EP3874819A1

EP3874819A1 - Method and apparatus for handover

Info

Publication number: EP3874819A1
Application number: EP18796440.8A
Authority: EP
Inventors: Klaus Hoffmann
Original assignee: Nokia Solutions and Networks GmbH and Co KG
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2018-11-01
Filing date: 2018-11-01
Publication date: 2021-09-08
Also published as: WO2020088769A1

Abstract

Delaying transmission of at least one first user plane packet, a delay of the first user plane packet being dependent on a timing difference between a control plane path and a user plane path.

Description

Title

METHOD AND APPARATUS FOR HANDOVER

Field

The present application relates to a method, apparatus, and computer program in particular but not exclusively related to methods, apparatus and computer programs used for handover.

Background

A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations/access points and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided, for example, by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

Summary

According to an aspect, there is provided an apparatus comprising means for: delaying transmission of at least one first user plane packet, a delay of said user plane packet being dependent on a timing difference between a control plane path and a user plane path.

The means may be for causing a second user plane packet to be transmitted to a target base station and for determining a user plane path delay dependent on a time taken for a response to said second user plane packet to be received.

The means may be for receiving user plane path delay information providing a user plane path delay, said user plane path delay information being between a source base station and a target base station.

The user plane path information may be received from a database.

The means may be for receiving information about a control plane path delay.

The means may be for receiving said information about a control plane path delay in a handover command message.

The means may be for determining said timing difference using said user plane path delay and said received information about said control plane path delay. According to an aspect, there is an apparatus comprising means for: determining a control plane path delay; and causing the control plane path delay to be provided to a base station.

The means may be for causing the control plane path delay to be provided to a network entity in a handover command message.

The means may be for causing a first request message to be transmitted to a source base station and for determining a first control plane delay, dependent on a time taken for a response message to said first request to be received.

The means may be for causing the first request message to be transmitted to a source base station in a session request message.

The means may be for determining if a procedure taking into account control plane and user plane delays is supported by the source base station.

The means may be for determining if a procedure taking into account control plane and user plane delays is supported by the source base station based on an indication received from said source base station.

The means may be for storing the determined first control plane delay.

The means may be for receiving a second control plane delay, the second control plane delay being dependent on a control plane delay between a target core network function and a target base station.

The means may be for determining if a procedure taking into account control plane and user plane delays is supported by the target core network function.

The means may be for determining if a procedure taking into account control plane and user plane delays is supported by the target base station.

The means may be for receiving a second time difference from the target core network function.

The means may be for determining the control plane path delay by combining one or more of a first control plane delay, which is dependent on a control plane path to source base station, a second control plane delay which is dependent on a control path between a target core network function and a target base station, and a third control plane delay which is dependent on a control plane path to the target core network function.

The means may be for receiving the third control plane delay from a network function.

According to another aspect, there is provided an apparatus comprising means for: causing a request message to be transmitted to a target base station and for determining a control plane delay, dependent on a time taken for an acknowledgment message to said request message to be received.

The means may be for causing the request message to be transmitted to the target base station in a handover request message. The means may be for determining if a procedure taking into account control plane and user plane delays is supported by the target base station.

The means for determining if a procedure taking into account control plane and user plane delays is supported by the target base station may be based on an indication received from said target base station.

The means may be for storing the determined control plane delay.

The means may be for providing the determined control plane delay to a core network entity.

According to another aspect, there is provided an apparatus comprising means for: receiving a request message; causing, in response to said request message, an acknowledgment message to be transmitted to a target core network node, such that the target core network node can determine a control plane delay, dependent on a time at which the acknowledgement message is received at the target core network node, after the target core network node had sent the request message.

The means may be for causing the acknowledgment message to be transmitted to the target core network node in a handover request acknowledgment message.

The means may be for causing the acknowledgment message to comprise an indication of whether the apparatus supports a procedure taking into account control plane and user plane delay.

The means may be for receiving a user plane packet from a source base station and causing a response to be transmitted back to the source base station, such that the source base station can determine a user plane path delay.

The user plane packet may be a protocol data unit packet.

