Patent Publication Number: US-2022232046-A1

Title: 5g system (5gs) failure detection monitoring of proxy - call session control function (p-cscf) of an internet protocol (ip) multimedia system (ims) for efficient restoration of ims service

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to telecommunications systems, and more particularly to 5G System (5GS) failure detection monitoring of a Proxy-Call Session Control Function (P-CSCF) of an Internet Protocol (IP) Multimedia System (IMS) for efficient restoration of IMS service for multiple mobile devices. 
     BACKGROUND 
     Traditionally, voice call services have been provided over a circuit-switched type network. Today, voice and video call services for mobile devices may be provided over an IP packet-switched network using an IP Multimedia Subsystem (IMS). In general, IMS is an architectural framework for delivering IP multimedia services. Voice and video call services based on IMS are critical services that every service provider (SP) mobile operator would like to offer. 
     In a Fifth Generation (5G) network, a Voice over New Radio (VoNR) service may be offered. VoNR provides significantly lower latency and improved sound &amp; picture quality, resulting in an extremely elevated calling experience. An SP mobile operator would like to ensure that services, such as VoNR, are provided with high availability and reliability. Given that service failures may occur, an efficient service failure detection and restoration should be considered. 
     In a 5G system (5GS) deployment, a Proxy-Call Session Control Function (P-CSCF) is the IMS core component that performs IMS signaling processing for IMS services. To establish service, a user equipment (UE) may receive a P-CSCF address of the P-CSCF in a message which includes a Protocol Configuration Options (ePCO) container. During operation, the P-CSCF may fail and, as a result, service may become unavailable. 
     An SP mobile operator should expect that failures of IMS components/instances are quickly detected by the 5G core for proactive restoration of services to all impacted voice or video call users—not merely a reactive restoration of service for a single user at a time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the present disclosure can be understood by those of ordinary skill in the art, a more detailed description may be had by reference to aspects of some illustrative implementations, some of which are shown in the accompanying drawings. 
         FIG. 1A  is an illustrative representation of a basic network architecture of a Fifth Generation (5G) network; 
         FIG. 1B  is an illustrative representation of a more detailed network architecture of the 5G network of  FIG. 1A , showing a Service-Based Architecture (SBA) or an enhanced SBA (eSBA) of the 5G network; 
         FIG. 1C  is an illustration of a network architecture including one or more IP Multimedia Subsystem (IMS) networks that may interconnect with the 5G network of  FIG. 1B ; 
         FIG. 2  is a flowchart for describing a method of failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure (e.g. for 3GPP Pre-Release 16); 
         FIG. 3  is an illustration of a network node arrangement involving a message flow for describing failure detection monitoring of an application or control function for efficient restoration according to some implementations (e.g. for 3GPP Pre-Release 16); 
         FIG. 4  is a call flow diagram for describing a call flow for failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure (e.g. for 3GPP Pre-Release 16); 
         FIG. 5A  is a flowchart for describing a method of failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure, which may be a first type of failure detection monitoring procedure (e.g. for 3GPP Release 16); 
         FIG. 5B  is a flowchart for describing a method of failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure, which may be a second type of failure detection monitoring procedure (e.g. for 3GPP Pre-Release 16); 
         FIG. 6  is a call flow diagram for describing a call flow for failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure (e.g. for 3GPP Release 16); 
         FIGS. 7A-7B  are illustrative representations of network node arrangements involving first and second parts of message flows for use in failure detection monitoring of an application or control function according to some implementations of the present disclosure (e.g. for 3GPP Release 16); 
         FIG. 8  is an illustrative example of a data table of stored information (e.g. at the SMF) for a plurality of application or control functions, including stored associations between a plurality of address informations of the application or control functions and a respective plurality of monitoring type indications associated with the application or control functions (e.g. for both for 3GPP Pre-Release 16 and 3GPP Release 16); 
         FIG. 9  is a flowchart for describing a method for use in failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure, which involves the use of the first and the second types of failure detection monitoring procedures (e.g. the methods of  FIG. 5A and 5B , respectively) (e.g. for both 3GPP Pre-Release 16 and 3GPP Release 16); and 
         FIG. 10  illustrates a hardware block diagram of a computing device that may perform functions associated with operations discussed herein. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Numerous details are described in order to provide a thorough understanding of the example implementations shown in the drawings. However, the drawings merely show some example aspects of the present disclosure and are therefore not to be considered limiting. Those of ordinary skill in the art will appreciate that other effective aspects and/or variants do not include all of the specific details described herein. Moreover, well-known systems, methods, components, devices and circuits have not been described in exhaustive detail so as not to obscure more pertinent aspects of the example implementations described herein. 
     Overview 
     Techniques and mechanisms for 5G system (5GS) failure detection monitoring of an application or control function in a network for efficient restoration of service are described herein. The network may be an Internet Protocol (IP) Multimedia Subsystem (IMS) network and the voice or data service may be an IMS service that utilizes Session Initiation Protocol (SIP) signaling. The application or control function may be a Proxy-Call Session Control Function (P-CSCF) of the IMS network; alternatively, the application or control function may be an application function (AF). 
     In a first aspect of the present disclosure, a UPF of a mobile network may be configured to forward traffic for a voice or data service between one or more UEs operative in the mobile network and an application or control function of a network. In some implementations, the UPF may receive, from an SMF, a message which includes address information of the application or control function and store the address information in memory. The UPF may invoke a failure detection monitoring procedure for monitoring the application or control function associated with the address information of the application or control function. The failure detection monitoring procedure may include regularly performing a ping procedure (or health check procedure) with the application or control function using the address information. Sometime during operation, the UPF may identify a failure of the application or control function from the failure detection monitoring procedure. Based on the identifying, the UPF may send, to the SMF, a message for reporting the failure of the application or control function. The message may trigger, at the SMF, an initiation of an address list update procedure for a reselection of a new application or control function of the network for the voice or data service by the one or more UEs. The one or more UEs may be a plurality of UEs which are updated with new address information for the voice or data service. In some implementations, the ping procedure may involve sending a SIP OPTIONS message to query for operational status of the application or control function. In other implementations, the ping procedure may involve sending an ICMP echo request message to the application or control function. According to the first aspect, the UPF which performs the failure detection monitoring procedure may be for use in the mobile network which interconnects to the IMS network via a Diameter Rx interface or an SBI without eSBA support (e.g. 3GPP Pre-release 16). 
     In a second aspect of the present disclosure, an SMF of the mobile network may be configured to manage one or more sessions of a UPF which is operative to forward traffic for a voice or data service between one or more UEs in the mobile network and an application or control function of a network. The SMF may invoke a failure detection monitoring procedure for monitoring the application or control function associated with address information which is stored at the SMF. In the failure detection monitoring procedure, the SMF may receive, from an NRF, a message comprising a notification or response which indicates a failure of the application or control function of the network. Based on receiving the message comprising the notification or response which indicates the failure, the SMF may initiate an address list update procedure for a reselection of a new application or control function for the voice or data service by the one or more UEs. The one or more UEs may be a plurality of UEs which are updated with new address information for the voice or data service. In some implementations, invoking the failure detection monitoring procedure may involve subscribing to notifications of the NRF based on the address information for identifying failure of the application or control function. In other implementations, invoking the failure detection monitoring procedure may involve initiating a regular sending, to the NRF, of a message which indicates a request for information associated with the application or control function for identifying failure of the application or control function. According to the second aspect, the SMF which performs the failure detection monitoring procedure may be configured for use in the mobile network which interconnects to the IMS network via the SBI with the eSBA support (e.g. 3GPP Release 16). 
     In a third aspect of the present disclosure, an SMF may maintain access to stored information for a plurality of selected application or control functions, including stored associations between a plurality of address informations of the selected application or control functions and a respective plurality of capability indications associated with the selected application or control functions. The SMF may invoke one of a first or a second type of failure detection monitoring procedure for a given one of the selected application or control functions based on a respective one of the capability indications associated therewith. In some implementations, the SMF may obtain a capability indication associated with address information of an application or control function which is stored at the SMF. If the capability indication indicates a first type of capability, the SMF may invoke the first type of failure detection monitoring procedure for monitoring the application or control function. On the other hand, if the capability indication indicates a second type of capability, the SMF may invoke the second type of failure detection monitoring procedure for monitoring the application or control function. In some implementations, the first type of failure detection monitoring procedure may be for use in a mobile network which interconnects to the IMS network via the SBI with the eSBA support (e.g. 3GPP Release 16). The second type of failure detection monitoring procedure may be for use in a mobile network which interconnects to the IMS network via a Diameter Rx interface or an SBI without eSBA support (e.g. 3GPP Pre-release 16). 
     Again, an SMF may maintain access to stored information for a plurality of selected application or control functions, and these selected application or control functions may include first and second application or control functions. In some preferred implementations of the third aspect, the SMF may invoke the first type of failure detection monitoring procedure for monitoring the first application or control function of a first network associated with first address information which is stored at the SMF. In the first type of failure detection monitoring procedure, the SMF may receive, from the NRF, a message comprising a notification or response which indicates a failure of the first application or control function of the first network. Based on receiving the message comprising the notification or response which indicates the failure, the SMF may initiate a first address list update procedure for a reselection of a first new application or control function for the voice or data service. The one or more UEs may be a plurality of UEs which are updated with new address information for the voice or data service. In some implementations, invoking the first type of failure detection monitoring procedure may involve subscribing to notifications of the NRF based on the first address information for identifying failure of the first application or control function. In other implementations, invoking the first type of failure detection monitoring procedure may involve initiating a regular sending, to the NRF, of a message which indicates a request for information associated with the first application or control function for identifying failure of the first application or control function. Also in the third aspect, the SMF may invoke the second type of failure detection monitoring procedure for monitoring the second application or control function of a second network associated with second address information which is stored at the SMF. Here, invoking the second type of failure detection monitoring procedure may involve sending, to the UPF, a message for configuring the second address information of the second application or control function in the UPF, so that the UPF is enabled to regularly perform a ping procedure (or health check procedure) with the second application or control function using the second address information. In the second type of failure detection monitoring procedure, the SMF may receive, from the UPF, a message for reporting a failure of the second application or control function. Based on receiving the message for reporting the failure, the SMF may initiate initiating a second address list update procedure for a reselection of a second new application or control function of the second network for the voice or data service. The one or more UEs may be a plurality of UEs which are updated with new address information for the voice or data service. In some implementations, the ping procedure may involve sending a SIP OPTIONS message to query for operational status of the second application or control function. In other implementations, the ping procedure may involve sending an ICMP echo request message to the second application or control function. 
