reduce system overheads caused by UP device switching, in an optional manner, if both the detection data c and the detection data d meet the network performance requirement of the user  4 , the CP device  1  may preferentially select the UP device  22  as the second UP device. Alternatively, if the detection data c does not meet the network performance requirement of the user  4 , but the detection data d meets the network performance requirement of the user  4 , the CP device  1  may select the UP device  23  as the second UP device. 
       414 : The CP device  1  sends fifth information to the SDN controller  6  based on the detection data c and the detection data d. 
     Refer to step  413 . The CP device  1  may determine, based on the detection data c and the detection data d, that detection data of the UP device  23  meets the network performance requirement of the user  4 . After sending the session table of the user  4  to the UP device  23 , the CP device  1  indicates the SDN controller  6  to configure the SF device  5 . For example, the CP device  1  sends the fifth information to the SDN controller  6 . The fifth information is used to indicate the SDN controller to send configuration information to the SF device. The configuration information is used to indicate the SF device to connect the session of the first user to the UP device  23 . 
       415 : The SDN controller  6  sends configuration information  2  to the SF device  5  based on the fifth information. 
       416 : The user  4  accesses the network through the SF device  5  and the UP device  23 . 
     For step  415  and step  416 , refer to related descriptions of step  316  and step  317  for understanding. Details are not described herein again. 
     In the method shown in  FIG.  4   , an execution sequence of step  401  and step  402  is not limited, and an execution sequence of step  410  and step  411  is not limited. In the method shown in  FIG.  4   , step  401 , step  402 , and step  403  are not limited to being performed before step  404 , provided that step  401 , step  402 , and step  403  are performed before step  406 . 
     In addition, because this embodiment of this application is intended to select, for the first user, a UP device whose network performance meets a requirement, the method shown in  FIG.  4    is not limited to step  401  and step  402 , provided that the CP device  1  obtains the detection data that meets the network performance requirement of the user  4 . For example, it is assumed that the detection data b meets the network performance requirement of the user  4 . In this case, before step  406 , the CP device  1  obtains only the detection data b, and may select the first UP device for the user  4  without obtaining the detection data a. 
     Step  401  to step  409  are used to select, for the user in a session establishment process, a UP device whose network performance meets the user requirement, to enable the user to access the network through the UP device. Step  410  to step  416  are used to select, for the user that has established a session, a UP device whose network performance meets the user requirement, to enable the user to access the network through the UP device. The method shown in  FIG.  4    may be applied to the session establishment process of the user, and may be applied to the established session of the user. Optionally, the method shown in  FIG.  4    may be applied only to the session establishment process of the user. For example, in this case, step  410  to step  416  may not be performed. Alternatively, the method shown in  FIG.  4    may be applied only to the established session of the user. For example, in this case, step  401  to step  409  may not be performed. 
     In an optional manner, the first device in the method shown in  FIG.  2    is a USF device. In this case, optionally, the first device may indicate a CP device to configure the UP device, and indicate an SDN controller to configure the SF device. With reference to  FIG.  5 A  and  FIG.  5 B , the following describes a network access method in this case by using an example.  FIG.  5 A  and  FIG.  5 B  are a schematic diagram of the network access method according to another embodiment of this application. The method shown in  FIG.  5 A  and  FIG.  5 B  is an example of the method shown in  FIG.  2   . Therefore, for some explanations of the method shown in  FIG.  5 A  and  FIG.  5 B , refer to the descriptions of the method shown in  FIG.  2   . The method shown in  FIG.  5 A  and  FIG.  5 B  includes steps  501  to  521 . For ease of description, an example in which the method shown in  FIG.  5 A  and  FIG.  5 B  is applied to the communication system shown in  FIG.  1    is used for description. The communication system shown in  FIG.  1    includes a USF device  8 . The USF device  8  is separately connected to an SDN controller  6  and a CP device  1 . The SDN controller  6   may not be connected to the CP device  1 . In addition, an example in which a first user is a user  4  is used for illustration. 
       501 : The SDN controller  6  obtains detection data a from a UP device  21 . 
       502 : The SDN controller  6  obtains detection data b from a UP device  22 . 
       503 : The USF device  8  obtains the detection data a and the detection data b from the SDN controller  6 . 
     The USF device  8  obtains the detection data a of network performance between an SF device  5  and the UP device  21 , and obtains the detection data b of network performance between the SF device  5  and the UP device  22 .  FIG.  5 A  and  FIG.  5 B  are illustrated by using an example in which both the detection data a and the detection data b that are obtained by the USF device  8  are from the SDN controller  6 . 