According to another aspect, there is provided an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: delaying transmission of at least one first user plane packet, a delay of said user plane packet being dependent on a timing difference between a control plane path and a user plane path.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing a second user plane packet to be transmitted to a target base station and for determining a user plane path delay dependent on a time taken for a response to said second user plane packet to be received.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving user plane path delay information providing a user plane path delay, said user plane path delay information being between a source base station and a target base station. The user plane path information may be received from a database.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving information about a control plane path delay.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving said information about a control plane path delay in a handover command message.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining said timing difference using said user plane path delay and said received information about said control plane path delay.

According to another aspect, there is provided an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: determining a control plane path delay; and causing the control plane path delay to be provided to a base station.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing the control plane path delay to be provided to a network entity in a handover command message.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing a first request message to be transmitted to a source base station and for determining a first control plane delay, dependent on a time taken for a response message to said first request to be received.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing the first request message to be transmitted to a source base station in a session request message.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining if a procedure taking into account control plane and user plane delays is supported by the source base station.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining if a procedure taking into account control plane and user plane delays is supported by the source base station based on an indication received from said source base station.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: storing the determined first control plane delay. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving a second control plane delay, the second control plane delay being dependent on a control plane delay between a target core network function and a target base station.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining if a procedure taking into account control plane and user plane delays is supported by the target core network function.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining if a procedure taking into account control plane and user plane delays is supported by the target base station.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving a second time difference from the target core network function.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining the control plane path delay by combining one or more of a first control plane delay, which is dependent on a control plane path to source base station, a second control plane delay which is dependent on a control path between a target core network function and a target base station, and a third control plane delay which is dependent on a control plane path to the target core network function.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving the third control plane delay from a network function.

According to another aspect, there is provided an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: causing a request message to be transmitted to a target base station and for determining a control plane delay, dependent on a time taken for an acknowledgment message to said request message to be received.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing the request message to be transmitted to the target base station in a handover request message.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining if a procedure taking into account control plane and user plane delays is supported by the target base station. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: determining if a procedure taking into account control plane and user plane delays is supported by the target base station based on an indication received from said target base station.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: storing the determined control plane delay.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: providing the determined control plane delay to a core network entity.

According to another aspect, there is provided an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: receiving a request message; causing, in response to said request message, an acknowledgment message to be transmitted to a target core network node, such that the target core network node can determine a control plane delay, dependent on a time at which the acknowledgement message is received at the target core network node, after the target core network node had sent the request message .

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing the acknowledgment message to be transmitted to the target core network node in a handover request acknowledgment message.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: causing the acknowledgment message to comprise an indication of whether the apparatus supports a procedure taking into account control plane and user plane delay.

The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to perform: receiving a user plane packet from a source base station and causing a response to be transmitted back to the source base station, such that the source base station can determine a user plane path delay.

The user plane packet may be a protocol data unit packet.

According to another aspect, there is provided a method comprising: delaying transmission of at least one first user plane packet, a delay of said user plane packet being dependent on a timing difference between a control plane path and a user plane path.

The method may comprise causing a second user plane packet to be transmitted to a target base station and for determining a user plane path delay dependent on a time taken for a response to said second user plane packet to be received. The method may comprise receiving user plane path delay information providing a user plane path delay, said user plane path delay information being between a source base station and a target base station.

The user plane path information may be received from a database.

The method may comprise receiving information about a control plane path delay.

The method may comprise receiving said information about a control plane path delay in a handover command message.

The method may comprise determining said timing difference using said user plane path delay and said received information about said control plane path delay.

According to another aspect, there is provided a method comprising: determining a control plane path delay; and causing the control plane path delay to be provided to a base station.

The method may comprise causing the control plane path delay to be provided to a network entity in a handover command message.

The method may comprise causing a first request message to be transmitted to a source base station and for determining a first control plane delay, dependent on a time taken for a response message to said first request to be received.

The method may comprise causing the first request message to be transmitted to a source base station in a session request message.

The method may comprise determining if a procedure taking into account control plane and user plane delays is supported by the source base station.

The method of determining if a procedure taking into account control plane and user plane delays is supported by the source base station may be based on an indication received from said source base station.

The method may comprise storing the determined first control plane delay.

The method may comprise receiving a second control plane delay, the second control plane delay being dependent on a control plane delay between a target core network function and a target base station.