     More detailed and alternative techniques and implementations are provided herein as described below. 
     EXAMPLE EMBODIMENTS 
     Techniques and mechanisms for Fifth Generation (5G) System (5GS) monitoring and detection of failure of a Proxy-Call Session Control Function (P-CSCF) of an IP Multimedia System (IMS) for efficient restoration of IMS service for multiple mobile devices are described herein. Other more detailed and alternative techniques and mechanisms of the present disclosure are described herein as well. 
     In some implementations of the present disclosure, a failure detection monitoring procedure may be compatible with the Third Generation Partnership Project (3GPP) Pre-Release 16 standard for 5G to support a Legacy Diameter Rx interface or a Service-Based Interface (SBI) without enhanced Service-Based Architecture (eSBA) support. With this failure detection monitoring procedure (e.g. with corresponding inventive method, mechanism, network element, and/or system), the 5GS monitoring and detection of failure of a P-CSCF may involve a session management function (SMF) programming of a user plane function (UPF) for UPF monitoring of the P-CSCF, using a ping procedure (or health check procedure), for (e.g. a more proactive) restoration of service for multiple mobile devices in response to P-CSCF failure. The ping procedure may involve a Session Initiation Protocol (SIP) OPTIONS ping or an Internet Control Message Protocol (ICMP) ping. 
     In other implementations of the present disclosure, a failure detection monitoring procedure may be compatible with 3GPP Release 16 standard for 5G to support SBI with eSBA support in both the 5G Core and the IMS core. With this failure detection monitoring procedure (e.g. with corresponding inventive method, mechanism, network element, and/or system), the 5GS monitoring and detection of failure of a P-CSCF may involve SMF monitoring of a P-CSCF via a Network Function (NF) Repository Function (NRF), using a subscription-notification or a request-response mechanism, for (e.g. a more proactive) restoration of service for multiple mobile devices in response to P-CSCF failure. 
     In yet other implementations of the present disclosure, the failure detection monitoring procedures may be utilized for compatibility with both 3GPP Pre-Release 16 and 3GPP Release 16 standards for 5G. With these failure detection monitoring procedures (e.g. with corresponding inventive method, mechanism, network element, or system), the 5GS monitoring and detection of failure of a P-CSCF may involve detection or identification of a capability associated with the P-CSCF (e.g. one of the 3GPP Pre-Release 16 or 3GPP Release 16 standard) and performance of the appropriate failure detection monitoring based on the detection or identification. 
     To better illustrate,  FIG. 1A  is an illustrative representation of a general network architecture  100 A of a 5G network. Network architecture  100 A includes common control network functions (CCNF)  105  and a plurality of slice-specific core network functions  106 . With network architecture  100 A, the 5G network may be configured to facilitate communications for a UE  102 . UE  102  may obtain access to the 5G network via a radio access network (RAN) or a Next Generation (NG) RAN (NG-RAN)  104 . NG-RAN  104  may include one or more base stations or gNodeBs (gNBs), such as a gNB  107 . UE  102  may be any suitable type of device, such as a cellular telephone, a smart phone, a tablet device, an Internet of Things (IoT) device, a Machine-to-Machine (M2M) device, and a sensor, to name but a few. 
     Network architecture  100 A of the 5G network includes an SBA which may provide a modular framework from which common applications can be deployed using components of varying sources and suppliers. The SBA of the 5G network may be configured such that control plane functionality and common data repositories are provided by way of a set of interconnected NFs, each with authorization to access each other&#39;s services. 
     Accordingly, CCNF  105  includes a plurality of NFs which commonly support all sessions for UE  102 . UE  102  may be connected to and served by a single CCNF  105  at a time, although multiple sessions of UE  102  may be served by different slice-specific core network functions  106 . CCNF  105  may include, for example, an Access and Mobility Management Function (AMF) and a Network Slice Selection Function (NSSF). UE-level mobility management, authentication, and network slice instance selection are examples of functionalities provided by CCNF  105 . On the other hand, slice-specific core network functions  106  of the network slices may be separated into control plane (CP) NFs  108  and user plane (UP) NFs  110 . In general, the user plane carries user traffic while the control plane carries network signaling. CP NFs  108  are shown in  FIG. 1A  as CP NF 1 through CP NF n, and UP NFs  110  are shown in  FIG. 1A  as UP NF 1 through UP NF n. CP NFs  108  may include, for example, an SMF, whereas UP NFs  110  may include, for example, a UPF. 
       FIG. 1B  is an illustrative representation of a more detailed network architecture  100 B of the 5G network of  FIG. 1A . As provided in 3GPP standards for 5G (e.g. 3GPP Technical Specifications or “TS” 23.501 and 23.502), network architecture  100 B for the 5G network may include an AMF  112 , an Authentication Server Function (AUSF)  114 , a Policy Control Function (PCF)  116 , an SMF  118 , and a UPF  120  which may connect to a Data Network (DN)  122 . Other NFs in the 5G network include an NSSF  134 , a network exposure function (NEF)  136 , an NRF  132 , and a Unified Data Management (UDM) function  130 . A plurality of interfaces and/or reference points N 1 -N 8 , N 10 -N 13 , and N 15  shown in  FIG. 1B  (as well as others) may define the communications and/or protocols between each of the entities, as described in the relevant (evolving) standards documents. 
     In  FIG. 1B , UPF  120  is part of the user plane and all other NFs (i.e. AMF  112 , AUSF  114 , PCF  116 , SMF  118 , and UDM  130 ) are part of the control plane. UPF  120  may carry data traffic in a session for UE  102  which is managed by SMF  118  over an N 4  interface using a Packet Forwarding Control Protocol (PFCP). Separation of user and control planes guarantees that each plane resource may be scaled independently. It also allows UPFs to be deployed separately from CP functions in a distributed fashion. The NFs in the CP are modularized functions; for example, AMF  112  and SMF  118  may be independent functions allowing for independent evolution and scaling. 
     The SBA of the 5G network is better illustrated in  FIG. 1B , again whereby the control plane functionality and common data repositories are provided by way of the set of interconnected NFs. Assuming the role of either service consumer or service producer, NFs may be self-contained, independent and reusable. With the SBA, each NF service may expose its functionality through an SBI message bus  150 . SBI message bus  150  may employ a Representational State Transfer (REST) interface (e.g. using Hypertext Transfer Protocol or “HTTP”/2). As indicated in  FIG. 1B , the SBI interfaces of SBI message bus  150  may include an Namf for AMF  112 , an Nausf for AUSF  114 , an Npcf for PCF  116 , an Nsmf for SMF  118 , an Nudm for UDM  130 , an Nnrf for NRF  132 , an Nnssf for NSSF  134 , an Nnef for NEF  136 , and an Naf for AF  140 . 
     Network slicing brings a high degree of deployment flexibility and efficient resource utilization when deploying diverse network services and applications. NSSF  134  may facilitate network slicing in the 5G network, as it operates to select network slice instances (NSIs) for UEs. A logical, end-to-end network slice may have predetermined capabilities, traffic characteristics, and service level agreements (SLAs), and may include the virtualized resources required to service the needs of a Mobile Virtual Network Operator (MVNO) or group of subscribers, including a dedicated UPF  120 , SMF  118 , and PCF  116 . 
     UDM  130  may provide services to SBA functions, such as AMF  112 , SMF  118  and NEF  136 . UDM  130  is typically recognized as a stateful message store, holding information in its local memory. Alternatively, UDM  130  may be stateless, storing information externally within a Unified Data Repository (UDR). UDM  130  may be considered to be analogous to a Home Subscriber Server (HSS), providing authentication credentials while being employed by AMF  112  and SMF  118  to retrieve subscriber data and context. 
     One or more application functions, such as an Application Function (AF)  140  may connect to the 5G network. AF  140  may interact with the network via NEF  136  in order to access network capabilities. NEF  136  may securely expose network capabilities and events provided by NFs to AF  140 , and may provide a means for AF  140  to securely provide information to the 5G network. 
     An NF instance is an identifiable instance of an NF. In general, NRF  132  may maintain NF profiles of available NF instances and their associated services, and support a service discovery function for service discovery associated with the NF profiles. NF profiles of NF instances maintained in NRF  132  may include NF instance ID, NF type (e.g. AMF, SMF, PCR, UPF, etc.), network slice identifiers such as NSI ID, NF capacity information, names of supported services, etc. For service discovery, NRF  132  may receive a discovery request from an NF instance and provide information associated with the discovered NF instance to the NF instance in response. 
     An eSBA architecture is defined in 3GPP TS 23.501 for Release 16 (see e.g. 3GPP TS 23.501, version 16.5.1 Release 16, 2020-08). The eSBA architecture introduces what are referred to as an NF Set and an NF Service Set. An NF Set is a group of interchangeable NF instances of the same type, supporting the same services and the same network slice. The NF instances of the same NF Set may be geographically distributed but have access to the same context data. On the other hand, an NF service is a functionality exposed by an NF through the SBI and consumed by other authorized NFs. An NF service instance is an identifiable instance of an NF service, and an NF service operation is an elementary unit that an NF service is composed of. An NF Service Set is a group of interchangeable NF service instances of the same service type within an NF instance. The NF service instances in the same NF Service Set have access to the same context data. 
       FIG. 1C  is an illustration of a network architecture  100 C including one or more IMS networks  180  and  190  that may interconnect with the 5G network of  FIG. 1B . More particularly, the 5G network may interconnect with IMS network  190  which is an SBI-compatible IMS network having an IMS core and one or more application or control functions. The one or more application or control functions of IMS network  190  may include an AF-1/P-CSCF-1  192  and an AF-2/P-CSCF-2  194 . In addition, or in the alternative, the 5G network may interconnect to IMS network  180  which is a legacy IMS network having an IMS core and one or more application or control functions. The one or more application or control functions of IMS network  180  may include an AF-3/P-CSCF-3  182  and an AF-4/P-CSCF-4  184 . 
     A P-CSCF is an IMS core component that performs IMS signaling processing for IMS services. To establish service, a UE may receive an address of the P-CSCF in a message which includes a Protocol Configuration Options (ePCO) container. During operation, the P-CSCF may fail and, as a result, service may become unavailable. However, a service provider (SP) should expect that failures of IMS components/instances are quickly detected by the 5G core, for proactive restoration of services to all impacted voice or video call users—not merely a reactive restoration of service for a single user at a time. Also, when a P-CSCF or P-CSCF service fails, it is possible that a failed or inaccessible P-CSCF would be included in an updated address list and sent to UEs during IMS Packet Data Unit (PDU) session setups (e.g. for new calls or as part of IMS restoration procedures). Further, if the P-CSCF fails after a PDU session is established, there is no current methodology to notify the UE about the failure of the P-CSCF until the UE initiates an IMS call (e.g. a UE-originated or terminated call). These issues would downgrade Key Performance Indicators (KPIs) for SIP and overall communication services served through the IMS PDU session. 
