Managing stale packet data unit session in a telecommunication network

Abstract

Embodiments herein provide a method and system for managing stale PDU session in a telecommunication network. The method includes receiving, by a source AMF or a source MME, a bearer context request message from a target MME to retrieve user information. The source AMF or the source MME identifies an inactive PDU session from the plurality of PDU sessions based on the EPS bearer status. The source AMF or a source MME deactivates the at least one inactive PDU session by initiating a PDU session release procedure. The source AMF or the source MME generates a bearer context response message by including PDN connection information for only the at least one active PDU session. Further the source AMF or the source MME transmits the bearer context response message to the target MME upon completion of the PDU session release procedure.

Description

MANAGING STALE PACKET DATA UNIT SESSION IN A TELECOMMUNICATION NETWORK

[0001] The disclosure relates to wireless communication and more particularly relates to a method and system for managing stale Packet Data Unit (PDU) session in a telecommunication network.

[0002] The evolution of mobile communication networks from 4G Long Term Evolution (LTE) to 5G networks has introduced new challenges in ensuring seamless connectivity and service continuity. The components that facilitate this transition is the N26 interface, which is employed for mobility between the 5G System (5GS) and the Evolved Packet System (EPS), the core network for 4G LTE. Specifically, the N26 interface manages the signaling required for handover processes when User Equipment (UE) transitions between 5G and 4G LTE networks. This interface acts as an inter-core network link between the LTE's Mobility Management Entity (MME) and the 5G core's Access and Mobility Management Function (AMF), ensuring continuous voice service during inter-Radio Access Technology (RAT) handovers.

[0003] The current implementation of the N26 interface and associated call flows presents several problems that can impact network performance and user experience. One notable issue arises during the 5GS to EPS Idle mode mobility using the N26 interface procedure, which can result in stale sessions at the Session Management Function and Packet Gateway (SMF+PGW). Similarly, the call flow for Serving Gateway (SGW) change during inter-MME Tracking Area Update (TAU) procedures can lead to stale sessions at the PGW. These stale sessions can cause resource allocation problems, potentially leading to a situation where no available resources exist at the SMF+PGW or PGW, thereby preventing subscribers from connecting and accessing services in the 5GS or EPS network.

[0004] Further, during the idle mode TAU procedure, the source core network may remain unaware of bearers that have been locally deleted at the UE, resulting in a failure to clean up resources. When the target MME verifies the EPS bearer status received from the UE against the bearer contexts received from the old MME or AMF, it releases any network resources associated with EPS bearers that are no longer active in the UE. However, this release of bearers at the target MME is not communicated to the SMF+PGW or PGW, causing a resource leak. Consequently, subscriber requests for attachment or new PDN connections may be rejected due to the lack of available resources at the PGW or SMF, further exacerbating connectivity issues.

[0005] Thus, it is desired to address the above-mentioned disadvantages, issues or other shortcomings or at least provide a useful alternative.

[0006] The principal object of the embodiments herein is to provide a system and method for managing stale PDU sessions in a telecommunication network.

[0007] Another object of the embodiments herein is to initiate the deactivation of the inactive PDU session, which is marked as inactive by the target MME, so that the marked inactive PDU session can be deleted upon transmission of a TAU accept message to the UE.

[0008] Yet another object of the embodiments herein is to prevent stale sessions in PGW in EPC or in co-located SMF+PGW combo node in EPC-5GS interworking.

[0009] In an aspect, the objects are achieved by providing a method for managing stale PDU sessions in a telecommunication network. The method includes receiving by a source AMF or a source MME a bearer context request message from a target MME to retrieve user information. The bearer context request message includes an Information Element (IE) indicating an Evolved Packet System (EPS) bearer status for at least one active PDU session from a plurality of PDU sessions associated with a UE. The source AMF or the source MME identifies an inactive PDU session from the plurality of PDU sessions based on the EPS bearer status. The source AMF or the source MME deactivates the at least one inactive PDU session by initiating a PDU session release procedure. The source AMF or the source MME generates a bearer context response message by including PDN connection information for the at least one active PDU session. Further, the source AMF or the source MME transmits the bearer context response message to the target MME upon completion of the PDU session release procedure.

[0010] In another aspect, the objects are achieved by providing a method for managing stale PDU sessions in a telecommunication network. The method includes receiving by a target Mobility Management Entity (MME) a Tracking Area Update (TAU) request message from a UE, wherein the TAU request message comprises an information element (IE) indicating EPS bearer status for at least one active PDU session from a plurality of PDU sessions associated with the UE. Further, the target MME generates a bearer context request message by including the IE indicating the EPS bearer status for at least one active PDU session. Further, the target MME transmits the bearer context request message including the EPS bearer status to a source Access and Mobility Management Function (AMF) or a source MME to retrieve user information. The target MME receives the bearer context response message from the source AMF or the source MME, wherein the bearer context response message comprises Packet Data Network (PDN) connection information only for the at least one active PDU session. The inclusion of the IE indicating the EPS bearer status only for at least one active PDU session in the bearer context request message prevents a Packet Gateway (PGW) from maintaining a stale PDU session for at least one inactive PDU session from the plurality of PDU sessions, and PDN connection information for the inactive PDU session is not transmitted over the telecommunication network.

[0011] In another aspect, the objects are achieved by providing a method for managing stale PDU sessions in a telecommunication network. The method includes receiving by the target MME the TAU request message from the UE. The TAU request message includes the IE indicating EPS bearer status for the active PDU session of the plurality of PDU sessions associated with the UE. The target MME transmits the bearer context request message to the source AMF or the source MME to retrieve user information. Further, the target MME receives the bearer context response message from the source AMF or the source MME. The bearer context response message includes the PDN connection information for both active PDU sessions and inactive PDU sessions of the plurality of PDU sessions. The target MME creates the bearer contexts for all PDN connections, including the inactive PDU session at the UE as indicated in the EPS bearer status. The target MME selects the target SGW based on the bearer contexts for all PDN connections. Further, the target MME generates the bearer context acknowledge message by including the SGW change indication indicating the selection of the target SGW and transmits the bearer context acknowledge message to the source AMF or the source MME.

[0012] In yet another aspect, the objects are achieved by providing a method for deactivating a stale session in a telecommunication network. The method includes receiving by the target MME the TAU request message from the UE. The TAU request message includes the IE indicating EPS bearer status for the active PDU session from the plurality of PDU sessions associated with the UE. The target MME transmits the bearer context request message to a source AMF or a source MME to retrieve user information. Further, the target MME receives the bearer context response message from the source AMF or the source MME. The bearer context response message includes PDN connection information for both active PDU sessions and inactive PDU sessions of the plurality of PDU sessions. Furthermore, the target MME selects the target SGW based on the bearer contexts for all PDN connections and determines the match between the EPS bearer status received from the UE and the PDN connection information received from the source AMF or the source MME. The target MME generates a bearer context acknowledge message by including the SGW change indication indicating a selection of the target SGW and the IE indicating the EPS bearer status for the active PDU session when the EPS bearer status received from the UE does not match with the PDN connection information received from the source AMF or the source MME. Also, the target MME transmits the bearer context acknowledge message to the source AMF or the source MME.

[0013] In yet another aspect, the objects are achieved by providing the source AMF or source MME for managing the stale PDU session in the telecommunication network. The source AMF or the source MME includes a memory, a processor, and a PDU session controller communicatively coupled with the memory and the processor. The source AMF or the source MME receives the bearer context request message from the target MME to retrieve user information. The bearer context request message includes the IE indicating the EPS bearer status for the active PDU session from the plurality of PDU sessions associated with the UE. The source AMF or the source MME identifies the inactive PDU session from the plurality of PDU sessions based on the EPS bearer status and deactivates the inactive PDU session by initiating a PDU session release procedure. The source AMF or the source MME generates the bearer context response message by including PDN connection information for only the at least one active PDU session and transmits the bearer context response message to the target MME upon completion of the PDU session release procedure.

[0014] In yet another aspect, the objects are achieved by providing the target MME for managing the stale PDU session in the telecommunication network. The target MME includes a memory, a processor, and a PDU session controller. The target MME receives the TAU request message from the UE. The TAU request message includes the IE indicating the EPS bearer status for the active PDU session from the plurality of PDU sessions associated with the UE. The target MME generates the bearer context request message by including an IE indicating the EPS bearer status for the active PDU session and transmits the bearer context request message including the EPS bearer status to a source AMF or a source MME to retrieve the user information. Further, the target MME receives the bearer context response message from the source AMF or the source MME, wherein the bearer context response message includes the PDN connection information only for the active PDU session. The inclusion of the IE indicating the EPS bearer status only for the active PDU session in the bearer context request message prevents the PGW from maintaining a stale PDU session for the inactive PDU session from the plurality of PDU sessions, and PDN connection information for the inactive PDU session is not transmitted over the telecommunication network.

[0015] In yet another aspect, the objects are achieved by providing the target MME for managing the stale PDU session in the telecommunication network. The target MME includes a memory, a processor, and a PDU session controller. The target MME receives the TAU request message from the UE. The TAU request message includes the IE indicating the EPS bearer status for the active PDU session of a plurality of PDU sessions associated with the UE. Further, the target MME transmits the bearer context request message to the source AMF or the source MME to retrieve user information. The target MME receives the bearer context response message from the source AMF or the source MME. The bearer context response message includes the PDN connection information for both active PDU session and inactive PDU session of the plurality of PDU sessions. The target MME creates the bearer contexts for all PDN connections, including the inactive PDU session at the UE as indicated in the EPS bearer status, and selects the target SGW based on the bearer contexts for all PDN connections. Furthermore, the target MME generates the bearer context acknowledge message by including an SGW change indication indicating the selection of the target SGW and transmits the bearer context acknowledge message to the source AMF or the source MME.

[0016] In yet another aspect, the target MME is provided for managing the stale PDU session in the telecommunication network. The target MME receives the TAU request message from the UE. The TAU request message includes the IE indicating the EPS bearer status for the active PDU session from a plurality of PDU sessions associated with the UE and transmits the bearer context request message to the source AMF or source MME to retrieve user information. Further, the target MME receives the bearer context response message from the source AMF or the source MME, where the bearer context response message includes the PDN connection information for both active PDU session and inactive PDU session of the plurality of PDU sessions. The target MME selects the target SGW based on the bearer contexts for all PDN connections and determines a match between the EPS bearer status received from the UE and the PDN connection information received from the source AMF or the source MME. Furthermore, the target MME generates a bearer context acknowledge message by including the SGW change indication indicating the selection of the target SGW and the IE indicating the EPS bearer status for the active PDU session when the EPS bearer status received from the UE does not match with the PDN connection information received from the source AMF or the source MME. The target MME transmits the bearer context acknowledge message to the source AMF or the source MME.