     For descriptions of the detection data a and the detection data b, refer to related descriptions of step  301  and step  302 . Details are not described herein again. 
       504 : The CP device  1  receives a go-online packet of the user  4 . 
       505 : An authentication server  7  performs authentication on the user  4 . 
     For step  504  and step  505 , refer to related descriptions of step  303  and step  304  for understanding. Details are not described herein again. 
       506 : The CP device  1  sends third information to the USF device  8 . 
       507 : The USF device  8  sends first information to the CP device  1  based on the third information, the detection data a, and the detection data b. 
       508 : The CP device  1  sends a session table of the user  4  to the UP device  22 . 
       509 : The CP device  1  sends response information for the first information to the USF device  8 . 
     For step  504  to step  509 , refer to related descriptions of step  303  to step  308  for understanding. Details are not described herein again. 
       510 : The USF device  8  sends second information to the SDN controller  6  based on the detection data a and the detection data b. 
     After the USF device  8  determines, based on the detection data a and the detection data b, that detection data of the UP device  22  meets a network performance requirement of the user  4 , the USF device  8  indicates the SDN controller  6  to configure the SF device  5 . For example, the USF device  8  sends the second information to the SDN controller  6 . The second information is used to indicate the SDN controller to send configuration information to the SF device. The configuration information is used to indicate the SF device to connect a session of the first user to the UP device  22 . 
       511 : The SDN controller  6  sends configuration information  1  to the SF device  5  based on the second information. 
       512 : The user  4  accesses a network through the SF device  5  and the UP device  22 . 
     For step  511  and step  512 , refer to related descriptions of step  309  and step  310  for understanding. Details are not described herein again. 
       513 : The SDN controller  6  obtains detection data c from the UP device  21 . 
       514 : The SDN controller  6  obtains detection data d from the UP device  22 . 
       515 : The USF device  8  obtains the detection data c and the detection data d from the SDN controller  6 . 
     For step  513  to step  515 , refer to step  410  to step  412  for understanding. Details are not described herein again. 
       516 : The USF device  8  sends fourth information to the CP device  1  based on the detection data c and the detection data d. 
       517 : The CP device  1  sends the session table of the user  4  to the UP device  23 . 
       518 : The CP device  1  sends response information for the fourth information to the SDN controller  6 . 
     For step  516  to step  518 , refer to related descriptions of step  313  to step  315  for understanding. Details are not described herein again. 
       519 : The USF device  8  sends fifth information to the SDN controller  6  based on the detection data c and the detection data d. 
       520 : The SDN controller  6  sends configuration information  2  to the SF device  5  based on the fifth information. 
       521 : The user  4  accesses the network through the SF device  5  and the UP device  23 . 
     For step  519  to step  521 , refer to related descriptions of step  414  to step  416  for understanding. Details are not described herein again. 
     In the method shown in  FIG.  5 A  and  FIG.  5 B , an execution sequence of step  501  and step  502  is not limited, and an execution sequence of step  513  and step  514  is not limited. In the method shown in  FIG.  5 A  and  FIG.  5 B , step  501 , step  502 , and step  503  only need to be performed before step  507 . 
     In addition, because this embodiment of this application is intended to select, for the first user, a UP device whose network performance meets a requirement, the method shown in  FIG.  3    is not limited to step  501  and step  502 , provided that the USF device  8  obtains the detection data that meets the network performance requirement of the user  4 . For example, it is assumed that the detection data b meets the network performance requirement of the user  4 . In this case, before step  507 , the USF device  8  obtains only the detection data b, and may select the first UP device for the user  4  without obtaining the detection data a. 
     Step  501  to step  512  are used to select, for the user in a session establishment process, a UP device whose network performance meets the user requirement, to enable the user to access the network through the UP device. Step  506  is used to provide an identifier of the user  4  and SLA information of the user  4  for the USF device  8 . Optionally, step  506  may not be performed in the method shown in  FIG.  5 A  and  FIG.  5 B , and the USF device  8  obtains the identifier and the SLA information of the user  4  in the session establishment process in another manner. 