The method may be for determining if a procedure taking into account control plane and user plane delays is supported by the target core network function.

The method may be for determining if a procedure taking into account control plane and user plane delays is supported by the target base station.

The method may comprise receiving a second time difference from the target core network function.

The method may comprise determining the control plane path delay by combining one or more of a first control plane delay, which is dependent on a control plane path to source base station, a second control plane delay which is dependent on a control path between a target core network function and a target base station, and a third control plane delay which is dependent on a control plane path to the target core network function.

The method may comprise receiving the third control plane delay from a network function.

According to another aspect, there is provided a method comprising: causing a request message to be transmitted to a target base station and for determining a control plane delay, dependent on a time taken for an acknowledgment message to said request message to be received.

The method may comprise causing the request message to be transmitted to the target base station in a handover request message.

The method may comprise determining if a procedure taking into account control plane and user plane delays is supported by the target base station.

The method of determining if a procedure taking into account control plane and user plane delays is supported by the target base station may be based on an indication received from said target base station.

The method may comprise storing the determined control plane delay.

The method may comprise providing the determined control plane delay to a core network entity.

According to another aspect, there is provided a method comprising: receiving a request message; causing, in response to said request message, an acknowledgment message to be transmitted to a target core network node, such that the target core network node can determine a control plane delay, dependent on a time at which the acknowledgement message is received at the target core network node, after the target core network node had sent the request message.

The method may comprise causing the acknowledgment message to be transmitted to the target core network node in a handover request acknowledgment message.

The method may comprise causing the acknowledgment message to comprise an indication of whether the apparatus supports a procedure taking into account control plane and user plane delay.

The method may comprise receiving a user plane packet from a source base station and causing a response to be transmitted back to the source base station, such that the source base station can determine a user plane path delay.

The user plane packet may be a protocol data unit packet.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions thereon for performing at least the following: delaying transmission of at least one first user plane packet, a delay of said user plane packet being dependent on a timing difference between a control plane path and a user plane path. According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions thereon for performing at least the following: determining a control plane path delay; and causing the control plane path delay to be provided to a base station.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions thereon for performing at least the following: causing a request message to be transmitted to a target base station and for determining a control plane delay, dependent on a time taken for an acknowledgment message to said request message to be received.

According to another aspect, there is provided a non-transitory computer readable medium comprising program instructions thereon for performing at least the following: receiving a request message; causing, in response to said request message, an acknowledgment message to be transmitted to a target core network node, such that the target core network node can determine a control plane delay, dependent on a time at which the acknowledgement message is received at the target core network node, after the target core network had sent the request message.

According to another aspect, there is provided a computer program comprising instructions stored thereon for performing at least the following: delaying transmission of at least one first user plane packet, a delay of said user plane packet being dependent on a timing difference between a control plane path and a user plane path.

According to another aspect, there is provided a computer program comprising instructions stored thereon for performing at least the following: determining a control plane path delay; and causing the control plane path delay to be provided to a base station.

According to another aspect, there is provided a computer program comprising instructions stored thereon for performing at least the following: causing a request message to be transmitted to a target base station and for determining a control plane delay, dependent on a time taken for an acknowledgment message to said request message to be received.

According to another aspect, there is provided a computer program comprising instructions stored thereon for performing at least the following: receiving a request message; causing, in response to said request message, an acknowledgment message to be transmitted to a target core network node, such that the target core network node can determine a control plane delay, dependent on a time at which the acknowledgement message is received at the target core network node, after the target core network node had sent the request message.

A computer product stored on a medium may cause an apparatus to perform the methods as described herein.

An electronic device may comprise apparatus as described herein. In the above, various aspects have been described. It should be appreciated that further aspects may be provided by the combination of any two or more of the various aspects described above.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims.