     Accordingly, techniques and mechanisms for 5GS monitoring and detection of failure of a P-CSCF of an IMS for efficient restoration of IMS service for multiple mobile devices are described herein. In some architecture configurations, IMS networks  180  and  190  may be 3GPP Pre-Release 16 compliant (e.g. Legacy Diameter Rx interface based, or Release 15 SBI based but without eSBA support) which may involve UPF-based failure detection monitoring according to the present disclosure. In other architecture configurations, IMS network  190  may be 3GPP Release 16 compliant (e.g. Release 16 SBI-based with eSBA support in both 5G Core and IMS core) which may involve SMF-based failure detection monitoring according to the present disclosure. 
     What is now described is a type of procedure involving a UPF-based failure detection monitoring (e.g. 3GPP Pre-Release 16 compliant; Legacy Diameter Rx interface based, or Release 15 SBI based but without eSBA support). 
       FIG. 2  is a flowchart  200  for describing a method for use in failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure. The method of  FIG. 2  involves a UPF-based failure detection monitoring which may be performed in relation to application or control functions in networks based on 3GPP Pre-release 16, Legacy Diameter Rx interface or SBI without eSBA support. The method of  FIG. 2  may be performed by a computing device or a network node configured to connect in a network for communication. In some implementations, the computing device or network node may include at least one or more interfaces configured to connect to a network for communication, one or more processors, one or more memory elements coupled to the one or more processors, and instructions stored in the one or more memory elements. The method may be embodied as a computer program product including a non-transitory computer readable medium (e.g. one or more memory elements) and instructions stored in the computer readable medium, where the instructions are executable on one or more processors for performing the steps of the method. In some implementations, the instructions stored in the one or more memory elements may be executable on the one or more processors for operation as a UPF. 
     In particular, the method of  FIG. 2  may be performed by a UPF which is configured to forward traffic for a voice or data service between one or more UEs operative in the mobile network and an application or control function of a network. Beginning at a start block  202 , the UPF may receive, from the SMF, a message which includes address information of the application or control function and store the address information in memory (step  204  of  FIG. 2 ). The UPF may invoke a failure detection monitoring procedure for monitoring the application or control function associated with the address information (step  206  of  FIG. 2 ). The failure detection monitoring procedure may include regularly performing a ping procedure (or health check procedure) with the application or control function using the address information. In some implementations, the ping procedure may involve sending a SIP OPTIONS message to query for operational status of the application or control function. In other implementations, the ping procedure may involve sending an ICMP echo request message to the application or control function. Sometime during operation, the UPF may identify a failure of the application or control function from the failure detection monitoring procedure (step  208  of  FIG. 2 ). Based on the identifying, the UPF may send, to the SMF, a message for reporting the failure of the application or control function (step  210  of  FIG. 2 ). The message for reporting the failure may be for triggering an initiation of an address list update procedure for a reselection of a new application or control function of the network for the voice or data service by the one or more UEs. Thus, in some implementations, the restoration procedure may be triggered for all users associated with a particular application or control function that was detected to have failed or become inaccessible. 
       FIG. 3  is an illustrative representation of a network node arrangement  300  with a message flow for describing failure detection monitoring of an application or control function for efficient restoration according to some implementations. As shown in  FIG. 3 , SMF  118  may send to UPF  120  a message which includes address information of P-CSCF-1  192 . UPF  120  may receive the message which includes the address information and store the address information in association with a rule for monitoring (“host monitor rule install”). In some implementations, the address information may include an IP address, a port number, and a protocol type (e.g. a first or a second protocol type, or ICMP or SIP OPTIONS type). In response, UPF  120  may invoke a failure detection monitoring procedure for monitoring the P-CSCF-1  192 . As shown, UPF  120  may perform the failure detection monitoring procedure which includes a regularly performing of a ping procedure (or health check procedure) with the P-CSCF-1  192  using the address information. Here, a SIP OPTIONS ping may be used for checking the health of the SIP service or process within the P-CSCF node of the IMS core, and a ICMP-based ping may be used generally to check if the P-CSCF node is alive or not. In the example of  FIG. 3 , UPF  120  may utilize a light-weight SIP protocol stub to monitor the operational status of the SIP service/process of P-CSCF-1  192 . 
       FIG. 4  is a call flow diagram  400  for describing a call flow for failure detection monitoring of an application or control function for efficient service restoration according to some implementations. The call flow of  FIG. 4  may involve the UPF-based failure detection monitoring of  FIGS. 2-3 , performed in relation to application or control functions in networks based on 3GPP Pre-release 16, Legacy Diameter Rx interface or SBI without eSBA support. In  FIG. 4 , UE  102  may send a message for registration in the mobile network and establish a PDU session via a PDU establishment procedure (step  402  of  FIG. 4 ). UE  102  has address information, stored in memory, associated with a P-CSCF for an IMS service. Using the address information, UE  102  may send to P-CSCF-1  192  a message for SIP registration (step  404  of  FIG. 4 ). P-CSCF-1  192  may then send to PCF  116  a message which includes the address information of P-CSCF-1  192  (step  406  of  FIG. 4 ) and PCF  116  sends a response back to P-CSCF-1  192  for acknowledgement (step  408  of  FIG. 4 ). PCF  116  may send to SMF  118  a message which includes a notification of the address information of P-CSCF-1  192  (step  410  of  FIGS. 4 ) and SMF  118  sends a response back to PCF  116  for acknowledgement (step  412  of  FIG. 4 ). 
     SMF  118  may then send to UPF  120  a message which includes address information of P-CSCF-1  192  (step  414  of  FIG. 4 ). UPF  120  may receive the message which includes the address information and store the address information in association with a rule for monitoring (“Host Monitoring rule is installed”). In some implementations, the address information may include an IP address, a port number, and a type (e.g. a first or a second protocol type, or an ICMP or SIP OPTIONS type). In response, UPF  120  may invoke a failure detection monitoring procedure for monitoring the P-CSCF-1  192  (step  416  of  FIG. 4 ). As shown, UPF  120  may perform the failure detection monitoring procedure which includes a regular or periodic performing of a ping procedure (or health check procedure) (e.g. a SIP OPTIONS ping) with the P-CSCF-1  192  using the address information (steps  418  and  420  of  FIG. 4 ). Here, UPF  120  may utilize a timer for the regular or periodic performing the ping procedure (or health check procedure). 
     In some implementations, UPF  120  may carry a light-weight SIP protocol stub to perform the SIP OPTIONS ping or a mechanism for an ICMP ping reachability check to monitor the operational status of the service. In particular implementations, the ping procedure may utilize SIP OPTIONS ping which is based on P. Jones, Internet Draft, “Using OPTIONS to Query for Operation Status in the Session Initiation Protocol (SIP),” draft-jones-sip-options-ping-01.txt, May 4, 2010. 
     Here, in step  418 , UPF  120  may send a SIP OPTIONS message to query for operational status of P-CSCF-1  192 . In step  420 , when the service of P-CSCF-1  192  is available, P-CSCF-1  192  may send back to UPF  120  a 200 OK message, where UPF  120  detects that P-CSCF-1  192  is reachable (step  421  of  FIG. 4 ). On the other hand, UPF  120  may send a SIP OPTIONS message to query for operational status of P-CSCF-1  192  (step  422  of  FIG. 4 ) and, when the service of P-CSCF-1  192  is unavailable, P-CSCF-1  192  may send back to UPF  120  a message with a response code of 503 or 486 (step  424  of  FIG. 4 ), where UPF  120  detects that P-CSCF-1  192  is unreachable (step  426  of  FIG. 4 ). 
     UPF  120  may employ a monitoring status update procedure (step  430  of  FIG. 4 ) to report host availability status and/or loss status to SMF  118 . Such a procedure may be or include a regular or periodic reporting or, alternatively, a detection-triggered based reporting. Here, UPF  120  may send to SMF  118  a message for reporting the failure/loss status of the P-CSCF-1  192  (step  428  of  FIG. 4 ). The message may be used for triggering an initiation of an address list update procedure with UE  102  and other UEs (step  432  of  FIG. 4 ), for a reselection of a new P-CSCF for the service by UE  102  as well as the other UEs. The reselection may be performed with use of a procedure for session release with reactivation (step  434  of  FIG. 4 ). 
     Thus, in some implementations, the restoration procedure may be triggered for all users associated with a particular P-CSCF that was detected to have failed or become inaccessible. When P-CSCF failure is detected, SMF  118  may refrain from sending the failed P-CSCF address to UE  102  and other UEs. In some implementations, SMF  118  may use restoration procedures based on 3GPP TS 23.380, Section 5.8.3.2, to send a new P-CSCF address to all UEs that are using UPF  120  that reported the P-CSCF service failure. Although this is a failure detection for a single UE  102 , the restoration action may be triggered for all UEs associated with that UPF  120  with the failed P-CSCF. This may therefore be considered to be a proactive IMS service recovery operation that is achieved for multiple UEs. In alternative implementations, SMF  118  may refrain from utilizing UPF  120  (e.g. isolate it) for a new IMS, DNN based PDU session. Even further, SMF  118  may switch (the anchor) UPF  120  for the sessions or force reactivation of IMS PDU session. 
     Note that 3GPP TS 29.244 (e.g. V16.6.0 (2020-12)), “Interface between the Control Plane and the User Plane nodes,” specifies the PFCP used on the interface between the CP function (e.g. the SMF) and the UP function (e.g. the UPF). In some implementations of the present disclosure, new features and information elements (IEs) may be defined in relation to the PFCP protocol stack (e.g. in relation to programming the UPF by the SMF, and/or in relation to UPF reporting of P-CSCF failure to the SMF). 
     In some implementations, a new feature in the CP Function Features of Section 8.2.58 of 3GPP TS 29.244 may be defined. This new feature may be referred to as an application function path status reporting (AFPSR) feature. In specific implementations that impact Table 8.2.58-1 of Section 8.2.58, the AFPSR may be associated with “Feature Octet/Bit=6/x”, “Interface=Sxb, N4”, and a description that the CP function supports the AF path Status Reporting feature, i.e. the receiving and handling of an AF path status Information IE (see clause 7.4.4.x). 
     In some implementations, a new feature in the UP Function Features of Section 8.2.25 of 3GPP TS 29.244 may be defined. This new feature may also be referred to as the AFPSR feature. In specific implementations that impact Table 8.2.25-1 of Section 8.2.25, the AFPSR feature may be associated with “Feature Octet/Bit=10/x”, “Interface =Sxb, N4”, and a description that the UP function supports performing a reachability test towards the application function and report the path status to the CP function. 
     In some implementations, a new information element in a PFCP Association Update Request of 3GPP TS 29.244 may be provided. This new information element may be referred to as an AF Path Information IE. In specific implementations that impact Table 7.4.4.3-1, the AF Path Information IE may be associated with “P=O ” and a condition/comment that the CP function may include it if both UP and CP functions support the AF path failure report feature; several IEs with same type may be present to represent path information of multiple application functions. For the PFCP Association Update Request, in a Section 7.4.4.3.x of 3GPP TS 29.244, the AF path information grouped IE may be encoded as shown in the following Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 AF Path Information IE within PFCP Association Update Request 
               