     Step  509  is used to notify that configuration of the UP device  22  is completed. If the CP device  1  fails to configure the UP device  22 , indicating, by the USF device  8 , the SDN controller  6  to configure the SF device  5  easily results in that the user  4  cannot access the network. In the method shown in  FIG.  5 A  and  FIG.  5 B , step  509  is not necessarily limited to being performed. Similarly, step  518  is used to notify that configuration of the UP device  23  is completed. In the method shown in  FIG.  5 A  and  FIG.  5 B , step  518  is not necessarily limited to being performed. 
     Step  513  to step  521  are used to select, for the user that has established a session, a UP device whose network performance meets the user requirement, to enable the user to access the network through the UP device. Information and the SLA information of the user may be obtained and saved by the USF device  8  by using step  506 . Optionally, the USF device  8  may obtain, in another manner, the identifier and the SLA information of the user that has established the session. 
     The method shown in  FIG.  5 A  and  FIG.  5 B  may be applied to the session establishment process of the user, and may be applied to the established session of the user. Optionally, the method shown in  FIG.  5 A  and  FIG.  5 B  may be applied only to the session establishment process of the user. For example, in this case, step  513  to step  521  may not be performed. Alternatively, the method shown in  FIG.  5 A  and  FIG.  5 B  may be applied only to the established session of the user. For example, in this case, step  501  to step  512  may not be performed. 
       FIG.  6    is a flowchart of a network access method according to another embodiment of this application. The method in the embodiment corresponding to  FIG.  6    may be applied to the communication system shown in  FIG.  1   , or may be applied to another communication system. This is not limited in this embodiment of this application. Optionally, a first device in the network access method shown in  FIG.  6    may be an execution body (namely, the first device) of the method shown in  FIG.  2   , or the SDN controller in the method shown in  FIG.  3   , or the USF device in the method shown in  FIG.  5 A  and  FIG.  5 B . Refer to  FIG.  6   . The network access method in this embodiment of this application includes step  601  and step  602 . 
       601 : A CP device receives first information sent by the first device. 
     The CP device is a CP device (for example, the CP device  1  in  FIG.  1   ) in a CU separation communication system. A first UP device is a UP device (for example, the UP device  22  in  FIG.  1   ) in the communication system. 
     The first information is used to indicate that a first user corresponds to the first UP device in the communication system. Detection data of network performance between an SF device and the first UP device meets a network performance requirement of the first user. 
       602 : The CP device sends a session table of the first user to the first UP device. 
     For step  602 , refer to step  307  for understanding. Details are not described herein again. 
     In an optional manner, refer to a dashed line part in  FIG.  6   . After step  602 , the method shown in  FIG.  6    may further include step  603 . 
       603 : The CP device sends response information for the first information to the first device. 
     The response information for the first information is used to indicate that the session table of the first user has been delivered to the first UP device. The first device configures the SF device based on the response information. This helps increase a rate of successfully accessing a network by the user  4 . 
     In an optional manner, still refer to the dashed line part in  FIG.  6   . Before step  601 , the method shown in  FIG.  6    may further include step  604  and step  605 . 
       604 : The CP device receives a go-online request packet of the first user. 
       605 : The CP device sends third information to the first device. 
     The third information is used to request the first device to determine a UP device in the communication system corresponding to the first user. Between step  604  and step  605 , the CP device may further request an authentication server to perform authentication on the first user. 
     For step  604  and step  605 , refer to step  303  and step  305  for understanding. Details are not described herein again. 
       FIG.  7    is a flowchart of a network access method according to another embodiment of this application. The method in the embodiment corresponding to  FIG.  7    may be applied to the communication system shown in  FIG.  1   , or may be applied to another communication system. This is not limited in this embodiment of this application. Optionally, a first device in the network access method shown in  FIG.  7    may be an execution body (namely, the first device) of the method shown in  FIG.  2   , or the CP device in the method shown in  FIG.  4   , or the USF device in the method shown in  FIG.  5 A  and  FIG.  5 B . Refer to  FIG.  7   . The network access method in this embodiment of this application includes step  701  and step  702 . 
       701 : An SDN controller sends detection data of network performance between an SF device and a first UP device to the first device. 
     The first UP device is a UP device in a CU separation communication system. Optionally, the detection data is detection data of network performance of a layer  2  tunnel between the SF device and the first UP device. 
       702 : The SDN controller receives second information sent by the first device. 
     The second information is used to indicate that a first user corresponds to the first UP device. The detection data of the network performance between the SF device and the first UP meets a network performance requirement of the first user. 
     For step  702 , refer to step  407  for understanding. Details are not described herein again. 
       703 : The SDN controller sends configuration information to the SF device. 
