CN111148274A - Method for session establishment, session management function entity, base station and storage medium - Google Patents

Abstract

The embodiment of the disclosure provides a method for session establishment, which includes: receiving a message for creating a session management context; selecting a user plane function entity UPF for redundant session handling in response to the message; and establishing a Packet Data Unit (PDU) session corresponding to the UPF. A method for session establishment by a base station and related equipment are also provided. The technical scheme can realize the reliability of service transmission.

Description

Method for session establishment, session management function entity, base station and storage medium

Technical Field

The present disclosure relates to the field of communications technologies, and in particular, to a method for session establishment, a session management function entity, a base station, and a storage medium.

Background

Modern mobile communications are increasingly tending to provide users with multimedia services for high-rate transmission, some of which require low-latency, highly reliable service transmission. In order to support such features, a concept is proposed to guarantee the reliability of service transmission by means of two Packet Data Unit (PDU) sessions established by two user plane functional entities (UPFs). No specific scheme is given as to how to establish the two PDU sessions.

Therefore, a session establishment scheme is required to achieve high reliability of traffic transmission.

Disclosure of Invention

To this end, the embodiments of the present disclosure propose a method for session establishment, a session management function entity, a base station, and a storage medium.

According to a first aspect of the present disclosure, there is provided a method for session establishment, comprising:

receiving a message for creating a session management context;

selecting a user plane function entity (UPF) for redundant session handling in response to the message for creating a session management context;

and establishing a PDU session corresponding to the UPF.

In some embodiments, selecting a user plane functional entity UPF for redundant session handling in response to said message for creating a session management context comprises:

determining whether the session requiring creation of the session management context is a redundant session and whether the redundant session is a first redundant session or a second redundant session based on at least one of:

the message for creating the session management context contains information related to redundant sessions;

a data network name DNN or single network slice selection assistance information S-NSSAI and operator network configuration;

based on the determination, a UPF for redundant session handling is selected in accordance with an identity of a serving base station of the user equipment UE.

In some embodiments, the method further comprises:

receiving a first base station identifier of a base station where the first redundant session is established and a second base station identifier of a base station where the second redundant session is established, selecting a UPF for the first redundant session according to the first base station identifier, and selecting a UPF for the second redundant session according to the second base station identifier; or

And receiving the base station identification of the base station where the second redundant session is established, and selecting the UPF for the second redundant session according to the base station identification.

According to a second aspect of the present disclosure, there is provided a method for session establishment, wherein the first base station establishes a first redundant session for redundancy handling, the method comprising:

receiving a message for establishing a second redundant session for redundant processing;

determining whether to add a second base station for processing the second redundant session in response to the message; and

configuring the second redundant session to be handled by the second base station if it is determined to add the second base station.

In some embodiments, determining whether to add a second base station for processing the second redundant session in response to the message comprises:

determining whether the first base station supports dual connectivity for the first redundant session and the second redundant session; and

determining to add the second base station to configure the second redundant session for processing by the second base station if the first base station supports the dual connectivity, otherwise determining not to add the second base station.

In some embodiments, the method further comprises:

storing information required for establishing the second redundant session when the first base station does not support the dual connectivity; and

when it is determined that the first base station is capable of supporting dual connectivity, determining to add the second base station using the saved information to configure the second redundant session for processing by the second base station.

In the above embodiment, configuring the second redundant session to be processed by the second base station includes:

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session;

receiving resources configured for the second redundant session by the user equipment; and

transmitting the configured resources to the second device to establish the second redundant session at the second base station.

Alternatively, configuring the second redundant session for processing by the second base station comprises:

establishing the second redundant session at the first base station;

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session; and

receiving resources configured for the second redundant session by the user equipment;

handing over the second redundant session to the second base station using the configured resources.

According to a third aspect of the present disclosure, there is provided a method for switching a master base station for redundant session processing, including:

receiving a switching request message sent by a third base station, wherein the switching request message requests that a master control function of redundant session processing of the third base station is switched to the first base station;

establishing a connection of User Equipment (UE) corresponding to the redundant session processing based on the switching request message; and

and sending a path switching request message to the mobile management control entity.

In some embodiments, the method further comprises:

in response to the handover request message, adding a fourth base station for processing of a second one of the redundant sessions of the third base station

According to a fourth aspect of the present disclosure, there is provided a session management function entity, including:

a processing unit; and

a storage unit for storing machine-readable instructions which, when executed by the processing unit, configure the processing unit to perform the method according to the first aspect described above.

According to a fifth aspect of the present disclosure, there is provided a base station comprising:

a processing unit; and

a storage unit for storing machine-readable instructions which, when executed by the processing unit, configure the processing unit to perform the method according to the second aspect described above.

According to a sixth aspect of the present disclosure, there is provided a session management function entity, comprising:

a message receiving unit for receiving a message for creating a session management context;

a UPF selecting unit, for responding to the message for creating the session management context, selecting a user plane functional entity UPF for redundant session processing; and

and the session establishing unit is used for establishing a Packet Data Unit (PDU) session corresponding to the UPF.

According to a seventh aspect of the present disclosure, there is provided a base station comprising:

a message receiving unit configured to receive a message for establishing a second redundant session for redundant processing;

a base station addition determination unit for determining whether to add a second base station for processing the second redundant session in response to the message; and

a second redundant session configuration unit configured to configure the second redundant session to be processed by the second base station if it is determined to add the second base station.

According to an eighth aspect of the present disclosure, there is provided a base station comprising:

a message receiving unit, configured to receive a handover request message sent by a third base station, where the handover request message requests that a master control function of redundant session processing of the third base station be handed over to the first base station;

a connection establishing unit, configured to establish a connection with the UE corresponding to the redundant session processing based on the handover request message; and

and the message sending unit is used for sending the path switching request message to the mobile management control entity.

According to a ninth aspect of the present disclosure, there is provided a computer readable storage medium having stored thereon executable instructions, which when executed by a processor, cause the processor to perform the method according to the first or second aspect described above.

The embodiment of the invention ensures the reliability of service transmission by respectively establishing the two redundant PDU sessions to the two base stations.

Drawings

The above and additional aspects and advantages of the present disclosure will become more apparent and readily appreciated from the following description taken in conjunction with the accompanying drawings, in which:

fig. 1 shows a system architecture diagram of System Architecture Evolution (SAE).

Fig. 2 is a system architecture diagram of a next generation network or a fifth generation 5G network.

Fig. 3 shows a timing diagram of a method for session establishment according to an embodiment of the invention.

Fig. 4 schematically shows a timing diagram of a method of handing over a second PDU session to a secondary base station according to an embodiment of the present disclosure.

Fig. 5 schematically shows a timing diagram of a method of handing over a PDU session for redundant session handling to another base station according to an embodiment of the present disclosure.

Fig. 6 schematically shows a timing diagram of another method of handing over a PDU session for redundant session handling to another base station according to an embodiment of the present disclosure.

Fig. 7 schematically shows a timing diagram of another one of the methods for session establishment according to an embodiment of the present disclosure.

Fig. 8 schematically shows a timing diagram of a further method of the method for session establishment according to an embodiment of the present disclosure.

Fig. 9 schematically shows a schematic diagram of a system supporting session transport reliability according to an embodiment of the present disclosure.

Fig. 10 shows a schematic flow chart of a method for session establishment according to an embodiment of the invention.

Fig. 11 shows a schematic flow chart of another method for session establishment according to an embodiment of the invention.

Fig. 12 shows a schematic block diagram of an SMF for session establishment according to an embodiment of the present invention.

Fig. 13 shows a schematic block diagram of a base station for session establishment according to an embodiment of the present invention.

Fig. 14 shows a schematic flow chart of a method for switching a master base station for redundant session handling according to an embodiment of the present invention.

Fig. 15 shows a schematic block diagram of an apparatus for handing over a master base station for redundant session processing according to an embodiment of the present invention.

Fig. 16 schematically illustrates a block diagram of a computing system that may be used to implement an SMF or base station of the present disclosure, in accordance with an embodiment of the present disclosure.

In the drawings, the same or similar structures are identified by the same or similar reference numerals.

Detailed Description

The present disclosure is described in detail below with reference to the attached drawings and detailed description. It should be noted that the present disclosure should not be limited to the specific embodiments described below. The specific embodiments illustrated herein are exemplary only, and are not to be construed as limiting the disclosure. In addition, for the sake of brevity, detailed descriptions of well-known technologies not directly related to the present disclosure are omitted to prevent confusion of understanding of the present disclosure.

As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or wirelessly coupled. As used herein, the term "and/or" includes all or any element and all combinations of one or more of the associated listed items.

It will be understood by those within the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Fig. 1 shows a system architecture diagram of System Architecture Evolution (SAE). Among them, a User Equipment (UE)101 is a terminal device for receiving data. An evolved universal terrestrial radio access network (E-UTRAN)102 is a radio access network that includes macro base stations (eNodeB/NodeB) that provide access to a radio network interface for UEs. A Mobility Management Entity (MME)103 is responsible for managing mobility context, session context and security information of the UE. Serving Gateway (SGW)104 mainly provides the functions of the user plane, and MME103 andSGW 104 may be in the same physical entity. A packet data network gateway (PGW)105 is responsible for charging, lawful interception, etc., and may also be in the same physical entity as theSGW 104. A Policy and Charging Rules Function (PCRF)106 provides quality of service (QoS) policy and charging criteria. The general packet radio service support node (SGSN)108 is a network node device in the Universal Mobile Telecommunications System (UMTS) that provides routing for the transmission of data. The Home Subscriber Server (HSS)109 is the home subsystem of the UE and is responsible for protecting user information including the current location of the user equipment, the address of the serving node, user security information, the packet data context of the user equipment, etc.

