Improved method of 3gpp session establishment procedure and user equipment thereof

Abstract

The present application is directed to the processing of the maximum transmission unit (MTU) parameter under the inter-system change between the 5GS and the EPS, and proposes a session establishment procedure improvement method and a user equipment. Specifically, the PDU session of the "Ethernet" or "unstructured" PDU session type can be transferred to the PDN connection of the "non-IP" PDN type, therefore, the UE can request the MTU parameter of the non-IP link in the PDU session establishment process. On the other hand, the PDN connection of the "non-IP" PDN type can be transferred to the PDU session of the "unstructured" PDU session type, therefore, the UE can request the MTU parameter of the unstructured link in the default EPS bearer context activation process. The session establishment procedure improvement method and the user equipment provided by the present application can improve the user experience.

Description

[0001] Cross-referencing

[0002] This application claims priority under 35 U.S.SC §119 to the following: U.S. Provisional Patent Application No. 63 / 232,286, filed August 12, 2021, entitled “Enhanced 3GPP Session Establishment Procedure,” the contents of which are incorporated herein by reference. Technical Field

[0003] This invention generally relates to wireless communication in 5G networks. In particular, it relates to methods for improving PDU sessions and the PDU connection establishment process. Background Technology

[0004] Wireless communication networks have grown exponentially over the years. Long-Term Evolution (LTE) systems offer peak data rates, low latency, improved system capacity, and low operating costs due to a simpler network architecture. LTE systems, also known as 4G systems, also provide seamless integration with legacy wireless networks such as GSM, CDMA, and the Universal Mobile Telecommunication System (UMTS). In LTE systems, the evolved universal terrestrial radio access network (E-UTRAN) comprises multiple evolved Node Bs (eNodeBs or eNBs) that communicate with multiple mobile stations, referred to as user equipment (UEs). 3GPP networks typically include hybrid 2G / 3G / 4G systems. The Next Generation Mobile Network (NGMN) committee has decided to focus future NGMN activities on defining the end-to-end requirements for 5G New Radio (5GS) systems.

[0005] In 4G evolved packet system (EPS), the Packet Data Network (PDN) connection process is a crucial step for LTE communication systems accessing the packet data network. The purpose of the PDN connection process is to establish a default EPS bearer between the UE and the packet data network. In 5G, Protocol Data Unit (PDU) session establishment is a parallel process to the PDN connection process in 4G. A PDU session defines the association between the UE and the data network providing PDU connection services. Each PDU session is identified by a PDU session ID (PSI) and can include multiple QoS flows and QoS rules.

[0006] In system transition scenarios, a PDU session in 5G can be transferred to a PDN connection in 4G, and vice versa. In one example, after interfacing from N1 mode to S1 mode, a PDU session of "Ethernet" or "unstructured" PDU session type can be transferred to a PDN connection of "non-IP" PDN type. The UE knows the Maximum Transmission Unit (MTU) of the Ethernet and unstructured links, but not the MTU of the non-IP link. Similarly, after interfacing from S1 mode to N1 mode, a PDN connection of "non-IP" PDN type can be transferred to a PDU session of "unstructured" PDU session type. The UE knows the MTU of the non-IP link, but not the MTU of the unstructured link. Furthermore, the upper layers of the UE are unaware of the change in PDU / PDN type.

[0007] Provide a solution. Summary of the Invention

[0008] This invention addresses the handling of Maximum Transmission Unit (MTU) parameters under inter-system variations between 5GS and EPS, proposing an improved session establishment process method and its corresponding user equipment. PDU sessions of "Ethernet" or "unstructured" PDU session type can be transferred to a "non-IP" PDN type PDN connection; therefore, the UE can request the MTU parameter of the non-IP link during the PDU session establishment process. The non-IP link MTU size corresponds to the maximum length of user data that can be sent in the user data container in the ESM data transmission message or via the S1-U interface. Conversely, a "non-IP" PDN type PDN connection can be transferred to a PDU session of "unstructured" PDU session type; therefore, the UE can request the unstructured link MTU parameter during the UE-requested PDN connection process. For unstructured PDU session type PDU sessions, the unstructured link MTU size corresponds to the maximum length of user data packets that can be sent via the control plane or the N3 interface.