            
           
           
               
               
            
               
                 Octets 1 and 2 
                 AF Path Information IE Type = xxx (decimal) 
               
               
                 Octets 3 and 4 
                 Length = n 
               
            
           
           
               
               
               
               
               
            
               
                 Information 
                   
                   
                 Appl. 
                 IE  
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 elements 
                 P 
                 Condition/Comment 
                 Sxa 
                 Sxb 
                 Sxc 
                 N4 
                 Type 
               
               
                   
               
               
                 AF IP  
                 M 
                 This IE shall contain  
                 — 
                 X 
                 — 
                 X 
                 AF IP 
               
               
                 Address 
                   
                 an IPv4 and/or  
                   
                   
                   
                   
                 Address 
               
               
                   
                   
                 IPv6 address of an  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function  
                   
                   
                   
                   
                   
               
               
                   
                   
                 needs to be  
                   
                   
                   
                   
                   
               
               
                   
                   
                 monitored. 
                   
                   
                   
                   
                   
               
               
                 Path  
                 M 
                 This IE shall be  
                 — 
                 X 
                 — 
                 X 
                 Path 
               
               
                 Information 
                   
                 included to indicate  
                   
                   
                   
                   
                 Infor- 
               
               
                   
                   
                 the application/ 
                   
                   
                   
                   
                 mation 
               
               
                   
                   
                 transport protocol,  
                   
                   
                   
                   
                   
               
               
                   
                   
                 monitoring  
                   
                   
                   
                   
                   
               
               
                   
                   
                 and path status of the  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function 
               
               
                   
               
            
           
         
       
     
     In some implementations, a new information element in a PFCP Association Update Response of 3GPP TS 29.244 may be provided. This new information element may also be referred to as the AF Path Information IE. In specific implementations that impact Table 7.4.4.4-1, the AF Path Information IE may again be associated with “P=O” and a condition/comment that the CP function may include it if both UP and CP functions support the AF path failure report feature; several IEs with same type may be present to represent path information of multiple application functions. For the PFCP Association Update Response, in Section 7.4.4.4.x of 3GPP TS 29.244, the AF path information grouped IE may be encoded as shown in the following Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 AF Path Information IE within PFCP Association Update Response 
               
            
           
           
               
               
            
               
                 Octets 1 and 2 
                 AF Path Information IE Type = xxx (decimal) 
               
               
                 Octets 3 and 4 
                 Length = n 
               
            
           
           
               
               
               
               
               
            
               
                 Information 
                   
                   
                 Appl. 
                 IE  
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 elements 
                 P 
                 Condition/Comment 
                 Sxa 
                 Sxb  
                 Sxc 
                 N4 
                 Type 
               
               
                   
               
               
                 AF IP  
                 M  
                 This IE shall contain  
                 — 
                 X 
                 — 
                 X 
                 AF IP 
               
               
                 Address 
                   
                 an IPv4 and/or IPv6  
                   
                   
                   
                   
                 Address 
               
               
                   
                   
                 address of an  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function  
                   
                   
                   
                   
                   
               
               
                   
                   
                 needs to be  
                   
                   
                   
                   
                   
               
               
                   
                   
                 monitored. 
                   
                   
                   
                   
                   
               
               
                 Path 
                 M  
                 This IE shall be  
                 — 
                 X 
                 — 
                 X 
                 Path 
               
               
                 Information 
                   
                 included to  
                   
                   
                   
                   
                 Infor- 
               
               
                   
                   
                 indicate the 
                   
                   
                   
                   
                 mation 
               
               
                   
                   
                 application/transport 
                   
                   
                   
                   
                   
               
               
                   
                   
                 protocol, monitoring  
                   
                   
                   
                   
                   
               
               
                   
                   
                 and path status of the  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function. 
               
               
                   
               
            
           
         
       
     
     In some implementations, a new information element in a PFCP Node Report Request of 3GPP TS 29.244 may be provided. This new information element may also be referred to as the AF Path Information IE. In specific implementations that impact Table 7.4.5.1.1-1, the AF Path Information IE may again be associated with “P=O” and a condition/comment that the CP function may include it if both UP and CP functions support the AF path failure report feature; several IEs with same type may be present to represent path information of multiple application functions. For the PFCP Node Report Request, in Section 7.4.5.1.1 of 3GPP TS 29.244, the AF path information grouped IE may be encoded as shown below in the Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 AF Path Information IE within PFCP Node Report Request 
               
            
           
           
               
               
            
               
                 Octet 1 and 2 
                 AF Path Information IE Type = xxx (decimal) 
               
               
                 Octets 3 and 4 
                 Length = n 
               
            
           
           
               
               
               
               
               
            
               
                 Information 
                   
                   
                 Appl. 
                 IE  
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 elements 
                 P  
                 Condition/Comment 
                 Sxa 
                 Sxb  
                 Sxc 
                 N4 
                 Type 
               
               
                   
               
               
                 AF IP  
                 M 
                 This IE shall contain  
                 — 
                 X 
                 — 
                 X 
                 AF IP 
               
               
                 Address 
                   
                 an IPv4 and/or IPv6  
                   
                   
                   
                   
                 Address 
               
               
                   
                   
                 address of an  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function 
                   
                   
                   
                   
                   
               
               
                   
                   
                 needs to be monitored. 
                   
                   
                   
                   
                   
               
               
                 Path 
                 M 
                 This IE shall be  
                 — 
                 X 
                 — 
                 X 
                 Path 
               
               
                 Information 
                   
                 included to indicate  
                   
                   
                   
                   
                 Infor- 
               
               
                   
                   
                 the application/ 
                   
                   
                   
                   
                 mation 
               
               
                   
                   
                 transport protocol,  
                   
                   
                   
                   
                   
               
               
                   
                   
                 monitoring and  
                   
                   
                   
                   
                   
               
               
                   
                   
                 path status of the  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function. 
               
               
                   
               
            
           
         
       
     
     In some implementations, a new information element in a PFCP Node Report Response of 3GPP TS 29.244 may be provided. This new information element may also be referred to as the AF Path Information IE. In specific implementations that impact Table 7.4.5.1.1-1, the AF Path Information IE may again be associated with “P=O” and a condition/comment that the CP function may include it if both UP and CP functions support the AF path failure report feature; several IEs with same type may be present to represent path information of multiple application functions. In Section 7.4.5.1.1 of 3GPP TS 29.244, the AF path information grouped IE may be encoded as shown in the following Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 AF Path Information IE within PFCP Node Report Response 
               
            
           
           
               
               
            
               
                 Octets 1 and 2 
                 AF Path Information IE Type = xxx (decimal) 
               
               
                 Octets 3 and 4 
                 Length = n 
               
            
           
           
               
               
               
               
               
            
               
                 Information 
                   
                   
                 Appl. 
                 IE  
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 elements 
                 P 
                 Condition/Comment 
                 Sxa 
                 Sxb  
                 Sxc 
                 N4 
                 Type 
               
               
                   
               
               
                 AF IP 
                 M 
                 This IE shall contain  
                 — 
                 X 
                 — 
                 X 
                 AF IP 
               
               
                 Address 
                   
                 an IPv4 and/or  
                   
                   
                   
                   
                 Address 
               
               
                   
                   
                 IPv6 address of an  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function  
                   
                   
                   
                   
                   
               
               
                   
                   
                 needs to be  
                   
                   
                   
                   
                   
               
               
                   
                   
                 monitored. 
                   
                   
                   
                   
                   
               
               
                 Path 
                 O 
                 This IE shall be  
                 — 
                 X 
                 — 
                 X 
                 Path 
               
               
                 Information 
                   
                 included to indicate  
                   
                   
                   
                   
                 Infor- 
               
               
                   
                   
                 the application/ 
                   
                   
                   
                   
                 mation 
               
               
                   
                   
                 transport 
                   
                   
                   
                   
                   
               
               
                   
                   
                 protocol, monitoring  
                   
                   
                   
                   
                   
               
               
                   
                   
                 and path status of the  
                   
                   
                   
                   
                   
               
               
                   
                   
                 application function. 
               
