METHOD, SYSTEM AND APPARATUS OF TIME SYNCHRONIZATION SWITCHING

A wireless communication method for use in a first wireless network node is disclosed. The method includes receiving, from at least one second wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

TECHNICAL FIELD

This document is directed generally to wireless communications, and in particular to 5G communications.

BACKGROUND

Existing 5G systems (5GS) support time synchronization service to user equipment (UE). For example, an NG-RAN (next generation radio access network) can provide precise time information to the UE via a 5G AS (access stratum) signaling, which is called 5G access stratum time distribution. The 5GS (5G system) also supports a (g)PTP ((general) Precision Time Protocol) based time synchronization service, which depends on the 5G access stratum time distribution capability. To support the (g)PTP time synchronization service, the NG-RAN and a UPF/NW-TT (user plane function/network side Time Sensitive Network (TSN) translator) shall be time synchronized with a 5G internal GM (Grand master) clock.

In order to support a Disaster Tolerance, the 5GS needs to support a Timing Resiliency. That is, when a time source (i.e. 5G GM) fails or degrades, the time source can be switched to another 5G GM. Because the switching related to 5G GMs in the NG-RAN and the UPF/NW-TT are independent/asynchronous, the switching may cause the times of the NG-RAN and the UPF to be asynchronous in certain period. The (g)PTP base time synchronization may fail because of the time asynchronization.

SUMMARY

This document relates to methods, systems, and devices for time synchronization switching, and in particular to methods, systems, and devices for time synchronization switching for a 5GS.

The present disclosure relates to a wireless communication method for use in a first wireless network node. The method includes:receiving, from at least one second wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

Various embodiments may implement the following features.

In some embodiments, the time synchronization status information includes at least one of:information on at least one grandmaster clock candidate to which the grandmaster clock is switched, ora switching time configured for the switching of the grandmaster clock.

In some embodiments, the wireless communication method further includes transmitting, to the at least one second wireless network node, a time switch request associated with the switching of the grandmaster clock.

In some embodiments, the time switch request includes at least one of:information on a grandmaster clock candidate to which the grandmaster clock is switched, oran instructed switching time of switching the grandmaster clock to the grandmaster clock candidate.

In some embodiments, the information on the grandmaster clock candidate includes at least one of a grandmaster type, a grandmaster identifier, a grandmaster address or a grandmaster quality.

In some embodiments, the wireless communication method further includes transmitting, to the at least one second wireless network node, a subscription request for the time synchronization status information.

In some embodiments, the first wireless network node includes at least one of a session management function, a time sensitive communication and time synchronization function or a time sensitive networking adaptation function.

In some embodiments, the at least one second wireless network node includes at least one of a user plane function, a network time sensitive networking translator, or a radio access network node.

In some embodiments, the first network node includes a time sensitive communication and time synchronization function and/or a time sensitive networking adaptation function. In some embodiments, a signaling path between the first wireless network node and the at least one second wireless network node includes a policy control function and/or an access and mobility management function.

In some embodiments, the signaling path further includes a session management function.

The present disclosure further relates to a wireless communication method for use in a second wireless network node. The method includes:transmitting, to a first wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

Various embodiments may implement the following features.

In some embodiments, the time synchronization status information includes at least one of:information on at least one grandmaster clock candidate to which the grandmaster clock is switched, ora switching time configured for the switching of the grandmaster clock.

In some embodiments, the wireless communication method further includes receiving, from the first wireless network node, a time switch request associated with the switching of the grandmaster clock.

In some embodiments, the time switch request includes at least one of:information on a grandmaster clock candidate to which the grandmaster clock is switched, oran instructed switching time of switching the grandmaster clock to the selected grandmaster clock candidate.

In some embodiments, the information on the grandmaster clock candidate includes at least one of a grandmaster type, a grandmaster identifier, a grandmaster address or a grandmaster quality.

In some embodiments, the wireless communication method further includes receiving, from the first wireless network node, a subscription request for the time synchronization status information.

In some embodiments, the first wireless network node includes at least one of a session management function, a time sensitive communication and time synchronization function or a time sensitive networking adaptation function.

In some embodiments, the second wireless network node includes at least one of a user plane function, a network time sensitive networking translator, or a radio access network node.

In some embodiments, the first network node includes a time sensitive communication and time synchronization function and/or a time sensitive networking adaptation function. In some embodiments, a signaling path between the first wireless network node and the at least one second wireless network node includes a policy control function and/or an access and mobility management function.

In some embodiments, the signaling path further includes a session management function.

The present disclosure further relates to a wireless communication method for use in a second wireless network node. The method includes:receiving, from a first wireless network node, a time switch request associated with a switching of a grandmaster clock.

Various embodiments may implement the following features.

In some embodiments, the time switch request includes at least one of:information on a grandmaster clock candidate to which the grandmaster clock is switched, oran instructed switching time of switching the grandmaster clock to the selected grandmaster clock candidate.

In some embodiments, the information on the grandmaster clock candidate includes at least one of a grandmaster type, a grandmaster identifier, a grandmaster address or a grandmaster quality.

In some embodiments, the wireless communication method further includes receiving, from the first wireless network node, a subscription request for the time synchronization status information.

In some embodiments, the first wireless network node includes at least one of a session management function, a time sensitive communication and time synchronization function or a time sensitive networking adaptation function.

In some embodiments, the second wireless network node includes at least one of a user plane function, a network time sensitive networking translator, or a radio access network node.