Fig. 2 is a system architecture diagram of a next generation network or a fifth generation 5G network. Among them, a User Equipment (UE)101 is a terminal device for receiving data. The next generation radio access network (NG-RAN)102 is a radio access network including base stations (gbbs or enbs connected to a 5G core network 5 GC) that provide access to radio network interfaces for UEs. An access control and mobility management function (AMF)103 is responsible for managing the mobility context and security information of the UE. A user plane functional entity (UPF)104 mainly provides the functions of the user plane. The session management function SMF105 is responsible for session management. The Data Network (DN)106 contains services such as the operator, access to the internet, and services for third parties.

Regarding how to support low-latency and high-reliability service transmission, the Rel-15 is mainly considered from the air interface, and the architecture and the session establishment method of the network side for supporting various services are the same.

In order to support low-latency and highly reliable service transmission, one scheme discussed now is to establish a redundant user plane, i.e. to ensure the reliability of service transmission by establishing two PDU sessions through two UPFs. However, there is no specific discussion about how to establish two PDU sessions, and in particular, how to select an appropriate UPF, how to support handover, and the like during the PDU session establishment process.

The following describes aspects of the present disclosure in detail with reference to the accompanying drawings.

Fig. 3 shows a timing diagram of a method for session establishment according to an embodiment of the invention. Detailed descriptions of steps not related to the present invention are omitted herein. The method comprises the following steps:

in step 301, the UE sends a PDU session setup request message to the AMF. The UE sends a PDU session establishment request message to the base station through an RRC message. The base station transmits a PDU session setup request message to the AMF through an NG Access Protocol (AP) message. The base station here is a NG-RAN node 1. The PDU session establishment request message includes a Redundant Sequence Number (RSN). The redundant sequence number indicates redundant processing. The value of RSN indicates whether the first or second PDU session is established.

At step 302, the AMF sends a create session management context request message to the SMF.

In this embodiment, there are three methods for selecting the UPF:

in the first method, for the first PDU session and the second PDU session of the redundant process, the UPF is selected according to the identification of the main base station. Corresponding to the method, in this step, the AMF sends the base station identifier of the base station accessed by the UE to the SMF or the NG-RAN node 1 sends the identifier of the main base station or the cell identifier accessed by the UE on the main base station to the SMF through the AMF. The cell is a primary cell accessed by the UE on the primary base station, and is specifically described in this step below.

In step 304, the SMF selects a UPF according to the existing mechanism, and through steps 311 and 312, the NG-RAN includes the base station identifier where each PDU session is established or the cell identifier of the UE access on the base station in a PDU session establishment confirmation message and sends the PDU session establishment confirmation message to the SMF through the AMF, the SMF reselects UPFs for the first PDU session and the second PDU session respectively, and the SMF selects UPFs serving the first PDU session and the second PDU session respectively considering the primary base station identifier and the secondary base station identifier. Here, the cell accessed by the UE on the base station is a primary cell accessed by the UE on the base station, for example, a primary cell on a primary base station or a primary cell on a secondary base station. This explanation can be made in the present invention, and will not be described below when referring to the cell accessed by the UE on the base station. If the SMF receives the cell identifier on the base station, the SMF may obtain the base station identifier according to the cell identifier, which is the same as described below and is not described again. The SMF may select a UPF that is close to the primary and secondary base stations, respectively.

In the third method, for the first PDU session and the second PDU session processed redundantly, the SMF selects a UPF in step 304 according to the identifier of the primary base station, which is described in this step. Through steps 311 and 312, the NG-RAN includes the identity of the secondary base station where the second PDU session is established in the PDU session establishment confirmation message and sends the PDU session establishment confirmation message to the SMF through the AMF, the SMF reselects the UPF for the second PDU session, and the SMF selects the UPF serving the second PDU session considering the identity of the secondary base station or the identity of the cell on the secondary base station. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification. The SMF may select a UPF that is close to the secondary base station. It should be noted that, for convenience of description, in the method of the present invention, the first PDU session is established at the primary base station, and the second PDU session is established at the secondary base station to establish dual connectivity for the redundant PDU session, which PDU session is actually established to the primary base station, and which PDU session is established at the secondary base station may be determined by SMF or NG-RAN. In response to the SMF deciding method, the SMF indicates said information to the NG-RAN via the RSN.

And the AMF sends the base station identification of the base station accessed by the UE or the cell identification of the base station accessed by the UE to the SMF. The AMF receives the NGAP message from the base station, so the AMF knows the base station to which the UE is accessing. Here a NG-RAN node 1.

In step 303, the SMF sends a create session management context response message to the AMF.

At step 304, the SMF selects a UPF. The SMF selects the UPF taking into account the base station identity or cell identity received from the AMF. The base station identification received by the SMF may be a primary base station identification or a secondary base station identification. The secondary base station may also be called a second base station. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification. The SMF knows that the PDU session is to be redundantly processed and whether the PDU session is a first PDU session or a second PDU session based on the RSN received from the UE or based on Data Network Name (DNN) or single network slice selection assistance information (S-NSSAI) and network configuration. The SMF selects the UPF taking into account the first PDU session that is redundantly processed and the received base station identity or cell identity. When the SMF does not receive the RSN from the UE, the SMF may use DNN or S-NSSAI in conjunction with operator configuration to decide to establish the first or second PDU session for redundancy handling. The SMF selects a UPF using whether the first or second PDU session is to be established, in conjunction with other information.

At step 305, the SMF sends an N4 session setup or N4 session modify request message to the selected UPF. If the request type is an initial request, the SMF initiates an N4 session establishment procedure to the selected UPF, otherwise initiates an N4 session modification procedure to the selected UPF.

At step 306, the UPF sends an N4 session setup response or an N4 session modify response message to the SMF.

At step 307, the SMF sends an N1N2 messaging message to the AMF. The message contains a PDU session identification, N2 Session Management (SM) information, N1 session container. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate an association of two PDU sessions of redundant handling. The SMF may set the same RSN value for two PDU sessions to indicate that the two PDU sessions are associated PDU sessions for redundancy processing.

In step 308, the AMF sends a PDU session setup request message to the NG-RAN node 1. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. letting the NG-RAN know which two PDU sessions are redundant handled. The NG-RAN node 1 may be informed that the two PDU sessions are redundantly processed associated PDU sessions by setting the same value for both PDU sessions RSN in the message. In the present invention, the association relationship between two PDU sessions of redundancy processing can be indicated by the method, which is not described in detail below.

Based on the received PDU session setup request message, the NG-RAN node 1 knows that the PDU session to be established is a redundant process. The NG-RAN node 1 also knows whether the PDU session to be established is the first or the second PDU session, or the NG-RAN node 1 can also know which two PDU sessions are redundantly processed. If the established PDU session is redundantly processed and the PDU session to be established is a second PDU session, the NG-RAN node 1 establishes the second PDU session to a different base station than the first PDU session, e.g. if the first PDU session is a primary node (MN) terminated bearer, the second PDU session needs to be established as a Secondary Node (SN) terminated bearer. As an implementation of the present invention, the first PDU session is established as an MN terminated bearer and the second PDU session is established as an SN terminated bearer. The reverse is also permissible. The present invention is not limited as to whether the underlying resource is carried by MCG, SCG, or separately. For two PDU sessions processed redundantly, the MN terminated bearer is carried with MCG, and the SN terminated bearer is carried with SCG relatively simply.

The NG-RAN node 1 may directly establish the second PDU session on the secondary base station (for example, NG-RAN node 2), or may first establish the second PDU session on the NG-RAN node 1, and perform the SN increasing process after the UE is configured and the core network is responded, so as to switch the second PDU session to the secondary base station. For the latter method, i.e. the method of first establishing the second PDU session on the NG-RAN node 1, steps 309a, 309b and 310b need not be performed.

In step 309a, if NG-RAN node 1 decides to establish the second PDU session at NG-RAN node 2, NG-RAN node 1 sends a SN increase request message to NG-RAN node 2. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. letting the NG-RAN node 2 know which two PDU sessions are redundant handling. The NG-RAN node 2 keeps information of redundant PDU session handling, and the NG-RAN node 2 establishes the PDU session as an SN terminated bearer. The NG-RAN node 2 does not switch the bearer to the MN terminated bearer.

In step 309b, the NG-RAN node 2 sends a SN increase request acknowledge message to the NG-RAN node 1. The NG-RAN node 2 allocates NG interface downstream channel information for the PDU session to be established as a SN terminated bearer. The channel information includes channel end good and transport layer addresses.