               
                   
               
            
           
         
       
     
     The AF IP Address IE may contain an IPv4 and/or IPv6 address. It may be encoded as shown below in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 AF IP Address 
               
            
           
           
               
               
            
               
                   
                 Bits 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Octets 
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
               
               
                   
               
            
           
           
               
               
            
               
                 1 to 2 
                 Type = XXX (decimal) 
               
               
                 3 to 4 
                 Length = n 
               
            
           
           
               
               
               
               
            
               
                 5 
                 Spare 
                 V4 
                 V6 
               
            
           
           
               
               
            
               
                 p to (p + 3) 
                 IPv4 Address 
               
               
                 q to (q + 15) 
                 IPv6 Address 
               
               
                 m to (n + 4) 
                 These octet(s) is/are present  
               
               
                   
                 only if explicitly specified 
               
               
                   
               
            
           
         
       
     
     The following flags are coded within Octet 5:
         Bit 1-V6: If this bit is set to “1”, then the IPv6 address field may be present in the AF IP Address, otherwise the IPv6 address field shall not be present.   Bit 2-V4: If this bit is set to “1”, then the IPv4 address field may be present in the AF IP Address, otherwise the IPv4 address field may not be present.   Bit 3 to 8 Spare, for future use and set to “0”.
 
Octets “p to (p+3)” or “q to (q+15)” (IPv4 address/IPv6 address fields), if present, may contain the address value.
       

     The Path Information IE may be encoded as shown below in Table 6. It may indicate the application function monitoring status or “Monitor” (e.g. whether the Monitor is ON/OFF), the path status or “Path” (e.g. whether the Path is Accessible/Inaccessible), and the protocol type or “Protocol” (e.g. whether the Protocol is ICMP or PING). In some implementations, the Monitor, the Path, and Protocol may be defined as provided below in Tables 6A, 6B, and 6C, respectively. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Path Information IE 
               
            
           
           
               
               
            
               
                   
                 Bits 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Octets 
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
               
               
                   
               
            
           
           
               
               
            
               
                 1 to 2 
                 Type = xx (decimal) 
               
               
                 3 to 4 
                 Length = n 
               
            
           
           
               
               
               
               
               
            
               
                 5 
                 Spare 
                 Monitor 
                 Path 
                 Protocol 
               
            
           
           
               
               
            
               
                 6 to 
                 These octet(s) is/are present only  
               
               
                 (n + 4) 
                 if explicitly specified 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6A 
               
             
            
               
                   
               
               
                 Monitor 
               
            
           
           
               
               
               
            
               
                   
                   
                 Value 
               
               
                   
                 Monitor 
                 (Decimal) 
               
               
                   
               
               
                   
                 NA (Not Applicable) 
                 0 
               
               
                   
                 ON 
                 1 
               
               
                   
                 OFF 
                 2 
               
               
                   
                 For future use. Shall not be sent. If received,  
                 3 
               
               
                   
                 shall be interpreted as the value “0”. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6B 
               
             
            
               
                   
               
               
                 Path 
               
            
           
           
               
               
               
            
               
                   
                   
                 Value 
               
               
                   
                 Path 
                 (Decimal) 
               
               
                   
               
               
                   
                 NA (Not Applicable) 
                 0 
               
               
                   
                 ACCESSIBLE 
                 1 
               
               
                   
                 INACCESSIBLE 
                 2 
               
               
                   
                 For future use. Shall not be sent. If received,  
                 3 
               
               
                   
                 shall be interpreted as the value “1”. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6C 
               
             
            
               
                   
               
               
                 Protocol 
               
            
           
           
               
               
               
            
               
                   
                   
                 Value 
               
               
                   
                 Protocol 
                 (Decimal) 
               
               
                   
               
               
                   
                 ICMP 
                 0 
               
               
                   
                 SIP 
                 1 
               
               
                   
                 For future use. Shall not be sent. If received,  
                 2, 3 
               
               
                   
                 shall be interpreted as the value “0”. 
               
               
                   
               
            
           
         
       
     
