Method and apparatus for call establishment

Abstract

Various embodiments of the present disclosure provide a method for call establishment. The method executable by a session management node includes receiving an Evolved Packet System (EPS) fallback indicator from a mobility management node. In an embodiment, the EPS fallback indicator may indicate that a fallback to EPS for Internet Protocol Multimedia Subsystem (IMS) voice services is in progress. The method further includes reporting an EPS fallback event to a policy charging node according to the EPS fallback indicator.

Description

Technical Field

[0001] The present disclosure generally relates to communication networks, and more particularly, to methods and apparatuses for call establishment. Background Art

[0002] This section presents aspects that may facilitate a better understanding of the present disclosure. Accordingly, statements in this section will be read from this perspective and will not be construed as an admission of prior art or non-prior art.

[0003] Communication service providers and network operators have continuously faced challenges in delivering value and convenience to consumers, for example, by providing compelling network services and performance. With the rapid development of network and communication technologies, wireless communication networks (such as Long Term Evolution (LTE) / Fourth Generation (4G) networks and New Radio (NR) / Fifth Generation (5G) networks) are expected to achieve high traffic capacity and end-user data rates with low latency. To meet the diverse requirements of various industries for new services, the 3rd Generation Partnership Project (3GPP) is developing various network function services for the 5G System (5GS) architecture and the policy and charging control framework. This is achieved through distributed or centralized deployment between the control plane (CP) function and the user plane (UP) function and independent scaling for flexible network deployment and operation. Summary of the Invention

[0004] The Summary of the Invention is provided to introduce a selection of concepts that are further described below in the Detailed Description. The Summary of the Invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0005] In a communication system such as 5GS, a terminal device (such as a user equipment (UE)) residing on a next-generation radio access network (NG-RAN) may have one or more ongoing packet data unit (PDU) sessions, each session including one or more quality of service (QoS) flows. For example, a serving public land mobile network (PLMN) access and mobility management function (AMF) may send an indication to the UE during the registration process to support an Internet protocol multimedia subsystem (IMS) packet switched (PS) voice session, and the UE may register in the IMS. The NG-RAN may be configured to support evolved packet system (EPS) fallback for IMS voice and decide to trigger a fallback to EPS considering the UE's capabilities, an indication of "redirect for EPS fallback for voice is okay" from the AMF, network configuration, radio conditions, etc. For EPS fallback for IMS voice, when the EPS fallback is triggered by the NG-RAN, the packet gateway control plane function (PGW-C) associated with the session management function (SMF) may be notified, and the NG-RAN may initiate a handover (HO) or an access network (AN) release via an inter-system redirection to EPS. During the HO or redirection to EPS, the session initiation protocol (SIP) signaling exchange between the UE and the IMS network may still be in progress, but the default QoS flow / default bearer for the transmitted IMS signaling may be unavailable for a short period. This may result in the loss of SIP signaling and call establishment delay. Therefore, it is desirable to improve call establishment in the case of EPS fallback.

[0006] Various embodiments of the present disclosure propose a solution for optimizing call establishment, which can avoid the loss of call establishment signaling (such as SIP signaling) in EPS fallback, for example, by notifying the IMS of the EPS fallback event in an effective manner, so as to ensure successful call establishment in EPS fallback without significantly affecting the call establishment time of new radio voice (VoNR).

[0007] According to a first aspect of the present disclosure, a method executable by a session management node such as a PGW-SMF is provided. The method includes receiving an EPS fallback indicator from a mobility management node. The EPS fallback indicator may indicate that a fallback to EPS for IMS voice service is in progress. According to an exemplary embodiment, the method further includes reporting an EPS fallback event to a policy charging node based on the EPS fallback indicator.

[0008] According to some exemplary embodiments, in response to a subscription of the policy charging node to the EPS fallback event, the EPS fallback event may be reported to the policy charging node.

[0009] According to some exemplary embodiments, a session management node may be notified in a first notification from a policy charging node of the policy charging node's subscription to an EPS fallback event.

[0010] According to some exemplary embodiments, an EPS fallback event may be reported to a policy charging node in a second notification from a session management node.

[0011] According to a second aspect of the present disclosure, there is provided an apparatus that may be implemented as a session management node. The apparatus may include one or more processors and one or more memories storing computer program code. The one or more memories and the computer program code may be configured to, together with the one or more processors, cause the apparatus to perform at least any of the steps of the method according to the first aspect of the present disclosure.

[0012] According to a third aspect of the present disclosure, there is provided a computer-readable medium embodying computer program code that, when executed on a computer, causes the computer to perform at least any of the steps of the method according to the first aspect of the present disclosure.

[0013] According to a fourth aspect of the present disclosure, there is provided an apparatus that may be implemented as a session management node. The apparatus includes a receiving unit and a reporting unit. According to some exemplary embodiments, the receiving unit may be operable to perform at least the receiving step in the method according to the first aspect of the present disclosure. The reporting unit may be operable to perform at least the reporting step in the method according to the first aspect of the present disclosure.

[0014] According to a fifth aspect of the present disclosure, there is provided a method executable by a policy charging node. The method includes receiving an EPS fallback event report from a session management node. The method further includes reporting the EPS fallback event to a call control node according to the EPS fallback event report.