If the NG-RAN node 1 is not able to configure Dual Connectivity (DC) for the UE, e.g. according to the measurement report of the UE, the NG-RAN may not allocate resources for the second PDU session, which NG-RAN node 1 includes in step 311 in the list of PDU session resource failure establishments. The PDU session resource establishment failover information includes a reason for the failure, for example, the second PDU session cannot be established or does not support DC configuration. For the second PDU session that failed to be established, the SMF does not trigger the second PDU session establishment procedure to the NG-RAN. The NG-RAN node 1 may also configure the second PDU session to the NG-RAN node 1, as described in step 311.

In step 310, the NG-RAN node 1 sends an RRC connection reconfiguration message to the UE. The NG-RAN node 1 sends the received NAS message to the UE. The UE sends an RRC connection reconfiguration complete message to the NG-RAN node 1. Through this step resources are allocated for the PDU session to be established.

In step 310b, the NG-RAN node 1 sends a SN reconfiguration complete message to the NG-RAN node 2.

Wherein step 310b and step 311 have no absolute precedence order.

In step 311, NG-RAN node 1 sends a PDU session setup confirm message to the AMF.

Corresponding to the second UPF selection method, the NG-RAN node 1 includes, in the PDU session resource establishment request transfer, a base station identifier of a base station where the PDU is established or a cell identifier of UE access on the base station, for example, if the first PDU session is established at the NG-RAN node one, the response information of the first PDU session includes an identifier of the NG-RAN node 1 or a cell identifier of UE access on the NG-RAN node 1, the second PDU session is established at the NG-RAN node 2, and the response information of the second PDU session includes an identifier of the NG-RAN node 2 or a cell identifier of UE access on the NG-RAN node 2. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

Corresponding to the third UPF selection method, for the second PDU session establishment for redundant PDU processing, if the second PDU session establishment is on the secondary base station, the message contains the identity of the secondary base station or the cell identity of the UE access on the secondary base station, which in this embodiment is the identity of the NG-RAN node 2 or the cell identity of the UE access on the NG-RAN node 2. The message contains downlink channel information allocated by the NG-RAN for the PDU session to be established.

If the second PDU session is failed to be established to the secondary base station, the invention comprises two processing methods:

the method comprises the following steps: the NG-RAN does not allocate resources, including radio resources and network resources, for the second PDU session, which failed to establish. The NG-RAN node 1 includes the second PDU session in a PDU session setup response message in a list of failed setup of PDU session resources, the failed setup of PDU session resources includes a PDU session identity and a reason for the failure, and the reason for the failure is set to fail to establish the dual connectivity or not support the DC configuration. The SMF decides whether to maintain the first PDU session in the redundant PDU session or release the first PDU session in the redundant PDU session according to a local policy.

The second method comprises the following steps: the NG-RAN node 1 configures a second PDU session to the NG-RAN node 1, i.e. two PDU sessions that are not handled for redundancy are configured as a dual connection. NG-RAN node 1 contains the second PDU session in a list of PDU session resource setup responses in a PDU session setup response message, said PDU session resource setup response containing a PDU session identity. The PDU session resource establishment response further includes information that the dual connection is not configured or fails to be configured or is not established to the secondary base station. The NG-RAN node 1 may include the base station identity of the base station or the primary cell identity on the base station where the second PDU session is configured in said PDU session resource establishment response, and implicitly inform the SMF that the second PDU session is not configured to the secondary base station or that the two redundant PDU sessions are not configured in dual connectivity mode by the base station identity of the base station or the primary cell identity on the base station where the second PDU session is configured. The SMF knows that the two PDU sessions DC which are processed redundantly are not configured successfully according to the base station identification of the base station or the main cell identification on the base station and the identification of the main base station or the main cell identification on the main base station where the second PDU session is configured. For this implicit method of notifying that the SMF dual connectivity is not successfully configured, the NG-RAN node 1 may also send the base station identifier of the base station or the primary cell identifier on the base station where the first PDU session is configured to the SMF (for example, the identifier of the NG-RAN node 1), so that the SMF knows that the redundantly processed dual connectivity of the two PDU sessions is not successfully configured according to the base station identifier of the base station where the first PDU session is configured or the primary cell identifier on the base station and the base station identifier of the base station where the second PDU session is configured or the primary cell identifier on the base station. The NG-RAN node 1 may send the base station identity of the base station or the primary cell identity on the base station where the first PDU session is configured to the SMF during the first PDU session setup or may send it to the SMF in this step. The SMF decides whether to maintain the second PDU session or release the second PDU session according to local policy. For the method, if the NG-RAN does not receive the message to release the second PDU session, when the NG-RAN node 1 can handover the second PDU session to the secondary base station, the NG-RAN node 1 performs a Secondary Node (SN) addition procedure to establish the second PDU session to the secondary base station, and configures the second PDU session as a SN terminated bearer. The NG-RAN node 1 informs the SMF that the session configuration of the second PDU to the secondary base station is successful or the dual-connection configuration is successful, the NG-RAN node 1 can also inform the SMF of the identifier of the secondary base station or the identifier of the UE access cell on the secondary base station, and the SMF can use the base station identifier or the identifier of the cell on the secondary base station to decide whether to reselect the UPF for the session of the second PDU. The cell identifier on the secondary base station may be a cell identifier of a primary cell of the secondary base station selected for the UE.

At step 312, the AMF sends an update session management context request message to the SMF. And the AMF sends the main base station and/or the secondary base station identification received from the NG-RAN node 1, or the UE access cell identification on the main base station and/or the UE access cell identification on the secondary base station to the SMF. The AMF sends session management information received from the NG-RAN to the SMF.

Corresponding to the second UPF selection method, if the SMF receives the identifier of the base station or the identifier of the UE access cell on the base station, the SMF may reselect the UPF for the first PDU session and/or the second PDU session, respectively. The SMF selects UPFs serving the first and second PDU sessions in consideration of the primary and secondary base station identities, respectively. The SMF may select a UPF that is close to the primary and secondary base stations, respectively. The base station identity is the input for the UPF reselection. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

Corresponding to the third method for selecting the UPF, if the SMF receives the identifier of the secondary base station or the identifier of the cell to which the UE is accessed on the secondary base station, the SMF may reselect the UPF for the second PDU session. The secondary base station identity is the input for the UPF reselection. The SMF takes into account the secondary base station identity to select a UPF to serve the second PDU session. The SMF may select a UPF that is close to the secondary base station. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

The message contains channel information allocated by the NG-RAN for the PDU session to be established.

At step 313, the SMF sends an N4 session modification request message to the UPF. If the UPF is reselected, the SMF sends an N4 session modification request message to the reselected UPF. And the SMF sends the downstream channel information which is used for data transmission by the NG interface distributed by the NG-RAN to the UPF. For PDU session failed to be established by NG-RAN, SMF requests UPF to delete corresponding downlink user plane channel information, and UPF can delete the PDU session or mark the corresponding PDU session as inactive state.

At step 314, the UPF sends an N4 session modification response message to the SMF.

In step 315, the SMF sends an update session management context acknowledgement message to the AMF.

Thus, the description of the first method for supporting the session transmission reliability and the session establishment method of the present invention is completed. By the method, two redundant PDU sessions can be established on two base stations, the reliability of transmission is ensured, UPFs close to the two base stations can be respectively selected, and the transmission time delay is reduced.

Fig. 4 schematically shows a timing diagram of a method of handing over a second PDU session to a secondary base station, e.g. the NG-RAN node 2 in fig. 3), according to an embodiment of the present disclosure. Corresponding to the establishment of the second PDU session in the redundancy process, if the primary base station establishes the second PDU session on the primary base station (for example, NG-RAN node 1 in fig. 3) first, and after the UE is configured and the core network is responded, the SN increasing process is executed, and the second PDU session is switched to the method on the secondary base station (for example, NG-RAN node 2 in fig. 3), where the detailed description of the steps irrelevant to the present invention is omitted, including the steps of:

in step 401, the MN sends a SN addition request message to the SN. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. letting the SN know which two PDU sessions are redundant handling. The SN stores information of redundant PDU session handling, which the SN establishes as a SN terminated bearer. The SN does not switch the bearer to the MN terminated bearer.

In step 402, the SN sends a SN addition request acknowledgement message to the MN. The SN allocates channel information of NG interface downlink for the PDU session to be established as the bearing terminated by the SN. The channel information includes channel end good and transport layer addresses.