Description of Figures

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows a schematic diagram of an example communication system comprising a plurality of base stations and a plurality of communication devices;

Figure 2 shows a schematic diagram of an example communication device;

Figure 3 shows a schematic diagram of an example network function;

Figure 4 shows a schematic diagram of a distributed services network;

Figure 5 shows a schematic diagram of another distributed services network;

Figure 6 shows an example signalling diagram for a protocol data unit session establishment (for example 5G session establishment);

Figure 7 shows an example signalling diagram for inter new generation (NG) or 5G radio access network RAN node based handover in the preparation phase;

Figure 8 shows an example signalling diagram for the inter new generation (NG) or 5G radio access network RAN node based handover in the execution phase;

Figure 9 shows an example signalling diagram for an S1 -based handover;

Figure 10 shows an example of a signalling diagram between a source access and mobility management function (S-AMF) and a source radio access network (S-RAN).

Figure 1 1 shows an example of a signalling diagram between network functions;

Figure 12 shows another example of a signalling diagram between network functions;

Figure 13 shows another example of a signalling diagram between network functions; and

Figure 14 shows another example of a signalling diagram between network functions.

Detailed description

In general, the following disclosure relates to an example architecture, with associated apparatus, for a communication system. Some embodiments relate to an architecture and associated apparatus for a service based architecture with separate control and user planes.

A core network architecture may be service-based architecture (SBA), allowing some network functions (NFs), called NF service producers, to expose services to other authorized NFs, called NF service consumers, through a service-based interface. Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 2 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in Figure 1 , mobile communication devices or user apparatus (UE) 102, 104 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user is may be a user equipment (UE) or a machine type terminal or any other suitable device. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station or access point, and transmit and/or receive communications on the carrier.

The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved.

A base station may be referred to more generally as simply a network apparatus or a network access point. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatus. The controller apparatus may be part of the base station and/or provided by a separate entity such as a radio network controller. In Figure 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

In Figure 1 , base stations 106 and 107 are shown as connected to a wider communications network 1 13 via a gateway 1 12. A further gateway function may be provided to connect to another network.

There may be smaller base stations or cells (not shown) in some networks. These may be pico or femto level base stations or the like.

A possible communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device may be a user equipment (UE) or terminal. An appropriate communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, a machine type device or any combinations of these or the like.

The device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2, a transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204.

The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. This may be optional in some embodiments.

A display 208, a speaker and a microphone can be also provided. One or more of these may be optional in some embodiments.

A communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands- free equipment, thereto. One or more of these may be optional.

The communication devices may access the communication system based on various access techniques.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as 5G or New Radio (NR). The previous 3GPP based development is often referred to as 4G. Other examples of radio access system comprise those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMAX (Worldwide Interoperability for Microwave Access). It should be appreciated that although some embodiments are described in the context of a 4G and/or 5G system, other embodiments may be provided in any other suitable system including but not limited to subsequent systems or similar protocols defined outside the 3GPP forum.

An example apparatus is shown in Figure 3. Figure 3 shows an apparatus that could be comprised within a network function. As an example, the network function could be a base station, a management function, a serving gateway, a packet data network gateway, a user plane function, a mobility management function, an access and mobility management function or a session management function. The apparatus 300 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. For example the apparatus 300 can be configured to execute an appropriate software code to provide functions. The apparatus 300 may be included in a chipset apparatus.

It has been proposed to have control plane and user plane separation. This may enable flexible network deployment and operation, by distributed or centralized deployment. This may provide for the independent scaling between control plane and user plane functions, while not affecting the functionality of the existing nodes subject to this split.

Control and user plane separation (CUPS) of EPC (evolved packet core) nodes was introduced into 4G. CUPS is an architectural enhancement feature that introduces the concept of separation between the control plane and user plane of EPC nodes (such as for example S-GW (serving gateway), P-GW (packet data network gateway), and T-DF (traffic detection function)).

An example architecture for such 4G system with CUPS is shown in Figure 4.

The architecture shows a base station 401 (such as an evolved NodeB eNB) which can communicate with a mobile mobility management entity (MME) 403. The base station 401 may be in communication with one or more user equipment (UEs) (not shown). The MME 403 can communicate with a control plane serving gateway 405 (SGW-C) function which in turn can communicate with both a control plane portable gateway function 407 (PGW-C) and a user plane serving gateway function 409 (SGW-U). The SGW-U 409 is also able to communicate with a user plane portable gateway function 41 1 (PGW-U). The PGW- C function 407 can communicate with the PGW-U 41 1 .