[0009] In one embodiment, an improved session establishment process method is proposed, comprising: sending a Protocol Data Unit (PDU) session establishment request message through a user equipment to establish a PDU session in N1 mode in a mobile communication network, wherein the PDU session establishment request message includes a request for the Maximum Transmission Unit (MTU) parameter of an Ethernet or unstructured link in N1 mode and a request for the MTU parameter of a non-IP link in S1 mode; receiving the MTU parameter of the Ethernet or unstructured link in N1 mode from the mobile communication network, and receiving the MTU parameter of the non-IP link in S1 mode; performing an inter-system change from N1 mode to S1 mode, wherein the PDU session is transferred to a corresponding packet data network connection in S1 mode; and transmitting non-IP packets on the packet data network connection based on the MTU parameter of the non-IP link in S1 mode of the packet data network connection.

[0010] In another embodiment, an improved session establishment process method is proposed, comprising: sending a packet data network connection request message through a user equipment to establish a packet data network connection in S1 mode in a mobile communication network, wherein the packet data network connection request message includes a request for the maximum transmission unit parameter of a non-IP link in S1 mode and a request for the maximum transmission unit parameter of an unstructured link in N1 mode; receiving the maximum transmission unit parameter of the non-IP link in S1 mode from the mobile communication network, and receiving the maximum transmission unit parameter of the unstructured link in N1 mode; performing an inter-system change from S1 mode to N1 mode, wherein the packet data network connection is transferred to a corresponding protocol data unit session in N1 mode; and sending unstructured packets on the protocol data unit session based on the maximum transmission unit parameter of the unstructured link of the protocol data unit session in N1 mode.

[0011] The improved session establishment process method and user equipment provided by this invention can improve user experience.

[0012] Other embodiments and advantages are described in detail below. This summary is not intended to limit the invention. The invention is defined by the claims. Attached Figure Description

[0013] The following figures illustrate embodiments of the present invention, wherein the same reference numerals denote the same components.

[0014] Figure 1 Based on a novel aspect, an enhanced 3GPP session establishment process for MTU parameter processing during the transition between 5GS and EPS systems is described.

[0015] Figure 2 Based on novel aspects, a block diagram of the architecture including terminal equipment (TE) and mobile terminal (MT) is described.

[0016] Figure 3 The novel aspect describes the message flow of a PDU session established in 5G converted to a PDN connection in 4G, as well as the corresponding MTU size and Packet Data Protocol (PDP) type determined by the UE.

[0017] Figure 4 The novel aspect describes the message flow of a PDN connection established in 4G being converted into a PDU session in 5G, as well as the corresponding MTU size and PDP type determined by the UE.

[0018] Figure 5 This is an example of using AT commands to query PDP types under inter-system conversion based on novel aspects.

[0019] Figure 6A flowchart illustrating a method for determining the MTU size under system changes from N1 mode to S1 mode is shown according to a novel aspect.

[0020] Figure 7 A flowchart illustrating a method for determining the MTU size under system changes from S1 mode to N1 mode is shown according to a novel aspect. Detailed Implementation

[0021] Reference will now be made in detail to embodiments of the present invention, examples of which are shown in the accompanying drawings.