If the SN cannot accept the requested configuration, for example, due to a restriction of radio resources or a failure in SN increase preparation, the SN sends an SN increase request rejection message to the MN. The invention comprises two processing methods:

the method comprises the following steps: the MN maintains the second PDU session configuration on the MN. And the MN sends a message to the AMF, wherein the message contains the PDU session identification and the information of the dual-connection configuration failure. The message may be an existing PDU session resource modification request message or a PDU session resource notification message or a newly defined message. And the AMF sends the PDU session identification and the information of dual-connection configuration failure to the SMF. The MN may send the base station identifier of the base station or the primary cell identifier on the base station where the second PDU session is configured to the SMF, and implicitly notify the SMF that the second PDU session is not configured to the secondary base station or that two redundant PDU sessions are not configured in the dual connectivity mode through the base station identifier of the base station or the primary cell identifier on the base station where the second PDU session is configured. The SMF knows that the two PDU sessions DC which are processed redundantly are not configured successfully according to the base station identification of the base station or the main cell identification on the base station and the identification of the main base station or the main cell identification on the main base station where the second PDU session is configured. For the implicit method for notifying that the SMF dual connectivity is not successfully configured, the MN may also send the base station identifier of the base station or the primary cell identifier of the base station where the first PDU session is configured to the SMF (for example, the identifier of the MN), so that the SMF knows that the dual connectivity of the two redundant PDU sessions is not successfully configured according to the base station identifier of the base station where the first PDU session is configured or the primary cell identifier of the base station and the base station identifier of the base station where the second PDU session is configured or the primary cell identifier of the base station. The MN may send the base station identifier of the base station or the primary cell identifier on the base station where the first PDU session is configured to the SMF in the process of establishing the first PDU session, or may send the base station identifier or the primary cell identifier to the SMF in this step. The SMF decides whether to maintain the second PDU session or release the second PDU session according to local policy. Aiming at the method, if the MN does not receive the message of releasing the second PDU session, when the MN can switch the second PDU session to the auxiliary base station, the MN executes the SN adding process, establishes the second PDU session to the auxiliary base station and configures the second PDU session into the bearing terminated by SN. The MN informs the SMF that the session configuration of the second PDU to the secondary base station is successful or the dual-connection configuration is successful through the AMF, the MN can also inform the SMF of the identifier of the secondary base station or the identifier of the UE access cell on the secondary base station through the AMF, and the SMF can determine whether to reselect the UPF for the session of the second PDU or not by using the identifier of the secondary base station or the identifier of the cell on the secondary base station. The cell identifier on the secondary base station may be a cell identifier of a primary cell of the secondary base station selected for the UE.

The second method comprises the following steps: the MN releases the second PDU session. The MN sends a PDU session resource notification message to the AMF. And the PDU conversation resource release information in the PDU conversation resource notification message comprises a PDU conversation mark and a reason, wherein the reason is that the establishment of the double connection fails. And the AMF sends the PDU session information to the SMF. The SMF decides whether to maintain the first PDU session in the redundant PDU session or release the first PDU session in the redundant PDU session according to a local policy. If the MN receives the SN addition request rejection message sent by the SN, subsequent steps 403 to 412 need not be performed.

In step 403, the MN sends an RRC connection reconfiguration message to the UE.

In step 404, the UE sends an RRC connection reconfiguration complete message to the MN.

Resources are configured for the PDU session to be established through step 404 and step 404.

In step 405, the MN sends a SN reconfiguration complete message to the SN.

Wherein, the step 405, the step 407 and the step 409 have no absolute sequence.

For an SN terminated bearer using Radio Link Control (RLC) Acknowledged Mode (AM), the MN sends a Sequence Number (SN) status transfer message to the SN, step 406.

For SN terminated bearers using RLC AM, the MN may initiate a data forwarding procedure depending on the bearer characteristics of the corresponding QoS flow, step 407.

In step 408, for the SN terminated bearer, the MN sends a PDU session modification indication message to the AMF.

The message contains the identifier of the auxiliary base station or the cell identifier accessed by the UE on the auxiliary base station. And the secondary base station identification or the cell identification accessed by the UE on the secondary base station is contained in the PDU session modification indication transfer information. The message contains downlink channel information distributed by SN for establishing PDU conversation.

In step 409, the AMF sends an update session management context request message to the SMF. The AMF sends the secondary base station identification received from the NG-RAN node 1 or the cell identification accessed by the UE on the secondary base station to the SMF.

If the SMF receives the identity of the secondary base station or the cell identity of the UE accessing the secondary base station, the SMF may reselect the UPF for the second PDU session. The secondary base station identity is the input for the UPF reselection. The SMF takes into account the secondary base station identity to select a UPF to serve the second PDU session. The SMF may select a UPF that is close to the secondary base station. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

The message contains channel information allocated by the NG-RAN for the PDU session to be established.

At step 410, the SMF sends an N4 session modification request message to the UPF. If the UPF is reselected, the SMF sends an N4 session modification request message to the reselected UPF. And the SMF sends the downstream channel information which is used for data transmission by the NG interface distributed by the NG-RAN to the UPF. The UPF sends an N4 session modification response message to the SMF.

In step 411, the SMF sends an update session management context acknowledgement message to the AMF.

At step 412, the SMF sends a PDU session modify confirm message to the MN.

This completes the description of the method of the present invention in which the primary base station switches the second PDU session to the secondary base station. By the method, two redundant PDU sessions can be established on two base stations, the reliability of transmission is ensured, UPFs close to the two base stations can be respectively selected, and the transmission time delay is reduced.

Fig. 5 schematically shows a timing diagram of a method of handing over a PDU session for redundant session handling to another base station according to an embodiment of the present disclosure. Detailed descriptions of steps not related to the present invention are omitted herein. The method comprises the following steps:

in step 501, a source MN sends a handover request message to a destination MN. The source MN contains the UE XnAP identification of the source SN, the SN identification and the UE context at the source SN in the handover request message. The handover request message includes an MCG configuration and an SCG configuration. The handover request message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The redundant PDU session handling information may also indicate the association of two PDU sessions being redundantly handled, e.g. to let the destination MN know which two PDU sessions are redundantly handled. The destination MN stores information of redundant PDU session handling. The destination MN establishes the two PDU sessions processed redundantly as an MN terminated bearer and an SN terminated bearer respectively. For example, the MN establishes the first PDU session as an MN terminated bearer and the MN establishes the second PDU session as an SN terminated bearer.

The destination MN decides whether to leave the source SN unchanged or to select a new destination SN.

In step 502, the destination MN sends a SN addition request message to the SN. The SN may be either a source SN or a destination SN depending on whether the destination MN decides to retain the source SN or to select a new destination SN. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. letting the SN know which two PDU sessions are redundant handling. The SN stores information of redundant PDU session handling, which the SN establishes as a SN terminated bearer. The SN does not switch the bearer to the MN terminated bearer.

In step 503, the SN sends an SN increase request acknowledge message to the destination MN.

In step 504, the destination MN sends a handover request acknowledge message to the source MN.

In step 505a, the source MN sends a SN release request message to the source SN. If the source SN receives the indication information of UE context reservation, the source SN reserves the UE context.

In step 505b, the source SN sends a SN release request acknowledge message to the source MN.

In step 506, the source MN sends an RRC connection reconfiguration message to the UE.

In step 507, the UE synchronizes to the destination MN.

In step 508, the UE sends an RRC connection reconfiguration complete message to the destination MN.

In step 509, if the bearer using SCG radio resources is configured, the UE synchronizes to the SN, and if the MN selects a new SN, the SN is the destination SN.

Step 510, after the RRC connection reconfiguration is successful, the destination MN sends a SN reconfiguration complete message to the SN.

In step 511, for the bearer using RLC AM mode, the source MN sends an SN status transfer message to the destination MN.

In step 512, the source MN forwards the data to the destination MN. If the SN is reserved, the SCG bearer and the SCG separate bearer do not require data forwarding.

In step 513, the destination MN sends a path switch request message to the AMF.

The destination MN includes, in the path switching request transfer, a base station identifier of a base station where the PDU is established or a cell identifier of UE access on the base station, for example, if the first PDU session is established at the destination MN, the path switching request transfer information of the first PDU session includes an identifier of the destination MN or a cell identifier of UE access on the destination MN, the second PDU session is established at the destination SN or the source SN, and the path switching request transfer information of the second PDU session includes an identifier of the destination SN or an identifier of the source SN or a cell identifier of UE access cell on the destination SN or a cell identifier of UE access cell on the source SN.

For the second PDU session establishment for redundant PDU processing, if the second PDU session establishment is established on the secondary base station, the message includes the identifier of the secondary base station or the cell identifier of the UE access cell on the secondary base station, in this embodiment, the identifier of the destination SN or the identifier of the source SN or the cell identifier of the UE access cell on the destination SN or the cell identifier of the UE access cell on the source SN. The message contains downlink channel information allocated by the NG-RAN for the PDU session to be established.

The message comprises the identification of the auxiliary base station or the cell identification of the UE access cell on the auxiliary base station. And the auxiliary base station identification or the cell identification of the UE access cell on the auxiliary base station is contained in the path switching request transfer information. The message contains downlink channel information distributed by SN for establishing PDU conversation.

If the redundantly processed two PDU sessions are not configured as dual connectivity at the destination base station, the destination base station informs the SMF of this information. The destination base station may inform the SMF by means of a display, for example, by including an information element that the DC has not been successfully configured in the path switch request message. The destination base station can also inform the SMF in an implicit mode, that is, the destination base station informs the SMF of a base station identifier of a base station or a primary cell identifier on the base station where each PDU session is established, the SMF knows whether the DC configuration is successful according to the information, and the SMF determines whether to maintain the second PDU session or release the second PDU session according to a local policy.

At step 514, the AMF sends an update session management context request message to the SMF. The AMF transmits the base station identity or cell identity received from the destination MN to the SMF. For each PDU conversation, if the SMF receives the base station identification or the cell identification established by the PDU conversation, the SMF selects the UPF used by the PDU conversation by using the received base station identification. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

If the SMF receives the identity of the secondary base station or the cell identity of the UE access cell on the secondary base station, the SMF may reselect the UPF for the second PDU session. The secondary base station identity is the input for the UPF reselection. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

The message contains channel information allocated by the NG-RAN for the PDU session to be established.