     What is next described is a type of procedure involving a SMF-based failure detection monitoring (e.g. 3GPP Release 16 compliant; Release 16 SBI-based with eSBA support in both 5G Core and IMS core). 
       FIG. 5A  is a flowchart  500  for describing a method for use in failure detection monitoring of an application or control function for efficient service restoration according to some implementations. The method of  FIG. 5A  involves an SMF-based failure detection monitoring which may be performed in relation to application or control functions in networks based on 3GPP Release 16, SBI with eSBA support in both the 5G Core and the IMS core. The method of  FIG. 5A  may be performed by a computing device or a network node configured to connect in a network for communication. In some implementations, the computing device or network node may include at least one or more interfaces configured to connect to a network for communication, one or more processors, one or more memory elements coupled to the one or more processors, and instructions stored in the one or more memory elements. The method may be embodied as a computer program product including a non-transitory computer readable medium (e.g. one or more memory elements) and instructions stored in the computer readable medium, where the instructions are executable on one or more processors for performing the steps of the method. In some implementations, the instructions stored in the one or more memory elements may be executable on the one or more processors for operation as an SMF. 
     In particular, the method of  FIG. 5A  may be performed by an SMF configured to manage one or more sessions of a UPF which is operative to forward traffic for a voice or data service between one or more UEs in the mobile network and an application or control function of a network. Beginning at a start block  502 , the SMF may invoke a failure detection monitoring procedure for monitoring the application or control function associated with address information which is stored at the SMF (step  504  of  FIG. 5A ). In step  504 , invoking the failure detection monitoring procedure may involve subscribing to notification of the NRF based on the address for identifying failure of the application or control function (step  506  of  FIG. 5A ). Alternatively, in step  504 , invoking the failure detection monitoring procedure may involve initiating a regular sending of, to the NRF, a message which indicates a request for information associated with the application or control function for identifying failure of the application or control function (step  508  of  FIG. 5A ); this may be considered to be a dynamic querying of the NRF for status. Here, the SMF may utilize a timer for the regular or periodic querying for the information. In the failure detection monitoring procedure, the SMF may receive, from an NRF, a message comprising a notification or response which indicates a failure of the application or control function of the network (step  510  of  FIG. 5A ). Based on the receiving the message comprising the notification or response which indicates the failure, the SMF may initiate an address list update procedure for a reselection of a new application or control function of the network for the voice or data service by the one or more UEs (step  512  of  FIG. 5A ). 
     The SMF configured to perform the method of  FIG. 5A  may also control and/or manage the UPF-based failure detection monitoring as described above in relation to  FIGS. 2-4  (e.g. for 3GPP Pre-Release 16 compliant; Legacy Diameter Rx interface based, or Release 15 SBI based but without eSBA support), which is now described in relation to  FIG. 5B . 
       FIG. 5B  is a flowchart  520  for describing a method for use in failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure. The SMF method of  FIG. 5B  involves the UPF-based failure detection monitoring which may be performed in relation to application or control functions in networks based on 3GPP Pre-release 16, Legacy Diameter Rx interface or SBI without eSBA support. The method of  FIG. 5B  may be performed by a computing device or a network node configured to connect in a network for communication. In some implementations, the computing device or network node may include at least one or more interfaces configured to connect to a network for communication, one or more processors, one or more memory elements coupled to the one or more processors, and instructions stored in the one or more memory elements. The method may be embodied as a computer program product including a non-transitory computer readable medium (e.g. one or more memory elements) and instructions stored in the computer readable medium, where the instructions are executable on one or more processors for performing the steps of the method. In some implementations, the instructions stored in the one or more memory elements may be executable on the one or more processors for operation as an SMF. 
     In particular, the method of  FIG. 5B  may be performed by an SMF configured to manage one or more sessions of a UPF which is operative to forward traffic for a voice or data service between one or more UEs in the mobile network and an application or control function of a network. Beginning at a start block  522 , the SMF may invoke a failure detection monitoring procedure for monitoring the application or control function associated with address information which is stored at the SMF (step  524  of  FIG. 5B ). In step  524 , invoking the failure detection monitoring procedure may involve sending, to the UPF, a message for configuring the second address information of the second application or control function in the UPF, so that the UPF is enabled to regularly perform a ping procedure (or health check procedure) with the second application or control function using the second address information (step  526  of  FIG. 5B ). In the failure detection monitoring procedure, the SMF may receive, from the UPF, a message for reporting a failure of the second application or control function (step  528  of  FIG. 5B ). Based on the receiving the message for reporting the failure, the SMF may initiate an address list update procedure for a reselection of a new application or control function of the network for the voice or data service by the one or more UEs (step  530  of  FIG. 5B ). 
       FIG. 6  is a call flow diagram  600  for describing a call flow for failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure. The call flow of  FIG. 6  may involve the SMF-based failure detection monitoring as described in relation to  FIG. 5A , with respect to application or control functions in networks based on 3GPP Release 16, SBI with eSBA support in both the 5G Core and the IMS core. Initially, P-CSCF-1  192  may register with NRF  132  using an HTTP PUT request (step  604  of  FIG. 6 ) which is acknowledged by NRF  132  as created (step  606  of  FIG. 6 ). In addition, SMF  118  may have invoked a failure detection monitoring procedure with respect to P-CSCF-1  192 , by subscribing to notifications of NRF  132  based on address information of P-CSCF-1  192 , or by initiating a regular sending, to NRF  132 , of a message which indicates a request for information associated with P-CSCF-1  192  (e.g. a dynamic querying of NRF  132  for status). Here, SMF  118  may utilize a timer for the regular or periodic querying for the information. In some implementations, P-CSCF registration and subscriptions with NRF  132  may be performed based on the description in relation to  FIG. 7A-7B . 
     In  FIG. 6 , UE  102  may send a message for registration in the mobile network and establish a PDU session via a PDU establishment procedure (step  602  of  FIG. 6 ). UE  102  has address information, stored in memory, associated with a P-CSCF for an IMS service. Using the address information, UE  102  may send to P-CSCF-1  192  a message for SIP registration for the service (step  608  of  FIG. 6 ). P-CSCF-1  192  may then send to PCF  116  a message which includes the address information of P-CSCF-1  192  (step  610  of  FIG. 6 ), where PCF  116  sends a response back to P-CSCF-1  192  for acknowledgement (step  612  of  FIG. 6 ). PCF  116  may send to SMF  118  a message which includes a notification of the address information of P-CSCF-1  192  (step  614  of  FIG. 6 ), where SMF  118  sends a response back to PCF  116  for acknowledgement (step  616  of  FIG. 6 ). 
     Again, SMF  118  may have earlier invoked a failure detection monitoring procedure with respect to P-CSCF-1  192  (step  618  of  FIG. 6 ), by subscribing to notifications of NRF  132  based on address information of P-CSCF-1  192 , or by initiating a regular sending, to NRF  132 , of a message which indicates a request for information associated with P-CSCF-1  192 . In any event, SMF  118  may receive from NRF  132  a message comprising a notification or response which indicates a failure of P-CSCF-1  192 . In the example of  FIG. 6 , SMF  118  may send to NRF  132  a message indicating a request for information associated with P-CSCF-1  192  (e.g. a regular, dynamic querying of NRF  132  for status, for example, using a timer) (e.g. using an HTTP GET message) (step  620  of  FIG. 6 ) and may receive from NRF  132  the information associated with P-CSCF-1  192  (step  622  of  FIG. 6 ). The message in step  622  may be a message indicating a response which indicates a failure of P-CSCF-1  192 . The message may trigger an initiation of an address list update procedure with UE  102  as well as other UEs (step  624  of  FIG. 6 ), for a reselection of a new P-CSCF for the service by UE  102  as well as the other UEs. The reselection may be performed with use of a procedure for session release with reactivation (step  626  of  FIG. 6 ). 
     In some implementations of the present disclosure, the SMF may operate to refrain from including address information of a failed P-CSCF in a list within ePCO containers during IMS PDU establishment. Once the P-CSCF is detected to be available again, the SMF may then again offer the address information of the P-CSCF in the ePCO containers for new calls. 
     In additional or alternative implementations, the SMF may be configured with a retry or guard mechanism which provides one or more retries or delays prior to declaring an P-CSCF to be unavailable or inaccessible. This retry or guard mechanism may operate to retry a P-CSCF, after initial detection of its failure, a predetermined number of times or over a predetermined time period, prior to declaring the P-CSCF to be unavailable or inaccessible. 
     In other additional or alternative implementations, the SMF may be configured with a blacklisting mechanism for blacklisting a failed P-CSCF for a predetermined time period after detection of its failure. In response to an expiration of the predetermined time period, the SMF may operate to again check for accessibility or operational status of the P-CSCF and, if available, again offer the P-CSCF for new calls. 
       FIGS. 7A-7B  are illustrative representations of network node arrangements with first and second parts of message flows for use in failure detection monitoring of an application or control function according to some implementations of the present disclosure (e.g. for 3GPP Release 16), which may be used in relation to the SMF-based failure detection monitoring in  FIG. 5A  and/or the call flow of  FIG. 6 . 
       FIG. 7A  is an illustrative representation of a network node arrangement  700  involving a first part of a message flow (e.g. NRF registration and SMF-PCSCF binding) for use in failure detection monitoring of an application or control function according to some implementations of the present disclosure. The first part of the message flow may be performed prior to invoking the failure detection monitoring. Initially, P-CSCF-1  192  and P-CSCF-2  194  of the same set (e.g. P-CSCF Set 1) may register with NRF  132  with address information. Specifically, P-CSCF-1  192  may register with NRF  132 , indicating a P-CSCF Set 1 and an IP address 1, as well as a Service A (svc-a) with associated address information (e.g. an IP address and port number) and a Service B (svc-b) with associated address information (e.g. an IP address and port number) (step  0   a  of  FIG. 7A ). In addition, P-CSCF-2  194  may register with NRF  132 , indicating the P-CSCF Set 1 and an IP address 2, as well as the Service A (svc-a) with the associated address information (step  0   b  of  FIG. 7A ). After P-CSCF registration with NRF  132 , SMF  118  may send to NRF  132  a message indicating a request for profile information for the P-CSCFs (step  1  of  FIG. 7A ). NRF  132  may send back to SMF  118  a message indicating a response which includes the profile information of P-CSCF-1  192  and P-CSCF-2  194  (step  2  of  FIG. 7A ). SMF  118  may select the Service A (svc-a) of P-CSCF-1  192 , and send to NRF  132  a message indicating a binding indication for the Service A (svc-a) of P-CSCF-1  192  of Set 1 (step  3  of  FIG. 7A ). NRF  132  may send back to SMF  118  a message indicating a response which confirms creation of the binding (step  4  of  FIG. 7A ). 
       FIG. 7B  is an illustrative representation of the network node arrangement  700  of  FIG. 7A  involving a second part of the message flow (e.g. SMF detection of P-CSCF failure) for use in the failure detection monitoring of the application of control function according to some implementations of the present disclosure. The second part of the message flow involves the invoking of the failure detection monitoring and the P-CSCF failure detection. After NRF registration and SMF-PCSCF binding, SMF  118  may send to NRF  132  a request for subscribing to notifications of NRF  132  based on the address information, for identifying any service failure of P-CSCF-1  192  and P-CSCF-2  194  (step  0  of  FIG. 7B ). Sometime during operation, P-CSCF-1  192  may experience a service failure and NRF  132  may identify this service failure (step  1  of  FIG. 7B ). Being subscribed to notifications, SMF  118  may receive from NRF  132  a message comprising a notification which indicates a failure of the Service A (svc-a) P-CSCF-1  192  (step  2  of  FIG. 7B ). In response, SMF  118  may select the Service A (svc-a) of P-CSCF-2  194 , and send to NRF  132  a message indicating a binding indication for the Service A (svc-a) of P-CSCF-2  194  of Set 1 (step  3  of  FIG. 7B ). SMF  118  then initiates an address list update procedure for a reselection of the Service A (svc-a) of P-CSCF-2  194  for the UE as well as other UEs. 
     What is now described is a configuration utilizing both a first type of procedure involving a SMF-based failure detection monitoring (e.g. 3GPP Release 16 compliant; Release 16 SBI-based with eSBA support in both 5G Core and IMS core) (e.g.  FIGS. 5A, 6, and 7A-7B ) and a second type of procedure involving a UPF-based failure detection monitoring (e.g. 3GPP Pre-Release 16 compliant; Legacy Diameter Rx interface based, or Release 15 SBI based but without eSBA support) (e.g.  FIGS. 2-4 and 5B ). 
       FIG. 8  is an illustrative example of a data table  800  of stored information for a plurality of application or control functions (e.g. P-CSCFs or AFs). Data table  800  may be utilized for both a first type of procedure involving an SMF-based failure detection monitoring and a second type of procedure involving a UPF-based failure detection monitoring. The stored information may be stored at the SMF or at least locally accessible by the SMF. The stored information may include stored associations between a plurality of address informations of the application or control functions and a respective plurality of capability indications associated with the application or control functions. 