[0022] Figure 1 According to a novel aspect, an enhanced 3GPP session establishment process for handling Maximum Transmission Unit (MTU) parameters during inter-system switching between 5GS and EPS is described. The 5GS / EPS 100 includes an application server 111 that provides various services by communicating with multiple user equipments (UEs), including UE 101. Figure 1 In the example, application server 111 and packet data network gateway (PDN GW) 112 are part of the 5G core or evolved packet core network 5GC / EPC 110. UE 101 and its serving base station gNB / eNB 102 are part of radio access network (RAN) 120. RAN 120 provides radio access to UE 101 via radio access technology (RAT) (e.g., 5G NR or 4G LTE). Application server 111 communicates with UE 101 via PDN GW 112, one or more user plane functions (UPFs) 113 and 114, and gNB / eNB 102. Access and mobility management function (AMF) 115 communicates with gNB / eNB 102, UPFs 113 / 114, and PDN GW 112 for access and mobility management of radio access devices in the 5GS / EPS network 100. UE 101 may be equipped with one or more radio frequency (RF) transceivers for different application services via different RAT / CNs. For example, UE 101 may be a smartphone, wearable device, Internet of Things (IoT) device, and tablet. Alternatively, UE 101 may be a laptop or personal computer with a data card inserted or installed, which includes a modem and RF transceiver to provide wireless communication capabilities.

[0023] In 4G Evolved Packet System (EPS), the Packet Data Network (PDN) connection process is a crucial step for LTE communication systems accessing the packet data network. The purpose of the PDN connection process is to establish a default EPS bearer between the UE and the packet data network. In 5G, Protocol Data Unit (PDU) session establishment is a parallel process to the PDN connection process in 4G. A PDU session defines the association between the UE and the data network providing PDU connection services. Each PDU session is identified by a PDU Session ID (PSI) and may include multiple QoS flows and QoS rules.

[0024] In the event of an inter-system transition, a PDU session in 5G can be transferred to a 4G PDN connection, and vice versa (e.g., PDU session / PDN connection 130). In one example, a PDU session of the "Ethernet" or "unstructured" PDU session type can be transferred to a "non-IP" PDN type PDN connection after interoperation. The UE knows the MTU of the Ethernet and unstructured links, but not the MTU of the non-IP link. Similarly, after interoperation from S1 mode to N1 mode, a "non-IP" PDN type PDN connection can be transferred to an "unstructured" PDU session type PDU session. The UE knows the MTU of the non-IP link, but not the MTU of the unstructured link. Without knowing the actual MTU size, if the packet size exceeds the MTU, the packet will be fragmented or dropped. Furthermore, without instructions from the UE's lower layer, the UE's upper layer cannot know about the change in PDP type (Packet Data Protocol type) during an inter-system transition.

[0025] According to the novel aspect, the present invention proposes an improved session establishment process (140) for MTU parameter processing under inter-system changes between 5GS and EPS. When establishing a PDN connection / PDU session 130, UE 101 should also request the MTU size value of the target PDN / PDU type after the inter-system change. In 5GS, a PDU session of the “Ethernet” or “unstructured” PDU session type can be transferred to a PDN connection of the “non-IP” PDN type; therefore, the UE can request the non-IP link MTU parameter during the PDU session establishment process. In EPS, a PDN connection of the “non-IP” PDN type can be transferred to a PDU session of the “unstructured” PDU session type; therefore, the UE can request the unstructured link MTU parameter during the PDN connection process.

[0026] Furthermore, the upper layers of UE 101 can query the current PDU / PDN type via AT commands. AT commands are used to control mobile terminal (MT) functions and GSM / UMTS network services from terminal equipment (TE) 105 via Terminal Adaptor (TA) 103. AT commands can be notifications with unsolicited result codes or configuration commands. Specifically, AT commands can be notifications with unsolicited result codes (URCs) indicating a change in PDU / PDN type. For example, in... Figure 1 In the process, MT 104 sends URC+CGEV to TA 103 to indicate a change in PDU / PDN type, and then receives the AT command +CGCONTRDP from TE 105 to query the PDU / PDN type. In response, MT 104 sends the MT status back to TA 103, which converts it into a response to be sent to TE 105 to indicate the current PDU / PDN type.