At step 515, the SMF sends an N4 session modification request message to the UPF. The SMF sends N4 session modification request messages to the UPF redundantly handling the first PDU session and the UPF of the second PDU session, respectively. If a UPF is reselected for a PDU session, the SMF sends an N4 session modification request message to the reselected UPF. And the SMF sends the downstream channel information which is used for data transmission by the NG interface distributed by the NG-RAN to the corresponding UPF.

The UPF receiving the N4 session modification request message sends an N4 session modification response message to the SMF.

At step 516, the SMF sends an update session management context acknowledgement message to the AMF.

Step 517, the UPF sends data to the NG-RAN. And the UPF sends downlink data to the NG-RAN according to the received downlink channel information distributed by the NG-RAN. For MN terminated bearers, the corresponding UPF (e.g., UPF1) sends downstream data to the destination MN. For SN terminated bearers, a corresponding UPF (e.g., UPF2) sends downstream data to either the source SN or the destination SN (depending on whether the SN has changed)

In step 518, the SMF sends a path switch request acknowledge message to the destination MN.

In step 519, the destination MN sends a UE context release message to the source MN.

In step 520, the source MN sends a UE context release message to the source SN.

Thus, the description of the first method for supporting session transmission reliability and the switching method of the present invention is completed. By the method, two redundant PDU sessions can be established on the two base stations after switching, the reliability of transmission is ensured, and simultaneously, UPFs close to the two base stations can be respectively selected, so that the transmission time delay is reduced.

Fig. 6 schematically shows a timing diagram of another method of handing over a PDU session for redundant session handling to another base station according to an embodiment of the present disclosure. Detailed descriptions of steps not related to the present invention are omitted herein. As shown in fig. 6, the method includes the steps of:

step 601, the source MN sends a handover request message to the destination base station. The destination base station here may be a gNB or an LTE base station gn-eNB connected to a 5G core network.

The source MN contains the UE XnAP identification of the source SN, the SN identification and the UE context at the source SN in the handover request message. The handover request message includes an MCG configuration and an SCG configuration. The handover request message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. to let the destination base station know which two PDU sessions are redundant handled. The destination base station stores the information of redundant PDU session processing.

If the destination base station cannot configure dual connectivity, for example, there are no available secondary base station cells according to the measurement report of the UE, the destination base station has two processing methods:

the method comprises the following steps: the destination base station does not need to allocate resources, including radio resources and network resources, for the second PDU session, which fails to be established. The destination base station only configures resources for the first PDU session.

The second method comprises the following steps: the destination base station configures both the first and second PDU sessions to the destination base station, i.e. two PDU sessions that are not handled for redundancy are configured as a dual connection.

In step 602, the destination base station sends a handover request acknowledgement message to the source MN. Corresponding to the first processing method of the destination base station in step 601, the destination base station includes the second PDU session in the list that the PDU session resource is not confirmed. And the message contains the reason for the failure, e.g. that the second PDU session cannot be established or does not support DC configuration. Corresponding to the second processing method of the destination base station in step 601, the destination base station includes the first PDU session and the second PDU session in the PDU session resource confirmation list.

In step 603a, the source MN sends a SN release request message to the source SN.

In step 603b, the source SN sends a SN release request acknowledge message to the source MN.

In step 604, the source MN sends an RRC connection reconfiguration message to the UE.

In step 605, the UE synchronizes to the destination base station.

Step 606, the UE sends an RRC connection reconfiguration complete message to the destination base station.

In step 607, for SCG terminated bearers using RLC AM mode, the source SN sends an SN status transfer message to the source MN.

In step 607b, the source MN sends an SN status transfer message to the destination base station.

The source SN forwards the data to the source MN, step 608. The source MN forwards the data to the destination base station.

In step 609, the destination base station sends a path switch request message to the AMF.

The destination base station includes, in the path switching request transfer, a base station identifier of a base station where the PDU is established or a cell identifier of a UE access cell on the base station, for example, if the first PDU session is established at the destination base station, the path switching request transfer information of the first PDU session includes an identifier of the destination base station or a cell identifier of a UE access cell on the destination base station.

Corresponding to the first processing method of the destination base station in step 601, the destination base station includes a list of failed path PDU session resources established by the second PDU session that cannot be configured to the secondary base station. The PDU session resource failed establishment contains a PDU session identity and a reason for the failure, e.g. the second PDU session cannot be established or does not support DC configuration. The SMF decides whether to maintain the first PDU session in the redundant PDU session or release the first PDU session in the redundant PDU session according to a local policy.

Corresponding to the second processing method of the destination base station in step 601, the destination base station includes a PDU session resource downlink list to be switched of the second PDU session in the path switching request message, and the PDU session resource information to be switched includes a PDU session identifier. The PDU session resource to be switched also comprises information that the dual connection is not configured or fails to be configured or is not established to the secondary base station. The destination base station may send the base station identifier of the base station or the primary cell identifier on the base station where the second PDU session is configured to the SMF, and implicitly notify the SMF that the second PDU session is not configured to the secondary base station or that two redundant PDU sessions are not configured in the dual connectivity mode through the base station identifier of the base station or the primary cell identifier on the base station where the second PDU session is configured. The SMF knows that the two PDU sessions DC which are processed redundantly are not configured successfully according to the base station identification of the base station or the main cell identification on the base station and the identification of the main base station or the main cell identification on the main base station where the second PDU session is configured. For the implicit method for notifying that the SMF dual connectivity is not successfully configured, the destination base station may also send the base station identifier of the base station where the first PDU session is configured or the primary cell identifier of the base station to the SMF (for example, the identifier of the destination base station), so that the SMF knows that the dual connectivity of the two redundant PDU sessions is not successfully configured according to the base station identifier of the base station where the first PDU session is configured or the primary cell identifier of the base station and the base station identifier of the base station where the second PDU session is configured or the primary cell identifier of the base station. The SMF decides whether to maintain the second PDU session or release the second PDU session according to local policy. According to the method, if the target base station does not receive the message for releasing the second PDU session, when the target base station can switch the second PDU session to the auxiliary base station, the target base station executes an auxiliary node (SN) adding process, establishes the second PDU session to the auxiliary base station, and configures the second PDU session into a bearing with SN termination. The target base station informs the SMF that the session configuration of the second PDU to the auxiliary base station is successful or the dual-connection configuration is successful, the target base station can also inform the SMF of the identifier of the auxiliary base station or the identifier of the UE access cell on the auxiliary base station, and the SMF can use the base station identifier or the identifier of the cell on the auxiliary base station to determine whether to reselect the UPF for the session of the second PDU. The cell identifier on the secondary base station may be a cell identifier of a primary cell of the secondary base station selected for the UE. In fact, the destination base station is the base station serving the UE after the handover is successful, and for the purpose of describing the method, the term of the destination base station is also used.

At step 610, the AMF sends an update session management context request message to the SMF. The AMF transmits the base station identity or cell identity received from the destination base station to the SMF. The SMF sends session management information received from the NG-RAN to the SMF. For each PDU conversation, if the SMF receives the base station identification or the cell identification established by the PDU conversation, the SMF selects the UPF used by the PDU conversation by using the received base station identification. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

The message contains channel information allocated by the NG-RAN for the PDU session to be established. For the second PDU session that failed to be established, the SMF does not trigger the second PDU session establishment procedure to the NG-RAN.

Instep 611, the SMF sends an N4 session modification request message to the UPF. The SMF sends N4 session modification request messages to the UPF (e.g., UPF1) redundantly handling the first PDU session and the UPF (e.g., UPF2) of the second PDU session, respectively. If a UPF is reselected for a PDU session, the SMF sends an N4 session modification request message to the reselected UPF. And the SMF sends the downstream channel information which is used for data transmission by the NG interface distributed by the NG-RAN to the corresponding UPF. For PDU session failed to be established by NG-RAN, SMF requests UPF to delete corresponding downlink user plane channel information, and UPF can delete the PDU session or mark the corresponding PDU session as inactive state.

The UPF receiving the N4 session modification request message sends an N4 session modification response message to the SMF.

At step 612, the SMF sends an update session management context acknowledgement message to the AMF.

The UPF sends the data to the NG-RAN, step 613. And the UPF sends downlink data to the NG-RAN according to the received downlink channel information distributed by the NG-RAN.

In step 614, the SMF sends a path switch request acknowledge message to the destination base station.

Step 615, the destination base station sends a UE context release message to the source MN.

In step 616, the source MN sends a UE context release message to the source SN.

Thus, the description of the method for supporting session transmission reliability and the method for switching the session transmission reliability of the present invention is completed. By the method, resources are not allocated to the second PDU session under the condition that the target base station cannot configure the DC in the switching process, so that resource waste and redundant user plane configuration failure are avoided.