     The configuration information is used to indicate the SF to connect a session of the first user to the first UP device. 
     For step  702 , refer to step  309  for understanding. Details are not described herein again. 
     In an optional manner, in the network access method shown in  FIG.  7   , step  702  and step  703  may not be performed. The SDN controller sends the detection data of the network performance between the SF device and the first UP device to the first device. This helps the first device select, for the first user, a UP device that meets the requirement and configure the first user to access a network through the UP device, and ensures network use experience of the first user. 
     In an optional manner, in the network access method shown in  FIG.  7   , step  701  may not be performed. The SDN controller performs step  702  and step  703 . This helps configure, according to an indication of the first device, the first UP device that meets the requirement of the first user, helps the first user access the network through the first UP device, and ensures the network use experience of the first user. 
     The foregoing describes the network access methods in embodiments of this application, and the following describes a structure of a network apparatus in this application. The network apparatus may be the first device in the method shown in  FIG.  2   , or the SDN controller or the CP device in the method shown in  FIG.  3   , or the CP device or the SDN controller in the method shown in  FIG.  4   , or the USF device or the SDN controller or the CP device in the method shown in  FIG.  5 A  and  FIG.  5 B , or the CP device in the method shown in  FIG.  6   , or the SDN controller in the method shown in  FIG.  7   . Alternatively, the network apparatus may be an apparatus that can be used together with a corresponding device. The network apparatus may be installed in the corresponding device. For example, the network apparatus may be a chip system. In embodiments of this application, the chip system may include a chip, or may include a chip and another discrete component. 
       FIG.  8    is a schematic diagram of a structure of a network apparatus according to an embodiment of this application. Refer to  FIG.  8   . The network apparatus includes a processor  801  and a memory  802 . 
     The processor  801  may be one or more CPUs, and the CPU may be a single-core CPU, or may be a multi-core CPU. 
     The memory  802  includes but is not limited to a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), a flash memory, an optical memory, or the like. The memory  802  stores code of an operating system and program instructions. 
     Optionally, the network apparatus further includes a communication interface  803 . The communication interface  803  may be a wired interface, for example, a fiber distributed data interface (FDDI) or a gigabit Ethernet (GE) interface. Alternatively, the communication interface  803  may be a wireless interface. The communication interface  803  is configured to receive network data from an internal network and/or an external network. 
     Optionally, the network apparatus further includes a bus  804 . The processor  801  and the memory  802  are usually connected to each other through the bus  804 , or may be connected to each other in another manner. 
     Optionally, the processor  801  implements the network access method in embodiments of this application by reading the program instructions stored in the memory  802 . Alternatively, the processor  801  may implement the network access method in embodiments of this application by using internally stored program instructions. For example, the processor  801  performs, based on the instructions stored in the memory  802 , the steps in the method shown in  FIG.  2   , the steps performed by the SDN controller or the CP device in the method shown in  FIG.  3   , the steps performed by the CP device or the SDN controller in the method shown in  FIG.  4   , the steps performed by the USF device, the SDN controller, or the CP device in the method shown in  FIG.  5 A  and  FIG.  5 B , the steps in the method shown in  FIG.  6   , or the steps in the method shown in  FIG.  7   . For more details about implementing the foregoing steps by the processor  801 , refer to the descriptions in the foregoing method embodiments. Details are not described herein again. 
     An embodiment of this application further provides a network apparatus.  FIG.  9    is a schematic diagram of a structure of the network apparatus according to this embodiment of this application. Refer to  FIG.  9   . The network apparatus  9  includes a receiving module  901  and a configuration module  902 . For example, the receiving module  901  is configured to perform step  201 , step  203 , step  301 , step  302 , step  305 , step  308 , step  311 , step  312 , step  315 , step  403 , step  404 , step  412 , step  503 , step  506 , step  509 , step  515 , step  518 , or the like. The configuration module  902  is configured to perform step  202 , step  204 , step  305 , step  309 , step  313 , step  316 , step  406 , step  407 , step  413 , step  414 , step  507 , step  510 , step  516 , step  519 , or the like. For a specific execution process, refer to the detailed descriptions of the corresponding steps in the foregoing method embodiments. Details are not described herein again. 