In some embodiments, the first network node includes a time sensitive communication and time synchronization function and/or a time sensitive networking adaptation function. In some embodiments, a signaling path between the first wireless network node and the at least one second wireless network node includes a policy control function and/or an access and mobility management function.

In some embodiments, the signaling path further includes a session management function.

The present disclosure relates to a first wireless network node. The first wireless network node includes:a communication unit, configured to receive, from at least one second wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

Various embodiments may implement the following feature.

In some embodiments, the first wireless network node further includes a processor configured to perform any of the aforementioned wireless communication methods.

The present disclosure relates to a second wireless network node. The second wireless network node includes:a communication unit, configured to transmit, to a first wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

Various embodiments may in some embodiments implement the following feature.

In some embodiments, the second wireless network node further includes a processor configured to perform any of the aforementioned wireless communication methods.

The present disclosure relates to a second wireless network node. The second wireless network node includes:a communication unit, configured to receive, from a first wireless network node, a time switch request associated with a switching of a grandmaster clock.

Various embodiments may implement the following feature.

In some embodiments, the second wireless network node further includes a processor configured to perform any of the aforementioned wireless communication methods.

The present disclosure relates to a computer program product comprising a computer-readable program medium code stored thereupon, the code, when executed by a processor, causing the processor to implement a wireless communication method recited in any one of foregoing methods.

The exemplary embodiments disclosed herein are directed to providing features that will become readily apparent by reference to the following description when taken in conjunction with the accompany drawings. In accordance with various embodiments, exemplary systems, methods, devices and computer program products are disclosed herein. It is understood, however, that these embodiments are presented by way of example and not limitation, and it will be apparent to those of ordinary skill in the art who read the present disclosure that various modifications to the disclosed embodiments can be made while remaining within the scope of the present disclosure.

Thus, the present disclosure is not limited to the exemplary embodiments and applications described and illustrated herein. Additionally, the specific order and/or hierarchy of steps in the methods disclosed herein are merely exemplary approaches. Based upon design preferences, the specific order or hierarchy of steps of the disclosed methods or processes can be re-arranged while remaining within the scope of the present disclosure. Thus, those of ordinary skill in the art will understand that the methods and techniques disclosed herein present various steps or acts in a sample order, and the present disclosure is not limited to the specific order or hierarchy presented unless expressly stated otherwise.

DETAILED DESCRIPTION

FIG.1shows a schematic diagram of a network (architecture) according to an embodiment of the present disclosure. InFIG.1, the network includes the following network functions/entities:1) User equipment (UE):

The UE accesses the 5GS and obtains services via the NG-RAN and interacts with an Access and Mobility Control Function (AMF) of the core network via the NAS signaling. The Device side TSN translator (DS-TT) is inside the UE and provides a (g)PTP port functionality for the time synchronization.2) Next generation radio access network (NG-RAN):

The NG-RAN may also be called 5G-AN (5G Access network, i.e. 5G Radio Access Network). The NG-RAN is responsible for an air interface resource scheduling and an air interface connection management of the network to which the UE is accessed. In the present disclosure, the NG-RAN may be equal to NG-RAN node or RAN (node).3) Access and Mobility Management function (AMF):

The AMF includes the following functionalities: Registration management, Connection management, Reachability management and Mobility Management. This network function also performs an access authentication and an access authorization. The AMF is a non-access stratum (NAS) security termination and relays session management (SM) NAS among the UE and a session management function (SMF), . . . , etc.4) Session Management function (SMF):

The SMF includes the following functionalities: Session Management (e.g. Session establishment, modify and release), UE IP address allocation & management (including optional Authorization), Selection and control of UP function, downlink data notification, etc.5) User plane function (UPF):

The UPF includes the following functionalities: Anchor point for Intra-/Inter-RAT mobility, Packet routing & forwarding, Traffic usage reporting, QoS handling for user plane, Downlink packet buffering and downlink data notification triggering, etc. The Network side TSN translator (DS-TT) is inside/included in the UPF and provides the (g)PTP port functionality for the time synchronization.6) Policy Control Function (PCF):

The PCF includes the following functionality: Supports unified policy framework to govern network behavior, provides policy rules to Control Plane function(s) to enforce the policy rule, implements a Front End to access subscription information relevant for policy decisions in a User Data Repository (UDR).7) Network Exposure Function (NEF):

The NEF is deployed optionally for exchanging information between 5GC (5G core network) and an external Application Function (AF). In the present disclosure, the NEF/AF is used to present the NEF and AF for brevity.8) Time Sensitive Communication and Time Synchronization function (TSCTSF):

The TSCTSF controls the time synchronization services by controlling the NG-RAN to enable the 5G Access stratum time distribution and configuring the DS-TT and NW-TT when the 5GS is not integrated with a TSN network.9) Time Sensitive Network Adaptation Function (TSN AF):

The TSN AF provides interworking and adaptation with Centralized Network Configuration (CNC) in an external TSN network.

To support PTP based time synchronization services, the 5GS simulates/acts as a bridge to an external PTP network (e.g. a TSN network, or a network supporting a standard IEEE 1588). This TSN bridge is called virtual/logical bridge. The “logical” TSN Bridge includes TSN Translator (TT) functionalities (i.e. the DS-TT in the UE and the NW-TT in the UPF) for interoperation between the PTP network and the 5GS.

In the present disclosure, the PTP may be equal to gPTP (i.e. IEEE 8201.AS) since the PTP may be compatible with the gPTP.

In the present disclosure, the term GM may be equal to “GM clock”.