[0027] Figure 2 A simplified block diagram of an architecture including a terminal device (TE) and a mobile terminal (MT) is described based on novel aspects. TE 200 includes a processor 201, memory 202, and a protocol stack 210, which includes an application (APP) layer, a transport (TCP / UDP) layer, a network (IP) layer, a data link layer, and a physical (PHY) layer. TE 200 also includes system control modules and circuitry 220, including a user interface, configuration and control modules, a PDU session processor, a QoS stream processor, a QoS rule processor, and a telephone module. Processor 201 processes different applications and calls different system control modules to execute various functions of TE 200. Memory 202 stores program instructions and data 203 to control the operation of TE 200. The system control modules and circuitry can be implemented and configured to perform the functional tasks of TE 200. Note that TE 200 can also be referred to as an application processor (AP). Typically, TE 200 is also equipped with telephone framework circuitry (e.g., a dialer, call manager, etc.) to support voice call functionality. In addition, the TE 200 also supports AT commands defined in 3GPP TS 27.007, which are used to control MT functions and GPRS packet domain services based on the context of each PDP / PDN / PDU session identified by the CID.

[0028] The MT 250 has an antenna 256 for transmitting and receiving radio signals. An RF transceiver module 254, coupled to the antenna, receives RF signals from the antenna 256, converts them into baseband signals, and sends them to the processor 251 via a baseband module 255. The RF transceiver 254 also converts baseband signals received from the processor 251 into RF signals via the baseband module 255 and sends them to the antenna 256. The processor 251 processes the received baseband signals and calls different functional modules to perform functions within the MT 250. A memory 252 stores program instructions and data 253 to control the operation of the MT 250. The MT 250 also includes a protocol stack 260 and control circuitry comprising various system modules 270 to perform the functional tasks of the MT 250. The protocol stack 260 includes a Non-Access Stratum (NAS) layer, a Radio Resource Control (RRC) layer, a Packet Data Convergence Protocol / Radio Link Control (PDCP / RLC) layer, a Media Access Control (MAC) layer, and a Physical (PHY) layer. System module 270 includes a configuration module, a control module, a PDU session processor, a QoS stream processor, and a QoS rule processor. Note that the MT 250 can also be referred to as a modem. Figure 2 In the example, MT 250 also includes a terminal adapter (TA 280) that receives and sends AT commands and translates them into commands for processing by processor 251 to control MT functions. In one example, TA 280 receives an AT read command from TE 200 so that MT 250 can provide TE 200 with the current PDU / PDN type after an inter-system change.

[0029] Figure 3 The novel aspect describes the message flow for converting a PDU session established in 5G to a PDN connection in 4G, as well as the corresponding MTU size and PDP type determined by the UE. UE 301 includes AP 302 and modem 303. In step 311, UE 301 performs a PDU session establishment process for NR 5GC (N1 mode). During the PDU session establishment process, UE 301 sends a PDU session establishment request message to 5GC with PDU session type = "Ethernet" or "Unstructured". Typically, the request message includes a request for MTU parameters for the Ethernet link or unstructured link (e.g., in PCO / ePCO IE). However, the "Ethernet" or "Unstructured" PDU session type can later be transferred to a PDN connection of the "Non-IP" PDN type.

[0030] In a novel aspect, UE 301 also requests non-IP link MTU parameters for the corresponding PDN connection during the PDU session establishment process, for example, carried by the same PDU session establishment request message in step 311. In step 312, in response, 5GC sends a PDU session establishment accept message back to UE 301, containing the requested MTU parameters for the Ethernet or unstructured link in N1 mode and the MTU parameters for the non-IP link in S1 mode. In step 313, a PDU session with an unstructured PDU session type is established. UE 301 knows the MTU size of the unstructured link type of the PDU session and can send unstructured data packets according to the MTU size accordingly. The unstructured link MTU size corresponds to the maximum length of the user data packet, which is sent through the control plane or N3 interface for the PDU session of the unstructured PDU session type.

[0031] In step 321, UE 301 performs an inter-system transition from N1 mode of 5GS to S1 mode of EPS. As a result, the PDU session is transferred to the corresponding PDN connection with a non-IP PDN type (step 322). In step 331, modem 303 sends URC+CGEV to AP 302, indicating the change in PDP type. In step 332, modem 303 receives AT command +CGCONTRDP from AP 302 to query the PDU / PDN type. In response, modem 303 sends the MT status back to AP 302 to provide the PDU / PDN type. When the UE knows that the PDN / PDU type has changed to a non-IP link, the UE can consider the corresponding non-IP MTU. Since UE 301 has already obtained the non-IP link MTU parameters for the PDN connection in step 312, UE 301 can send non-IP packets based on the non-IP link MTU parameters (step 341).