[0015] According to some exemplary embodiments, in response to a call control node's subscription to an EPS fallback event, the EPS fallback event may be reported to the call control node.

[0016] According to some exemplary embodiments, a policy charging node may be notified in an authentication and authorization request from a call control node of the call control node's subscription to an EPS fallback event.

[0017] According to some exemplary embodiments, an EPS fallback event may be reported to a call control node in a re-authentication request from a policy charging node.

[0018] According to a sixth aspect of the present disclosure, there is provided an apparatus that can be implemented as a policy charging node. The apparatus includes one or more processors and one or more memories storing computer program code. The one or more memories and the computer program code may be configured to, together with the one or more processors, cause the apparatus to perform at least any step of the method according to the fifth aspect of the present disclosure.

[0019] According to a seventh aspect of the present disclosure, there is provided a computer-readable medium having embodied thereon computer program code that, when executed on a computer, causes the computer to perform at least any step of the method according to the fifth aspect of the present disclosure.

[0020] According to an eighth aspect of the present disclosure, there is provided an apparatus that can be implemented as a policy charging node. The apparatus includes a receiving unit and a reporting unit. According to some exemplary embodiments, the receiving unit is operable to perform at least the receiving step in the method according to the fifth aspect of the present disclosure. The reporting unit is operable to perform at least the reporting step in the method according to the fifth aspect of the present disclosure.

[0021] According to a ninth aspect of the present disclosure, there is provided a method executable by a call control node. The method includes receiving an EPS fallback event report from a policy charging node. The method further includes processing signaling at least partly based on the EPS fallback event report.

[0022] According to some exemplary embodiments, in response to a call control node's subscription to an EPS fallback event, an EPS fallback event report may be received from a policy charging node.

[0023] According to some exemplary embodiments, a call control node's subscription to an EPS fallback event may be notified to a policy charging node in an authentication authorization request from the call control node.

[0024] According to some exemplary embodiments, an EPS fallback event report may be received in a re-authentication request from a policy charging node.

[0025] According to some exemplary embodiments, processing signaling may include at least one of the following: buffering call establishment signaling, extending the transmission time of call establishment signaling, and holding one or more SIP signals.

[0026] According to some exemplary embodiments, the method according to the ninth aspect of the present disclosure may further include: resuming call establishment in response to an access type change event.

[0027] According to some exemplary embodiments, an access type change event may include at least one of the following: a radio access technology (RAT) type change event, and an IP connectivity access network (IP CAN) change event.

[0028] According to a tenth aspect of the present disclosure, there is provided an apparatus that can be implemented as a call control node. The apparatus includes one or more processors and one or more memories storing computer program code. The one or more memories and the computer program code can be configured to, together with the one or more processors, cause the apparatus to perform at least any step of the method according to the ninth aspect of the present disclosure.

[0029] According to an eleventh aspect of the present disclosure, there is provided a computer-readable medium having embodied thereon computer program code that, when executed on a computer, causes the computer to perform at least any step of the method according to the ninth aspect of the present disclosure.

[0030] According to a twelfth aspect of the present disclosure, there is provided an apparatus that can be implemented as a call control node. The apparatus includes a receiving unit and a processing unit. According to some exemplary embodiments, the receiving unit is operable to perform at least the receiving step in the method according to the ninth aspect of the present disclosure. The processing unit is operable to perform at least the processing step in the method according to the ninth aspect of the present disclosure.

[0031] The proposed solution according to some exemplary embodiments can enable EPS fallback to be recognized by IMS at an early stage, so that the call establishment process can be optimized to reduce latency and enhance resource efficiency. On the other hand, some exemplary embodiments can support the adaptive processing of SIP signaling to ensure successful call establishment in EPS fallback without affecting other services such as VoNR. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present disclosure itself, preferred usage modes, and other purposes are best understood by referring to the following detailed description of the embodiments when read in conjunction with the accompanying drawings, wherein:

[0033] Figure 1 is a diagram showing an example of EPS fallback for IMS voice according to an embodiment of the present disclosure;

[0034] Figure 2 is a diagram showing an example of retransmission during EPC fallback according to an embodiment of the present disclosure;

[0035] Figure 3 is a diagram showing an example of EPS fallback subscription and reporting according to an embodiment of the present disclosure;

[0036] Figure 4 is a diagram showing an example of SIP message processing according to an embodiment of the present disclosure;

[0037] Figure 5 is a flowchart showing a method according to some embodiments of the present disclosure;

[0038] Figure 6 is a flowchart showing another method according to some embodiments of the present disclosure;

[0039] Figure 7 is a flowchart showing yet another method according to some embodiments of the present disclosure;

[0040] Figure 8 is a block diagram showing a device according to some embodiments of the present disclosure;

[0041] Figure 9 is a block diagram showing another device according to some embodiments of the present disclosure;

[0042] Figure 10 is a block diagram showing yet another device according to some embodiments of the present disclosure; and

[0043] Figure 11 is a block diagram showing another device according to some embodiments of the present disclosure. Detailed Description of Specific Embodiments

[0044] Embodiments of the present disclosure are described in detail with reference to the accompanying drawings. It should be understood that these embodiments are only discussed to enable those skilled in the art to better understand and thus implement the present disclosure, rather than to impose any limitation on the scope of the present disclosure. References to features, advantages, or similar language throughout this specification do not imply that all features and advantages that can be achieved by the present disclosure should be present in or in any single embodiment of the present disclosure. On the contrary, language referring to features and advantages is understood to mean that a particular feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Moreover, the described features, advantages, and characteristics of the present disclosure may be combined in any manner in one or more embodiments. Those skilled in the relevant art will recognize that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present disclosure.