InFIG.1, the network (architecture) includes a 5G internal GM clock which is used as a time source (e.g. GPS clock or GM clock) in the network. The NG-RAN and the UPF/NW-TT perform a time synchronization with the 5G GM separately. In other words, the NG-RAN and the UPF are assumed to be synchronous.

In addition, the UE also needs to be synchronized with the network. There are 2 time distribution methods for synchronizing the UE.

1) 5G Access Stratum Time Distribution

FIG.2shows schematic diagram of a time synchronization between the UE and the NG-RAN according to an embodiment of the present disclosure. Particularly,FIG.2shows how the UE obtains the 5G precise time over the air interface from the NG-RAN.

In step201, the NG-RAN sends ReferenceTimeInfo to the UE in a SIB9 (System information Block 9) or RRC (radio resource control) message(s).

The ReferenceTimeInfo (i.e. reference time information) at least includes the following information elements/fields:referenceSFN: This field indicates a reference SFN (System Frame number) corresponding to a reference time and/or ReferenceTimeInfo.Time (ReferenceTime): The time field indicates the (reference) time at a boundary (e.g. a start or an end) of the reference SFN.

In step202, the UE synchronize with (the time in) the NG-RAN based on the received ReferenceTimeInfo.

After steps201and202, it is assumed that the UE/DS-TT, the NG-RAN and the UPF/NW-TT are synchronized in time. That is the UE/DS-TT, the NG-RAN and the UPF/NW-TT are assumed to share/have the same 5GS clock time.

2) (g)PTP Time Synchronization Over the 5GS

As above discussed, the 5GS supports the (g)PTP based time synchronization. In the (g)PTP based time synchronization, the 5GS acts as a Bridge node (e.g. TSN Bridge). That is, from the outside of the 5GS, the 5GS acts/looks like a bridge between the DS-TT and the NW-TT interworking with the PTP network outside of the 5GS. For example, the PTP network may be a TSN network, an IEEE 1588 network, etc.

FIG.3shows a schematic diagram of the (g)PTP time synchronization according to an embodiment of the present disclosure.

In step301, the NG-RAN provides the 5GS precise time to the UE/DS-TT via an AS level signaling. For example, the procedure shown inFIG.2may be performed. After step301, the UPF, the NG-RAN and the UE (are assumed to) have the same precise time. That is the time in the UPF, the NG-RAN and the UE are synchronized.

In step302, the TSCTSF/TSN AF reads/configures a PTP port in the UE/DS-TT by using a PMIC (Port Management information Container) which is carried in a signaling for a PDU (protocol data unit) session. The signaling between the TSCTSF/TSN AF and the UE/DS-TT may be transmitted via the PCF, the SMF, the AMF and the NG-RAN.

In step303, the TSCTSF/TSN AF reads/configures a PTP port in the UPF/NW-TT by using the PMIC and a UMIC (User-plane node Management information Container) which is carried in the signaling for the PDU session. The signaling between the TSCTSF/TSN AF and the UPF/NW-TT is transmitted via the PCF and the SMF.

In step304, the UPF/NW-TT port receives a (g)PTP time synchronization message from an interface N6 between the UPF/NW-TT and the (g)PTP network.

In step305, upon receiving the (g)PTP (synchronization) message from an upstream PTP instance/node in the (g)PTP network, the NW-TT (i.e. ingress TT in this embodiment) makes an ingress timestamp TSi for the received (g)PTP message. The ingress time stamp TSi is made based on the synchronized 5GS time.

In step306, the UPF/NW-TT adds the ingress time stamp TSi in a Suffix field of the (g)PTP message and sends the (g)PTP message to the UE in the user plane (via PDU session).

In step307, the UE/DS-TT (i.e. egress TT in this embodiment) creates an egress timestamp TSe when receiving the (g)PTP messages. The difference between the TSi and the TSe is considered to be residence time spent on the 5GS Bridging of this (g)PTP message. The egress timestamp TSe is made also based on the synchronized 5GS time. That is the residence time is calculated in the 5GS time domain.

In step308, the UE/DS-TT converts the residence time spent on the 5GS bridging to the (g)PTP time domain, modifies the payload of the (g)PTP message and sends the (g)PTP message to a downstream (g)PTP node in the PTP network.

After the procedure shown in theFIG.3completes, the UE/DS-TT and UPF/NW-TT are time synchronized with the GM clock in the PTP network. In other words, the UE/DS-TT keeps the 5GS internal time (i.e. 5G GM clock) and an external time (PTP network GM clock) simultaneously.

FIG.3shows the (g)PTP time synchronization from the UPF/NW-TT to the UE/DS-TT. The (g)PTP time synchronization may be performed in the direction from the UE/DS-TT to the UPF/NW-TT. In the (g)PTP time synchronization from the UE/DS-TT to the UPF/NW-TT, the UE/DS-TT becomes the ingress TT and the UPF/NW-TT becomes the egress TT. Specifically, when the UE/DS-TT receives a (g)PTP (synchronization) message from a (g)PTP node, the DS-TT (i.e. ingress TT in this example) creates the ingress timestamp TSi and send the (g)PTP message comprising the ingress timestamp TSi to the UPF/NW-TT (i.e. egress TT in this example). The NW-TT creates the egress time stamp TSe and calculates the residence time. The UPF/NW-TT converts the residence time spent on the 5GS bridging to the (g)PTP time domain and modifies the payload of the (g)PTP message which will be sent to the downstream (g)PTP node in the PTP network.