Therefore, as seen in Figure 4 the MME 403, the SGW-C and the PGW-C make up the control plane function, while the eNB 401 , the SGW-U 409 and the PGW-U 41 1 make up the user plane function. The eNB 401 may consist of both user plane functions and control plane functions.

5G architecture has been proposed with the control plane and user plane separate. This may provide for greater flexibility and/or other network improvements.

The proposed 5G system supports a service based architecture. A service based architecture utilises a service based framework for a variety of communications-related processes, such as service registration, deregistration, discovery, selection, routing, etc. A service-based architecture is characterised by, instead of having predefined interfaces between network elements, using a services model in which components query a network function repository function (NRF) to discover and communicate with each other over application programming interfaces (APIs). An API is a function and/or procedure that supports an application which access the features or data of an operating system, application or other service.

To support this service architecture, a plurality of functional entities (also known as network functions, NFs) may be provided. Network functions may comprise one or more of:

• Access and mobility management function (AMF): the AMF may provide features relating to UE-based authentication, authorisation, registration, mobility and connection management. The AMF may be independent of access technology type, and so a UE may be connected to an AMF regardless of the access technology used;

• Network Repository Function (NRF): the NRF may support service discovery functions, maintain NF profiles and available NF instances.

• Session Management function (SMF): the SMF may provide session management functions, including allocating Internet Protocol (IP) addresses to UEs. If a UE has multiple sessions, different SMFs may be allocated to each session to manage them individually;

• Policy control function (PCF): the PCF may use information on the packet flow between two communicating entities to determine policies about mobility and session management for a given UE for the AMF and SMF to enforce this;

• Unified data management function (UDM): the UDM may store subscription data for a UE;

• Application function (AF): the AF may provide information on the packet flow to the PCF for supporting quality of services; and

• Authentication server function (AUSF): the AUSF may support authentication of a UE.

It has been proposed that some network functions (NFs), called NF service producers, expose services to other authorized NFs, called NF service consumers, through a service-based interface.

An example architecture for such a services-based architecture is depicted in Figure 5.

The architecture shows a user equipment (UE) 501 connected to a (radio) access network ((R) AN 503 at the access stratum, as well as an access and mobility management function (AMF) 511 at the non-access stratum. The RAN represents a base station.

The 5G core network (5GC) consists of various network functions (NFs) as discussed previously. In Figure 5 there are ten 5G core NFs. An access and mobility management function (AMF) 511 , a session management function (SMF) 509, a policy control function (PCF) 521 , an application function (AF) 525, an authentication server function (AUSF) 513, a user plane function (UPF) 505, unified data management (UDM) 523, a NF repository function (NRF) 519, a network exposure function (NEF) 517 and a network slice selection function (NSSF) 515. A data network (DN) 507 is shown. In Figure 5 we see the following interfaces or references connecting the NFs:

N1 is the interface between the UE and the AMF.

N2 is the interface between the (R)AN and the AMF.

N3 is the interface between the (R)AN and the UPF.

N4 is the interface between the UPF and the SMF.

N6 is the interface between the UPF and the DN.

The NFs that are housed in the first dotted box 527 are the control plane functions of the 5G architecture. These NFs are the AUSF 513, the AMF 51 1 , the SMF 509, the NSSF 515, the NEF 517, the NRF 519, the PCF 521 and the UDM 523. The second dotted box 529 shows the user plane function. The user plane NF is the UPF 505. Additionally the RAN provides a control plane function as well as a user plane function.

It has been appreciated that issues may arise in networks which use control and user plane separation. For example, the time difference in delays between the handovers in the control plane and the handovers in the user plane can lead to additional buffering and packet loss in the system.

For example, in 4G architectures the MME 403 may be in a central data centre (DC). The MME 403 may be say 5ms away from the eNB 401 . Therefore for an S1 handover, the eNB status transfer message may take approximately 10ms to travel from a source eNB (S- eNB) to the target eNB (T-eNB). However, the user plane functions (i.e. SGW-U and PGW- U) may be very close to each other, such as for example a 2ms packet delay. This means there may be time delay difference between the control plane and the user plane during handover.