[0017] In yet another aspect, the objects are achieved by providing a source AMF or the source MME with a memory, processor, and the PDU session controller. The source AMF or the source MME receives a bearer context request message from a target MME to retrieve user information and transmits a bearer context response message to the target MME. The bearer context response message includes the PDN connection information for both active PDU session and inactive PDU session of a plurality of PDU sessions. Furthermore, the source AMF or source MME transmits the bearer context acknowledge message to the target MME, wherein the bearer context acknowledge message comprises an SGW change indication indicating a selection of a target SGW by the target MME. The bearer context acknowledge message comprises an SGW change indication indicating a selection of the target SGW and the IE indicating an EPS bearer status for at least one active PDU session of the plurality of PDU sessions. The source AMF or the source MME identifies the inactive PDU session from the plurality of PDU sessions based on the EPS bearer status and deactivates the inactive PDU session by the source MME by initiating a PDU session release procedure.

[0018] These embodiments will be better understood through the following description and drawings. The descriptions illustrate preferred embodiments and specific details but are not limiting. Many changes and modifications can be made within the scope of these embodiments without departing from their spirit, and all such modifications are included.

[0019] The features, aspects, and advantages of the present embodiments are illustrated in the accompanying drawings, where like reference letters indicate corresponding parts across various figures. The embodiments will be better understood from the following description and drawings.

[0020] Fig. 1 illustrates the existing inter-RAT idle mode mobility using the N26 interface according to the prior art.

[0021] Fig. 2 illustrates the existing intra-RAT mobility according to the prior art.

[0022] Fig. 3 illustrates the UE registration and PDU session establishment in 5GS according to the prior art.

[0023] Fig. 4 illustrates the unavailability of the session at SMF+PGW due to the presence of unusable sessions according to the prior art.

[0024] Fig. 5 illustrates an example scenario of a session block leak which results in the unavailability of the sessions at SMF+PGW according to the embodiments as disclosed herein.

[0025] Fig. 6 is an example scenario of two UEs attached in the EPS network wherein the UEs create two PDN sessions to get the internet and the IMS services according to the prior art.

[0026] Fig. 7 is an example scenario of the existing TAU procedure where the unusable PDU sessions are stored at PGW according to the prior art.

[0027] Fig. 8 illustrates the unavailability of the session at PGW due to the presence of unusable sessions according to the prior art.

[0028] Fig. 9 is a block diagram that illustrates hardware features associated with the source AMF or the source MME according to the embodiments as disclosed herein.

[0029] Fig. 10 is a block diagram that illustrates the hardware features associated with the target MME according to the embodiments as disclosed herein.

[0030] Fig. 11 illustrates 5GS to EPS idle mode mobility using the N26 interface where the target MME triggers a delete session request for inactive PDN connection according to the embodiments as disclosed herein.

[0031] Fig. 12 is a sequence diagram that illustrates the 5GS to EPS idle mode mobility using the N26 interface through inactive bearer deletion initiated by the target MME according to the embodiments as disclosed herein.

[0032] Fig. 13 illustrates the deletion of stale PDU session initiated by the source AMF according to the embodiments as disclosed herein.

[0033] Fig. 14 is a sequence diagram that illustrates the deletion of stale PDU session initiated by the source AMF upon receiving the context request message from the target MME according to the embodiments as disclosed herein.

[0034] Fig. 15 illustrates the deletion of stale PDU session initiated by the source AMF upon receiving the context acknowledge message from the target MME according to the embodiments as disclosed herein.

[0035] Fig. 16 is a sequence diagram that illustrates the deletion of stale PDU session initiated by the source AMF upon receiving the context acknowledge message from the target MME according to the embodiments as disclosed herein.

[0036] Fig. 17 illustrates the initiation of deletion of the stale PDU session at the PGW by the target MME during the intra-RAT roaming according to the embodiments as disclosed herein.

[0037] Fig. 18 is a sequence diagram that illustrates the initiation of deletion of the stale PDU session at the PGW by the target MME during the intra-RAT roaming according to the embodiments as disclosed herein.

[0038] Fig. 19 illustrates the deletion of stale PDU session at the PGW upon the initiation of delete session request by the source MME according to the embodiments as disclosed herein.

[0039] Fig. 20 is a sequence diagram that illustrates the initiation of stale PDU session deletion by the source MME upon receiving the context request message from the target MME according to the embodiments as disclosed herein.

[0040] Fig. 21 illustrates the initiation of stale PDU session deletion by the source MME upon receiving the context acknowledge message from the target MME according to the embodiments as disclosed herein.

[0041] Fig. 22 is a sequence diagram that illustrates the initiation of stale PDU session deletion by the source MME upon receiving the context acknowledge message from the target MME according to the embodiments as disclosed herein.

[0042] Fig. 23 is a flow diagram that illustrates the deactivation of the inactive PDU session by the source AMF or source MME by initiating the PDU session release procedure according to the embodiments as disclosed herein.

[0043] Fig. 24 is a flow diagram that illustrates the deactivation of the inactive PDU session by the target MME according to the embodiments as disclosed herein.

[0044] Fig. 25 is a flow diagram that illustrates the deactivation of the inactive PDU session by the target MME upon receiving the context response message from the source AMF or the source MME according to the embodiments as disclosed herein.

[0045] Fig. 26 is a flow diagram that illustrates the initiation of deactivation of the inactive PDU session by the target MME according to the embodiments as disclosed herein.

[0046] Fig. 27 is a flow diagram that illustrates the initiation of the deletion of the stale session by the source AMF or the source MME upon receiving the context acknowledge message from the target MME according to the embodiments as disclosed herein.

[0047] The embodiments and their features are detailed with reference to the non-limiting examples illustrated in the accompanying drawings and description. Well-known components and techniques are omitted to avoid unnecessary obscurity. The described embodiments are not mutually exclusive and can be combined to form new embodiments. The term "or" is non-exclusive unless stated otherwise. The examples provided are for understanding and enabling skilled practitioners to implement the embodiments, and should not be seen as limiting their scope.

[0048] As is traditional in the field, embodiments are described and illustrated in terms of blocks that carry out a described function or functions.　These blocks, which referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and optionally be driven by firmware and software. The circuits, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like.　The circuits constituting a block be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments be physically separated into two or more interacting and discrete blocks without departing from the scope of the proposed method.　Likewise, the blocks of the embodiments be physically combined into more complex blocks without departing from the scope of the proposed method.

[0049] The drawings help illustrate the technical features, but the embodiments are not restricted to them. The proposed method includes any modifications, equivalents, and substitutes beyond those shown. Terms like "source" and "target" are used for distinction and do not limit the elements.

[0050] Embodiments disclosed herein provide a method and system for session management and optimization for seamless 5GC-EPC interworking. These embodiments prevent stale sessions and optimize the network by sharing an additional information element (IE), namely Active bearer status, in a context request message to inform the source MME about inactive bearers. The source MME deactivates inactive bearers after validating the context request message and sends a context response message that includes PDN connections for active bearers only.

[0051] In an embodiment, a method for preventing stale sessions in S / PGW in EPC or in a co-located SMF+PGW combo node in EPC-5GS interworking is described. The target MME detects possible stale sessions after receiving the GTP "Context Response" message from the source MME / AMF. The target MME creates the context and triggers the GTP "Create Session Request" message towards the target SGW for the inactive bearers along with active bearers, marking them inactive so they can be deleted after the ongoing TAU procedure. The SGW triggers the GTP "Modify Bearer Request" towards PGW or co-located SMF+PGW combo for the inactive bearers along with active bearers, thereby preventing stale sessions at PGW or SMF+PGW combo node. After sending the TAU accept to the UE, the target MME initiates the bearer deactivation procedure for inactive bearers only towards the target SGW, which further initiates the bearer deactivation procedure towards PGW or SMF+PGW combo node.

[0052] In an embodiment, the Target MME / co-located (MME+AMF) verifies the EPS bearer status received from the UE against the bearer contexts received from the source MME / AMF. The Target MME moves all the bearer contexts at the Target SGW, enabling the release of the EBI bearer contexts after the TAU procedure. Another approach involves the target MME sending the active bearer list in the GTP context request message to the source MME. In case of any mismatch, the source MME (or co-located AMF+MME) initiates deactivation (network-initiated) of inactive bearer contexts. Yet another approach has the target MME, after receiving the context response, compare the EBI bearer context info against the active bearer status received from the UE. The target MME then sends the context acknowledgment message to the source MME. In case of any mismatch, it sends only the active bearer list to the source MME / co-located (AMF+MME) as optional information in IE (EPS Bearer Status), allowing the source MME to initiate the deactivation (network-initiated) of inactive bearer contexts. As part of the network-initiated deactivation procedure initiated by the MME, SMF+S / PGW releases the inactive bearer contexts, avoiding the stale session phenomenon.

[0053] Stale sessions degrade network quality and result in revenue loss as end-users cannot connect due to unavailable network resources. The stale session issue is highly possible in case of bearer status mismatch between UE and core network, and 3GPP specs do not have any recommended solutions. This idea captures all possible scenarios and provides solutions.

[0054] The existing call flow for 5GS to EPS Idle mode mobility over the N26 interface can lead to stale sessions at co-located (SMF+S / PGW). Further, the existing idle mode mobility call flow during the inter-MME TAU procedure with SGW migration can lead to stale sessions at PGW. As 5GC / EPC is unaware of locally deleted bearers at UE, it does not clean up the network resources during the idle mode TAU procedure.

[0055] In a conventional system, the MME deactivates all those EPS bearer contexts locally which were present at the network side but are indicated by the UE as inactive. Prior art describes a method for efficient signal and resource use for wireless communications supporting circuit-switched (CS) and packet-switched sessions (PS). The conventional system discloses that a transmitter entity includes an EPS bearer context status information element (IE) in the next Non-Access Stratum (NAS) message to the receiver entity reflecting the bearer context status update. However, conventional systems do not explicitly disclose preventing stale sessions in S / PGW in EPC or co-located SMF+PGW combo node in EPC-5GS interworking during the mobility of UE in idle mode.

[0056] In the existing method, if the UE deletes EPS bearer locally and moves from 5GS to EPC in idle mode, it creates stale sessions in the SMF+PGW combo node. Further, if the UE deletes EPS bearer locally and moves from one MME to another MME, it creates stale sessions in S / PGW in the EPC node. Due to the growing stale sessions in S / PGW or in the SMF+PGW combo node, subscribers' service may be rejected by the core network.

[0057] The stale sessions issues were raised as BTSP (field) issues by a network operator, wherein the stale session problem is consuming the network resource, preventing users from connecting with the network. Further, the 3GPP specification doesn't provide any solution / approach to address the stale sessions.

[0058] The proposed solution uses EPS bearer context status IE in Context Request and Context Acknowledge GTP messages during the mobility of UE in idle mode to prevent stale sessions in the SMF+PGW node. The proposed solution provides three different solutions to address the above-mentioned problems. It removes any possibility of stale sessions at both AMF+MME or SMF+PGW combo nodes. Furthermore, there is at least 3X improvement with one of our proposed solutions.