     An embodiment of this application further provides a network apparatus.  FIG.  10    is a schematic diagram of a structure of the network apparatus according to this embodiment of this application. Refer to  FIG.  10   . The network apparatus  10  includes a receiving module  1001  and a sending module  1002 . For example, the receiving module  1001  is configured to perform step  303 , step  306 , step  313 , step  504 , step  507 , step  516 , step  601 , step  604 , or the like. The sending module  1002  is configured to perform step  605 , step  307 , step  308 , step  314 , step  315 , step  506 , step  508 , step  509 , step  517 , step  518 , step  602 , step  603 , step  605 , or the like. For a specific execution process, refer to the detailed descriptions of the corresponding steps in the foregoing method embodiments. Details are not described herein again. 
     An embodiment of this application further provides a network apparatus.  FIG.  11    is a schematic diagram of a structure of the network apparatus according to this embodiment of this application. Refer to  FIG.  11   . The network apparatus  11  includes a receiving module  1101  and a sending module  1102 . For example, the receiving module  1101  is configured to perform step  401 , step  402 , step  407 , step  410 , step  411 , step  414 , step  501 , step  502 , step  510 , step  513 , step  514 , step  519 , step  702 , or the like. The sending module  1102  is configured to perform step  403 , step  408 , step  412 , step  415 , step  503 , step  511 , step  515 , step  520 , step  703 , or the like. For a specific execution process, refer to the detailed descriptions of the corresponding steps in the foregoing method embodiments. Details are not described herein again. 
     An embodiment of this application further provides a network apparatus.  FIG.  12    is a schematic diagram of a structure of the network apparatus according to this embodiment of this application. Refer to  FIG.  12   . The network apparatus  12  includes a sending module  1201 . For example, the sending module  1201  is configured to perform step  403 , step  412 , step  503 , step  515 , or step  701 . For a specific execution process, refer to the detailed descriptions of the corresponding steps in the foregoing method embodiments. Details are not described herein again. 
     The coupling in embodiments of this application may be an indirect coupling or a communication connection between apparatuses, units, or modules in an electrical form, a mechanical form, or another form, and is used for information exchange between the apparatuses, the units, or the modules. 
     The apparatus embodiments described in  FIG.  9    to  FIG.  12    are merely examples. The modules in  FIG.  9    to  FIG.  12    may be implemented in a form of hardware, or may be implemented in a form of a software functional unit. For example, when software is used for implementation, the receiving module  901  and the configuration module  902  in the apparatus shown in  FIG.  9    may be implemented by one or more software functional modules generated after the processor  801  reads the program instructions stored in the memory  802 . In embodiments of this application, module division is an example, and is merely logical function division. During actual implementation, another division manner may be used. The modules in  FIG.  9   ,  FIG.  10   ,  FIG.  11   , or  FIG.  12    may be separately implemented by different hardware in the network apparatuses. For example, the receiving module  901  is implemented by the communication interface  803  in  FIG.  8   , and the configuration module  902  is jointly implemented by the processor  801  and the network interface  803  in  FIG.  8   . It is clear that the foregoing functional module may alternatively be implemented by using a combination of software and hardware. For example, the receiving module  901  is implemented by the communication interface  803 , and the configuration module  902  is a software functional module generated after the processor  80   1  reads the program instructions stored in the memory  802 . 
     For technical effects that can be implemented by the network apparatuses shown in  FIG.  9   ,  FIG.  10   ,  FIG.  11   , and  FIG.  12    and more details of implementing the foregoing functions by the modules, refer to corresponding descriptions in the foregoing method embodiments. Details are not described herein again. 
     Refer to  FIG.  13   . An embodiment of this application further provides a chip  13 . The chip  13  includes a processor  1301  and a communication interface  1302 . The communication interface  1302  is coupled to the processor  1301 . The processor  1301  is configured to run a computer program or instructions, to implement the method provided in any one of the foregoing method embodiments of this application. 
     In an example, the communication interface  1302  (or referred to as an interface circuit) may be, for example, an input/output interface, a pin, or a circuit on the chip  13 . The processor  1301  may execute computer instructions stored in a memory, to enable the chip  13  to perform any one of the foregoing method embodiments. Optionally, the memory may be a storage unit in the chip  13 , for example, a register or a cache. Alternatively, the memory may be a memory that is in a computer device and that is located outside the chip  13 , for example, a read-only memory (ROM) or another type of static storage device that can store static information and instructions, or a random access memory (RAM). Optionally, the processor  1301  maybe a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to control program execution of any one of the foregoing method embodiments. 
     All or a part of the foregoing embodiments may be implemented by using software, hardware, firmware, or any combination thereof. When the software is used for implementation, all or a part of the embodiments may be implemented in a form of a computer program product. 