Fig. 7 schematically shows a timing diagram of another one of the methods for session establishment according to an embodiment of the present disclosure. In the method of fig. 3, if the NG-RAN receives the information to establish the second PDU session from the core network, the NG-RAN cannot configure the DC for the UE, or the destination base station receives the information to establish the redundant user plane in the handover process corresponding to fig. 6, the destination base station cannot configure the DC for the UE, the base station or the destination base station stores the information to establish the second PDU session, and when the base station can configure the DC for the UE again, the base station configures the second PDU session to the secondary base station. Detailed descriptions of steps not related to the present invention are omitted herein. As shown in fig. 7, the method includes the steps of:

in step 701, the MN sends an SN addition request message to the SN. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. letting the SN know which two PDU sessions are redundant handling. The SN stores information of redundant PDU session handling, which the SN establishes as a SN terminated bearer. The SN does not switch the bearer to the MN terminated bearer.

In step 702, the SN sends a SN increase request acknowledgement message to the MN.

In step 703, the MN sends an RRC connection reconfiguration message to the UE.

In step 704, if a bearer using SCG radio resources is configured, the UE synchronizes to the SN.

Step 705, the UE sends an RRC connection reconfiguration complete message to the MN.

Step 706, after the RRC connection reconfiguration is successful, the MN sends a SN reconfiguration complete message to the SN.

In step 707, the MN sends a PDU session setup complete indication message to the AMF. The MN contains the PDU conversation mark of the second PDU conversation and the downlink channel information distributed by the SN in the PDU conversation establishment finishing indication message. The MN includes, in the PDU session establishment completion indication message, a base station identifier of a base station where the PDU is established or a cell identifier of a cell to which the UE accesses, for example, the second PDU session is established at the SN, and the PDU session establishment completion indication transfer information corresponding to the second PDU session includes an identifier of the SN or a cell identifier of a primary cell allocated to the UE at the SN.

At step 708, the AMF sends an update session management context request message to the SMF. The AMF transmits the base station identity or cell identity received from the MN to the SMF. The AMF sends the received session management information to the SMF. For each PDU conversation, if the SMF receives the base station identification or the cell identification established by the PDU conversation, the SMF selects the UPF used by the PDU conversation by using the received base station identification. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

If the SMF receives the identity of the secondary base station or the primary cell identity on the secondary base station, the SMF may select or reselect a UPF for the second PDU session. The secondary base station identity is the input for the UPF selection or reselection. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

The message contains channel information allocated by the NG-RAN for the PDU session to be established.

At step 709, the SMF sends an N4 session modification request message to the UPF. The SMF sends an N4 session modification request message to the UPF that redundantly processes the second PDU session. If a UPF is reselected for a PDU session, the SMF sends an N4 session modification request message to the reselected UPF. And the SMF sends the downstream channel information which is used for data transmission by the NG interface distributed by the NG-RAN to the corresponding UPF.

The UPF receiving the N4 session modification request message sends an N4 session modification response message to the SMF.

At step 710, the SMF sends an update session management context acknowledgement message to the AMF.

Step 711, the UPF sends the downlink data to the NG-RAN. And the UPF sends downlink data to the NG-RAN according to the received downlink channel information distributed by the NG-RAN. And for the bearing terminated by the SN, the corresponding UPF sends the downlink data to the SN.

In step 712, the SMF sends a PDU session setup complete indication acknowledge message to the destination MN.

Thus, the description of the second method for supporting the session transmission reliability and the PDU session establishment method of the present invention is completed. By the method, in the process of initial PDU session establishment or switching, if the NG-RAN cannot configure the redundant PDU session to a certain secondary base station, the NG-RAN stores information of a second PDU session, the NG-RAN configures the DC when the DC becomes possible and informs the SMF (sent by AMF) of the information of the second PDU session establishment, and also can inform the SMF of the identification of the secondary base station or the identification of a primary cell on the secondary base station, and the SMF selects the UPF serving the second PDU session by considering the identification of the secondary base station or the identification of the primary cell on the secondary base station. The reliability of transmission is ensured, and the time delay of transmission is reduced.

Fig. 8 schematically shows a timing diagram of a further method of the method for session establishment according to an embodiment of the present disclosure. Detailed descriptions of steps not related to the present invention are omitted herein. As shown in fig. 8, the method includes the steps of:

in step 801, the UE sends a PDU session setup request message to the AMF. The UE sends a PDU session establishment request message to the base station through an RRC message. The RRC message comprises indication information of redundant PDU session establishment or indication information of second PDU session establishment.

The base station (for example, NG-RAN node 1) accessed by the UE knows that the second PDU session is to be established, and the base station finds that the DC cannot be configured for the UE, for example, according to the measurement report of the UE, the base station includes information that the DC is not possible or information that the second PDU session cannot be currently established in the NGAP message of the non-access stratum message PDU session establishment request message to the AMF.

If the base station can configure the DC for the UE, e.g. according to the measurement report of the UE, the base station includes the identity of the secondary base station or the identity of the secondary base station cell that may be established in the NGAP message that sends the non-access stratum message PDU session establishment request message. The AMF sends the possible secondary base station identity or identity of the secondary base station cell to the SMF, via step 802. The SMF selects a UPF serving the second PDU session taking into account the identity of the secondary base station or the identity of the secondary base station cell. The identity of the secondary base station that may be configured for the UE is considered in the UPF selection of step 804, for example. If the SMF receives the cell identification on the base station, the SMF can obtain the base station identification according to the cell identification.

The base station sends a PDU session establishment request message to the AMF through the NGAP message.

The PDU session establishment request message includes a Redundant Sequence Number (RSN). The redundant sequence number indicates redundant processing. The value of RSN indicates whether the first or second PDU session is established.

In step 802, the AMF sends a create session management context request message to the SMF. If the AMF receives information from the NG-RAN that the DC is impossible or information that the second PDU session cannot be currently established, the AMF transmits the information that the DC is impossible or the information that the second PDU session cannot be currently established to the SMF. The SMF stores information of the second PDU session to be established.

In step 803, the SMF sends a create session management context response message to the AMF.

The SMF may trigger steps 804 through 813 in the method of the present invention. As another method of the present invention, steps 804 to 813 may not be triggered.

At step 804, the SMF selects a UPF. The SMF selects the UPF taking into account the base station identity or cell identity received from the AMF. The SMF knows that the PDU session is to be redundantly processed and whether the PDU session is a first PDU session or a second PDU session based on the RSN received from the UE or based on Data Network Name (DNN) or single network slice selection assistance information (S-NSSAI) and network configuration. The SMF selects a UPF using whether the first or second PDU session is to be established, in conjunction with other information.

805, the SMF sends an N4 session setup or N4 session modify request message to the selected UPF. If the request type is an initial request, the SMF initiates an N4 session establishment procedure to the selected UPF, otherwise initiates an N4 session modification procedure to the selected UPF.

At step 806, the UPF sends an N4 session establishment response or an N4 session modification response message to the SMF.

At step 807, the SMF sends an N1N2 messaging message to the AMF. The message contains a PDU session identification, N2 Session Management (SM) information, N1 session container.

In step 808, the AMF sends a PDU session setup request message to the NG-RAN node 1. The message contains information of redundant PDU session handling. The information of the redundant PDU session handling may indicate whether the first PDU session or the second PDU session using RSN. The information of redundant PDU session handling may also indicate the association of two PDU sessions of redundant handling, e.g. letting the NG-RAN know which two PDU sessions are redundant handled.

Based on the received PDU session setup request message, the NG-RAN node 1 knows that the PDU session to be established is a redundant process. The NG-RAN node 1 also knows whether the PDU session to be established is the first or the second PDU session, or the NG-RAN node 1 can also know which two PDU sessions are redundantly processed. If the established PDU session is redundantly processed and the PDU session to be established is a second PDU session, the NG-RAN node 1 cannot configure the DC for the UE, and the NG-RAN node 1 saves information of the second PDU session to be established.

If the NG-RAN node 1 cannot configure dual connectivity for the UE, for example, according to the measurement report of the UE, the NG-RAN has two processing methods, which are the same as those described in step 311 and are not described herein again.

In step 809, the NG-RAN node 1 sends a PDU session setup confirm message to the AMF.

At step 810, the AMF sends an update session management context request message to the SMF.

At step 811, the SMF sends an N4 session modification request message to the UPF. For PDU session failed to be established by NG-RAN, SMF requests UPF to delete corresponding downlink user plane channel information, and UPF can delete the PDU session or mark the corresponding PDU session as inactive state.

At step 812, the UPF sends an N4 session modification response message to the SMF.

At step 813, the SMF sends an update session management context acknowledgement message to the AMF.

The NG-RAN node 1 monitors the information whether DC is possible, and the NG-RAN configures the DC when it becomes possible, performing the procedure described in fig. 7.

A system for supporting session transfer reliability of the present invention is shown in fig. 9. A redundant user plane is established for UE, two UPFs are respectively connected to two different centralized unit user plane entities (CU-UP) of the same base station, and the two CU-UP respectively send data of two PDU sessions to the UE through one DU respectively connected with the two CU-UP. Unlike the prior art, instead of sending data of two redundant PDU sessions to the UE through two base stations, data of two redundant PDU sessions are sent to the UE through two CU-UPs and two DUs of the same base station.

Fig. 10 shows a schematic flow chart of a method for session establishment according to an embodiment of the invention. As shown in fig. 10, the method includes:

step S1010: a message for creating a session management context is received.

In some examples, the message may be a create session management context request message received from the AMF, but the technical solution of the embodiment of the present invention is not limited to a specific message/message name.