[0045] As used herein, the term "communication network" refers to a network that follows any suitable communication standard (such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), etc.). In addition, the communication between the terminal device and the network node in the communication network may be performed according to any suitable generation of communication protocol, including but not limited to the first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), 4G, 4.5G, 5G communication protocols and / or any other protocol known currently or to be developed in the future.

[0046] As used herein, the terms "first", "second", etc. refer to different elements. Unless the context clearly indicates otherwise, the singular forms "a" and "an" are also intended to include the plural forms. As used herein, the terms "comprises", "comprising", "has", "having", "includes" and / or "including" specify the presence of the stated features, elements, and / or components, etc., but do not preclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. The term "based on" will be understood to mean "at least partially based on". The terms "one embodiment" and "an embodiment" will be understood to mean "at least one embodiment". The term "another embodiment" will be understood to mean "at least one other embodiment". Other definitions, whether explicit or implicit, may be included below.

[0047] As used herein, a network "node" may be implemented as a network element on dedicated hardware, a software instance running on dedicated hardware, or a virtualized function instantiated on a suitable platform (e.g., cloud infrastructure).

[0048] Figure 1 is a diagram showing an example of EPS fallback for IMS voice according to an embodiment of the present disclosure. In Figure 1 some exemplary network elements are depicted, such as a UE, an NG-RAN, an evolved universal terrestrial radio access network (E-UTRAN), an access and mobility management function, and a mobility management entity (AMF-MME), a serving gateway (SGW), a PGW-C-SMF (also referred to as PGW-C+SMF or PGW-SMF in some embodiments), a policy charging function (PCF), a proxy call session control function (P-CSCF), and an IMS-Core. According to Figure 1In the illustrated embodiment, in step 101, IMS PDU session establishment and IMS registration in 5GS can be implemented for the UE. Then in step 102, an SIP call can be initiated in 5GS, and the P-CSCF can receive SIP signaling for call establishment, such as via "SIP INVITE / SIP 18x". In step 103, the P-CSCF can request voice resource reservation in 5GS from the PCF and subscribe to "Internet Protocol Connectivity Access Network (IP CAN) change", such as via a signaling message such as Authentication Authorization Request / Authentication Authorization Answer (AAR / AAA). In step 104, the PCF can request voice resource reservation in 5GS (e.g., voice QoS flow reservation) from the PGW-C-SMF and subscribe to "Radio Access Technology (RAT) type change", such as via a signaling message such as Npcf_SMPolicyControl_UpdateNotify. In step 105, the PGW-C-SMF can initiate voice QoS flow establishment. For example, the network (NW) can initiate a PDU session modification to establish a QoS flow for IMS voice. The NG-RAN can reject the QoS flow establishment and trigger EPS fallback. Accordingly, due to IMS voice EPS fallback, the NG-RAN can notify the PGW-C-SMF of the rejection.

[0049] In step 106, the NG-RAN can initiate a handover or redirection to EPS. Then in step 107, the SGW can send a modify bearer request to the PGW-C-SMF. After establishing an IMS Packet Data Network (PDN) connection in EPS, in step 108, the PGW-C-SMF can report the RAT type change to the PCF, such as via a signaling message such as Npcf_SMPolicyControl_UpdateNotify. In step 109, the PCF can report the IP CAN change to the P-CSCF, such as via a signaling message such as Re-Authentication Request / Re-Authentication Answer (RAR / RAA). At this time, the P-CSCF can know that EPS fallback has occurred. In step 110, the PGW-C-SMF can send a modify bearer response to the SGW. After the handover is completed in step 111, the IMS PDN connection is ready in EPS. In step 112, the PGW-C-SMF can send a create bearer request to the SGW. In the case of creating a dedicated bearer in step 113, in step 114, the SGW can send a create bearer response to the PGW-C-SMF. Accordingly, in step 115, the PGW-C-SMF can report successful resource allocation to the PCF and then to the P-CSCF.

[0050] Although SIP signaling exchange between the UE and the IMS network may still be ongoing during a handover or redirection to EPS, the default QoS flow or default bearer for IMS signaling may be unavailable for a certain period of time. There may be some options to avoid SIP signaling loss in EPS fallback. For example, in one option, the 5GS and the RAN may need to support a forwarding tunnel (direct or indirect tunnel), but in the initial commercial deployment, most products may not support this option, e.g., due to its complexity. Alternatively, signaling caching and delayed transmission may be used in the IMS / P-CSCF and the UE. Since the IMS / P-CSCF cannot distinguish between EPS fallback and VoNR, the signaling caching and delayed transmission scheme can be used for VoNR. In a case where an IMS network supports both VoNR and EPS fallback, this alternative option may extend the setup time for VoNR. There is no solution in 3GPP to notify the P-CSCF of EPS fallback early to avoid the impact on VoNR.