When the 5G GM, which is currently the time source of the 5GS, degrades or is down, another 5G GM will be used as the time source of the 5GS. That is, the time source of the 5GS may change or switch from the initial 5G GM to another 5G GM (which may be called new 5G GM in the following). Because the time resource switching in the NG-RAN and the UPF are independent/asynchronous, the time in the NG-RAN and the UPF may become asynchronous for a certain period. The time asynchronization between the UPF and the NG-RAN (and UE/DS-TT) may result in a failure of the (g)PTP base time synchronization.

FIG.4shows a schematic diagram of the 5G GM (clock) switching according to an embodiment of the present disclosure.

In step401, the NG-RAN node provides the 5GS precise time to the UE/DS-TT via an AS level signaling. For example, the procedure shown inFIG.2may be performed. After step401, the UPF, the NG-RAN and the UE (are assumed to) have the same precise time since the NG-RAN node and the UPF are synchronized with the initial 5G GM. That is the time in the UPF, the NG-RAN and the UE are (assumed to be) synchronized.

In step402, the initial 5G GM degrades or is down.

In step403, the NG-RAN switches to a new 5G GM, i.e., is synchronized with the new 5G GM. Note that, the NG-RAN may provide the precise time to UE (e.g. via the procedure inFIG.2). Thus, the UE is synchronized with the new 5G GM via the NG-RAN.

In step404, the UPF/NW-TT receives a (g)PTP message on the interface N6 (e.g. from an upstream PTP instance/node in the PTP network). Note that the UPF/NW-TT has not switched to/synchronized with the new 5G GM.

In step405, upon receiving the (g)PTP message from the upstream PTP instance, the NW-TT makes an ingress timestamping TSi based on the initial 5G GM.

In step406, the UPF/NW-TT adds the TSi in the Suffix field of the (g)PTP message and send the (g)PTP message to the UE in the user plane (via a PDU session).

In step407, the UE/DS-TT creates an egress timestamp TSe based on the new 5G GM when receiving the (g)PTP messages. The UE/DC-TT calculate the residence time by:

Residence time=TSe (based on the new 5G GM clock)−TSi (based on initial 5G GM clock).

In step408, the UE/DS-TT converts the calculated residence time to the (g)PTP time domain, modifies the payload of the (g)PTP message and sends the (g)PTP message to the PTP network.

In step409, the UPF/NW-TT switches its time resource to the new 5G GM. The UPF/NW-TT synchronize with the new 5G GM.

InFIG.4, there is an out-of-synchronization period from the step403to the step409. In the out-of-synchronization period, the time resource of the NG-RAN (and UE/DS-TT) is different from that of the UPF/NW-TT. The offset between the new 5G GM and the initial 5G GM introduces an offset error in the calculated residence time, which may result in serious issues in time sensitive services/applications.

In some embodiments, when detecting that the current 5G GM clock (e.g. GM1) degrades or fails, the NG-RAN and/or the UPF/NW-TT may need to switch the time resource from the current/initial 5G GM clock GM1 to another/new 5G GM clock GM2. Under such conditions, the NG-RAN and/or the UPF/NW-TT reports its time synchronization status to a control point. The time synchronization status may include at least one of:information on the GM1 (e.g. quality/status/type of the GM1);associated capability (hold over time);information on a list of 5G GM candidates for the GM2 to which the time resource is switched (e.g. GM type and/or GM identifier/address and/or quality of each 5G GM candidate); ora switching time configured for switching from the GM1 to the GM2.

In some embodiments, the NG-RAN and/or the UPF/NW-TT may be predefined to report the time synchronization status to the control point.

In some embodiments, the control point may subscribe to the NG-RAN and/or the UPF/NW-TT for the time synchronization status. For example, the control point may transmit a subscription request to the NG-RAN and/or the UPF/NW-TT, to request the NG-RAN and/or the UPF/NW-TT to report the time synchronization status when detecting the current 5G GM clock degrades or fails.

In some embodiment, the control point includes at least one of the SMF, the TSCTSF or the TSN AF. In the present disclosure, a device/node includes a network function indicates that the device/node performs at least part of functionalities of the network function.

In some embodiments, after receiving the time synchronization status, the control point sends a time switch request to the NG-RAN and/or UPF/NW-TT. The time switch request includes at least one of:information on the GM2 to which the time resource is switched (e.g. GM type and/or GM identifier/address and/or quality of the 5G GM candidate); oran instructed switching time of switching from the GM1 to the GM2.

In some embodiments, the control point may receive the time synchronization status from one of the NG-RAN and the UPF/NW-TT and transmit the time switch request to at least one of the NG-RAN or the UPF/NW-TT (e.g. another one of the NG-RAN and the UPF/NW-TT).

In some embodiments, the control point may receive the time synchronization status from both the NG-RAN and the UPF/NW-TT and transmit the time switch request to at least one of the NG-RAN or the UPF/NW-TT.

In some embodiments, the control point receives the time synchronization status from both the NG-RAN and the UPF/NW-TT and determines whether to transmit the time switch request to at least one of the NG-RAN or the UPF/NW-TT based on the received time synchronization status.

In an embodiment, based on the time synchronization status from both the NG-RAN and the UPF/NW-TT, the control point may determine that the 5G GM switching performed by the NG-RAN and the UPF/NW-TT do not introduce the offset error and/or do not cause effects on the time sensitive applications/services. For example, based on the time synchronization status from both the NG-RAN and the UPF/NW-TT, the control point may determine that the 5G GM clock GM2 to which the NG-RAN will switch is the same with that to which the UPF/NW-TT will switch and that the switching time of the NG-RAN is approximately the same with that of the UPF/NW-TT. Under such conditions, the control point determines not to transmit the time switch request. In an embodiment, two switching times are approximately the same if a difference between these two switching times is smaller than a threshold, e.g. 1 ms (millisecond), 5 ms, etc.