[0059] Unlike the existing system, the proposed solution includes EPS bearer context status IE in Context Request and Context Acknowledge GTP messages during the mobility of UE in idle mode to prevent stale sessions in the SMF+PGW node. Further, the system helps in preventing the stale session in the SMF+PGW node during the mobility of UE in idle mode, also optimizing the EPS / 5GS network by reducing the buffer size of the GTP message Context Response.

[0060] The proposed method provides that the inactive EPS bearers in the UE shall be deleted during the idle mode mobility from 5GS to EPC to prevent stale sessions in the SMF+PGW combo node. The inactive EPS bearers in the UE shall also be deleted during the inter-MME idle mode mobility to prevent stale sessions in the PGW node.

[0061] Referring now to the drawings and more particularly to Figs. 1 through 27, where similar reference characters denote corresponding features consistently throughout the figures, these are shown preferred embodiments.

[0062] Fig. 1 shows the existing inter-RAT idle mode mobility using the N26 interface. The UE (107) is registered in the 5GS network with multiple PDU sessions. When the RRC connection is released, the UE (107) enters an idle state with one PDU session deactivated locally. The UE (107) then transitions to the EPS network.

[0063] After establishing the RRC connection (S101), the UE (107) triggers a Tracking Area Update (TAU) request, including the mapped EPS bearer ID in the EPS bearer Status IE for active PDU sessions. The eNB (106) selects the target MME (101) and forwards the TAU request (S102). The target MME (101) sends a Context Request to the source AMF (100) to retrieve user information (S103).

[0064] The source AMF (100) includes the PDN Connection IE in the Context response for all PDU sessions (S104). The target MME (101) creates contexts for active PDN connections and releases network resources for inactive EPS bearers. The target SGW (103) is selected, and a Context Acknowledge with SGW change indication is sent to the source AMF (100) (S105). The target MME (101) sends Create session requests for active PDN connections, and the target SGW (103) triggers Modify bearer requests to the SMF+PGW (104) (S106).

[0065] After updating the target SGW information, the SMF+PGW (104) sends Modify bearer responses to the target SGW (103), which then sends Create session responses to the target MME (101) (S109). The target MME (101) sends the TAU accept message to the UE (107) (S110).

[0066] The 5GS to EPS Idle mode mobility using the N26 interface does not provide a method for deleting bearer contexts and releasing resources at the PGW / SMF for inactive bearers. It also lacks information on reducing buffer size for the context response message for locally deleted bearers and cleaning up resources for stale sessions at the PGW / SMF. Further, there is no method for identifying stale sessions at the PGW / SMF, leading to potential resource leaks and rejected subscriber requests.

[0067] Fig. 2 shows the existing intra-RAT mobility. The UE (107) is attached to the EPS network with the source MME (100) and SGW 1 (100a). After attachment, two additional PDNs are created. The RRC connection is released, and the UE (107) enters an idle state with one EPS bearer deactivated locally. The UE (107) then moves to a new tracking area served by the target MME (101). Upon RRC connection establishment, the UE (107) triggers a TAU request (S201).

[0068] The inactive bearer is indicated in the EPS bearer Status IE. The target eNB forwards the TAU request to the target MME (101). The target MME (101) sends a Context Request to the source MME (100) to retrieve user information (S202). The source MME (100) responds with a Context Response message, including PDN connections for all three PDNs (S203).

[0069] The target MME (101) creates contexts for all bearers, including inactive ones. The target SGW is selected, and a Context Acknowledge with SGW change indication is sent to the source MME (100). The target MME (101) sends Create Session requests for active PDN connections. The target SGW (103) triggers Modify Bearer requests to the PGW (S204). After updating the new SGW information, the PGW (105) sends Modify Bearer responses to the target SGW (103), which then sends Create Session responses to the target MME (101). The target MME (101) sends a TAU accept message to the UE (107).

[0070] The conventional method does not show how to delete bearer contexts and release resources at the PGW for inactive bearers. It also lacks information on reducing buffer size for the Context Response message for locally deleted bearers and cleaning up resources for stale sessions at the PGW. There is no method for identifying stale sessions at the PGW, leading to potential resource leaks and rejected subscriber requests.

[0071] Fig. 3 shows UE registration and PDU session establishment in 5GS. Two UEs, UE 1 (108) and UE 2 (109), are registered in the 5G network (S301, S302). Four PDU sessions are created for DNN 1 and DNN 2. The AMF (111) allocates one session block per UE, while the SMF+PGW (112) allocates one block per PDU session. The PDU Session Establishment process involves establishing a data path between the UE and the 5G core network, representing a logical connection to a data network. The UE initiates the process by sending a request to the 5G core network, which includes the type of service and traffic. Once established, the UE can send and receive data, and the 5G core network manages resources to ensure efficient utilization and appropriate QoS. The DNN is used in PDU Session Establishment, UE registration, and SMF selection.

[0072] The terms PDU session, bearer, EPS bearer, and session are used interchangeably.

[0073] Fig. 4 illustrates the unavailability of the session at SMF+PGW due to the presence of unusable sessions according to the prior art. This figure depicts a scenario where two UEs, UE 1 (108) and UE 2 (109), are roaming from a 5G to a 4G network, and one bearer at each UE has been deleted locally during the movement. The UEs indicate only the active bearers to the network, as shown At step S401. Further, the 4G network transmits the active bearer indication to the MME (113) at step S402. At step S403, the MME (113) allocates one session block for each UE (108 and 109). The AMF (111) releases the used session, making it available for other sessions. The MME (113) transmits the context request message and receives the context response message from the AMF (111) as illustrated At steps S403 and S404. At step S406, the MME forwards the bearer information to the SGW (114), which allocates one session block for each PDU session associated with each UE. The SGW forwards the bearer information to the SMF+PGW (112) as illustrated at step S407. Consequently, the SMF+PGW (112) combo will have two unusable session blocks. These unusable sessions will continue to grow, resulting in the unavailability of session blocks for required bearers.

[0074] Fig. 5 illustrates an example scenario of a session block leak, which results in the unavailability of sessions at SMF+PGW according to the disclosed embodiments. The figure shows two UEs, UE 108 and UE 109, connected to 5G and 4G networks, respectively, requesting session establishment at the SMF+PGW through the AMF (111) and the MME (113). As the SMF+PGW stores stale sessions, it lacks session blocks to allocate for the requested sessions from the AMF (111) and the MME (113).

[0075] Fig. 6 presents an example scenario of two UEs attached to an EPS network, where the UEs create two PDN sessions to access internet and IMS services according to the prior art. This figure illustrates a scenario where two UEs, UE 1 (108) and UE 2 (109), are registered in a 4G network as shown At steps S601 and S602, and two PDN sessions are created to access internet and IMS services, respectively. The MME 1 (116) allocates one PDN session block for each registered UE, as illustrated at step S603. The MME 1 (116) forwards the PDN session information to the SGW 1 (117), which allocates a session block for each PDN session created at each UE. The SGW 1 (117) further forwards the PDN session information to the PGW (112), which then allocates one block for each PDN session created per UE.

[0076] Fig. 7 depicts an example scenario of the existing TAU procedure where unusable PDU sessions are stored at the PGW according to the prior art. The figure shows a scenario where two UEs, UE 1 (108) and UE 2 (109), are moving from one 4G network to another 4G network, and one bearer at each UE has been deleted locally during the movement. The UEs indicate the active bearer information to the MME 1 (121) through eNB, as illustrated at step S701. The MME 1 (121) allocates a session block for each UE and transmits the active bearer indication to the MME 2 (122) at step S702. At step S703, the MME 2 (122) allocates one session block for each UE (108 and 109). The MME 2 (122) releases the used session, making it available for other sessions. The MME 1 (121) transmits the context request message and receives the context response message from the MME 2 (122) as illustrated At steps S702 and S703. At step S706, the MME 1 (121) forwards the bearer information to the SGW 2 (123), which allocates one session block for each PDN session associated with each UE. The SGW 2 (123) forwards the bearer information to the PGW (125) as illustrated at step S706. Consequently, the PGW (125) will have two unusable session blocks. These unusable sessions will continue to grow, resulting in the unavailability of session blocks for required bearers.

[0077] Fig. 8 illustrates the unavailability of the session at PGW due to the presence of unusable sessions according to the prior art. The figure depicts two UEs, UE 1 (108) and UE 2 (109), connected to 4G. UE 1 (108) transmits bearer information to MME 1 (122), while UE 2 (109) transmits bearer information to MME 2 (121). MME 1 (122) and MME 2 (121) forward the bearer information to PGW (125) through SGW 1 (124) and SGW 2 (123), respectively, requesting session establishment at PGW (125). As PGW (125) stores stale sessions, it lacks session blocks to allocate for the requested sessions from MME 1 (122) and MME 2 (121).

[0078] Fig. 9 is a block diagram that illustrates hardware features associated with the source AMF or the source MME according to the disclosed embodiments. Examples of the wireless communication network system include, but are not limited to, Cellular Networks (such as 2G, 3G, 4G, 5G, Beyond 5G (B5G) / 6G, or advanced cellular networks), Local Area Networks (LANs) (such as Wi-Fi, Li-Fi, etc.), Personal Area Networks (PANs) (such as Bluetooth, Zigbee, Z-Wave, etc.), Wide Area Networks (WANs) (such as Satellite Communication Networks, Long Range Wide Area Network, Narrowband IoT, Low-bandwidth communication for IoT, etc.), Metropolitan Area Networks (MANs), Machine-to-Machine (M2M), Ad Hoc and Mesh Networks, and Emerging and Advanced Networks.

[0079] In an embodiment, the term "source network apparatus" is collectively used to refer to the source AMF in the case of roaming between 4G and 5G systems or the source MME during movement between two different 4G systems. With reference to Fig. 9, the source network apparatus (200) can encompass a diverse range of devices, including but not limited to AMF, MME, Session Management Function (SMF), Packet Control Function (PCF), Unified Data Management (UDM), Authentication Server Function (AUSF), Mobility Management Entity (MME), Packet Gateway (PGW), Service Gateway (SGW), Home Subscriber Server (HSS), Network Exposure Function (NEF), and others. The source network apparatus (200) interacts with the target MME (300) and provides active and stale session-related information. Further, the source network apparatus (200) supports interactions with the corresponding SMF+PGW for the deletion of stale sessions.