[0051] There are many problems in the existing solutions. For example, due to complexity, some 5GC and RAN products may not support the forwarding tunnel in customer trial tests and initial commercial launches. Even with signaling (e.g., Session Initiation Protocol / Transmission Control Protocol (SIP / TCP) signaling) retransmission, call establishment may still fail due to SIP signaling loss. On the other hand, setting up a forwarding tunnel in the 5GC or the RAN may extend the HO duration and ultimately the call establishment time. Also, in a case where an IMS network serves both VoNR and EPS fallback, SIP signaling caching and delayed transmission between the IMS P-CSCF and the UE may affect the VoNR call establishment time. During EPC fallback, the signaling bearer may be temporarily unavailable. However, for VoLTE and VoNR, the signaling bearer can always be available. This may be a dilemma for the P-CSCF. For example, if the P-CSCF continues the SIP signaling, in the case of EPC fallback, it may cause SIP retransmission (UDP) or TCP retransmission (TCP) with exponentially increasing retransmission intervals. This extends the call establishment. If the P-CSCF holds the SIP signaling for some time, in the case of EPC fallback, it can reduce the call establishment time. But for VoLTE and VoNR, this is completely unnecessary and it may extend the call establishment.

[0052] Figure 2 is a diagram showing an example of retransmission during EPC fallback according to an embodiment of the present disclosure. For simplicity, Figure 2Only exemplary elements in a communication system are depicted, such as a UE and a P-CSCF. In fact, a communication system may also include any additional elements suitable for supporting communication between wireless devices or between a wireless device and another communication device (such as a landline phone, a service provider, or any other network node or terminal device). The communication system may provide communication and various types of services to one or more wireless devices to facilitate access of the wireless devices to the communication system and / or use of the services provided by or via the communication system.

[0053] The initial part of the IMS INVITE (call session) establishment process is schematically described with respect to steps 201 - 216. As Figure 2 shown, the calling party may initiate 201 an INIVTE session (call) to the called party (i.e., the originating UE). The P-CSCF may forward 202 the INVITE to the UE. The UE may respond 203 with a "183 Session Description Protocol (SDP)", which may be forwarded 204 by the P-CSCF to the calling party. In this example, the P-CSCF may send 205 an AAR to request a dedicated bearer for IMS media (e.g., as described in connection with Figure 1 step 103). This may trigger EPS fallback, as described with respect to Figure 1 . According to the Figure 2 process shown, some signaling exchanges may occur between the calling party and the called party through the P-CSCF, for example, through signaling messages such as "PRACK" and "200 PRACK" in steps 206 - 209. EPS fallback may not be initiated until step 209, and the default bearer for IMS signaling may still be available in the 5G / NR network. Thus, there may still be an opportunity for some subsequent signaling to flow between the two parties.

[0054] In the Figure 2 example shown, radio communication may be falling back from the 5G / NR network to the 4G / LTE network, and no default bearer is available. The P-CSCF may not be aware that EPS fallback has been triggered. In this case, the P-CSCF may receive 210 a SIP UPDATE message and forward 211 the SIP UPDATE message to the UE, which may not have any default bearer. It can be appreciated that since no default bearer is available, the SIP UPDATE message may be retransmitted 212 - 213 to the UE. If the UPDATE message cannot reach the UE, retransmission of the SIP message from the P-CSCF to the UE may occur. In the case of the User Datagram Protocol (UDP), the retransmission time may be one second, which is more than the EPS fallback time. Thus, retransmission may increase the call establishment time. Only when the P-CSCF receives 214 an IP CAN change notification (e.g., as described in connection withFigure 1 As described in step 109 of (), by comparing the "Netloc" received in the "PANI" provided by the user in the INVITE and the received RAT type, the P-CSCF can know that this is EPS fallback. Then, the retransmission 215 of the UPDATE message can reach the UE. In response, the UE can send back "200 UPDATE" at 216 to indicate the reception of the UPDATE message.

[0055] To enhance transmission efficiency and improve network performance, various embodiments of the present invention propose a solution to solve the SIP signaling loss in EPS fallback. According to the proposed solution, 5GC EPS fallback events can be notified to specific network elements (such as policy nodes (such as PCF), IMS nodes (such as P-CSCF), combined function nodes (such as PGW+SMF, etc.)) to optimize call establishment, such as IMS call establishment, for example, by reducing the call establishment time for 5GC EPC fallback events. According to an exemplary embodiment, the PGW+SMF can report the EPS fallback event to the PCF immediately after receiving the EPS fallback indicator from the NG-RAN, and the PCF can report the EPS fallback event to the IMS (such as to the P-CSCF). Therefore, the IMS can know about EPS fallback earlier and process SIP signaling in an enhanced manner, such as buffering the signaling or extending the retransmission time until the PDN connection and the default bearer are ready in EPS (such as when the P-CSCF receives a change in the RAT type).