FIG.5shows a schematic diagram of the 5G GM (clock) switching according to an embodiment of the present disclosure. InFIG.5, the 5G GM switching is controlled by the SMF. Specifically, the 5G GM (clock) switching shown inFIG.5includes the following steps:Step501: The UPF/NW-TT and the NG-RAN are time synchronized with an initial/current 5G GM clock. The NG-RAN provides the precise time to UE (i.e. via the procedure shown inFIG.2).Step502: The SMF subscribes to a time synchronization status (information) from the UPF/NW-TT. That is the UPF/NW-TT may be requested to report new 5G GM information and possible switching time when detecting a degradation or failure of the initial/current 5G GM.Step503: The SMF subscribes to a time synchronization status (information) from the NG-RAN via the AMF. In other words, the UPF/NW-TT may be requested to report the new 5G GM info and possible switching time when detecting a degradation or failure of the initial/current 5G GM.Step504: When the UPF/NW-TT detects the 5G GM degrade or fails, it reports the time synchronization status to the SMF. The time synchronization status may include:old/initial/current 5G GM information;UPF/NW-TT capability (e.g. hold over time of the UPF/NW-TT);information on new 5G GM list (e.g. new GM type, new GM ID/address, quality of each 5G GM candidate for the new 5G GM);switching time of the switching from the old 5G GM to the new 5G GM.Step505: When the NG-RAN node detects that the old/initial/current 5G GM degrades or fails, the NG-RAN node reports the time synchronization status to the SMF via the AMF. In an embodiment, the NG-RAN sends the time synchronization status to the AMF in an N2 request, and AMF send it to the SMF in an SMF service operation (e.g. Nsfm_PDUSession_Update). The time synchronization status is similar with that in step504.

Based on the time synchronization status received from the NG-RAN and/or the UPF, the SMF determines a switching time that the NG-RAN and the UPF switching to the new 5G GM. The determined switching time may be expressed in the old 5G GM time, or the new 5G GM time.

In an embodiment, the SMF may further determine/select a 5G GM candidate as the new 5G GM based on the reported time synchronization status. For example, if the new GM type(s) and/or GM ID(s) of the 5G GM candidate(s) reported by the NG-RAN is different from the new GM type(s) and/or GM ID(s) of the 5G GM candidate(s) reported by the UPF, the SMF may need to determine/select one of the reported 5G GM candidates as the new 5G GM to which both the UPF and the NG-RAN switch. As an alternative or in addition, if the UPF/NG-RAN reports a plurality of 5G GM candidates (e.g. a list of 5G GM candidates), the SMF may also need to determine/select one of the reported 5G GM candidates as the new 5G GM to which both the UPF and the NG-RAN switch.

Note that the steps504and505may be parallel steps. As an alternative, one of the steps504and505may occur before another one of the steps504and505.Step506: The SMF sends Time synchronization switch information to the UPF/NW-TT, e.g., in an N4 request. The Time synchronization switch information may indicate at least one of a switching time or the (selected/determined) new 5G GM (e.g. GM type and/or GM ID). In an embodiment, the switching time may be expressed in the old 5G GM time, or the new 5G GM time.Step507: The SMF sends the Time synchronization switch information to the NG-RAN via the AMF. The Time synchronization switch information may indicate at least one of a switching time or the (selected/determined) new 5G GM (e.g. GM type and/or GM ID). In an embodiment, the switching time may be express in the old 5G GM time, or the new 5G GM time.Step508: The NG-RAN and the UPF/NW-TT switch to the new 5G GM at the instructed switched time.Step509: After step508, the UPF/NW-TT and NG-RAN are time synchronized with the new 5G GM clock. The NG-RAN provides the precise time to the UE (e.g. via the procedure shown inFIG.2).

FIG.6shows a schematic diagram of the 5G GM (clock) switching according to an embodiment of the present disclosure. InFIG.6, the 5G GM switching is controlled by the TSCTSF/TSN AF. Specifically, the 5G GM (clock) switching shown inFIG.6includes the following steps:Step601: The UPF/NW-TT and NG-RAN are time synchronized with the initial/current 5G GM clock. The NG-RAN provides the precise time to UE (e.g. via the procedure shown inFIG.2).Step602: The TSCTSF/TSN AF subscribes to time synchronization status (information) from the UPF/NW-TT and the NG-RAN. In an embodiment, the TSCTSF/TSN AF may request the UPF/NW-TT and the NG-RAN to report the new 5G GM info and possible switching time. The message between TSCTSF/TSN AF and the UPF/NW-TT may be carried in a PMIC (Port Management Information Container) or a UMIC (User-plane node Management Information Container). The TSCTSF/TSN AF may invoke an Npcf_Policy Authorization service to send the request to the PCF and the PCF may invoke an Npcf_SMPolicyControl service to send the subscription request to the SMF.Step603: The SMF subscribes to the time synchronization status from the UPF/NW-TT.Step604: The SMF subscribes to the time synchronization status from the NG-RAN via the AMF.Step605: When the UPF/NW-TT detects the initial/old 5G GM degrades or fails, the UPF/NW-TT reports the time synchronization status to the SMF. The time synchronization status may include at least one of:old/initial/current 5G GM information;UPF/NW-TT capability (e.g. hold over time of the UPF/NW-TT);information on new 5G GM list (e.g. new GM type, new GM ID/address, quality of each 5G GM candidate for the new 5G GM); orswitching time of the switching from the old 5G GM to the new 5G GM.Step606: When the NG-RAN detects the initial/old 5G GM degrades or fails, the NG-RAN reports the time synchronization status to the SMF via the AMF. In an embodiment, the NG-RAN sends the time synchronization status to the AMF in an N2 request and the AMF sends the time synchronization status to the SMF in an SMF service operation (e.g. Nsfm_PDUSession_Update). The time synchronization status is similar with that in step605.