[0080] In an embodiment, the source network apparatus (200) includes a memory (201), a processor (202), an I / O interface (204), and a PDU session controller (203). The memory (201) stores instructions for the processor (202) and can include non-volatile storage elements such as magnetic hard disks, optical disks, floppy disks, flash memories, EPROM, or EEPROM. The memory (201) is a non-transitory storage medium, meaning it is not a carrier wave or propagated signal, but it can be movable and store large amounts of information. It may also store data that changes over time, such as in RAM or cache. The memory (201) holds bearer information, UE identity, Tracking Area Identity (TAI), location information, EPS bearer IDs, handover information, and more.

[0081] The processor (202) may include one or multiple processors, such as a general-purpose CPU, an Application Processor (AP), a GPU, a Visual Processing Unit (VPU), or an AI-dedicated Neural Processing Unit (NPU). It may have multiple cores and is configured to execute instructions stored in the memory (201). The processor (202) fetches location information, user identity, security parameters, Tracking Area Identity (TAI), EPS bearer IDs, and handover information of the UE (400). Additionally, it retrieves and executes instructions.

[0082] The I / O interface (204) transmits information between the memory (201) and external peripheral devices associated with the source network apparatus (200). It receives data from various UEs, network devices, servers, etc., and synchronizes the processor's (202) operating speed with the input and output devices. Additionally, the I / O interface (204) connects different peripheral devices, such as the PDU session controller (203) and memory (201), to delete stale sessions.

[0083] In an embodiment, the PDU session controller (203) of the source network apparatus (200) communicates with the processor (202), the I / O interface (204), and the memory (201) to manage stale PDU sessions in the telecommunication network. The PDU session controller (203) receives a bearer context request message from the target MME (300) to retrieve user information, wherein the bearer context request message includes the IE indicating the EPS bearer status for at least one active PDU session from the plurality of PDU sessions associated with the UE (400). Further, the PDU session controller (203) identifies inactive PDU sessions from the plurality of PDU sessions based on the EPS bearer status and deactivates the inactive PDU sessions by initiating the PDU session release procedure. The PDU session controller (203) then generates the bearer context response message by including PDN connection information for only the at least one active PDU session and transmits the bearer context response message to the target MME upon completion of the PDU session release procedure.

[0084] In an embodiment, the PDU session controller (203) transmits the PDU session release request message to a combined Session Management Function and Packet Gateway (SMF+PGW) to release the inactive PDU session after validation of the bearer context request message. The PDU session release request message is transmitted for deactivation of at least one inactive PDU session. Furthermore, the PDU session controller (203) receives the PDU session release response message from the SMF+PGW after releasing the inactive PDU session.

[0085] In an embodiment, the inclusion of the IE indicating the EPS bearer status only for active PDU sessions in the bearer context request message prevents the SMF+PGW or the PGW from maintaining stale PDU sessions for inactive PDU sessions from the plurality of PDU sessions, and PDN connection information for the inactive PDU sessions is not transmitted over the telecommunication network.

[0086] In an embodiment, the method includes transmitting by the PDU session controller (203) a bearer context acknowledge message to the target MME (300). The bearer context acknowledge message includes an SGW change indication indicating the selection of the target SGW by the target MME (300).

[0087] In an embodiment, the PDU session controller (203) receives the bearer context request message from the target MME (300) to retrieve user information and transmits the bearer context response message to the target MME (300). The bearer context response message includes the PDN connection information for both active and inactive PDU sessions of a plurality of PDU sessions. The PDU session controller (203) transmits the bearer context acknowledge message to the target MME (300), which includes the SGW change indication indicating the selection of the target SGW by the target MME (300). The bearer context acknowledge message includes an SGW change indication indicating a selection of the target SGW (500) and the IE indicating the EPS bearer status for at least one active PDU session of the plurality of PDU sessions. The PDU session controller (203) identifies the inactive PDU sessions from the plurality of PDU sessions based on the EPS bearer status and deactivates the inactive PDU sessions by initiating a PDU session release procedure.

[0088] In an embodiment, the source network apparatus (200) transmits the PDU session release request message to the SMF+PGW (600) to release the inactive PDU session after validation of the bearer context request message. The PDU session release request message is transmitted for deactivation of at least one inactive PDU session. The source network apparatus (200) receives the PDU session release response message from the SMF+PGW (600) after releasing the inactive PDU session.

[0089] In an embodiment, the inclusion of the IE indicating the EPS bearer status in the bearer context acknowledge message prevents the SMF+PGW from maintaining stale PDU sessions for the PDU sessions from the plurality of PDU sessions, and PDN connection information for the inactive PDU sessions is not transmitted over the telecommunication network.

[0090] Fig. 10 is a block diagram illustrating the hardware features associated with the target MME according to the disclosed embodiments. In an embodiment, the PDU session controller (303) receives the Tracking Area Update (TAU) request message from the UE (400). This TAU request message includes the Information Element (IE) indicating the EPS bearer status for the active PDU session from the plurality of PDU sessions associated with the UE (400). Further, the PDU session controller (303) generates the bearer context request message by including the IE indicating the EPS bearer status for the active PDU session and transmits the bearer context request message, including the EPS bearer status, to the source network apparatus (200) to retrieve user information. The PDU session controller (303) then receives the bearer context response message from the source AMF or the source MME, wherein the bearer context response message includes the Packet Data Network (PDN) connection information only for the active PDU session. The inclusion of the IE indicating the EPS bearer status only for the active PDU session in the bearer context request message prevents the PGW from maintaining the stale PDU session for the inactive PDU session from the plurality of PDU sessions, and PDN connection information for the inactive PDU session is not transmitted over the telecommunication network.

[0091] In an embodiment, the PDU session controller (303) selects the target SGW (500) based on the bearer context response message. Furthermore, the PDU session controller (303) transmits the bearer context acknowledge message to the source network apparatus (200), wherein the bearer context acknowledge message includes the SGW change indication indicating the selection of the target SGW (500).

[0092] In an embodiment, the PDU session controller (303) generates the create session request message by including the PDN connection information only for the active PDU session and transmits the create session request message to the target SGW (500). The PDU session controller (303) then receives the create session response message from the target SGW (500). This create session response message is received after updating SGW information for the PDN connection information for the active PDU session. Further, the PDU session controller (303) transmits the TAU accept message to the UE (400).

[0093] In yet another embodiment, the target SGW (500) transmits the modify bearer request message to SMF+PGW after receiving the create session request message from the target MME (300). The modify bearer request message includes the SGW information for the PDN connection information for the active PDU session. The target SGW (500) then receives the modify bearer response message from SMF+PGW (600) after updating the SGW information for the PDN connection information for the active PDU session. Furthermore, the target SGW (500) transmits the create session response message to the target MME after receiving the modify bearer response message from the SMF+PGW (600).

[0094] In an embodiment, the UE (400) registers in the 5GS network, establishes the plurality of PDU sessions, releases the Radio Resource Control (RRC) connection information, and transitions the UE (400) into the idle state. The UE (400) deactivates the PDU session locally and transitions to an Evolved Packet System (EPS) network. Upon re-establishing the RRC connection information, the UE (400) triggers the TAU request message by including the mapped EPS bearer ID in the IE indicating EPS bearer status for at least one active PDU session. The UE (400) selects the target MME (300) in the EPS network and forwards a Non-Access Stratum (NAS) TAU request message to the target MME (300).

[0095] In an embodiment, the PDU session controller (303) receives the TAU request message from the UE. This TAU request message includes the IE indicating the EPS bearer status for the active PDU session of a plurality of PDU sessions associated with the UE (400). The PDU session controller (303) transmits the bearer context request message to the source AMF or the source MME (200) to retrieve user information. Further, the PDU session controller (303) receives the bearer context response message from the source AMF or the source MME (200). This bearer context response message includes PDN connection information for both the active PDU session and the inactive PDU session of the plurality of PDU sessions. The PDU session controller (303) creates the bearer contexts for all PDN connections, including the inactive PDU session at the UE as indicated in the EPS bearer status. The PDU session controller (303) then selects the target SGW (500) based on the bearer contexts for all PDN connections. The PDU session controller (303) generates the bearer context acknowledge message by including an SGW change indication indicating a selection of the target SGW (500) and transmits the bearer context acknowledge message to the source network apparatus (200).

[0096] In an embodiment, the PDU session controller (303) generates the create session request message by including the PDN connection information for both the active PDU session and the inactive PDU session of the plurality of PDU sessions. The inactive PDU session is marked as inactive by the target MME (300) so that the marked inactive PDU session can be deleted upon transmission of a TAU accept message to the UE (400). The PDU session controller then transmits the create session request message to the target SGW (500) and receives the create session response message from the target SGW (500). This create session response message is received after updating SGW information for the PDN connection information for at least one active PDU session. The PDU session controller (303) Further transmits the TAU accept message to the UE (400).

[0097] In an embodiment, the target SGW (500) transmits the modify bearer request message to SMF+PGW (600) after receiving the create session request message from the target MME (300). The modify bearer request message includes the SGW information for the PDN connection information for both the active PDU session and the inactive PDU session of the plurality of PDU sessions. The target SGW (500) receives the modify bearer response message from the SMF+PGW (600) after updating the SGW information for the PDN connection information for both the active PDU session and the inactive PDU session of the plurality of PDU sessions. Furthermore, the target SGW (600) transmits the create session response message to the target MME (300) after receiving the modify bearer response message from the SMF+PGW (600).

[0098] In an embodiment, the target SGW (500) receives the delete session request message from the target MME (300). The delete session request message includes the PDN connection information for the inactive PDU session. The target SGW (500) transmits the delete session request message to the SMF+PGW (600) to delete the bearer contexts of the inactive PDU session. The delete or update of the bearer contexts at the SMF+PGW (600) for the inactive PDU session deletes the bearer contexts for the inactive PDU session at the UE (400).

[0099] In an embodiment, the UE (400) registers in the 5G network and establishes a plurality of PDU sessions. The UE (400) releases the RRC connection information and transitions the UE (400) into the idle state. The UE (400) deactivates the PDU session locally at the UE (400) and transitions to the EPS network. Further, the UE (400), upon re-establishing the RRC connection information, triggers the TAU request message by including the mapped EPS bearer ID in the IE indicating the EPS bearer status for the active PDU session. Further, the UE (400) selects the target MME (300) in the EPS network and forwards the NAS TAU request message to the target MME (300).

[0100] In an embodiment, the PDU session controller (303) receives the TAU request message from the UE (400). The TAU request message includes the IE indicating EPS bearer status for the active PDU session from the plurality of PDU sessions associated with the UE (400). The PDU session controller (303) transmits the bearer context request message to the source network apparatus (200) to retrieve the user information. The PDU session controller (303) receives the bearer context response message from the source network apparatus (200). The bearer context response message includes the PDN connection information for both active PDU session and inactive PDU session of the plurality of PDU sessions. The PDU session controller (303) selects the target SGW (500) based on the bearer contexts for all PDN connections and determines the match between the EPS bearer status received from the UE (400) and the PDN connection information received from the source network apparatus (200). The PDU session controller (303) generates the bearer context acknowledge message by including an SGW change indication indicating the selection of the target SGW (500) and the IE indicating the EPS bearer status for the at least one active PDU session when the EPS bearer status received from the UE (400) does not match with the PDN connection information received from the source network apparatus (200). Further, the PDU session controller (303) transmits the bearer context acknowledge message to the source network apparatus (200).