[0056] Figure 3 is a diagram showing an example of EPS fallback subscription and reporting according to an embodiment of the present disclosure. Similar to Figure 1 , Figure 3 depicts some exemplary network elements, such as UE, NG-RAN, E-UTRAN, AMF-MME, SGW, PGW-C-SMF, PCF, P-CSCF, and IMS-Core. Different from the process shown in Figure 1 , the process shown in Figure 3 introduces new event subscriptions and reports on the interface (such as N7) between the PGW-C-SMF and the PCF and on the interface (such as N5 / Rx) between the PCF and the P-CSCF. It can be understood that although only the Rx case is shown in Figure 3 , the proposed solution can also be applied to the N5 case or other possible cases.

[0057] According to Figure 3For the process shown, in step 301, IMS PDU session establishment and IMS registration in 5GS can be implemented for the UE. Then in step 302, a SIP call can be initiated in 5GS, and the P-CSCF can receive SIP signaling for call establishment, for example, via "SIP INVITE / SIP 18x". In step 303, the P-CSCF can request voice resource reservation in 5GS and subscribe to "IP CAN change" and "IMS voice EPS fallback" from the PCF, for example, via signaling messages such as AAR / AAA. In step 304, the PCF can request voice resource reservation in 5GS (e.g., voice QoS flow reservation) and subscribe to "RAT type change" and "IMS voice EPS fallback" from the PGW-C-SMF, for example, via signaling messages such as Npcf_SMPolicyControl_UpdateNotify. In step 305, the PGW-C-SMF can initiate voice QoS flow establishment. For example, the NW can initiate a PDU session modification to establish a QoS flow for IMS voice. The NG-RAN can reject the QoS flow establishment and trigger EPS fallback. Accordingly, due to IMS voice EPS fallback, the NG-RAN can notify the PGW-C-SMF of this rejection.

[0058] According to an exemplary embodiment, in step 306, the PGW-C-SMF can report "IMS voice EPS fallback" to the PCF, for example, via signaling messages such as Npcf_SMPolicyControl_UpdateNotify. Then in step 307, the PCF can report "IMS voice EPS fallback" to the P-CSCF, for example, via signaling messages such as RAR / RAA. At this time, the P-CSCF can know that EPS fallback has occurred. In step 308, the P-CSCF can process the SIP signaling in an optimized manner, for example, as described in Figure 4 .

[0059] According to Figure 3In the process shown, in step 309, the NG-RAN may initiate a handover or redirection to EPS, and in step 310, the SGW may send a modify bearer request to the PGW-C-SMF. After the IMS PDN connection is established in EPS, in step 311, the PGW-C-SMF may report the RAT type change to the PCF, for example, via a signaling message such as Npcf_SMPolicyControl_UpdateNotify. In step 312, the PCF may report the IP CAN change to the P-CSCF, for example, via a signaling message such as RAR / RAA. The IP CAN change report received by the P-CSCF may indicate the success of EPS fallback with a default bearer. After receiving the IP CAN change report, the P-CSCF may process the SIP signaling in a normal manner (e.g., as described regarding Figure 1 ), and resume or continue call establishment in step 313.

[0060] Similar to the process as shown in Figure 1 , Figure 3 the PGW-C-SMF in

[0061] Figure 4 may send a modify bearer response to the SGW in step 314. After the handover is completed in step 315, the IMS PDN connection is ready in EPS. In step 316, the PGW-C-SMF may send a create bearer request to the SGW. In the case of creating a dedicated bearer in step 317, in step 318, the SGW may send a create bearer response to the PGW-C-SMF. Correspondingly, in step 319, the PGW-C-SMF may report successful resource allocation to the PCF and then to the P-CSCF.

[0061] Figure 4 FIG. Figure 2 is a diagram showing an example of SIP message processing according to an embodiment of the present disclosure. Similar to Figure 4 , Figure 2 depicts exemplary elements in a communication system, such as a UE and a P-CSCF. Different from the process shown in Figure 4 , Figure 4 the process shown in Figure 4 introduces some enhanced SIP signaling processing in the P-CSCF. It can be understood that although it is described regarding Figure 4 how the P-CSCF may process SIP messages based on the Rx event report for IMS call EPS fallback, however, the proposed solution may also be applicable to the N5 case or other possible cases.

[0062] Similar to Figure 2 , the initial part of the IMS INVITE (call session) establishment process is schematically described regarding steps 401 - 414. As shown in Figure 4As shown, the calling party may initiate a 401 INVITE session (call) to the called party (i.e., the originating UE). The P-CSCF may forward 402 the INVITE to the UE. The UE may respond 403 with “183 SDP”, which may be forwarded 404 by the P-CSCF to the calling party. In this example, the P-CSCF may send 405 an AAR to request a dedicated bearer for IMS media (e.g., as described in step 303 in connection with Figure 3 ). According to an exemplary embodiment, EPS fallback events and / or IP-CAN change events may be subscribed to, and the AAR may trigger EPS fallback, as described with respect to Figure 3 .

[0063] According to Figure 4 the process shown, some signaling exchanges may occur between the calling party and the called party through the P-CSCF, e.g., via signaling messages such as “PRACK” and “200 PRACK” in steps 406-409. The fallback may not be initiated until step 409, and the default bearer for IMS signaling may still be available in the 5G / NR network. Thus, there may still be an opportunity for some subsequent signaling to flow between the two parties.