Note that the steps605and606may be parallel steps. As an alternative, one of the steps605and606may occur before another one of the steps605and606.Step607: The SMF notifies the TSCTSF/TSN AF via the PCF of the received time synchronization status. For example, the SMF sends the time synchronization status by invoking an Npcf_SMPolicyControl_Update service operation towards the PCF and the PCF sends the time synchronization status by invoking an Npcf_PolicyAuthorization_Notify service operation towards the TSCTSF/TSN AF.

In an embodiment, the step607may be triggered by step605or step606. As an alternative, the SMF may initiates the step607after receiving the time synchronization status from both the UPF and the NG-RAN.Step608: The TSCTSF/TSN AF determines the switching time that the NG-RAN and UPF need to switch to the new 5G GM. The switching time can be expressed in the old 5G GM time, or the new 5G GM time.

In an embodiment, the TSCTSF/TSN AF may further determine/select a 5G GM candidate as the new 5G GM based on the reported time synchronization status. For example, if the new GM type(s) and/or GM ID(s) of the 5G GM candidate(s) reported by the NG-RAN is different from the new GM type(s) and/or GM ID(s) of the 5G GM candidate(s) reported by the UPF, the TSCTSF/TSN AF may need to determine/select one of the reported 5G GM candidates as the new 5G GM to which both the UPF and the NG-RAN switch. As an alternative or in addition, if the UPF/NG-RAN reports a plurality of 5G GM candidates (e.g. a list of 5G GM candidates), the TSCTSF/TSN AF may also need to determine/select one of the reported 5G GM candidates as the new 5G GM to which both the UPF and the NG-RAN switch.

The TSCTSF/TSN AF sends time synchronization switch information to the SMF via the PCF. The time synchronization switch information may include/indicate the determined switching time and/or the new 5G GM (e.g. GM type and/or GM ID of the new 5G GM). The switching time can be expressed in the old 5G GM time or the new 5G GM time. The TSCTSF/TSN AF may send the time synchronization switch information to the PCF by invoking an Npcf_PolicyAuthorization_Update. The PCF may send the time synchronization switch information to the SMF by invoking an Npcf_SMPolicyControl_Update.

In an embodiment, the time synchronization switch information sent to the PCF may be carried in the PMIC or the UMIC.Step609: The SMF sends the time synchronization switch information to the UPF/NW-TT in an N4 request. The time synchronization switch information may include/indicate the determined switching time and/or the new 5G GM (e.g. GM type and/or GM ID of the new 5G GM). The switching time can be expressed in the old 5G GM time or the new 5G GM time.Step610: The SMF sends the time synchronization switch information to the NG-RAN via the AMF. The time synchronization switch information may include/indicate the determined switching time and/or the new 5G GM (e.g. GM type and/or GM ID of the new 5G GM). The switching time can be expressed in the old 5G GM time or the new 5G GM time.Step611: The NG-RAN and UPF/NW-TT switch to the new 5G GM at the switching time indicated/included in the time synchronization switch information.Step612: The UPF/NW-TT and NG-RAN are time synchronized with new 5G GM clock and NG-RAN provides the precise time to UE (e.g. via the procedure shown inFIG.2).

FIG.7shows a schematic diagram of the 5G GM (clock) switching according to an embodiment of the present disclosure. InFIG.7, the signaling path from the TSCTSF and the NG-RAN does not include the SMF. Specifically, the 5G GM (clock) switching shown inFIG.7includes the following steps:Step701: The TSCTSF/TSN AF subscribes to the time synchronization status from the NG-RAN. The TSCTSF/TSN AF may request the NG-RAN to report the new 5G GM information and possible switching time. The TSCTSF/TSN AF send the subscription request to the AMF.

InFIG.7, the TSCTSF/TSN AF checks the UDM to find the AMF serving the UE and sends the subscription request to the AMF.

In an embodiment, the TSCTSF/TSN AF may check a BSF (binding support function) to find the PCF (e.g. access and mobility management PCF (AM-PCF)) and send the subscription request to the PCF. The PCF sends the subscription request to the AMF.Step702: The AMF subscribes to the time synchronization status from the NG-RAN.Step703: When the NG-RAN detects the (initial/current) 5G GM degrades or fails, the NG-RAN reports the time synchronization status to the AMF in an N2 request. The time synchronization status may include:

The time synchronization status may include at least one of:old/initial/current 5G GM information;UPF/NW-TT capability (e.g. hold over time of the UPF/NW-TT);information on new 5G GM list (e.g. new GM type, new GM ID/address, quality of each 5G GM candidate for the new 5G GM); orswitching time of the switching from the old 5G GM to the new 5G GM.Step704: The AMF sends the time synchronization status to the TSCTSF/TSN AF. In this embodiment, the time synchronization status may be sent to the TSCTSF/TSN AF via the PCF.Step705: The TSCTSF/TSN AF determines the switching time that the NG-RAN needs to switch to the new 5G GM. The determined switching time may be expressed in the old 5G GM time, or the new 5G GM time. The TSCTSF/TSN AF may also determine the new 5G GM to which the NG-RAN switches.InFIG.7, the TSCTSF/TSN AF sends the time sync switch information to the AMF.Step706: The AMF sends the time sync switch information to the NG-RAN.Step707: The NG-RAN switches to the new 5G GM at the switching time indicated/included in the time sync switch information.