Step S1020, in response to the message for creating the session management context, selects a UPF for redundant session processing.

Step S1030, a packet data unit PDU session corresponding to the UPF is established.

In some embodiments, selecting a UPF for redundant session handling in response to the message for creating a session management context may include:

determining whether the session requiring creation of the session management context is a redundant session and whether the redundant session is a first redundant session or a second redundant session based on at least one of:

the message (e.g., PDU session setup request message) for creating the session management context contains information related to a redundant session;

data Network Name (DNN) or single network slice selection assistance information (S-NSSAI) and operator network configuration;

based on the determination, a UPF for redundant session handling is selected in accordance with an identity of a serving base station of the user equipment UE.

For example, the UPFs are selected according to the identity of the primary base station (e.g., the serving base station of the UE) for both the first and second redundant sessions. Of course, other approaches are possible, and embodiments of the invention are not limited thereto.

For example, selection of a UPF may be implemented at other times. In some embodiments, after the UPFs are selected for the first and second redundancy sessions, reselection may also occur at an appropriate time thereafter. Based on this, the method may further comprise: and receiving a first base station identifier of a base station established by the first redundant session or a cell identifier of a UE access cell on the first base station and a second base station identifier of a base station established by the second redundant session or a cell identifier of a UE access cell on the second base station, selecting UPF used for the first redundant session according to the first base station identifier, and selecting UPF used for the second redundant session according to the second base station identifier. If the cell identifier on the base station is received, the base station identifier can be known according to the cell identifier. Or the method may also include: and receiving a base station identifier or a cell identifier of a base station where the second redundant session is established, and selecting the UPF for the second redundant session according to the base station identifier. Here, the rule of selection may be as close as possible to the base station where the session is established, or other distance-related conditions and combinations of distance-related conditions and other selection criteria.

Fig. 11 shows a schematic flow chart of another method for session establishment according to an embodiment of the invention. The method is performed at a first base station (e.g., a primary/serving base station of a UE) that establishes a first redundant session for redundancy handling. As shown in fig. 11, the method includes:

in step S1110, a message for establishing a second redundancy session for redundancy processing is received.

The message may be a PDU session setup request message received from the AMF, but the technical solution of the embodiment of the present invention is not limited to a specific message/message name.

Step S1120, in response to the message, determining whether to add a second base station for processing the second redundant session.

Step S1130, if it is determined to add the second base station, configuring the second redundant session to be processed by the second base station.

In some embodiments, determining whether to add a second base station for processing the second redundant session in response to the message may include:

determining whether the first base station supports dual connectivity for the first redundant session and the second redundant session; and

determining to add the second base station to configure the second redundant session for processing by the second base station if the first base station supports the dual connectivity, otherwise determining not to add the second base station.

In a case where the first base station does not support the dual connectivity, the base station may store information required to establish the second redundant session, and when it is determined that the first base station can support the dual connectivity, determine to add the second base station using the stored information to configure the second redundant session to be processed by the second base station.

In the above embodiment, configuring the second redundant session to be processed by the second base station may include:

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session;

receiving resources configured for the second redundant session by the user equipment; and

transmitting the configured resources to the second device to establish the second redundant session at the second base station.

Alternatively, configuring the second redundant session for processing by the second base station may comprise:

establishing the second redundant session at the first base station;

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session; and

receiving resources configured for the second redundant session by the user equipment;

handing over the second redundant session to the second base station using the configured resources.

Fig. 12 shows a schematic block diagram of an SMF for session establishment according to an embodiment of the present invention. As shown in fig. 12, the SMF includes amessage receiving unit 1210, aUPF selecting unit 1220, and asession establishing unit 1230. Themessage receiving unit 1210 is configured to receive a message for creating a session management context. TheUPF selecting unit 1220 is configured to select a user plane function entity UPF for redundant session handling in response to the message for creating a session management context. Thesession establishing unit 1230 is used for establishing a packet data unit PDU session corresponding to the UPF

In some examples, the received message may be a create session management context request message received from the AMF, but the technical solution of the embodiment of the present invention is not limited to a specific message/message name.

In some examples, theUPF selection unit 1220 may be to:

determining whether the session requiring creation of the session management context is a redundant session and whether the redundant session is a first redundant session or a second redundant session based on at least one of:

information related to a redundant session contained in the message (e.g., PDU session setup request message) for creating the session management context;

data Network Name (DNN) or single network slice selection assistance information (S-NSSAI) and operator network configuration;

based on the determination, a UPF for redundant session handling is selected based on an identity of a serving base station of the user equipment UE or a cell identity of a UE access cell on a base station.

For example, the UPFs are selected according to the identity of the primary base station (e.g., the serving base station of the UE) for both the first and second redundant sessions. Of course, other approaches are possible, and embodiments of the invention are not limited thereto.

For example, selection of a UPF may be implemented at other times. In some embodiments, after the UPFs are selected for the first and second redundancy sessions, reselection may also occur at an appropriate time thereafter. Based on this, theUPF selection unit 1220 may also be used to: and receiving a first base station identifier of a base station established by the first redundant session or a cell identifier of a UE access cell on the first base station and a second base station identifier of a base station established by the second redundant session or a cell identifier of a UE access cell on the second base station, selecting UPF used for the first redundant session according to the first base station identifier, and selecting UPF used for the second redundant session according to the second base station identifier. If the cell identifier on the base station is received, the base station identifier can be known according to the cell identifier. Or theUPF selection unit 1220 may also be used to: and receiving a base station identifier or a cell identifier of a base station where the second redundant session is established, and selecting the UPF for the second redundant session according to the base station identifier. If the cell identifier on the base station is received, the base station identifier can be known according to the cell identifier. Here, the rule of selection may be as close as possible to the base station where the session is established, or other distance-related conditions and combinations of distance-related conditions and other selection criteria.

Fig. 13 shows a schematic block diagram of a base station for session establishment according to an embodiment of the present invention. As shown in fig. 13, the base station includes a message receiving unit 1310, a base station addition determining unit 1320, and a second redundant session configuring unit 1330. The message receiving unit 1310 is configured to receive a message for establishing a second redundancy session for redundancy processing. The base station addition determining unit 1320 is configured to determine whether to add a second base station for processing the second redundant session in response to the message. The second redundant session configuration unit 1330 is configured to configure the second redundant session to be processed by the second base station if it is determined to add the second base station.

The received message may be a PDU session establishment request message received from the AMF, but the technical solution of the embodiment of the present invention is not limited to a specific message/message name.

In some embodiments, the base station addition determination unit 1320 may be configured to:

determining whether the first base station supports dual connectivity for the first redundant session and the second redundant session; and

determining to add the second base station to configure the second redundant session for processing by the second base station if the first base station supports the dual connectivity, otherwise determining not to add the second base station.

In a case where the first base station does not support the dual connectivity, the base station may store information required to establish the second redundant session, and when it is determined that the first base station can support the dual connectivity, determine to add the second base station using the stored information to configure the second redundant session to be processed by the second base station.

In the above embodiment, the second redundant session configuration unit 1330 may be configured to:

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session;

receiving resources configured for the second redundant session by the user equipment; and

transmitting the configured resources to the second device to establish the second redundant session at the second base station.

Alternatively, the second redundant session configuration unit 1330 may be configured to:

establishing the second redundant session at the first base station;

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session; and

receiving resources configured for the second redundant session by the user equipment;

handing over the second redundant session to the second base station using the configured resources.

In the above embodiments, the first base station acts as a master base station for redundant session processing. In some embodiments, the master function may be handed off from another base station (e.g., a third base station below) acting as a master base station for further redundant session processing. Fig. 14 shows a schematic flow chart of a method for switching a master base station for redundant session handling according to an embodiment of the present invention. As shown in fig. 14, the method includes:

step S1410, receiving a handover request message sent by a third base station, where the handover request message requests to handover a master control function of redundant session processing of the third base station to the first base station.

Step S1420, establishing a connection with the user equipment UE corresponding to the redundant session processing based on the handover request message.

Step S1430, sends a path switching request message to the mme.

In some embodiments, the method may further comprise: in response to the handover request message, adding a fourth base station for processing of a second one of the redundant sessions of the third base station.

In some embodiments, the first base station may also switch its master function of redundant session handling to another base station. In this case, the first base station may send a handover request message to the other base station and release resources upon receiving an acknowledgement message of the other base station.

Fig. 15 shows a schematic block diagram of an apparatus for handing over a master base station for redundant session processing according to an embodiment of the present invention. The apparatus may be the first base station described above. As shown in fig. 15, the apparatus includes amessage receiving unit 1510, a connection establishing unit 1520, and amessage transmitting unit 1530. Themessage receiving unit 1510 is configured to receive a handover request message sent by a third base station, where the handover request message requests that a master control function of redundant session processing of the third base station is handed over to the first base station. The connection establishing unit 1520 is configured to establish a connection of the user equipment UE corresponding to the redundant session processing based on the handover request message. Themessage sending unit 1530 is configured to send a path switching request message to the mobility management control entity.

In some embodiments, the apparatus may further include a base station adding unit 1540 for adding a fourth base station for processing of a second one of the redundant sessions of the third base station in response to the handover request message.

In some embodiments, the first base station may also switch its master function of redundant session handling to another base station. In this case, the first base station may send a handover request message to the other base station and release resources upon receiving an acknowledgement message of the other base station.