[0064] In Figure 4 the example shown, the P-CSCF may receive 410 an EPS fallback notification (e.g., as indicated in step 307 in Figure 3 ). This may be an indication that EPS fallback is about to start. According to an embodiment, the radio communication may be falling back from the 5G / NR network to the 4G / LTE network and no default bearer is available. The P-CSCF may receive 411 a SIP UPDATE message and hold 411a the signaling message to the UE that may not have any default bearers. Thus, retransmission of SIP messages by the calling party may be avoided. This may reduce session establishment latency. In this case, the held signaling message (such as the SIP UPDATE message) will be forwarded. It can be appreciated that the signaling message to be forwarded may be any other signaling message, depending on the call flow and network latency situation. In response to receiving 412 an IP-CAN change notification (e.g., as described in step 312 in connection with Figure 3 ), the P-CSCF may know that the default bearer is available. The P-CSCF may send 413 the buffered UPDATE message to the called UE. In response, the UE may send 414 back “200 UPDATE” to indicate receipt of the UPDATE message.

[0065] It can be understood that Figures 1 to 4The signaling messages and network elements shown are merely examples, and according to the exemplary embodiments of the present disclosure, more or fewer alternative signaling messages and network elements may be involved in call establishment.

[0066] Note that some embodiments of the present disclosure are mainly described with respect to 5G or NR specifications that serve as non-limiting examples of certain exemplary network configurations and system deployments. Accordingly, the description of the exemplary embodiments given herein specifically references terms directly relevant thereto. Such terms are used only in the context of the non-limiting examples and embodiments presented and do not in any way naturally limit the present disclosure. On the contrary, any other system configuration or radio technology may be similarly utilized as long as the exemplary embodiments described herein are applicable.

[0067] Figure 5 is a flowchart showing a method 500 according to some embodiments of the present disclosure. Figure 5 The method 500 shown may be performed by a session management node or a device communicatively coupled to the session management node. According to an exemplary embodiment, the session management node may include a PGW-SMF, a PGW+SMF, a PGW-C-SMF (such as Figure 3 the PGW-C-SMF shown) or any other suitable network entity or instance that may act as a packet gateway supporting session management functions.

[0068] According to Figure 5 the exemplary method 500 shown, the session management node may receive an EPS fallback indicator from a mobility management node (e.g., Figure 3 the AMF-MME shown in ), as shown in block 502. According to an exemplary embodiment, the EPS fallback indicator may indicate that a fallback to EPS for IMS voice services is in progress. Based on the EPS fallback indicator, the session management node may report an EPS fallback event to a policy charging node (e.g., Figure 3 the PCF shown in ), as shown in block 504.

[0069] According to some exemplary embodiments, the EPS fallback event may be reported to the policy charging node in response to a subscription by the policy charging node to the EPS fallback event. Optionally, the subscription by the policy charging node to the EPS fallback event may be notified to the session management node in a first notification from the policy charging node (e.g., Figure 3 the "Npcf_SMPolicyControl_UpdateNotify" shown in step 304 of ).

[0070] In an exemplary embodiment, it may be in a second notification from the session management node (e.g., Figure 3Report the EPS fallback event to the policy charging node in "Npcf_SMPolicyControl_UpdateNotify" as shown in step 306.

[0071] Figure 6 is a flowchart showing a method 600 according to some embodiments of the present disclosure. Figure 6 The method 600 shown can be executed by a policy charging node or a device communicatively coupled to the policy charging node. According to an exemplary embodiment, the policy charging node may include a PCF (such as Figure 3 the PCF shown in

[0072] According to Figure 6 the exemplary method 600 shown, the policy charging node can receive an EPS fallback event report from a session management node (e.g., the session management node described with respect to Figure 5 ), as shown in block 602. According to the EPS fallback event report, the policy charging node can report the EPS fallback event to a call control node (e.g., Figure 3 and Figure 4 the P-CSCF shown in Figure 3 ), as shown in block 604. In an exemplary embodiment, the EPS fallback event can be reported to the call control node in a re-authentication request from the policy charging node (e.g., the RAR shown in step 307 of

[0073] According to some exemplary embodiments, the EPS fallback event can be reported to the call control node in response to a subscription by the call control node to the EPS fallback event. Optionally, the subscription of the call control node to the ESP fallback event can be notified to the policy charging node in an authentication authorization request from the call control node (e.g., the AAR shown in step 303 of Figure 3 ).

[0074] Figure 7 is a flowchart showing a method 700 according to some embodiments of the present disclosure. Figure 7 The method 700 shown can be executed by a call control node or a device communicatively coupled to the call control node. According to an exemplary embodiment, the call control node may include a P-CSCF (such as Figure 3 and Figure 4 the P-CSCF shown in

[0075] According to Figure 7 the exemplary method 700 shown, the call control node can receive from a policy charging node (e.g., as described with respect toFigure 6 The described policy charging node) receives an EPS fallback event report, as shown in block 702. According to some exemplary embodiments, the EPS fallback event report may be received in a re-authentication request from the policy charging node (e.g., Figure 3 the RAR shown in step 307 of ). The call control node may process the signaling at least in part based on the EPS fallback event report, as shown in block 704. According to some exemplary embodiments, processing the signaling may include at least one of the following: buffering call establishment signaling (e.g., SIP UPDATE messages, etc.), extending the transmission time of the call establishment signaling (e.g., the (re-)transmission time of SIP UPDATE messages, etc.), and holding one or more SIP signals. It will be appreciated that in response to the EPS fallback event report, the call control node may be able to process any possible message signaling in any suitable manner.