FIG.8relates to a schematic diagram of a wireless terminal80according to an embodiment of the present disclosure. The wireless terminal80may be a user equipment (UE), a mobile phone, a laptop, a tablet computer, an electronic book or a portable computer system and is not limited herein. The wireless terminal80may include a processor800such as a microprocessor or Application Specific Integrated Circuit (ASIC), a storage unit810and a communication unit820. The storage unit810may be any data storage device that stores a program code812, which is accessed and executed by the processor800. Embodiments of the storage unit810include but are not limited to a subscriber identity module (SIM), read-only memory (ROM), flash memory, random-access memory (RAM), hard-disk, and optical data storage device. The communication unit820may a transceiver and is used to transmit and receive signals (e.g. messages or packets) according to processing results of the processor800. In an embodiment, the communication unit820transmits and receives the signals via at least one antenna822shown inFIG.8.

In an embodiment, the storage unit810and the program code812may be omitted and the processor800may include a storage unit with stored program code.

The processor800may implement any one of the steps in exemplified embodiments on the wireless terminal80, e.g., by executing the program code812.

The communication unit820may be a transceiver. The communication unit820may as an alternative or in addition be combining a transmitting unit and a receiving unit configured to transmit and to receive, respectively, signals to and from a wireless network node (e.g. a base station).

FIG.9relates to a schematic diagram of a wireless network node90according to an embodiment of the present disclosure. The wireless network node90may be a satellite, a base station (BS), a network entity, a Mobility Management Entity (MME), Serving Gateway (S-GW), Packet Data Network (PDN) Gateway (P-GW), a radio access network (RAN) node, a next generation RAN (NG-RAN) node, a gNB, an eNB, a gNB central unit (gNB-CU), a gNB distributed unit (gNB-DU) a data network, a core network or a Radio Network Controller (RNC), and is not limited herein. In addition, the wireless network node90may include/perform at least one network function such as an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a policy control function (PCF), an application function (AF), a time sensitive communication and time synchronization function (TSCTSF) or a time sensitive networking adaptation function (TSN AF), etc. The wireless network node90may include a processor900such as a microprocessor or ASIC, a storage unit910and a communication unit920. The storage unit910may be any data storage device that stores a program code912, which is accessed and executed by the processor900. Examples of the storage unit910include but are not limited to a SIM, ROM, flash memory, RAM, hard-disk, and optical data storage device. The communication unit920may be a transceiver and is used to transmit and receive signals (e.g. messages or packets) according to processing results of the processor900. In an example, the communication unit920transmits and receives the signals via at least one antenna922shown inFIG.9.

In an embodiment, the storage unit910and the program code912may be omitted. The processor900may include a storage unit with stored program code.

The processor900may implement any steps described in exemplified embodiments on the wireless network node90, e.g., via executing the program code912.

The communication unit920may be a transceiver. The communication unit920may as an alternative or in addition be combining a transmitting unit and a receiving unit configured to transmit and to receive, respectively, signals to and from a wireless terminal (e.g. a user equipment or another wireless network node).

FIG.10shows a flowchart of a method according to an embodiment of the present disclosure. The method shown inFIG.10may be used in a first wireless network node (e.g. the SMF, the TSCTSF, the TSN AF, a wireless network node comprising at least one of the SMF, the TSCTSF or the TSN AF or a wireless network node performing at least part of functionalities of at least one of the SMF, the TSCTSF and the TSN AF) and includes the following step:Step1001: Receive, from at least one second wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

In the embodiment shown inFIG.10, the first wireless network node receives time synchronization status information from at least one second wireless network node. The time synchronization status information is associated with a switching of a (5G) GM clock (e.g. switching from a first GM clock to a second GM clock). For example, the time synchronization status information includes at least one of:information on an initial GM clock from which the GM clock is switched (i.e. the first GM clock),a wireless network node capability (e.g. hold over time of the first wireless network node)information on at least one GM clock candidate to which the GM clock is switched (e.g. a list of grandmaster clock candidate(s) for the second GM clock), ora switching time configured for the switching of the GM clock (e.g. the time of the first wireless network node planning to switch the GM clock from the first GM clock to the second GM clock).

In an embodiment, the first wireless network node may transmit a time switch request/information associated with the switching of the GM clock to the second wireless network node(s). Note that the first wireless network node may be predefined to transmit the time switch request/information in response to the received the time synchronization status information. As an alternative or in addition, based on the received the time synchronization status information, the first wireless network node may determine whether to transmit the time switch request/information and/or the second wireless network node to which the time switch request/information is sent/transmitted.In an embodiment, the time switch request/information includes at least one of:information on a GM clock candidate to which the grandmaster clock is switched (i.e. the second GM clock), oran instructed switching time of switching the grandmaster clock to the GM clock candidate.

In an embodiment, the first wireless network node may determine/select a GM clock candidate to which the GM clock is switched (i.e. the second GM clock) and/or an instructed switching time of switching the GM clock to the determined/selected GM clock candidate.

In an embodiment, the information on the GM clock or the GM clock candidate includes at least one of: a GM type, a GM ID, a GM address or a GM (clock) quality.

In an embodiment, the first wireless network node transmits a subscription request for the time synchronization status information to the second wireless network node(s), to subscribe to the time synchronization status information.

In an embodiment, the second wireless network node includes at least one of a UPF, a NW-TT, or a RAN node (e.g. NG-RAN).