As another example, in 5G architectures the AMF 51 1 may also be in a central data centre (DC). The AMF 51 1 may be 5ms away from the RAN 503. Therefore for an N2 handover, the SN status transfer message may take approximately 10ms to travel from a source RAN (S-RAN) to the target RAN (T-RAN). However, the UPFs may be very close to each other, such as for example having a 2ms packet delay. This means that there may be a time delay difference between control plane and user plane. This may be an issue for the slicing concept in 5G systems whereby there may be a single AMF for all network slices.

In these examples, the information sent via the control plane in the sequence number as part of the (SN) status transfer, the eNB status transfer and/or the MME status transfer may, depending on the topology, arrive later at the user plane than the user plane packets. This may lead to packet loss and/or to additional buffering and corresponding delay. In some cases, such as low and ultra-low latency services this may be undesirable. This may result in a service requirement not being met.

Some embodiments may provide that the user plane and the control plane paths have the same delay by collocation of the user plane path or control plane path network functions. In some embodiments, a time difference delay between the control plane (CP) and the user plane (UP) messages during a handover may be taken into account.

For example, the source base station or source radio access network may take into account the additional delay by postponing the switching of downlink DL packets from the communication device to target base station or target radio access network to a later sequence number (SN). In some embodiments, the amount of time of the postponement may be approximately the same the difference between the CP and UP delay. For example, if the CP delay is longer than the UP delay, the switching of the communications device to the target base station or radio access network shall be earlier. If the CP delay is shorter than the UP delay, then nothing may need to be done as that information may be there earlier due to the deployed topology. In some embodiments, there may be no time delay difference between the CP and the UP.

Some embodiments may be arranged to work in conjunction with legacy systems. For example if a network function is capable of supporting one or more embodiments, the network function may provide an indication of this. In some embodiments, the network functions participating in these procedures may indicate in the signalling messages that they are capable. For example, the base station and/or RAN and/or the MME and/or AMF may signal and/or evaluate these indications. This may allow the differentiation of these one or more network functions from network functions which may be legacy versions and unable to support one or more embodiments.

It should be appreciated that in some embodiments, there may be no need to provide support for any legacy functions.

In some embodiments, the control plane signalling may arrive at the user plane of a target base station before the user plane packets arrive at the target base station. The related control plane signalling may be in a SN status transfer message and/or a MME/base station status transfer message.

Some embodiments will now be described in the context of 4G and 5G networks. However, it should be appreciated that this is by way of example only and other embodiments may be described in the context of other networks. Some embodiments may be used in any suitable network where there is a separation of the control and user plane functions.

In some embodiments, the AMF 51 1 in a 5G network (or the MME 403 in a 4G network) determines the user plane delay and the control plane delay between the sNR-U (source NR (new generation) user plane) and the TNR-U (target NR user plane) or SeNB- U (source eNB user plane) and the TeNB-U (target eNB user plane) respectively.

It is to be appreciated that the mobile core network function is separated into control plane and user plane parts and/or even the base station and/or the RAN. See for instance 3GPP TS 38.401 . In embodiments, during the handover preparation, the source base station or source RAN may report the delay between its user plane and control plane in a message sent to the MME or AMF. The message may be a preparation message handover request or any other suitable message type. The MME or AMF may store this message for later usage.

The target base station or target RAN reports the delay between its user plane and control plane a message sent to the AMF or MME. This message may be a preparation message handover request acknowledgement or any of other suitable message type.

If the user plane and control plane is collocated then the base stations and/or RANs do not signal any delay or a delay of zero milliseconds (ms) is signalled. This process will be discussed in more detail below in relation to Figure 10.

In some embodiments, the control plane delay between base station and the MME or AMF will be calculated. This may be an end-to-end delay potentially consisting of several hops. For example for S1 (MME/base station) or N2 (AMF/RAN) handover it may not be calculated from just the time difference between sending the handover request message and the receipt of the handover request acknowledgement message (although this might be the case in some embodiments). This may be because the handover preparation procedure may have a plurality of interactions with one or more of for example, an AMF, a SMF and one or more UPFs. These interactions may mean control plane estimation based on the SN status transfer time between the source base station via the S-MME and the T- MME to the target base station may not be reasonable.