[0101] In an embodiment, the inclusion of the IE indicating the EPS bearer status in the bearer context acknowledge message prevents the SMF+PGW (600) from maintaining the stale PDU session for the inactive PDU session from the plurality of PDU sessions, and the PDN connection information for the inactive PDU session is not transmitted over the telecommunication network.

[0102] In an embodiment, the PDU session controller (303) generates the create session request message by including the PDN connection information only for the at least one active PDU session and transmits the create session request message to the target SGW (500). Further, the PDU session controller (303) receives the create session response message from the target SGW (500). The create session response message is received after updating SGW information for the PDN connection information for the at least one active PDU session. Further, the PDU session controller (303) transmits the TAU accept message to the UE (400).

[0103] In an embodiment, the target SGW (500) transmits the modify bearer request message to SMF+PGW (600) after receiving the create session request message from the target MME (300). The modify bearer request message includes the SGW information for the PDN connection information for the at least one active PDU session. Further, the target SGW (500) receives the modify bearer response message from the SMF+PGW (600) after updating the SGW information for the PDN connection information for the at least one active PDU session and transmits the create session response message to the target MME (300) after receiving the modify bearer response message from the SMF+PGW (600).

[0104] In an embodiment, the UE (400) registers in the 5G network and establishes PDU sessions. The UE (400) releases the RRC connection information and transitions into the idle state. Further, the UE (400) deactivates the PDU session locally and transitions into the EPS network. Upon re-establishing the RRC connection information, the UE triggers the TAU request message by including a mapped EPS bearer ID in the IE indicating EPS bearer status for at least one active PDU session. The UE (400) further selects the target MME (300) in the EPS network and forwards the NAS TAU request message to the target MME (300).

[0105] Figs. 9 and 10 show the hardware components of the source network apparatus (200) and the target MME (300), respectively. Alternative embodiments may include different or additional components. The labels are illustrative and do not limit the disclosure's scope. Components may also be combined to perform similar functions.

[0106] Fig. 11 illustrates 5GS to EPS Idle mode mobility using the N26 interface where the target MME (300) triggers the delete session request for inactive PDN connection according to the embodiments as disclosed herein. The illustrates the UE (400) registered in the 5GS network and established three PDU sessions. The preconditions includes the RRC connection is released and the UE (400) move into idle state, one PDU session gets deactivated locally in the UE (400), and the UE (400) moves to EPS network.

[0107] Following the RRC connection establishment at step S1101, the UE (400) triggers the TAU request. The UE (400) includes the mapped EPS bearer ID in the EPS bearer Status IE for two active PDU sessions, and the eNB (700) selects the target MME (300) in the EPS network and forwards the NAS Tracking area update request message. At step S1102, the target MME (300) sends a Context Request to the source AMF (200) to retrieve user information. The source AMF (200) includes the PDN Connection IE in the Context response message for all three PDU sessions established in 5GS and transmits the Context response message to the target MME (300), as depicted At step S1104.

[0108] At step S1105, the target MME (300) creates contexts for all the PDN connections, including the PDN inactive at the UE (400) as indicated in the EPS bearer Status. The target SGW (500) is selected by the target MME (300), and a Context Acknowledge with SGW change indication is sent to the source AMF (200), as shown At step S1105. At step S1106, the target MME (300) sends Create session requests for the inactive PDN connection as well. Further, the target SGW (500) triggers Modify bearer requests to the SMF+PGW (600), as illustrated at step S1107. After updating the SGW information for the PDN session, the SMF+PGW (600) sends Modify bearer responses to the target SGW (500), as shown At step S1108. At step S1109, the target SGW (500) sends Create session responses to the target MME (300).

[0109] At step S1110, the target MME (300) sends the TAU accept message to the UE (400) and then initiates network-initiated bearer deactivation for the inactive bearer. Further, the target MME (300) triggers a Delete session request to the target SGW (500) for the inactive PDN connection, as shown At step S1111, and the target SGW (500) forwards the message to the SMF+PGW (600). After deleting, the SMF+PGW (600) sends a Delete session response to the target SGW (500), which then forwards it to the target MME (300).

[0110] In the figure, steps S1106 and S1107 include creating and updating the bearer context at the target SGW (500) and the SMF+PGW (600), respectively, for inactive PDNs. This process helps in deleting the bearer context for inactive bearers at the UE (400). Otherwise, there could have been stale sessions in the SMF+PGW (600).

[0111] Fig. 12 is a sequence diagram that illustrates the 5GS to EPS Idle mode mobility using the N26 interface through inactive bearer deletion initiated by the target MME, according to the embodiments disclosed herein. At step S1201, the UE (400) initiates the TAU procedure by sending a TAU Request message (which includes EPS bearer status with EBI1 and EBI2 as active) to the eNB (700). The eNB derives the MME address from the RRC parameters and forwards the TAU Request message to the MME, as illustrated at step S1202.

[0112] The target MME (300) uses the GUTI received from the UE (400) to derive the source AMF address and sends a Context Request message to the source AMF (200) at step S1203. Further, at step S1204, the source AMF (200) sends an Nsmf_PDUSession_Context Request to the SMF+PGW (600), including any EBI values that cannot be transferred. The SMF+PGW (600) responds with an Nsmf_PDUSession_Context response to the source AMF (200) at step S1205. The source AMF (200) then prepares a Context Response message (including all PDN connections: PDN1, PDN2, PDN3) and sends it to the target MME (300).

[0113] At step S1207, the target MME (300) sends a Context Acknowledge (Serving GW change indication) message to the source AMF (200). The target MME then sends a Create Session Request for each PDN connection (including PDN3, which was inactive at the UE) received from the source AMF (200) to the target SGW (500) at step S1208. The Serving GW prepares and sends a Modify Bearer request to the SMF+PGW (600) at step S1209. The SMF+PGW (600) updates the PDU contexts and sends a Modify Bearer Response to the SGW, as shown At step S1210. The target SGW (500) sends a Create Session Response to the target MME (300) at step S1211. Further, at step S1212, the target MME (300) sends an Update Location Request message to HSS+UDM (900). The HSS+UDM (900) sends a Nudm_UECM_DeregistrationNotification to notify the source AMF (200) associated with 3GPP access, with the reason being 5GStoEPSMobility.

[0114] When the UE (400) decides to deregister over non-3GPP access or the source AMF (200) decides not to maintain the UE (400) registration for non-3GPP access anymore, the source AMF (200) deregisters from UDM by sending a Nudm_UECM_Deregistration service operation, unsubscribes from Subscription Data updates by sending a Nudm_SDM_Unsubscribe service operation to UDM, and releases all the AMF and AN resources related to the UE (400). The HSS+UDM (900) acknowledges the Update Location Request message by sending an Update Location Ack to the target MME (300).

[0115] At step S1216, the target MME (300) sends a TAU Accept message (including EPS bearer status with EBI1 and EBI2 as active) to the UE (400). If the GUTI was included in the TAU Accept, the UE acknowledges the received message by returning a TAU Complete message to the MME, as shown At step S1217. The target MME (300) then starts network-initiated bearer deactivation for the inactive bearer marked earlier. At step S1218, it triggers a Delete Session request (with PDN3 as inactive at the UE) to the target SGW (500).

[0116] The target SGW (500) forwards the Delete Session request to the SMF+PGW (600) at step S1219. The SMF+PGW (600) cleans up the resources and responds with a Delete Session response to the target SGW (500) at step S1220. The target SGW (500) cleans up the resources and responds with a Delete Session response to the target MME (300), as shown At step S1221.

[0117] Fig. 13 illustrates the deletion of a stale PDU session initiated by the source AMF according to the embodiments disclosed herein. The figure shows that the UE (400) is registered in the 5GS network and has established three PDU sessions. The RRC connection is released, and the UE (400) moves into an idle state. One PDU session is deactivated locally in the UE (400). Further, the UE (400) transitions to the EPS network. Upon RRC connection establishment, the UE (400) triggers a TAU request, as shown At step S1301. The UE (400) includes the mapped EPS bearer ID in the EPS bearer Status IE for two active PDU sessions. The eNB (700) selects the target MME (300) in the EPS network and forwards the NAS Tracking Area Update request message.

[0118] At step S1302, the target MME (300) sends a Context Request to the AMF to retrieve user information. The target MME (300) includes the EPS bearer Status in the Context Request message. The source AMF (200) identifies one PDU session as inactive at the UE (400), as indicated in the EPS bearer Status, and initiates the network-initiated PDU session release procedure. Step S1303 represents the PDU session release request sent by the source AMF (200), and step S1304 shows the source AMF (200) receiving the PDU session release response from the SMF+PGW (600). After completing the PDU session release procedure, the source AMF (200) sends a Context Response to the target MME (300), as illustrated At step S1305. The Context Response contains PDN connection information for only active PDU sessions. The target SGW (500) is selected by the target MME (300), and a Context Acknowledge with the target SGW (500) change indication is sent to the source AMF (200), as shown At step S1306.

[0119] At step S1307, the target MME (300) sends Create Session requests to the target SGW for active PDN connections. Step S1308 illustrates the target SGW triggering Modify Bearer requests to the SMF+PGW (600) corresponding to all CSR received from the target MME (300). After updating the target SGW (500) information for the PDN session At step S1309, the SMF+PGW (600) sends Modify Bearer responses to the target SGW. The target SGW (500) then sends Create Session responses to the target MME (300).

[0120] At step S1311, the target MME (300) sends a TAU accept message to the UE (400). As shown in Fig. 13, by sending a conditional IE EPS bearer status, the following features can be achieved: preventing the PGW from having a stale session for the inactive PDU session and ensuring that PDN connection information for the inactive bearer is not sent over the network. This approach prevents the overhead of creating and then deleting bearers that were inactive at the UE (400) and known beforehand.

[0121] Fig. 14 is a sequence diagram illustrating the deletion of a stale PDU session initiated by the source AMF (200) upon receiving a context request message from the target MME (300) according to the disclosed embodiments. At step S1401, the UE (400) initiates the TAU procedure by sending a TAU Request message, which includes EPS bearer status with EBI1 and EBI2 as active, to the eNB (700). The eNB (700) then derives the target MME (300) address from the RRC parameters and forwards the TAU Request message to the target MME (300) as depicted At step S1402.