In an embodiment of the first wireless network node comprising/being the TSCTSF/TSN AF, a signaling path between the first wireless network node and the second wireless network node(s) includes a PCF and/or an AMF.

In an embodiment, the signaling path between the first wireless network node and the second wireless network node(s) may further include an SMF.

FIG.11shows a flowchart of a method according to an embodiment of the present disclosure. The method shown inFIG.11may be used in a second wireless network node (e.g. the UPF, the NW-TT, the RAN node, a wireless network node comprising at least one of the UPF, the NW-TT and the RAN node or a wireless network node perform at least part of functionalities of at least one of the UPF, the NW-TT or the RAN node) and includes the following step:Step1101: Transmit, to a first wireless network node, time synchronization status information associated with a switching of a grandmaster clock.

In this embodiment, the second wireless network node transmits time synchronization status information associated with a switching of a grandmaster clock (e.g. from a first GM clock to a second GM clock). For example, the second wireless network node may transmit the time synchronization status information when detecting that the first/current GM clock (e.g. initial 5G GM shown inFIG.3or4) degrades or fails or is down and/or when determining to switch the GM clock from the first GM clock to the second GM clock.

In an embodiment, the time synchronization status information includes at least one of:information on an initial GM clock from which the GM clock is switched (i.e. the first GM clock),a wireless network node capability (e.g. hold over time of the first wireless network node)information on at least one GM clock candidate to which the GM clock is switched (e.g. a list of grandmaster clock candidate(s) for the second GM clock), ora switching time configured for the switching of the GM clock (e.g. the time of the first wireless network node planning to switch the GM clock from the first GM clock to the second GM clock).

In an embodiment, the second wireless network node may receive a time switch request/information from the first wireless network node. The time switch request/information is associated with the switching of the GM clock.

In an embodiment, the time switch request/information includes at least one of:information on a GM clock candidate to which the grandmaster clock is switched (i.e. the second GM clock), oran instructed switching time of switching the grandmaster clock to the GM clock candidate.

In an embodiment, the information on the GM clock or the GM clock candidate includes at least one of: a GM type, a GM ID, a GM address or a GM (clock) quality.

In an embodiment, the second wireless network node may be predefined to transmit the time synchronization status information to the first wireless network node.

In an embodiment, the second wireless network node receives, from the first wireless network node, a subscription request for (subscribing to) the time synchronization status information.

In an embodiment, the first wireless network node may include/be an SMF and/or a TSCTSF and/or a TSN AF.

In an embodiment of the first wireless network node comprising/being the TSCTSF and/or the TSN AF, a signaling path between the first wireless network node and the second wireless network node includes a PCF and/or an AMF.

In an embodiment, the signaling path between the first wireless network node and the second wireless network node may further include an SMF.

FIG.12shows a flowchart of a method according to an embodiment of the present disclosure. The method shown inFIG.12may be used in a second wireless network node (e.g. the UPF, the NW-TT, the RAN node, a wireless network node comprising at least one of the UPF, the NW-TT and the RAN node or a wireless network node perform at least part of functionalities of at least one of the UPF, the NW-TT or the RAN node) and includes the following step:Step1201: Receive, from a first wireless network node, a time switch request associated with a switching of a grandmaster clock.

InFIG.12, the second wireless network node receives a time switch request/information associated with (e.g. indicating) a switching of a GM clock. For example, the time switch request may indicate the switching from a first GM clock to a second GM clock. Note that the second wireless network node may not transmit time synchronization status information associated with the switching of the GM clock prior to/before receiving the time switch request/information in this embodiment.

In an embodiment, the time switch request/information includes at least one of:information on a GM clock candidate to which the grandmaster clock is switched (i.e. the second GM clock), oran instructed switching time of switching the grandmaster clock to the GM clock candidate.

In an embodiment, the information on the GM clock or the GM clock candidate includes at least one of: a GM type, a GM ID, a GM address or a GM (clock) quality.

In an embodiment, the first wireless network node may include/be an SMF and/or a TSCTSF and/or a TSN AF.

In an embodiment of the first wireless network node comprising/being the TSCTSF and/or the TSN AF, a signaling path between the first wireless network node and the second wireless network node includes a PCF and/or an AMF.

In an embodiment, the signaling path between the first wireless network node and the second wireless network node may further include an SMF.

A skilled person would further appreciate that any one of the various illustrative logical blocks, units, processors, means, circuits, methods and functions described in connection with the aspects disclosed herein can be implemented by electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two), firmware, various forms of program or design code incorporating instructions (which can be referred to herein, for convenience, as “software” or a “software unit”), or any combination of these techniques.

To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, units, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. Skilled artisans can implement the described functionality in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, unit, etc. can be configured to perform one or more of the functions described herein. The term “configured to” or “configured for” as used herein with respect to a specified operation or function refers to a processor, device, component, circuit, structure, machine, unit, etc. that is physically constructed, programmed and/or arranged to perform the specified operation or function.

Furthermore, a skilled person would understand that various illustrative logical blocks, units, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, units, and circuits can further include antennas and/or transceivers to communicate with various components within the network or within the device. A general purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein. If implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer-readable medium.

Computer-readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

In this document, the term “unit” as used herein, refers to software, firmware, hardware, and any combination of these elements for performing the associated functions described herein. Additionally, for purpose of discussion, the various units are described as discrete units; however, as would be apparent to one of ordinary skill in the art, two or more units may be combined to form a single unit that performs the associated functions according embodiments of the present disclosure.