[0032] Figure 4 The novel aspect describes the message flow for converting a PDN connection established in 4G to a PDU session in 5G, along with the corresponding MTU size and PDP type determined by the UE. UE 401 includes AP 402 and modem 403. In step 411, UE 401 performs a PDN connection establishment process in 4GEPC (S1 mode). During the PDN connection establishment process, UE 401 sends a PDN connection establishment request message with PDN connection type = "non-IP" to EPC. Typically, the request message includes non-IP link MTU parameters (e.g., in PCO / ePCO IE). However, the "non-IP" PDN connection type can later be transferred to a PDU session of the "unstructured" PDU session type.

[0033] In a novel aspect, UE 401 also requests unstructured link MTU parameters for the corresponding PDU session during the PDN connection establishment process, for example, carried by the same PDN connection establishment request message in step 411. In step 412, in response, EPC sends a PDN connection establishment accept message back to UE 401, containing the MTU parameters for the unstructured link in N1 mode and the requested MTU parameters for the non-IP link in S1 mode. In step 413, a PDN connection with a non-IP PDN type is established. UE 401 knows the MTU size of the non-IP link type of the PDN connection and can send non-IP data packets according to the MTU size. The non-IP link MTU size corresponds to the maximum length of user data, which is sent in an ESM DATA TRANSPORT message or via the S1-U interface.

[0034] In step 421, UE 401 performs an inter-system transition from S1 mode of EPS to N1 mode of 5GS. As a result, the PDN connection is transferred to the corresponding PDU session with an unstructured PDU session type (step 422). In step 431, modem 403 of UE 401 sends URC+CGEV to AP 402 of UE 401, indicating the change in PDP type. In step 432, modem 403 receives AT command +CGCONTRDP from AP 402 to query the PDU / PDN type. In response, modem 403 sends the MT status back to AP 402 to provide the PDU / PDN type. When the UE knows that the PDN / PDU type has changed to an unstructured link, the UE can consider the corresponding unstructured link MTU. Since UE 401 has already obtained the unstructured link MTU parameters for the PDU session in step 412, UE 401 can send unstructured packets according to the unstructured link MTU parameters (step 441).

[0035] In an alternative embodiment, after an inter-system change, if the PDN / PDU type changes, the UE should request the corresponding MTU size through the appropriate NAS process (e.g., a 5GSM / ESM modification process with PCO / ePCO IE or 5GSM / ESM status messages). In another alternative embodiment, the UE can reuse the original PDN / PDU type MTU after an inter-system change. For example, from N1 mode to S1 mode, the UE can use the N1 mode Ethernet MTU when switching to S1 mode; from S1 to N1 mode, the UE can use the non-IP MTU in S1 mode when performing an inter-system switch to N1 mode.

[0036] Figure 5This is an example of using AT commands to query PDP types under inter-system conversion, based on novel aspects. Application Programming Interfaces (APIs) based on Packet Data Protocol (PDP) contexts can be used to provide PDU sessions and corresponding session management functions to applications and terminal devices. A PDP context can be viewed as a data record characterizing a specific bearer and parameters of connection to the target PDN. As shown in Table 510,<PDP_type> Represented as a string, it can be used to indicate the PDP type of a PDN connection (e.g., non-IP) or a PDU session (e.g., Ethernet or unstructured).