In some embodiments, for any instance of any AMF, the AMF will store the time difference between sending a N2 PDU (packet data unit) session request or similar message to the RAN and receipt of the N2 PDU session request acknowledgment message or a similar message from the RAN. These messages are typically exchanged during PDU session establishment, see for example Figure 6, or a similar message from the RAN. This provides a reasonable estimate of the delay between the source base station and the S- AMF.

In a 4G architecture, a delay between an eNB and an MME may be measured via an S1 setup or modification procedure. For example, the MME may store a time difference between sending an MME configuration update message or a similar message to the eNB, and receiving an MME configuration update acknowledgement message from the eNB or a similar message. A similar procedure may be found for 5G in 3GPP TS 38.413.

In this regard, reference is made to Figure 10 which shows an example of a signalling diagram between an S-AMF and an S-RAN.

At step 1 , the S-AMF may store/record a time at which the N2 PDU session request was transmitted to the S-RAN. The storing/recording may use timestamps or the like to determine the time. At step 2, the S-RAN provides an N2 PDU session request acknowledgment message to the S-AMF.

At step 3, the S-AMF stores the time difference (TD) between sending the N2 PDU session request to the S-RAN and the receipt of the N2 PDU session request acknowledgment message sent by the S-RAN. This time difference may be stored as a first time difference (TD). The first TD may provide an estimation for the control plane delay between the S-RAN and the S-AMF.

Any instance of any AMF may store the time difference between sending a handover request or similar message to a target RAN and the receipt of a handover acknowledgement message or a similar message from the target RAN. This may provide a reasonable estimate of the delay between the target base station and the target AMF. This may become the new control plane delay between the new S-AMF and the new source base station after the handover.

In this regard, reference is made to Figure 1 1 which shows an example of a signalling diagram between a T-AMF and a T-RAN.

Step 1 shows the T-AMF providing a handover request message to the T-RAN. The T-AMF may store/record a time at which the handover request message was provided to the T-RAN. The storing/recording may use timestamps to determine a time.

Step 2 shows the T-RAN providing a handover request acknowledgment message to the T-AMF.

At step 3, the T-AMF stores the time difference (TD) between sending the handover request to the T-RAN and the receipt of the handover request acknowledgment message sent by the T-RAN. This time difference may be stored as a second TD. The second TD may provide an estimation for the control plane delay between the T-RAN and the T-AMF. The second TD may become the new first TD between the new S-RAN and new S-AMF after a handover has been completed.

The T-AMF may forward the second time difference to the S-AMF. This may provide the delay between the target base station and the T-AMF. This may be added to the control plane delay. The delay associated with the signalling between the S-AMF and the T-AMF may also be added. This may be done at the same time or separately. The control plane delay information may be passed to the source RAN or base station.

Figure 12 shows an example of a signalling diagram between the T-AMF, the S- AMF and the S-RAN.

In step 1 , the T-AMF provides the second TD, to the S-AMF. The message may be a create UE context response message such a Namf_communication_createUEcontext response message or similar message.

In step 2, the S-AMF adds the received second TD to the first TD. Additionally the S-AMF adds a delay between the T-AMF and the S-AMF to the CP delay value. As an example, the delay between the T-AMF and the S-AMF may have been configured or it may have been retrieved from the new radio function or the like when selecting the T-AMF.

In step 3, the S-AMF provides a handover command message or similar message which includes the CP delay value to the S-RAN. Therefore, the S-RAN may know the control plane delay. However, at this stage the S-RAN may not know the user plane delay.

Figure 13 shows an example of a signalling diagram between the S-RAN and the T-

RAN.

In step 1 , the S-RAN transmits a PDU packet (via the user plane) to the T-RAN. This may be a packet which is only for the purpose of determining the user plane delay. In other embodiments, the S-RAN may transmit any other suitable type of packet.

In step 2, the S-RAN will store the timestamp of the transmitted PDU packet.

In step 3, the T-RAN will retransmit the PDU packet immediately after it has been received by the T-RAN.

In step 4, on receipt of the retransmitted PDU packet, the S-RAN will use the stored timestamp to calculate a third TD between sending and receiving the PDU packet. The determined third TD may represent double the user plane delay. Therefore, the S-RAN may half the third TD in order to determine a user plane delay value. The S-RAN is able to calculate a time delay difference between the user plane and the control plane by subtracting the user plane delay value from the control plane delay value.