[0122] At step S1403, the target MME (300) uses the GUTI received from the UE (400) to derive the source AMF address and sends a Context Request message to the source AMF (200), including the EPS bearer status. The source AMF (200) responds at step S1404 by sending an Nsmf_PDUSession_Context Request to the SMF+PGW (600), including any EBI values that cannot be transferred. The source AMF (200) includes the inactive bearers in the not ToTransferEbiList IE in the message and does not retrieve the context for a PDU Session corresponding to inactive EPS bearers if the EBI value of the QoS Flow is associated with the default QoS Rule.

[0123] At step S1405, the SMF+PGW (600) responds with an Nsmf_PDUSession_Context response to the AMF. If the Context Request message has an EPS Bearer Status IE, the source AMF (200) matches the active bearers in the UE (400) and PDU sessions in the source AMF (200) at step S1406. If any PDU session present in the source AMF (200) has become inactive in the UE (400), the source AMF (200) invokes the Nsmf_PDUSession_ReleaseSMContext request to the SMF+PGW (600) to request the release of the PDU Session. Step S1407 illustrates the SMF+PGW (600) cleaning up the resources and responding with an Nsmf_PDUSession_ReleaseSMContext response.

[0124] At step S1408, the source AMF (200) sends a Context Response message, indicating the PDN connection for active bearers, to the target MME (300). The target MME (300) then sends a Context Acknowledge message, indicating a Serving GW change, to the source AMF (200) at step S1409. At step S1410, the target MME (300) sends a Create Session Request for each PDN connection received from the AMF to the target SGW (500). Step S1411 illustrates the target SGW (500) transmitting a Modify Bearer request to the SMF+PGW (600). The SMF+PGW (600) updates the bearer context and sends a Modify Bearer Response to the target SGW (500) at step S1412. At step S1413, the target SGW (500) updates the bearer context and sends a Create Session Response to the target MME (300). The target MME (300) sends an Update Location Request message to the HSS+UDM (900) at step S1414.

[0125] At step S1415, the HSS+UDM (900) sends a Nudm_UECM_DeregistrationNotification to notify the AMF associated with 3GPP access, with the reason being 5GStoEPSMobility. When the UE (400) decides to deregister over non-3GPP access or the source AMF (200) decides not to maintain the UE (400) registration for non-3GPP access anymore, the source AMF (200) deregisters from the UDM by sending a Nudm_UECM_Deregistration service operation and unsubscribes from Subscription Data updates by sending a Nudm_SDM_Unsubscribe service operation to the UDM, releasing all the source AMF and AN resources related to the UE (400) at step S1416.

[0126] The HSS+UDM acknowledges the Update Location Request message by sending an Update Location Ack to the target MME (300) at step S1417. The target MME (300) then sends a TAU Accept message, which includes EPS bearer status with EBI1 and EBI2 as active, to the UE (400) at step S1418. If the GUTI was included in the TAU Accept, the UE acknowledges the received message by returning a TAU Complete message to the MME, as illustrated At step S1419.

[0127] The deletion of a stale PDU session initiated by the source AMF upon receiving the context acknowledge message from the target MME is illustrated in Fig. 15, according to the disclosed embodiments. The UE (400) is registered in the 5GS network and has established three PDU sessions. After the RRC connection is released, the UE (400) moves into an idle state, and one PDU session is deactivated locally in the UE. Further, the UE (400) transitions to the EPS network. Upon RRC connection establishment, the UE (400) triggers a Tracking Area Update (TAU) request, as depicted At step S1501. The UE (400) includes the mapped EPS bearer ID in the EPS bearer Status IE for the two active PDU sessions. The eNB selects the target MME in the EPS network and forwards the NAS TAU request message.

[0128] At step S1502, the target MME sends a Context Request to the source AMF (200) to retrieve user information. The source AMF (200) transfers all the PDN connections to the target MME (300). The target MME (300) verifies the EPS bearer status received from the UE with the PDN connection received from the source AMF (200). If there is any mismatch, the target MME sends the EPS bearer status to the source MME in the "Context Acknowledge" message, as shown At step S1504. A new SGW is selected by the target MME, and the Context Acknowledge message with the target SGW (500) change indication is sent to the source AMF (200). The source AMF (200) identifies one PDU session as inactive at the UE, as indicated in the EPS bearer Status, and initiates the network-initiated PDU session release procedure, as depicted At steps S1505 and S1506.

[0129] At step S1507, the target MME (300) sends Create Session requests to the source SGW for active PDN connections. Further, at step S1508, the target SGW (500) triggers Modify Bearer requests to the SMF+PGW corresponding to all CSR received from the target MME (300). After updating the target SGW information for the PDN session, the SMF+PGW (600) sends Modify Bearer responses to the target SGW (500). The target SGW sends Create Session responses to the MME, as depicted At step S1509. At step S1511, the target MME (300) sends a TAU accept message to the UE (400).

[0130] In the above procedure, sending the optional IE EPS bearer status for inactive bearer(s) in the Context Acknowledge message prevents the SMF+PGW (600) from having a stale session for the inactive PDU session. This approach prevents the overhead of creating and then deleting bearer(s) that were inactive at the UE and known beforehand.

[0131] Fig. 16 is a sequence diagram that illustrates the deletion of a stale PDU session initiated by the source AMF upon receiving the context acknowledgment message from the target MME, according to the embodiments disclosed herein. The UE initiates the TAU procedure by sending a TAU Request (including EPS bearer status with EBI1 and EBI2 as active) message to the eNB, as shown At step S1601.

[0132] At step S1602, the eNB derives the target MME (300) address from the RRC parameters. The eNB then forwards the TAU Request message to the MME. At step S1603, the target MME uses the GUTI received from the UE to derive the old AMF address and sends a Context Request message to the AMF. The source AMF sends an Nsmf_PDUSession_Context Request to SMF+PGW (600) at step S1604. Step S1605 illustrates the SMF+PGW responding with an Nsmf_PDUSession_Context response to the source AMF (200).

[0133] At step S1606, the source AMF (200) sends a Context Response message to the target MME (300). The target MME (300) sends a Context Acknowledge (Serving GW change indication) message to the source AMF. The target MME (300) includes EPS bearer status in the Context Acknowledge message only if any bearer contexts received from the source AMF (200) are inactive at the UE (400). At step S1608, the source AMF (200) invokes the Nsmf_PDUSession_ReleaseSMContext request to SMF+PGW (600) to request the release of the PDU session corresponding to the EPS bearer inactive at the UE (400).

[0134] The SMF+PGW clean up the resources and respond with an Nsmf_PDUSession_ReleaseSMContext response at step S1609. At step S1610, the target MME (300) sends a Create Session Request (for each PDN connection received from AMF) to the new SGW. The target SGW (500) prepares and sends a Modify Bearer request to SMF+PGW (600) at step S1611. At step S1612, the SMF+PGW (600) update the bearer context and send a Modify Bearer Response to the target SGW. The target SGW updates the bearer context and sends a Create Session Response to the target MME (300) at step S1613.

[0135] The target MME sends an Update Location Request message to HSS+UDM at step S1614. The HSS+UDM sends a Nudm_UECM_DeregistrationNotification to notify the AMF associated with 3GPP access with the reason as 5GStoEPSMobility at step S1615. When the UE decides to deregister over non-3GPP access or the old AMF decides not to maintain a UE registration for non-3GPP access anymore, the old AMF then deregisters from UDM by sending a Nudm_UECM_Deregistration service operation, unsubscribes from Subscription Data updates by sending a Nudm_SDM_Unsubscribe service operation to UDM, and releases all the AMF and AN resources related to the UE at step S1616.

[0136] Step S1617 illustrates the HSS+UDM acknowledging the Update Location Request message by sending an Update Location Ack to the MME. At step S1618, the MME sends a TAU Accept (including EPS bearer status with EBI1 and EBI2 as active) message to the UE. If the GUTI was included in the TAU Accept, the UE acknowledges the received message by returning a TAU Complete message to the MME, as illustrated at step S1619.

[0137] The initiation of deletion of the stale PDU session at the PGW by the target MME during intra-RAT roaming is illustrated in Fig. 17 according to the disclosed embodiments. Fig. 17 shows the UE attached to the EPS network with MME1 and SGW1 as the serving nodes. After attachment, two additional PDNs are created, the RRC connection is released, and the UE moves into an idle state. One EPS bearer is deactivated locally at the UE, which then moves to a new tracking area served by MME2.

[0138] Upon RRC connection establishment at step S1701, the UE triggers a Tracking Area Update (TAU) request. The locally deleted bearer is indicated as inactive in the EPS bearer Status IE. The target eNB forwards the TAU request message to the new target MME (MME2). At step S1702, the target MME sends a Context Request to the old MME to retrieve user information. In response, at step S1703, the source MME provides a Context Response message, which includes PDN connections for all three PDNs present in the network. The target MME creates contexts for all the bearers, including the one that was inactive at the UE.

[0139] A new SGW is selected by the MME, and a Context Acknowledge with SGW change indication is sent to the source MME, as shown At step S1704. At step S1705, the target MME sends Create Session Requests for all PDN connections. The new SGW triggers Modify Bearer Requests to the PGW corresponding to all CSR received from the MME. After updating the new SGW information for the EPS bearer context(s), the PGW sends Modify Bearer Responses to the SGW, as shown At step S1706. At step S1708, the SGW sends Create Session Responses to the MME. Further, at step S1709, the target MME sends a TAU Accept message to the UE and initiates network-initiated bearer deactivation for the previously marked inactive bearer.

[0140] At step S1710, the target MME triggers a Delete Session Request to the SGW, which forwards the message to the PGW, as shown At step S1711. The PGW deletes the context for EPS bearer 7 and sends a Delete Session Response to the SGW, which then forwards it to the target MME. In this scenario, steps S1705 and S1706 depict the creation and updating of the bearer context at the SGW and PGW, respectively, for inactive bearers. This process aids in deleting the bearer context for inactive bearers at the UE, preventing stale sessions in the PGW.

[0141] Fig. 18 is a sequence diagram illustrating the initiation of deletion of a stale PDU session at the PGW by the target MME during intra-RAT roaming, according to the disclosed embodiments. The UE initiates the TAU procedure by sending a TAU Request message, which includes the EPS bearer status with EBI1 and EBI2 as active, to the eNB. At step S1802, the eNB derives the target MME address from the RRC parameters and forwards the TAU Request message to the target MME.

[0142] At step S1803, the target MME uses the GUTI received from the UE to derive the old MME address and sends a Context Request message. The Source MME (200) prepares a Context Response message, which includes all PDN connections (PDN1, PDN2, PDN3), and sends it to the target MME (300) at step S1804. Further, at step S1805, the target MME (300) sends a Context Acknowledge (Serving GW change indication) message to the source MME (200). The target MME then sends a Create Session Request for each PDN connection, including UE inactive PDNs, to the target SGW (500) at step S1806.