[0037] For external applications, session management functions can be provided via the AT command API according to 3GPP TS 27.007 "AT Command Set for User Equipment (UE)". AT commands are used to control mobile terminal (MT) functions and GSM / UMTS network services from the terminal equipment (TE) via the terminal adapter (TA). In one example, an AT command can be a notification of a non-requested result code (URC) indicating a change in PDU / PDN type. For example, URC+CGEV can be used to indicate a change in PDU / PDN type. When changing from 5GS to EPS or vice versa between systems, the upper layer of the UE is unaware of the PDP context modification and the actual PDU / PDN type. The lower layer can use URC+CGEV, where,<change reason> The setting "PDP address or PDP type has changed" is sent from the lower layer to the upper layer of the UE. Upon receiving the URC, the upper layer uses the AT command +CGCONTRDP to query the PDU / PDN type. As shown in Table 500, the AT command +CGCONTRDP is modified to indicate the inclusion of the packet data protocol type.<PDP_type> .

[0038] Figure 6According to a novel aspect, a flowchart of a method for determining the MTU size during an inter-system change from N1 mode to S1 mode is shown. In step 601, the UE sends a PDU session establishment request message to establish a PDU session in N1 mode within the mobile communication network. The PDU session establishment request message includes a request for the Maximum Transmission Unit (MTU) parameter of the Ethernet or unstructured link in N1 mode and a request for the MTU parameter of the non-IP link in S1 mode. In step 602, the UE receives the MTU parameter of the Ethernet or unstructured link in N1 mode from the network and receives the MTU parameter of the non-IP link in S1 mode. In step 603, the UE performs an inter-system change from N1 mode to S1 mode. The PDU session is transferred to the corresponding PDN connection in S1 mode. In step 604, based on the MTU parameter of the non-IP link in S1 mode of the PDN connection, the UE sends non-IP packets on the PDN connection. Furthermore, when the inter-system change occurs from N1 mode to S1 mode, the modem provides an Attention (AT) command to the application processor (AP), and the AP can query the PDP type accordingly.

[0039] Figure 7 According to a novel aspect, a flowchart of a method for determining the MTU size during an inter-system change from S1 mode to N1 mode is shown. In step 701, the UE sends a PDN connection request message to establish a PDN connection in S1 mode within the mobile communication network. The PDN connection request message includes a request for the Maximum Transmission Unit (MTU) parameter of the non-IP link in S1 mode and a request for the MTU parameter of the unstructured link in N1 mode. In step 702, the UE receives the MTU parameters of the non-IP link in S1 mode and the MTU parameters of the unstructured link in N1 mode from the network. In step 703, the UE performs an inter-system change from S1 mode to N1 mode. The PDN connection is transferred to the corresponding PDU session in N1 mode. In step 704, based on the MTU parameters of the unstructured link in the PDU session in N1 mode, the UE sends unstructured packets on the PDU session. Furthermore, when the inter-system change occurs from S1 mode to N1 mode, the modem provides an Attention (AT) command to the application processor (AP), and the AP can query the PDP type accordingly.

[0040] While the present invention has been disclosed above with reference to specific embodiments, it is not intended to limit the invention. Therefore, various adjustments, modifications, or combinations can be made to the various features of the described embodiments without departing from the scope of the invention, and the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for improving the session establishment process, comprising: The user equipment sends a Protocol Data Unit Session Establishment Request message to establish a Protocol Data Unit session in N1 mode within the mobile communication network. The protocol data unit session establishment request message includes requests for the maximum transmission unit parameter for Ethernet or unstructured links in N1 mode and requests for the maximum transmission unit parameter for non-IP links in S1 mode. The maximum transmission unit parameter of the Ethernet or unstructured link in N1 mode is received from the mobile communication network, and the maximum transmission unit parameter of the non-IP link in S1 mode is also received. Perform an inter-system change from N1 mode to S1 mode, wherein the protocol data unit session is transferred to the corresponding packet data network connection in S1 mode; as well as Based on the maximum transmission unit parameter of the non-IP link in S1 mode of the packet data network connection, non-IP packets are sent on the packet data network connection.

2. The improved session establishment process method as described in claim 1, characterized in that, This protocol data unit session has the Ethernet or unstructured protocol data unit session type in N1 mode.

3. The improved session establishment process method as described in claim 1, characterized in that, The corresponding packet data network connection has a non-IP packet data network connection type in S1 mode.