[0076] According to some exemplary embodiments, in response to a subscription by the call control node to an EPS fallback event, an EPS fallback event report may be received from the policy charging node. Optionally, the subscription by the call control node to the ESP fallback event may be notified to the policy charging node in an authentication authorization request from the call control node (e.g., Figure 3 the AAR shown in step 303 of ).

[0077] According to some exemplary embodiments, the call control node may resume call establishment in response to an access type change event. According to some exemplary embodiments, the access type change event may include at least one of the following: a RAT type change event, and an IP CAN change event. Alternatively or additionally, the access type change event may include any other suitable event indicating a change in radio communication connectivity.

[0078] The proposed solution according to some exemplary embodiments can solve the problem of SIP signaling loss in EPS fallback. In an exemplary embodiment, a functional node such as a PGW-SMF can report an EPS fallback event to a PCF immediately after receiving an EPS fallback indicator from the NG-RAN, and the PCF can report the EPS fallback event to a P-CSCF for IMS. Thus, the P-CSCF / IMS can know the EPS fallback in a timely manner and process SIP signaling in a flexible and efficient way, for example, by buffering the signaling or extending the (re)transmission time until the PDN connection and the default bearer are ready in EPS (e.g., in the case where the P-CSCF receives a change in RAT type). The proposed solution can avoid SIP signaling loss in EPS fallback and ensure a successful call. Some embodiments can be applied in the early stage of the introduction / deployment of Standalone (SA) 5GS, for example, as a quick solution for customer trial testing and early commercial deployment. Compared with the solution of the forwarding tunnel in 5GC and RAN, the proposed solution can simplify network implementation. On the other hand, some embodiments can be implemented as a network-based method for identifying EPS fallback and can avoid or reduce the impact on the call establishment time of VoNR.

[0079] Figures 5 to 7 Each block shown can be regarded as a method step, and / or an operation resulting from computer program code, and / or a plurality of coupled logic circuit elements configured to perform the associated (one or more) functions. The schematic flowcharts described above are generally presented as logical flowcharts. Thus, the depicted order and the labeled steps indicate particular embodiments of the presented method. Other steps and methods can be envisioned that are equivalent in function, logic, or effect to one or more steps or portions thereof of the shown method. Additionally, the order in which a particular method occurs can or can not strictly adhere to the order of the corresponding steps shown.

[0080] Figure 8 is a block diagram showing an apparatus 800 according to various embodiments of the present disclosure. As Figure 8 shown, the apparatus 800 can include one or more processors (such as a processor 801) and one or more memories (such as a memory 802 storing computer program code 803). The memory 802 can be a non-transitory machine / processor / computer-readable storage medium. According to some exemplary embodiments, the apparatus 800 can be implemented as an integrated circuit chip or module that can be inserted into or installed in a session management node as described with respect to Figure 5 as described with respect to Figure 6 a policy charging node as described with respect to Figure 7 a call control node as described with respect toFigure 5 The described session management node, such as regarding Figure 6 The described policy charging node or such as regarding Figure 7 The described call control node.

[0081] In some embodiments, one or more memories 802 and computer program code 803 may be configured to, together with one or more processors 801, cause the apparatus 800 to perform at least any of the operations of the method as described in connection with Figure 5 The described method. In some embodiments, one or more memories 802 and computer program code 803 may be configured to, together with one or more processors 801, cause the apparatus 800 to perform at least any of the operations of the method as described in connection with Figure 6 The described method. In other embodiments, one or more memories 802 and computer program code 803 may be configured to, together with one or more processors 801, cause the apparatus 800 to perform at least any of the operations of the method as described in connection with Figure 7 The described method. Alternatively or additionally, one or more memories 802 and computer program code 803 may be configured to, together with one or more processors 801, cause the apparatus 800 to perform more or fewer operations of implementing the proposed method according to the exemplary embodiments of the present disclosure.

[0082] Figure 9 Is a block diagram showing an apparatus 900 according to some embodiments of the present disclosure. As Figure 9 Shown, the apparatus 900 may include a receiving unit 901 and a reporting unit 902. In an exemplary embodiment, the apparatus 900 may be implemented in a session management node, such as Figure 3 The PGW-SMF shown in. The receiving unit 901 may be operable to perform the operation in block 502, and the reporting unit 902 may be operable to perform the operation in block 504. Optionally, the receiving unit 901 and / or the reporting unit 902 may be operable to perform more or fewer operations of implementing the proposed method according to the exemplary embodiments of the present disclosure.

[0083] Figure 10 Is a block diagram showing an apparatus 1000 according to some embodiments of the present disclosure. As Figure 10 Shown, the apparatus 1000 may include a receiving unit 1001 and a reporting unit 1002. In an exemplary embodiment, the apparatus 1000 may be implemented in a policy charging node, such as Figure 3The PCF shown in []. The receiving unit 1001 may be operable to perform the operations in block 602, and the reporting unit 1002 may be operable to perform the operations in block 604. Optionally, the receiving unit 1001 and / or the reporting unit 1002 may be operable to perform more or fewer operations for implementing the proposed method according to an exemplary embodiment of the present disclosure.