     As illustrated in the example of  FIG. 8 , a first entry  802  of data table  800  indicates a P-CSCF address of a first P-CSCF corresponding to “1.1.1.1” and having a Fully-Qualified Domain Name (FQDN) of “ims1.pcscf.domain.com”; a second entry  804  indicates a P-CSCF address of a second P-CSCF corresponding to “2.2.2.2” and having a FQDN of “ims2.pcscf.domain.com”; a third entry  806  indicates a P-CSCF address of a third P-CSCF corresponding to “3.3.3.3” and having a FQDN of “ims1.e-pcscfdomain.com”; and a fourth entry 808 indicates a P-CSCF address of a fourth P-CSCF corresponding to “4.4.4.4” and having a FQDN of “ims2.e-pcscf.domain.com”. Each entry of data table  800  may include an indication of the Service Set to which the P-CSCF belongs (e.g. fourth entry  808  of data table  800  belongs to the Service Set corresponding to “PCSCF1.APP”). 
     As further illustrated in the example of  FIG. 8 , each entry of data table  800  may include an indicator for P-CSCF service accessibility (e.g. Yes or No) which indicates whether the service is available or unavailable (e.g. detected failure). As further illustrated in the example of  FIG. 8 , each entry of data table  800  may include an indication for P-CSCF capability which indicates whether the P-CSCF is for 3GPP Release 16 (SBI with eSBA support in both the 5G Core and the IMS core) or for 3GPP Pre-release 16 (e.g. Legacy Diameter Rx interface or SBI without eSBA support). In some implementations, the SMF may invoke or utilize a first type of failure detection monitoring procedure for a P-CSCF associated with a first capability indication, and the SMF may invoke or utilize a second type of failure detection monitoring procedure for a P-CSCF associated with a second capability indication. See e.g. the method described in relation to  FIG. 9 . 
       FIG. 9  is a flowchart  900  for describing a method for use in failure detection monitoring of an application or control function for efficient service restoration according to some implementations of the present disclosure. The method of  FIG. 9  may be utilized for selection and use of a first type of procedure involving an SMF-based failure detection monitoring or a second type of procedure involving a UPF-based failure detection monitoring. The method of  FIG. 9  may be performed by a computing device or a network node (e.g. an SMF) configured to connect in a network for communication. In some implementations, the computing device or network node may include at least one or more interfaces configured to connect to a network for communication, one or more processors, one or more memory elements coupled to the one or more processors, and instructions stored in the one or more memory elements. The method may be embodied as a computer program product including a non-transitory computer readable medium (e.g. one or more memory elements) and instructions stored in the computer readable medium, where the instructions are executable on one or more processors for performing the steps of the method. In some implementations, the instructions stored in the one or more memory elements may be executable on the one or more processors for operation as an SMF. 
     In the method of  FIG. 9 , the SMFmay maintain access to stored information associated with a plurality of application or control functions (e.g. P-CSCFs or AFs). The plurality of application or control functions may be referred to as a plurality of selected application or control functions. The stored information may include stored associations between a plurality of address informations of these application or control functions and a respective plurality of capability indications associated with these application or control functions. For example, the SMF may maintain stored information and/or the data table  800  of  FIG. 8  as described above. 
     Beginning at a start block  902 , the SMFmay obtain a capability indication associated with address information of an application or control function which is stored at the SMF (step  904  of  FIG. 9 ). If the capability indication indicates a first type of capability (as identified at step  906  of  FIG. 9 ), the SMF may invoke a first type of failure detection monitoring procedure for monitoring the application or control function (step  908  of  FIG. 9 ). In some implementations, the first type of failure detection monitoring procedure may be the SMF-based failure detection monitoring procedure described in relation to the method of  FIG. 5A  (e.g. for 3GPP Release 16, SBI with eSBA support in both the 5G Core and the IMS core). On the other hand, if the capability indication indicates a second type of capability (as identified at step  906  of  FIG. 9 ), the SMF may invoke a second type of failure detection monitoring procedure for monitoring the application or control function (step  908  of  FIG. 9 ). In some implementations, the second type of failure detection monitoring procedure may be the UPF-based failure detection monitoring procedure described in relation to the method of  FIG. 5B  (e.g. for 3GPP Pre-release 16, Legacy Diameter Rx interface or SBI without eSBA support). 
       FIG. 10  illustrates a hardware block diagram of a computing device  1000  that may perform functions associated with operations discussed herein in connection with the techniques described in relation to the above figures, especially in relation to  FIGS. 2-4, 5A-5B, 6, 7A-7B, 8, and 9 . In various embodiments, a computing device, such as computing device  1000  or any combination of computing devices  1000 , may be configured as any entity/entities as discussed for the techniques depicted in connection with the figures in order to perform operations of the various techniques discussed herein. 
     In at least one embodiment, the computing device  1000  may include one or more processor(s)  1002 , one or more memory element(s)  1004 , storage  1006 , a bus  1008 , one or more network processor unit(s)  1010  interconnected with one or more network input/output (I/O ) interface(s)  1012 , one or more I/O interface(s)  1014 , and control logic  1020 . In various embodiments, instructions associated with logic for computing device  1000  can overlap in any manner and are not limited to the specific allocation of instructions and/or operations described herein. 
     In at least one embodiment, processor(s)  1002  is/are at least one hardware processor configured to execute various tasks, operations and/or functions for computing device  1000  as described herein according to software and/or instructions configured for computing device  1000 . Processor(s)  1002  (e.g., a hardware processor) can execute any type of instructions associated with data to achieve the operations detailed herein. In one example, processor(s)  1002  can transform an element or an article (e.g., data, information) from one state or thing to another state or thing. Any of potential processing elements, microprocessors, digital signal processor, baseband signal processor, modem, PHY, controllers, systems, managers, logic, and/or machines described herein can be construed as being encompassed within the broad term ‘processor’. 
     In at least one embodiment, memory element(s)  1004  and/or storage  1006  is/are configured to store data, information, software, and/or instructions associated with computing device  1000 , and/or logic configured for memory element(s)  1004  and/or storage  1006 . For example, any logic described herein (e.g., control logic  1020 ) can, in various embodiments, be stored for computing device  1000  using any combination of memory element(s)  1004  and/or storage  1006 . Note that in some embodiments, storage  1006  can be consolidated with memory element(s)  1004  (or vice versa), or can overlap/exist in any other suitable manner. 
     In at least one embodiment, bus  1008  can be configured as an interface that enables one or more elements of computing device  1000  to communicate in order to exchange information and/or data. Bus  1008  can be implemented with any architecture designed for passing control, data and/or information between processors, memory elements/storage, peripheral devices, and/or any other hardware and/or software components that may be configured for computing device  1000 . In at least one embodiment, bus  1008  may be implemented as a fast kernel-hosted interconnect, potentially using shared memory between processes (e.g., logic), which can enable efficient communication paths between the processes. 
     In various embodiments, network processor unit(s)  1010  may enable communication between computing device  1000  and other systems, entities, etc., via network I/O interface(s)  1012  to facilitate operations discussed for various embodiments described herein. In various embodiments, network processor unit(s)  1010  can be configured as a combination of hardware and/or software, such as one or more Ethernet driver(s) and/or controller(s) or interface cards, Fibre Channel (e.g., optical) driver(s) and/or controller(s), and/or other similar network interface driver(s) and/or controller(s) now known or hereafter developed to enable communications between computing device  1000  and other systems, entities, etc. to facilitate operations for various embodiments described herein. In various embodiments, network I/O interface(s)  1012  can be configured as one or more Ethernet port(s), Fibre Channel ports, and/or any other I/O port(s) now known or hereafter developed. Thus, the network processor unit(s)  1010  and/or network I/O interface(s)  1012  may include suitable interfaces for receiving, transmitting, and/or otherwise communicating data and/or information in a network environment. 
     I/O interface(s)  1014  allow for input and output of data and/or information with other entities that may be connected to computer device  1000 . For example, I/O interface(s)  1014  may provide a connection to external devices such as a keyboard, keypad, a touch screen, and/or any other suitable input and/or output device now known or hereafter developed. In some instances, external devices can also include portable computer readable (non-transitory) storage media such as database systems, thumb drives, portable optical or magnetic disks, and memory cards. In still some instances, external devices can be a mechanism to display data to a user, such as, for example, a computer monitor, a display screen, or the like. 
     In various embodiments, control logic  1020  can include instructions that, when executed, cause processor(s)  1002  to perform operations, which can include, but not be limited to, providing overall control operations of computing device; interacting with other entities, systems, etc. described herein; maintaining and/or interacting with stored data, information, parameters, etc. (e.g., memory element(s), storage, data structures, databases, tables, etc.); combinations thereof; and/or the like to facilitate various operations for embodiments described herein. 
     The programs described herein (e.g., control logic  1020 ) may be identified based upon application(s) for which they are implemented in a specific embodiment. However, it should be appreciated that any particular program nomenclature herein is used merely for convenience; thus, embodiments herein should not be limited to use(s) solely described in any specific application(s) identified and/or implied by such nomenclature. 
     In various embodiments, entities as described herein may store data/information in any suitable volatile and/or non-volatile memory item (e.g., magnetic hard disk drive, solid state hard drive, semiconductor storage device, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM), application specific integrated circuit (ASIC), etc.), software, logic (fixed logic, hardware logic, programmable logic, analog logic, digital logic), hardware, and/or in any other suitable component, device, element, and/or object as may be appropriate. Any of the memory items discussed herein should be construed as being encompassed within the broad term ‘memory element’. Data/information being tracked and/or sent to one or more entities as discussed herein could be provided in any database, table, register, list, cache, storage, and/or storage structure: all of which can be referenced at any suitable timeframe. Any such storage options may also be included within the broad term ‘memory element’ as used herein. 
     Note that in certain example implementations, operations as set forth herein may be implemented by logic encoded in one or more tangible media that is capable of storing instructions and/or digital information and may be inclusive of non-transitory tangible media and/or non-transitory computer readable storage media (e.g., embedded logic provided in: an ASIC, digital signal processing (DSP) instructions, software [potentially inclusive of object code and source code], etc.) for execution by one or more processor(s), and/or other similar machine, etc. Generally, memory element(s)  1004  and/or storage  1006  can store data, software, code, instructions (e.g., processor instructions), logic, parameters, combinations thereof, and/or the like used for operations described herein. This includes memory element(s)  1004  and/or storage  1006  being able to store data, software, code, instructions (e.g., processor instructions), logic, parameters, combinations thereof, or the like that are executed to carry out operations in accordance with teachings of the present disclosure. 
     In some instances, software of the present embodiments may be available via a non-transitory computer useable medium (e.g., magnetic or optical mediums, magneto-optic mediums, CD-ROM, DVD, memory devices, etc.) of a stationary or portable program product apparatus, downloadable file(s), file wrapper(s), object(s), package(s), container(s), and/or the like. In some instances, non-transitory computer readable storage media may also be removable. For example, a removable hard drive may be used for memory/storage in some implementations. Other examples may include optical and magnetic disks, thumb drives, and smart cards that can be inserted and/or otherwise connected to a computing device for transfer onto another computer readable storage medium. 
     Thus, techniques and mechanisms for 5GS failure detection monitoring of an application or control function in a network for efficient restoration of service have been described. The network may be an IMS network and the voice or data service may be an IMS service that utilizes SIP signaling. The application or control function may be a P-CSCF of the IMS network; alternatively, the application or control function may be an AF. 
     In a first aspect of the present disclosure, a UPF of a mobile network may be configured to forward traffic for a voice or data service between one or more UEs operative in the mobile network and an application or control function of a network. In some implementations, the UPF may receive, from an SMF, a message which includes address information of the application or control function and store the address information in memory. The UPF may invoke a failure detection monitoring procedure for monitoring the application or control function associated with the address information of the application or control function. The failure detection monitoring procedure may include regularly performing a ping procedure (or health check procedure) with the application or control function using the address information. Sometime during operation, the UPF may identify a failure of the application or control function from the failure detection monitoring procedure. Based on the identifying, the UPF may send, to the SMF, a message for reporting the failure of the application or control function. The message may trigger, at the SMF, an initiation of an address list update procedure for a reselection of a new application or control function of the network for the voice or data service by the one or more UEs. The one or more UEs may be a plurality of UEs which are updated with new address information (e.g. without the failed address information) for the voice or data service. In some implementations, the ping procedure may involve sending a SIP OPTIONS message to query for operational status of the application or control function. In other implementations, the ping procedure may involve sending an ICMP echo request message to the application or control function. According to the first aspect, the UPF which performs the failure detection monitoring procedure may be for use in a mobile network which interconnects to the IMS network via a Diameter Rx interface or an SBI without eSBA support (e.g. Pre-release 16). 