4. The improved session establishment process method as described in claim 1, characterized in that, In S1 mode, the corresponding packet data network connection is configured with the maximum transmission unit parameter of the non-IP link requested during the establishment of the protocol data unit session in N1 mode.

5. The improved session establishment process method as described in claim 1, characterized in that, It further includes: providing attention commands to the application processor via the modem when the system changes from N1 mode to S1 mode.

6. The improved session establishment process method as described in claim 5, characterized in that, This attention command is the non-requested result code +CGEV, indicating a change in the packet data protocol type.

7. The improved session establishment process method as described in claim 6, characterized in that, The application processor sends a second attention command +CGCONTRDP to the modem to query the changed packet data protocol type.

8. An improved method for session establishment process, comprising: The user equipment sends a packet data network connection request message to establish a packet data network connection in S1 mode within the mobile communication network. The packet data network connection request message includes requests for the maximum transmission unit parameter for non-IP links in S1 mode and requests for the maximum transmission unit parameter for unstructured links in N1 mode. Receive the maximum transmission unit parameter of the non-IP link in S1 mode from the mobile communication network, and receive the maximum transmission unit parameter of the unstructured link in N1 mode. Perform an inter-system change from S1 mode to N1 mode, wherein the packet data network connection is transferred to the corresponding protocol data unit session in N1 mode; as well as Based on the maximum transmission unit parameter of the unstructured link of the protocol data unit session in N1 mode, unstructured packets are sent on the protocol data unit session.

9. The improved session establishment process method as described in claim 8, characterized in that, This packet data network connection has a non-IP packet data network connection type in S1 mode.

10. The improved session establishment process method as described in claim 8, characterized in that, The corresponding protocol data unit session has the unstructured protocol data unit session type in N1 mode.

11. The improved session establishment process method as described in claim 8, characterized in that, In N1 mode, the corresponding protocol data unit session is configured with the maximum transmission unit parameter of the unstructured link requested during the packet data network connection in S1 mode.

12. The improved session establishment process method as described in claim 8, characterized in that, It further includes: providing attention commands to the application processor via the modem when the system changes from S1 mode to N1 mode.

13. The improved session establishment process method as described in claim 12, characterized in that, This attention command is the non-requested result code +CGEV, indicating a change in the packet data protocol type.

14. The improved session establishment process method as described in claim 13, characterized in that, The application processor sends a second attention command +CGCONTRDP to the modem to query the changed packet data protocol type.

15. A user equipment for improving the session establishment process, comprising: Session or connection processing circuitry is used to establish a Protocol Data Unit (PDU) session in N1 mode by sending a request message in the mobile communication network, wherein... The request message includes requests for the maximum transmission unit parameter for unstructured links in N1 mode and requests for the maximum transmission unit parameter for non-IP links in S1 mode. A receiver is configured to receive the maximum transmission unit parameter of the unstructured link in N1 mode and the maximum transmission unit parameter of the non-IP link in S1 mode. Inter-system processing circuitry is used to perform an inter-system change from N1 mode to S1 mode, wherein the protocol data unit session is transferred to the corresponding packet data network connection in S1 mode. as well as A transmitter for transmitting non-IP packets on the packet data network connection based on the maximum transmission unit parameter of the non-IP link in S1 mode of the packet data network connection.

16. The user equipment as claimed in claim 15, characterized in that, This protocol data unit session has the unstructured protocol data unit session type in N1 mode.

17. The user equipment as claimed in claim 15, characterized in that, The corresponding packet data network connection has a non-IP packet data network connection type in S1 mode.

18. The user equipment as claimed in claim 15, characterized in that, In S1 mode, the corresponding packet data network connection is configured with the maximum transmission unit parameter of the non-IP link requested during the establishment of the protocol data unit session in N1 mode.

19. The user equipment as claimed in claim 15, characterized in that, Further includes: A modem used to send a non-requested result code +CGEV indicating a change in packet data protocol type when the system changes; as well as The application processor, in response to the non-requested result code, sends a second attention command +CGCONTRDP to the modem to query the changed packet data protocol type.

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