[0143] The SGW prepares and sends a Modify Bearer request to the PGW at step S1807. The PGW updates the PDN contexts and sends a Modify Bearer Response to the target SGW at step S1808. Following this, the Target SGW sends a Create Session Response to the target MME at step S1809. At step S1810, the Target MME sends an Update Location Request message to the HSS. The HSS responds by sending a Cancel Location (IMSI Cancellation Type) message to the old MME with the Cancellation Type set to Update Procedure at step S1811. The old MME acknowledges with a Cancel Location Ack message at step S1812. The HSS then acknowledges the Update Location Request message by sending an Update Location Ack to the target MME at step S1813. At step S1814, the MME sends a TAU Accept message, which includes the EPS bearer status with EBI1 and EBI2 as active, to the UE. If the GUTI was included in the TAU Accept, the UE acknowledges the received message by returning a TAU Complete message to the MME, as depicted At step S1815.

[0144] At step S1816, the Target MME initiates network-initiated bearer deactivation for the inactive bearer marked earlier. It triggers a Delete Session Request (with PDN3 as inactive at the UE) to the SGW. The SGW forwards the Delete Session Request to the PGW at step S1817. The PGW cleans up the resources and responds with a Delete Session Response to the SGW at step S1818. Finally, the SGW cleans up the resources and responds with a Delete Session Response to the target MME at step S1819.

[0145] The present disclosure relates to the deletion of stale PDU sessions at the PGW upon the initiation of a delete session request by the source MME, as illustrated in Fig. 19. The UE is attached to the EPS network with MME1 and SGW1 serving as nodes. After attachment, two additional PDNs are created, the RRC connection is released, and the UE moves into an idle state. One EPS bearer is deactivated locally at the UE. Further, the UE moves to a new tracking area served by MME2. Upon RRC connection establishment, the UE triggers a Tracking Area Update (TAU) request, as shown At step S1901. The locally deleted bearer is indicated as inactive in the EPS bearer Status IE. The target eNB forwards the TAU request message to the new target MME (MME2).

[0146] At step S1902, the target MME sends a Context Request to the old MME to retrieve user information, including the EPS bearer status. The source MME identifies the EPS bearer status for PDN3 as inactive and initiates the network-initiated bearer deactivation procedure, as depicted At steps S1903, S1904, S1905, and S1906. Upon completing the bearer deactivation procedure at step S1907, the source MME sends a Context Response to the target MME, which includes PDN connection information for PDN1 and PDN2. At step S1908, the new SGW is selected by the MME, and a Context Acknowledge with SGW change indication is sent to the old MME. Further, At step S1909, the new MME sends Create Session requests to the new SGW, which triggers Modify Bearer requests to the PGW corresponding to all CSR received from the MME.

[0147] After updating the new SGW information for the EPS bearer contexts, the PGW sends Modify Bearer responses to the SGW, as shown At step S1911. At step S1912, the SGW sends Create Session responses to the MME. Finally, At step S1913, the MME sends a TAU accept message to the UE. This procedure, by sending a conditional IE EPS bearer status, prevents the PGW from having stale sessions for inactive PDN connections. Further, it avoids the overhead of creating and then deleting bearers that were inactive at the UE and known beforehand.

[0148] Fig. 20 is a sequence diagram that illustrates the initiation of stale PDU session deletion by the source MME upon receiving the context request message from the target MME, according to the disclosed embodiments. The UE initiates the TAU procedure by sending a TAU Request (including EPS bearer status) message to the eNB, as shown At step S2001. From the RRC parameters, the eNB derives the MME address and forwards the TAU Request message, as illustrated At step S2002.

[0149] At step S2003, the new MME uses the GUTI received from the UE to derive the old MME address and sends a Context Request (EPS bearer status) message to the old MME to retrieve user information. If the Context Request message includes EPS Bearer Status IE, the old MME matches the active bearer in the UE with the bearer context present in the MME at step S2004. For any bearer present in the MME that became inactive in the UE, the MME triggers a Delete Session Request message for each PDN connection to the old SGW. The old SGW forwards this Delete Session Request message to the PGW, as depicted At step S2005. The PGW cleans up the resources and sends a Delete Session Response to the old SGW at step S2006.

[0150] The old SGW cleans up the resources and forwards the Delete Session Response to the old MME at step S2007. The source MME then sends a Context Response (PDN connection for active bearer(s)) message to the new MME. Further, the new MME sends a Context Acknowledge (Serving GW change indication) message to the old MME, as depicted At step S2009. At step S2010, the new MME sends a Create Session Request (for each PDN connection received from the old MME) to the new SGW. The Serving GW prepares and sends a Modify Bearer request to the PGW, as illustrated At step S2011. The PGW updates the bearer context and sends a Modify Bearer Response to the new SGW at step S2012. The new SGW updates the bearer context and sends a Create Session Response to the new MME at step S2013. The new MME then sends an Update Location Request message to the HSS, as shown At step S2014. The HSS sends a Cancel Location (IMSI Cancellation Type) message to the old MME with the Cancellation Type set to Update Procedure at step S2015. The old MME acknowledges with a Cancel Location Ack message, as illustrated At step S2016.

[0151] The HSS acknowledges the Update Location Request message by sending an Update Location Ack (IMSI Subscription Data) message to the new MME at step S2017. When the timer started At step S2003 expires at step S2018, the old MME releases any local MME bearer resources and deletes the EPS bearer resources by sending Delete Session Request (Cause Operation Indication) messages to the old Serving GW if it received the Serving GW change indication in the Context Acknowledge message At step S2009. If the Operation Indication flag is not set, it indicates to the old Serving GW that it shall not initiate a delete procedure towards the PDN GW. The Serving GW acknowledges with Delete Session Response (Cause) messages, as shown At step S2019. At step S2020, the MME sends a TAU Accept message to the UE. If the GUTI was included in the TAU Accept, the UE acknowledges the received message by returning a TAU Complete message to the MME, as illustrated At step S2021.

[0152] The initiation of stale PDU session deletion by the source MME upon receiving the context acknowledge message from the target MME is illustrated in Fig. 21, according to the embodiments disclosed herein. A UE is attached to the EPS network with MME1 and SGW1 as the serving node. After attachment, two additional PDNs are created, the RRC connection is released, and the UE moves into an idle state. One EPS bearer is deactivated locally at the UE, and the UE moves to a new tracking area served by MME2.

[0153] Upon RRC connection establishment, the UE triggers a Tracking Area Update (TAU) request, as shown At step S2101. The locally deleted bearer is indicated as inactive in the EPS bearer Status IE. The target eNB forwards the TAU request message to the new target MME (MME2). At step S2102, the target MME sends a Context Request to the old MME to retrieve user information. The source MME transfers all the PDN connections to the target MME. The target MME verifies the EPS bearer status received from the UE with the PDN connections received from the source MME.

[0154] If there is any mismatch, the target MME sends the EPS bearer status to the source MME in the "Context Acknowledge" message, as shown At step S2104. The MME selects a new SGW, and the Context Acknowledge with SGW change indication is sent to the old MME. The source MME finds the EPS bearer status for PDN3 inactive and initiates the network-initiated bearer deactivation procedure, as depicted At steps S2105, S2106, S2107, and S2108. At step S2109, the new MME sends Create Session requests to the new SGW. The target SGW triggers Modify Bearer requests to the PGW corresponding to all CSR received from the MME.

[0155] After updating the new SGW information for the EPS bearer context(s), the PGW sends Modify Bearer responses to the SGW, as depicted At step S2111. Further, at step S2112, the target SGW sends Create Session responses to the target MME. At step S2113, the MME sends a TAU accept message to the UE.

[0156] By sending the optional IE EPS bearer status for inactive bearer(s) in the Context Acknowledge message, the method prevents the PGW from having stale sessions for inactive PDN connections. This approach prevents the overhead of creating and then deleting bearer(s) that were inactive at the UE and known beforehand.

[0157] Fig. 22 is a sequence diagram that illustrates the initiation of stale PDU session deletion by the source MME upon receiving the context acknowledge message from the target MME, according to the embodiments as disclosed herein. At step S2201, the UE initiates the TAU procedure by sending a TAU Request (including EPS bearer status) message to the eNB. The eNB derives the MME address from the RRC parameters and forwards the TAU Request message, as shown At step S2202.

[0158] At step S2203, the new MME uses the GUTI received from the UE to derive the old MME address and sends a Context Request (EPS bearer status) message to the old MME to retrieve user information. If the Context Request message includes the EPS Bearer Status IE, the old MME matches the active bearer in the UE with the bearer context present in the MME. If any bearer present in the MME has become inactive in the UE, the MME triggers a Delete Session Request message for each PDN connection to the old SGW. The old SGW (501) forwards this Delete Session Request message to the PGW (600), as shown At step S2205.

[0159] At step S2206, the PGW cleans up the resources and sends a Delete Session Response to the old SGW. The old SGW then cleans up the resources and forwards the Delete Session Response to the old MME (200) at step S2207. Further, the old MME (200) sends a Context Response (PDN connection for active bearer(s)) message to the new MME, as shown At step S2208. The new MME sends a Context Acknowledge (Serving GW change indication) message to the old MME at step S2209.

[0160] At step S2210, the new MME sends a Create Session Request (for each PDN connection received from the old MME) to the new SGW. The Serving GW prepares and sends a Modify Bearer request to the PGW, as depicted At step S2211. The PGW updates the bearer context and sends a Modify Bearer Response to the new SGW at step S2212. The new SGW updates the bearer context and sends a Create Session Response to the new MME, as shown At step S2213.

[0161] At step S2214, the new MME sends an Update Location Request message to the HSS. The HSS sends a Cancel Location (IMSI Cancellation Type) message to the old MME with the Cancellation Type set to Update Procedure, as illustrated At step S2215. The old MME acknowledges with a Cancel Location Ack message at step S2216. The HSS acknowledges the Update Location Request message by sending an Update Location Ack (IMSI Subscription Data) message to the new MME, as illustrated At step S2217.

[0162] When the timer started At step S2203 expires, the old MME releases any local MME bearer resources and deletes the EPS bearer resources by sending Delete Session Request (Cause Operation Indication) messages to the old Serving GW, provided it received the Serving GW change indication in the Context Acknowledge message At step S2209. If the Operation Indication flag is not set, it indicates to the old Serving GW that it shall not initiate a delete procedure towards the PDN GW. The Serving GW acknowledges with Delete Session Response (Cause) messages at step S2219. At step S2220, the MME sends a TAU Accept message to the UE. If the GUTI was included in the TAU Accept, the UE acknowledges the received message by returning a TAU Complete message to the MME, as illustrated At step S2221.

[0163] In an embodiment, the terms MME1, old MME, and source MME are used interchangeably. Similarly, the terms MME2, new MME, and target MME are used interchangeably.