     The computer program product includes one or more computer instructions. When the computer-executable instructions are loaded and executed on a computer, the procedures or the functions according to embodiments of this application are all or partially generated. The computer may be a general-purpose computer, a dedicated computer, a computer network, or another programmable apparatus. The computer instructions may be stored in a computer-readable storage medium or may be transmitted from a computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from a website, computer, server, or data center to another website, computer, server, or data center in a wired (for example, a coaxial cable, an optical fiber, or a digital subscriber line (DSL)) or wireless (for example, infrared, radio, or microwave) manner. The computer-readable storage medium may be any usable medium accessible by a computer, or a data storage device, such as a server or a data center, integrating one or more usable media. The usable medium may be a magnetic medium (for example, a floppy disk, a hard disk, or a magnetic tape), an optical medium (for example, a DVD), a semiconductor medium (for example, a solid state disk (SSD)), or the like. 
     An embodiment of this application further provides a communication system. The communication system may include a first device, an SF device, and a UP device. The first device is configured to perform the method shown in  FIG.  2   . 
     An embodiment of this application further provides a communication system. The communication system includes a first device, an SDN controller, and a CP device. The first device is configured to perform the method shown in  FIG.  2   , the CP device performs the method shown in  FIG.  6   , and the SDN controller performs the method shown in  FIG.  7   . 
     An embodiment of this application further provides a communication system. The communication system includes an SDN controller and a CP device. The SDN controller performs the method performed by the SDN controller  6  shown in  FIG.  3   , and the CP device performs the method performed by the CP device  1  shown in  FIG.  3   . Alternatively, the CP device performs the method performed by the CP device  1  shown in  FIG.  4   , and the SDN controller performs the method performed by the SDN controller  6  shown in  FIG.  4   . For example, for the communication system in this case, refer to the SDN controller  6  and the CP device  1  in  FIG.  1    for understanding. 
     An embodiment of this application further provides a communication system. The communication system includes an SDN controller, a CP device, and a USF device. The USF device performs the method performed by the USF device  8  shown in  FIG.  5 A  and  FIG.  5 B , the SDN controller performs the method performed by the SDN controller  6  shown in  FIG.  5 A  and  FIG.  5 B , and the CP device performs the method performed by the CP device  1  shown in  FIG.  5 A  and  FIG.  5 B . For example, for the communication system in this case, refer to the USF device  8 , the SDN controller  6 , and the CP device  1  in  FIG.  1    for understanding. 
     In embodiments of this application, at least one means one or more, and a plurality of means two or more. This is not limited in this application. In embodiments of this application, “/” may represent an “or” relationship between associated objects. For example, A/B may represent A or B. “And/or” may be used to indicate that there are three relationships between associated objects. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists. A and B may be singular or plural. To facilitate description of the technical solutions in embodiments of this application, in embodiments of this application, terms such as “first” and “second” may be used to distinguish between technical features with same or similar functions. The terms such as “first” and “second” do not limit a quantity and an execution sequence, and the terms such as “first” and “second” do not indicate a definite difference. In embodiments of this application, the term such as “example” or “for example” is used to represent an example, an illustration, or a description. Any embodiment or design scheme described with “example” or “for example” should not be explained as being more preferred or having more advantages than another embodiment or design scheme. Use of the term such as “example” or “for example” is intended to present a related concept in a specific manner for ease of understanding. 
     Embodiments in this specification are all described in a progressive manner, for same or similar parts in embodiments, reference may be made to these embodiments, and each embodiment focuses on a difference from other embodiments. Especially, a system embodiment is basically similar to a method embodiment, and therefore is described briefly. For related parts, refer to partial descriptions in the method embodiment. 
     A person of ordinary skill in the art may understand that when software is used to implement the aspects or possible implementations of the aspects in embodiments of this application, all or a part of the aspects or the possible implementations of the aspects may be implemented in a form of a computer program product. The computer program product refers to computer-readable instructions stored in a computer-readable medium. When the computer instructions are loaded and executed on a computer, the procedures or functions according to embodiments of this application are all or partially generated. 
     The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium includes but is not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or apparatus, or any proper combination thereof. For example, the computer-readable storage medium is a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or a portable read-only memory (CD-ROM). 
     It is clear that a person skilled in the art may make various modifications and variations to the present invention without departing from the scope of the present invention. The present invention is intended to cover these modifications and variations provided that they fall within the scope of protection defined by the following claims.