     In a second aspect of the present disclosure, an SMF of the mobile network may be configured to manage one or more sessions of a UPF which is operative to forward traffic for a voice or data service between one or more UEs in the mobile network and an application or control function of a network. The SMFmay invoke a failure detection monitoring procedure for monitoring the application or control function associated with address information which is stored at the SMF. In the failure detection monitoring procedure, the SMF may receive, from an NRF, a message comprising a notification or response which indicates a failure of the application or control function of the network. Based on receiving the message comprising the notification or response which indicates the failure, the SMFmay initiate an address list update procedure for a reselection of a new application or control function for the voice or data service by the one or more UEs. The one or more UEs may be a plurality of UEs which are updated with new address information (e.g. without the failed address information) for the voice or data service. In some implementations, invoking the failure detection monitoring procedure may involve subscribing to notifications of the NRF based on the address information for identifying failure of the application or control function. In other implementations, invoking the failure detection monitoring procedure may involve initiating a regular sending, to the NRF, of a message which indicates a request for information associated with the application or control function for identifying failure of the application or control function. According to the second aspect, the SMF which performs the failure detection monitoring procedure may be configured for use in a mobile network which interconnects to the IMS network via the SBI with the eSBA support (e.g. 3GPP Release 16). 
     In a third aspect of the present disclosure, an SMF may maintain access to (or store) stored information for a plurality of selected application or control functions, including stored associations between a plurality of address informations of the selected application or control functions and a respective plurality of capability indications associated with the selected application or control functions. The SMFmay invoke one of a first or a second type of failure detection monitoring procedure for a given one of the selected application or control functions based on a respective one of the capability indications associated therewith. In some implementations, the SMF may obtain a capability indication associated with address information of an application or control function which is stored at the SMF. If the capability indication indicates a first type of capability, the SMF may invoke the first type of failure detection monitoring procedure for monitoring the application or control function. On the other hand, if the capability indication indicates a second type of capability, the SMF may invoke the second type of failure detection monitoring procedure for monitoring the application or control function. In some implementations, the first type of failure detection monitoring procedure may be used for a mobile network which interconnects to the IMS network via the SBI with the eSBA support (e.g. Release 16). The second type of failure detection monitoring procedure may be used for a mobile network which interconnects to the IMS network via a Diameter Rx interface or an SBI without eSBA support (e.g. 3GPP Pre-release 16). 
     Again, an SMF may maintain access to stored information for a plurality of selected application or control functions, and these selected application or control functions may include first and second application or control functions. In some preferred implementations, the SMF may invoke the first type of failure detection monitoring procedure for monitoring the first application or control function of a first network associated with first address information which is stored at the SMF. In the first type of failure detection monitoring procedure, the SMF may receive, from the NRF, a message comprising a notification or response which indicates a failure of the first application or control function of the first network. Based on receiving the message comprising the notification or response which indicates the failure, the SMFmay initiate a first address list update procedure for a reselection of a first new application or control function for the voice or data service. The one or more UEs may be a plurality of UEs which are updated with new address information (e.g. without the failed address information) for the voice or data service. In some implementations, invoking the first type of failure detection monitoring procedure may involve subscribing to notifications of the NRF based on the first address information for identifying failure of the first application or control function. In other implementations, invoking the first type of failure detection monitoring procedure may involve initiating a regular sending, to the NRF, of a message which indicates a request for information associated with the first application or control function for identifying failure of the first application or control function. Also in the third aspect, the SMFmay invoke the second type of failure detection monitoring procedure for monitoring the second application or control function of a second network associated with second address information which is stored at the SMF. Here, invoking the second type of failure detection monitoring procedure may involve sending, to the UPF, a message for configuring the second address information of the second application or control function in the UPF, so that the UPF is enabled to regularly perform a ping procedure (or health check procedure) with the second application or control function using the second address information. In the second type of failure detection monitoring procedure, the SMFmay receive, from the UPF, a message for reporting a failure of the second application or control function. Based on receiving the message for reporting the failure, the SMFmay initiate initiating a second address list update procedure for a reselection of a second new application or control function of the second network for the voice or data service. The one or more UEs may be a plurality of UEs which are updated with new address information (e.g. without the failed address information) for the voice or data service. In some implementations, the ping procedure may involve sending a SIP OPTIONS message to query for operational status of the second application or control function. In other implementations, the ping procedure may involve sending an ICMP echo request message to the second application or control function. 
     As is apparent, with the solutions described herein, the KPIs for Voice over 5G New Radio (VoNR) service availability will be improved and the user experience for voice and video services may be enhanced. 
     Variations and Implementations 
     Embodiments described herein may include one or more networks, which can represent a series of points and/or network elements of interconnected communication paths for receiving and/or transmitting messages (e.g., packets of information) that propagate through the one or more networks. These network elements offer communicative interfaces that facilitate communications between the network elements. A network can include any number of hardware and/or software elements coupled to (and in communication with) each other through a communication medium. Such networks can include, but are not limited to, any local area network (LAN), virtual LAN (VLAN), wide area network (WAN) (e.g., the Internet), software defined WAN (SD-WAN), wireless local area (WLA) access network, wireless wide area (WWA) access network, metropolitan area network (MAN), Intranet, Extranet, virtual private network (VPN), Low Power Network (LPN), Low Power Wide Area Network (LPWAN), Machine to Machine (M2M) network, Internet of Things (IoT) network, Ethernet network/switching system, any other appropriate architecture and/or system that facilitates communications in a network environment, and/or any suitable combination thereof 
     Networks through which communications propagate can use any suitable technologies for communications including wireless communications (e.g., 4G/5G/nG, IEEE 802.11 (e.g., Wi-Fi®/Wi-Fi6®), IEEE 802.16 (e.g., Worldwide Interoperability for Microwave Access (WiMAX)), Radio-Frequency Identification (RFID), Near Field Communication (NFC), BluetoothTM, mm.wave, Ultra-Wideband (UWB), etc.), and/or wired communications (e.g., T1 lines, T3 lines, digital subscriber lines (DSL), Ethernet, Fibre Channel, etc.). Generally, any suitable means of communications may be used such as electric, sound, light, infrared, and/or radio to facilitate communications through one or more networks in accordance with embodiments herein. Communications, interactions, operations, etc. as discussed for various embodiments described herein may be performed among entities that may directly or indirectly connected utilizing any algorithms, communication protocols, interfaces, etc. (proprietary and/or non-proprietary) that allow for the exchange of data and/or information. 
     In various example implementations, entities for various embodiments described herein can encompass network elements (which can include virtualized network elements, functions, etc.) such as, for example, network appliances, forwarders, routers, servers, switches, gateways, bridges, loadbalancers, firewalls, processors, modules, radio receivers/transmitters, or any other suitable device, component, element, or object operable to exchange information that facilitates or otherwise helps to facilitate various operations in a network environment as described for various embodiments herein. Note that with the examples provided herein, interaction may be described in terms of one, two, three, or four entities. However, this has been done for purposes of clarity, simplicity and example only. The examples provided should not limit the scope or inhibit the broad teachings of systems, networks, etc. described herein as potentially applied to a myriad of other architectures. 
     Communications in a network environment can be referred to herein as ‘messages’, ‘messaging’, ‘signaling’, ‘data’, ‘content’, ‘objects’, ‘requests’, ‘queries’, ‘responses’, ‘replies’, etc. which may be inclusive of packets. As referred to herein and in the claims, the term ‘packet’ may be used in a generic sense to include packets, frames, segments, datagrams, and/or any other generic units that may be used to transmit communications in a network environment. Generally, a packet is a formatted unit of data that can contain control or routing information (e.g., source and destination address, source and destination port, etc.) and data, which is also sometimes referred to as a ‘payload’, ‘data payload’, and variations thereof. In some embodiments, control or routing information, management information, or the like can be included in packet fields, such as within header(s) and/or trailer(s) of packets. Internet Protocol (IP) addresses discussed herein and in the claims can include any IP version 4 (IPv4) and/or IP version 6 (IPv6) addresses. 
     To the extent that embodiments presented herein relate to the storage of data, the embodiments may employ any number of any conventional or other databases, data stores or storage structures (e.g., files, databases, data structures, data or other repositories, etc.) to store information. 
     Note that in this Specification, references to various features (e.g., elements, structures, nodes, modules, components, engines, logic, steps, operations, functions, characteristics, etc.) included in ‘one embodiment’, ‘example embodiment’, ‘an embodiment’, ‘another embodiment’, ‘certain embodiments’, ‘some embodiments’, ‘various embodiments’, ‘other embodiments’, ‘alternative embodiment’, and the like are intended to mean that any such features are included in one or more embodiments of the present disclosure, but may or may not necessarily be combined in the same embodiments. Note also that a module, engine, client, controller, function, logic or the like as used herein in this Specification, can be inclusive of an executable file comprising instructions that can be understood and processed on a server, computer, processor, machine, compute node, combinations thereof, or the like and may further include library modules loaded during execution, object files, system files, hardware logic, software logic, or any other executable modules. 
     It is also noted that the operations and steps described with reference to the preceding figures illustrate only some of the possible scenarios that may be executed by one or more entities discussed herein. Some of these operations may be deleted or removed where appropriate, or these steps may be modified or changed considerably without departing from the scope of the presented concepts. In addition, the timing and sequence of these operations may be altered considerably and still achieve the results taught in this disclosure. The preceding operational flows have been offered for purposes of example and discussion. Substantial flexibility is provided by the embodiments in that any suitable arrangements, chronologies, configurations, and timing mechanisms may be provided without departing from the teachings of the discussed concepts. 
     As used herein, unless expressly stated to the contrary, use of the phrase ‘at least one of’, ‘one or more of’, ‘and/or’, variations thereof, or the like are open-ended expressions that are both conjunctive and disjunctive in operation for any and all possible combination of the associated listed items. For example, each of the expressions ‘at least one of X, Y and Z’, ‘at least one of X, Y or Z’, ‘one or more of X, Y and Z’, ‘one or more of X, Y or Z’ and ‘X, Y and/or Z’ can mean any of the following: 1) X, but not Y and not Z; 2) Y, but not X and not Z; 3) Z, but not X and not Y; 4) X and Y, but not Z; 5) X and Z, but not Y; 6) Y and Z, but not X; or 7) X, Y, and Z. 
     Additionally, unless expressly stated to the contrary, the terms ‘first’, ‘second’, ‘third’, etc., are intended to distinguish the particular nouns they modify (e.g., element, condition, node, module, activity, operation, etc.). Unless expressly stated to the contrary, the use of these terms is not intended to indicate any type of order, rank, importance, temporal sequence, or hierarchy of the modified noun. For example, ‘first X’ and ‘second X’ are intended to designate two ‘X’ elements that are not necessarily limited by any order, rank, importance, temporal sequence, or hierarchy of the two elements. Further as referred to herein, ‘at least one of’ and ‘one or more of’ can be represented using the ‘(s)’ nomenclature (e.g., one or more element(s)). 
     One or more advantages described herein are not meant to suggest that any one of the embodiments described herein necessarily provides all of the described advantages or that all the embodiments of the present disclosure necessarily provide any one of the described advantages. Numerous other changes, substitutions, variations, alterations, and/or modifications may be ascertained to one skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and/or modifications as falling within the scope of the appended claims.