[0084] Figure 11 is a block diagram showing a device 1100 according to some embodiments of the present disclosure. As Figure 11 shown, the device 1100 may include a receiving unit 1101 and a processing unit 1102. In an exemplary embodiment, the device 1100 may be implemented in a call control node, such as Figure 3 and Figure 4 the P-CSCF shown in []. The receiving unit 1101 may be operable to perform the operations in block 702, and the processing unit 1102 may be operable to perform the operations in block 704. Optionally, the receiving unit 1101 and / or the processing unit 1102 may be operable to perform more or fewer operations for implementing the proposed method according to an exemplary embodiment of the present disclosure.

[0085] Generally, the various exemplary embodiments may be implemented in hardware or a dedicated chip, circuit, software, logic, or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software executable by a controller, microprocessor, or other computing device, but the present disclosure is not limited thereto. Although aspects of the exemplary embodiments of the present disclosure may be illustrated and described as block diagrams, flowcharts, or using some other graphical representation, it should be understood that, by way of non-limiting example, the blocks, devices, systems, techniques, or methods described herein may be implemented in hardware, software, firmware, a dedicated circuit or logic, general hardware or a controller, or other computing device, or some combination thereof.

[0086] Accordingly, it should be understood that at least some aspects of the exemplary embodiments of the present disclosure may be practiced in various components, such as integrated circuit chips and modules. Accordingly, it should be understood that the exemplary embodiments of the present disclosure may be implemented in a device implemented as an integrated circuit, where the integrated circuit may include circuitry (and possibly firmware) for implementing at least one or more of the following: a data processor, a digital signal processor, a baseband circuit, and a radio frequency circuit configurable to operate according to an exemplary embodiment of the present disclosure.

[0087] It should be understood that at least some aspects of the exemplary embodiments of the present disclosure may be implemented in computer-executable instructions executed by one or more computers or other devices, such as in one or more program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types when executed by a processor in a computer or other device. The computer-executable instructions may be stored on a computer-readable medium, such as a hard disk, optical disk, removable storage medium, solid-state memory, random access memory (RAM), etc. As will be understood by those skilled in the art, in various embodiments, the functions of the program modules may be combined or distributed as desired. Additionally, the functionality may be implemented in whole or in part in firmware or hardware equivalents, such as integrated circuits, field-programmable gate arrays (FPGAs), etc.

[0088] The present disclosure includes any novel features or combinations of features or any generalizations thereof explicitly disclosed herein. Various modifications and adaptations of the foregoing exemplary embodiments of the present disclosure may become apparent to those skilled in the relevant art when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of the present disclosure.

Claims

1. A method performed by a session management node, comprising: receiving an evolved packet system (EPS) fallback indicator from a mobility management node, wherein the EPS fallback indicator indicates that a fallback to EPS for Internet Protocol Multimedia Subsystem (IMS) voice services is in progress; and reporting an EPS fallback event to a policy charging node according to the EPS fallback indicator in response to a subscription of the policy charging node to the EPS fallback event, wherein the subscription of the policy charging node to the EPS fallback event is notified to the session management node in a first notification from the policy charging node.

2. The method according to claim 1, wherein the EPS fallback event is reported to the policy charging node in a second notification from the session management node.

3. A method performed by a policy charging node, comprising: receiving an evolved packet system (EPS) fallback event report from a session management node; and reporting the EPS fallback event to a call control node according to the EPS fallback event report in response to a subscription of the call control node to the EPS fallback event, wherein the subscription of the call control node to the EPS fallback event is notified to the policy charging node in an authentication and authorization request from the call control node.

4. The method according to claim 3, wherein the EPS fallback event is reported to the call control node in a re-authentication request from the policy charging node.

5. A method performed by a call control node, comprising: receiving an EPS fallback event report from a policy charging node in response to a subscription of the call control node to an evolved packet system (EPS) fallback event, wherein the subscription of the call control node to the EPS fallback event is notified to the policy charging node in an authentication and authorization request from the call control node; and processing signaling at least partially based on the EPS fallback event report.

6. The method according to claim 5, wherein the receiving also responds to an Internet Protocol Connectivity Access Network (IP-CAN) change event, receiving the EPS fallback event report in a re-authentication request from the policy charging node, wherein the processing further comprises: receiving a Session Initiation Protocol (SIP) UPDATE message; holding the transmission of the SIP UPDATE message to a user equipment when the user equipment does not have a default bearer; and resuming call establishment in response to receiving the IP-CAN change event indicating that the default bearer is available.

7. A session management node, comprising: one or more processors; and one or more memories storing computer program code, wherein the one or more memories and the computer program code are configured to, together with the one or more processors, cause the session management node to perform the method according to any one of claims 1 to 2.

8. A policy charging node, comprising: one or more processors; and one or more memories storing computer program code, The one or more memories and the computer program code are configured to, with the one or more processors, cause the policy charging node to perform the method according to any one of claims 3 to 4.

9. A call control node, comprising: one or more processors; and one or more memories storing computer program code, the one or more memories and the computer program code are configured to, with the one or more processors, cause the call control node to perform the method according to any one of claims 5 to 6.

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