Fig. 16 schematically illustrates a block diagram of a computing system that may be used to implement SMF1200 or base station 1300 of the present disclosure, according to an embodiment of the present disclosure.

As shown in fig. 16,computing system 1600 includes aprocessor 1610, a computer-readable storage medium 1620, anoutput interface 1630, and aninput interface 1640. Thecomputing system 1600 may perform the methods described above with reference to fig. 10, 11, or 14.

In particular,processor 1610 may include, for example, a general-purpose microprocessor, an instruction set processor and/or related chipset and/or a special-purpose microprocessor (e.g., an Application Specific Integrated Circuit (ASIC)), or the like. Theprocessor 1610 may also include on-board memory for caching purposes.Processor 1610 may be a single processing unit or a plurality of processing units for performing the different actions of the method flows described with reference to fig. 10, 11 or 14.

Computer-readable storage medium 1620 may be, for example, any medium that can contain, store, communicate, propagate, or transport instructions. For example, a readable storage medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. Specific examples of the readable storage medium include: magnetic storage devices, such as magnetic tape or hard disk drives (hard disk drives, HDD for short); optical storage devices, such as Compact Disk Read Only Memory (CD-ROM); a Memory, such as a Random Access Memory (RAM) or a flash Memory; and/or wired/wireless communication links.

The computer-readable storage medium 1620 may include acomputer program 1621, whichcomputer program 1621 may include code/computer-executable instructions that, when executed by theprocessor 1610, cause theprocessor 1610 to perform a method flow, such as described above in connection with fig. 10, 11, or 14, and any variations thereof.

Thecomputer programs 1621 may be configured with computer program code, for example, including computer program modules. For example, in an example embodiment, code incomputer program 1621 may include one or more program modules, including, for example, 1621A, modules 1621B, … …. It should be noted that the division and number of modules are not fixed, and those skilled in the art may use suitable program modules or program module combinations according to actual situations, which when executed by theprocessor 1610, enable theprocessor 1610 to perform the method procedures described above with reference to fig. 1-3 and any variations thereof.

In accordance with an embodiment of the present disclosure,processor 1610 may useoutput interface 1630 andinput interface 1640 to perform the method flows described above in connection with fig. 10, 11, or 14, and any variations thereof.

Thus, the description of the method for supporting session transmission reliability, the session establishment method, and the handover method of the present invention is completed. The method can establish two redundant PDU sessions to two base stations respectively, ensure the reliability of service transmission, and reduce the transmission time delay by using the UPF selection method in the invention. Meanwhile, the switching method is provided, so that the low time delay and high reliability of service transmission after switching is finished can be ensured.

Those skilled in the art will appreciate that the methods illustrated above are exemplary only. The method of the present invention is not limited to the steps or sequence shown above. The base station and the user equipment shown above may comprise further modules, e.g. modules already developed or developed in the future, which may be available to the base station or the UE, etc. The various designations shown above are exemplary only and not limiting, and the invention is not limited to the specific names given as examples of such designations. Many variations and modifications may occur to those skilled in the art in light of the teachings of the illustrated embodiments.

Those skilled in the art will appreciate that the present disclosure includes apparatus relating to performing one or more of the operations described in the present application. These devices may be specially designed and manufactured for the required purposes, or they may comprise known devices in general-purpose computers. These devices have stored therein computer programs that are selectively activated or reconfigured. Such a computer program may be stored in a device (e.g., computer) readable medium, including, but not limited to, any type of disk including floppy disks, hard disks, optical disks, CD-ROMs, and magnetic-optical disks, ROMs (Read-Only memories), RAMs (Random Access memories), EPROMs (Erasable programmable Read-Only memories), EEPROMs (Electrically Erasable programmable Read-Only memories), flash memories, magnetic cards, or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a bus. That is, a readable medium includes any medium that stores or transmits information in a form readable by a device (e.g., a computer).

It will be understood by those within the art that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by computer program instructions. Those skilled in the art will appreciate that the computer program instructions may be implemented by a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, implement the aspects specified in the block or blocks of the block diagrams and/or flowchart illustrations of the present disclosure.

Those of skill in the art will appreciate that the various operations, methods, steps in the processes, acts, or solutions discussed in the present disclosure may be interchanged, modified, combined, or eliminated. Further, other steps, measures, schemes in various operations, methods, flows that have been discussed in this disclosure may also be alternated, altered, rearranged, broken down, combined, or deleted. Further, steps, measures, schemes in the prior art having various operations, methods, procedures disclosed in the present disclosure may also be alternated, modified, rearranged, decomposed, combined, or deleted.

The foregoing is only a partial embodiment of the present disclosure, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present disclosure, and these modifications and decorations should also be regarded as the protection scope of the present disclosure.

Claims (15)

1. A method for session establishment, comprising:

receiving a message for creating a session management context;

selecting a user plane function entity (UPF) for redundant session handling in response to the message for creating a session management context;

and establishing a Packet Data Unit (PDU) session corresponding to the UPF.

2. The method of claim 1, wherein selecting a user plane functional entity (UPF) for redundant session handling in response to the message for creating a session management context comprises:

determining whether the session requiring creation of the session management context is a redundant session and whether the redundant session is a first redundant session or a second redundant session based on at least one of:

the message for creating the session management context contains information related to redundant sessions;

a data network name DNN or single network slice selection assistance information S-NSSAI and operator network configuration;

based on the determination, a UPF for redundant session handling is selected in accordance with an identity of a serving base station of the user equipment UE.

3. The method of claim 2, further comprising:

receiving a first base station identifier of a base station where the first redundant session is established and a second base station identifier of a base station where the second redundant session is established, selecting a UPF for the first redundant session according to the first base station identifier, and selecting a UPF for the second redundant session according to the second base station identifier; or

And receiving the base station identification of the base station where the second redundant session is established, and selecting the UPF for the second redundant session according to the base station identification.

4. A method for session establishment, wherein a first redundant session for redundant processing is established by a first base station, the method comprising:

receiving a message for establishing a second redundant session for redundant processing;

determining whether to add a second base station for processing the second redundant session in response to the message; and

configuring the second redundant session to be handled by the second base station if it is determined to add the second base station.

5. The method of claim 4, wherein determining whether to add a second base station for processing the second redundant session in response to the message comprises:

determining whether the base station supports dual connectivity for the first redundant session and the second redundant session; and

determining to add the second base station to configure the second redundant session for processing by the second base station if the base station supports the dual connectivity, otherwise determining not to add the second base station.

6. The method of claim 5, further comprising:

storing information required for establishing the second redundant session when the first base station does not support the dual connectivity; and

when it is determined that the first base station is capable of supporting dual connectivity, determining to add the second base station using the saved information to configure the second redundant session for processing by the second base station.

7. The method of any of claims 4 to 6, wherein configuring the second redundant session for processing by the second base station comprises:

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session;

receiving resources configured for the second redundant session by the user equipment; and

transmitting the configured resources to the second device to establish the second redundant session at the second base station.

8. The method of any of claims 4 to 6, wherein configuring the second redundant session for processing by the second base station comprises:

establishing the second redundant session at the first base station;

requesting, from the second base station, establishment of the second redundant session at the second base station;

receiving a confirmation message of the second base station accepting to establish the second redundant session; and

receiving resources configured for the second redundant session by the user equipment;

handing over the second redundant session to the second base station using the configured resources.

9. A method for switching a master base station for redundant session processing, comprising:

receiving a switching request message sent by a third base station, wherein the switching request message requests that a master control function of redundant session processing of the third base station is switched to the first base station;

establishing a connection of User Equipment (UE) corresponding to the redundant session processing based on the switching request message; and

and sending a path switching request message to the mobile management control entity.

10. The method of claim 9, further comprising:

in response to the handover request message, adding a fourth base station for processing of a second one of the redundant sessions of the third base station.

11. A session management function entity, comprising:

a processing unit; and

a storage unit for storing machine-readable instructions which, when executed by the processing unit, configure the processing unit to perform the method of any of claims 1-3.

12. A base station, comprising:

a processing unit; and

a storage unit for storing machine-readable instructions which, when executed by the processing unit, configure the processing unit to perform the method of any of claims 4-8 or 9-10.

13. A session management function entity, comprising:

a message receiving unit for receiving a message for creating a session management context;

a UPF selecting unit, for responding to the message for creating the session management context, selecting a user plane functional entity UPF for redundant session processing; and

and the session establishing unit is used for establishing a Packet Data Unit (PDU) session corresponding to the UPF.

14. A base station, comprising:

a message receiving unit configured to receive a message for establishing a second redundant session for redundant processing;

a base station addition determination unit for determining whether to add a second base station for processing the second redundant session in response to the message; and

a second redundant session configuration unit configured to configure the second redundant session to be processed by the second base station if it is determined to add the second base station.

15. A base station, comprising:

a message receiving unit, configured to receive a handover request message sent by a third base station, where the handover request message requests that a master control function of redundant session processing of the third base station be handed over to the first base station;

a connection establishing unit, configured to establish a connection with the UE corresponding to the redundant session processing based on the handover request message; and

and the message sending unit is used for sending the path switching request message to the mobile management control entity.

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