[0164] Fig. 23 is a flow diagram illustrating the deactivation of an inactive PDU session by the source AMF or source MME through the initiation of the PDU session release procedure, according to the disclosed embodiments. At step S2301, the source AMF or source MME (200) receives a bearer context request message from a target MME to retrieve user information. This bearer context request message includes an IE indicating the EPS bearer status for at least one active PDU session from a plurality of PDU sessions associated with the UE. Further, at step S2302, the source network apparatus (200) identifies the inactive PDU session from the plurality of PDU sessions based on the EPS bearer status. At step S2303, the source network apparatus (200) deactivates the inactive PDU session by initiating a PDU session release procedure and generates a bearer context response message, including PDN connection information for only the at least one active PDU session, as illustrated at step S2304. Finally, at step S2305, the source network apparatus (200) transmits the bearer context response message to the target MME upon completion of the PDU session release procedure.

[0165] Fig. 24 is a flow diagram that illustrates the deactivation of the inactive PDU session by the target MME, according to the disclosed embodiments. At step S2401, the target MME (300) receives the TAU request message from the UE (400). The TAU request message comprises an IE indicating the EPS bearer status for the active PDU session from a plurality of PDU sessions associated with the UE (400). The inclusion of the IE indicating the EPS bearer status only for the active PDU session in the bearer context request message prevents the PGW from maintaining a stale PDU session for the inactive PDU session from the plurality of PDU sessions, and PDN connection information for the inactive PDU session is not transmitted over the telecommunication network. At step S2402, the target MME (300) generates the bearer context request message by including an IE indicating the EPS bearer status for the active PDU session. Further, at step S2403, the target MME (300) transmits the bearer context request message, including the EPS bearer status, to the source AMF or the source MME to retrieve user information. At step S2404, the target MME (300) receives the bearer context response message from the source AMF or the source MME, wherein the bearer context response message includes the PDN connection information only for the at least one active PDU session.

[0166] Fig. 25 is a flow diagram illustrating the deactivation of the inactive PDU session by the target MME upon receiving the context response message from the source AMF or the source MME, according to the embodiments disclosed herein. At step S2501, the target MME (300) receives the TAU request message from the UE (400). The TAU request message includes the IE indicating the EPS bearer status for the active PDU session of a plurality of PDU sessions associated with the UE (400). At step S2502, the target MME (300) transmits a bearer context request message to the source AMF or the source MME (200) to retrieve user information.

[0167] Further, at step S2503, the target MME (300) receives the bearer context response message from the source AMF or the source MME (200). The bearer context response message includes PDN connection information for both the active PDU session and the inactive PDU session of the plurality of PDU sessions. At step S2504, the target MME (300) creates the bearer contexts for all PDN connections, including the inactive PDU session at the UE, as indicated in the EPS bearer status. The target MME (300) selects the target SGW (500) based on the bearer contexts for all PDN connections. At step S2506, the target MME (300) generates the bearer context acknowledge message by including an SGW change indication indicating the selection of the target SGW (500) and transmits the bearer context acknowledge message to the source network apparatus (200).

[0168] Fig. 26 is a flow diagram illustrating the initiation of deactivation of the inactive PDU session by the target MME, according to the embodiments disclosed herein. At step S2601, the target MME (300) receives the TAU request message from the UE (400). The TAU request message includes the IE indicating EPS bearer status for the active PDU session from the plurality of PDU sessions associated with the UE (400). The target MME (300) transmits the bearer context request message to the source network apparatus (200) to retrieve the user information. The target MME (300) receives the bearer context response message from the source network apparatus (200). The bearer context response message includes the PDN connection information for both the active PDU session and the inactive PDU session of the plurality of PDU sessions.

[0169] At step S2604, the target MME (300) selects the target SGW (500) based on the bearer contexts for all PDN connections and determines the match between the EPS bearer status received from the UE (400) and the PDN connection information received from the source network apparatus (200), as illustrated at step S2605. At step S2606, the target MME (300) generates the bearer context acknowledge message by including an SGW change indication indicating the selection of the target SGW (500) and the IE indicating the EPS bearer status for at least one active PDU session when the EPS bearer status received from the UE (400) does not match with the PDN connection information received from the source network apparatus (200). Further, at step S2607, the target MME (300) transmits the bearer context acknowledge message to the source network apparatus (200).

[0170] Fig. 27 is a flow diagram illustrating the initiation of the deletion of the stale session by the source AMF or the source MME upon receiving the context acknowledge message from the target MME, according to the embodiments disclosed herein. At step S2701, the source AMF or the source MME (200) receives the bearer context request message from the target MME (300) to retrieve the user information and transmits the bearer context response message to the target MME (300), as illustrated at step S2702. The bearer context response message includes the PDN connection information for both the active PDU session and the inactive PDU session of a plurality of PDU sessions.

[0171] At step S2703, the source AMF or the source MME (200) transmits the bearer context acknowledge message to the target MME (300). The bearer context acknowledge message includes the SGW change indication indicating the selection of the target SGW by the target MME (300). The bearer context acknowledge message includes an SGW change indication indicating the selection of the target SGW (500) and the IE indicating the EPS bearer status for at least one active PDU session of the plurality of PDU sessions. At step S2704, the source AMF or the source MME (200) identifies the inactive PDU session from the plurality of PDU sessions based on the EPS bearer status and deactivates the inactive PDU session by initiating a PDU session release procedure, as illustrated at step S2705.

[0172] According to embodiments, a method may be performed by a new mobility management entity (MME) in a tracking area update (TAU) procedure with serving gateway (SGW) change. The method may comprise receiving, from a user equipment (UE), a TAU request including an evolved packet system (EPS) bearer status indicating an at least one active EPS bearer in the UE. The method may comprise, in response to transmitting, to an old MME, a context request to retrieve user information, receiving, from the old MME, a context response including packet data network (PDN) connection information. The method may comprise identifying an inactive EPS bearer based on the EPS bearer status and the PDN connection information. The method may comprise, before releasing any network resources associated with the inactive EPS bearer, transmitting, to a S-GW, a create session request regarding the inactive EPS bearer and the at least one active EPS bearer.

[0173] In an embodiment, the create session request indicates that the inactive EPS bearer is to be deleted.

[0174] In an embodiment, the method may comprise transmitting, to the UE, a TAU accept indicating the at least one active EPS bearer.

[0175] In an embodiment, the method may comprise, after transmitting the create session request, initiating a release of a PDN connection including the inactive EPS bearer. The method may comprise, in response to initiating the release of the PDN connection, transmitting, to the S-GW, a delete session request for the PDN connection including the inactive EPS bearer.

[0176] In an embodiment, the create session request may enable a packet gateway (PGW) to delete network resources for the inactive EPS bearer.

[0177] According to embodiments, a new mobility management entity (MME) in a tracking area update (TAU) procedure with serving gateway (SGW) change may include memory, including one or more storage media, storing instructions. The new MME may include at least one processor including processing circuitry. The instructions, when executed by the at least one processor, may cause the new MME to receive, from a user equipment (UE), a TAU request including an evolved packet system (EPS) bearer status indicating an at least one active EPS bearer in the UE. The instructions, when executed by the at least one processor, may cause the new MME to, in response to transmitting, to an old MME, a context request to retrieve user information, receive, from the old MME, a context response including packet data network (PDN) connection information. The instructions, when executed by the at least one processor, may cause the new MME to identity an inactive EPS bearer based on the EPS bearer status and the PDN connection information. The instructions, when executed by the at least one processor, may cause the new MME to, before releasing any network resources associated with the inactive EPS bearer, transmit, to a S-GW, a create session request regarding the inactive EPS bearer and the at least one active EPS bearer.

[0178] In an embodiment, the create session request may indicate that the inactive EPS bearer is to be deleted.

[0179] In an embodiment, the instructions, executed by the at least one processor, may cause the new MME to transmit, to the UE, a TAU accept indicating the at least one active EPS bearer.

[0180] In an embodiment, the instructions, when executed by the at least one processor, may cause the new MME to, after transmitting the create session request, initiate a release of a PDN connection including the inactive EPS bearer. The instructions, when executed by the at least one processor, may cause the new MME to, in response to initiating the release of the PDN connection, transmit, to the S-GW, a delete session request for the PDN connection including the inactive EPS bearer.

[0181] In an embodiment, the create session request may enable a packet gateway (PGW) to delete network resources for the inactive EPS bearer.

[0182] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method performed by a new mobility management entity (MME) in a tracking area update (TAU) procedure with serving gateway (SGW) change, comprising:receiving, from a user equipment (UE), a TAU request including an evolved packet system (EPS) bearer status indicating an at least one active EPS bearer in the UE;in response to transmitting, to an old MME, a context request to retrieve user information, receiving, from the old MME, a context response including packet data network (PDN) connection information;identifying an inactive EPS bearer based on the EPS bearer status and the PDN connection information; andbefore releasing any network resources associated with the inactive EPS bearer, transmitting, to a S-GW, a create session request regarding the inactive EPS bearer and the at least one active EPS bearer.2.The method of claim 1,wherein the create session request indicates that the inactive EPS bearer is to be deleted.3.The method of claim 1, further comprising:transmitting, to the UE, a TAU accept indicating the at least one active EPS bearer.4.The method of claim 1, further comprising:after transmitting the create session request, initiating a release of a PDN connection including the inactive EPS bearer; andin response to initiating the release of the PDN connection, transmitting, to the S-GW, a delete session request for the PDN connection including the inactive EPS bearer.5.The method of claim 1,wherein the create session request enables a packet gateway (PGW) to delete network resources for the inactive EPS bearer.6.A new mobility management entity (MME) in a tracking area update (TAU) procedure with serving gateway (SGW) change, comprising:memory, including one or more storage media, storing instructions; andat least one processor including processing circuitry, wherein the instructions, when executed by the at least one processor, cause the new MME to:receive, from a user equipment (UE), a TAU request including an evolved packet system (EPS) bearer status indicating an at least one active EPS bearer in the UE;in response to transmitting, to an old MME, a context request to retrieve user information, receive, from the old MME, a context response including packet data network (PDN) connection information;identity an inactive EPS bearer based on the EPS bearer status and the PDN connection information; andbefore releasing any network resources associated with the inactive EPS bearer, transmit, to a S-GW, a create session request regarding the inactive EPS bearer and the at least one active EPS bearer.7.The new MME of claim 6,wherein the create session request indicates that the inactive EPS bearer is to be deleted.8.The new MME of claim 6,wherein the instructions, executed by the at least one processor, cause the new MME to:transmit, to the UE, a TAU accept indicating the at least one active EPS bearer.9.The new MME of claim 6,wherein the instructions, when executed by the at least one processor, cause the new MME to:after transmitting the create session request, initiate a release of a PDN connection including the inactive EPS bearer; andin response to initiating the release of the PDN connection, transmit, to the S-GW, a delete session request for the PDN connection including the inactive EPS bearer.10.The new MME of claim 6,wherein the create session request enables a packet gateway (PGW) to delete network resources for the inactive EPS bearer.

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