As an alternative method to that shown in Figure 13, the S-RAN may be configured with the user plane delay towards each possible neighbour T-RAN for instance via a SON (self-organising network) function. In other embodiments, the S-RAN might retrieve the user plane delay information from the NRF.

In some embodiments, the S-RAN may send the SN status transfer message or similar message to the T-RAN, but the sending of the user plane packets is delayed by the time delay difference between the control plane and the user plane. This may ensure that the content of the control plane messages arrive before the user plane packets at the user plane of the T-RAN.

Therefore, the SN transfer information may be received at the T-RAN before the corresponding user plane packets are received at the user plane of the T-RAN. This may reduce buffering times to a minimum. This may allow the user plane at the T-RAN to be able to act on the packets received at the user plane immediately, for example, recognizing duplicates and ensuring in-sequence delivering of packets by considering the count value in the uplink and/or downlink direction.

Some embodiments may allow the size of the buffer at the T-RAN in the user plane to be reduced.

Some embodiments may reduce packet loss. Some embodiments may be provided in 4G systems for Xn and X2 handovers. References to the AMF in the previous examples may be replaced by references to MME. The control plane delay may be estimated by an source base station by measuring the time difference between sending the handover request message and the receipt of the corresponding acknowledgement message (i.e. time difference between steps 5 and 5a in Figure 9 described below). With respect to the user plane delay, in X2 and Xn handover the S-RAN and T-RAN may carry out a ping procedure in the user plane, similar to that described in relation to Figure 13.

Even in the case of architectures with a single slice, for example a 4G architecture, the same procedures shall be applied as in this case the time delay difference may be relatively large (between a source base station with an S-MME, and a T-MME with a target base station) in some deployments.

The control plane delay between two AMF’s may be determined in a similar way as described previously for the S1 procedure if the AMF is to be changed during HO or if there is a new message exchange. It should be appreciated that in the context of a 5G system the interface would be N2 and/or N 14 rather than S1 . Alternatively, in other embodiments, the AMFs might retrieve the delay information between the involved AMFs from the NRF rather than calculating the delay values as shown in Figures 6 to 10.

Some embodiments may be used to modify existing proposals.

Figure 6 shows an example signalling diagram for a protocol data unit (PDU) session establishment. Figure 6 is the signalling diagram presented as Figure 4.3.2.2.1 -1 of 3GPP TS 23.502.

At step 1 , a UE provides a PDU establishment request to an AMF.

At step 2, the AMF performs SMF selection.

At step 3, the AMF provides an Nsmf_PDUSession_CreateSMContext request to an

SMF.

In steps 4a-4b the SMF performs registration/subscription retrieval/subscription for updates with a UDM.

In step 5, the SMF provides an Nsmf_PDUSession_CreateSMContext response message to the AMF.

At step 6, there is an optional secondary authorization/authentication. If the Request Type in step 3 indicates Existing PDU Session, the SMF does not perform secondary authorization/authentication. If the Request Type received in step 3 indicates Emergency Request or Existing Emergency PDU Session, the SMF shall not perform secondary authorization/authentication. If the SMF needs to perform secondary authorization/authentication during the establishment of the PDU Session by a designated name - authentication, authorization, and accounting server (DN-AAA), the SMF triggers the PDU Session establishment authentication/authorization. At step 7a, the SMF performs PCF selection.

At step 7b the SMF performs SM policy association establishment or SMF initiated SM policy association modification.

At step 8, the SMF performs UPF selection.

At step 9, the SMF performs SMF initiated SM policy association modification.

At step 10a, the SMF provides an N4 session establishment/modification request to the UPF.

At step 10b, the UPF provides an N4 session establishment/modification response to the SMF.

At step 11 , the SMF provides a Namf_Communication_N1 N2MessageTransfer with the AMF.

At step 12, the AMF provides an N2 PDU session request message to a RAN.

At step 13, the UE and the RAN exchange AN-specific resource setup information. At step 14, the RAN provides an N2 PDU session request acknowledgement to the

AMF.

The message exchange of Figure 10 (e.g. step 1 and step 2) may use or replace the messages of steps 12 and 14 of Figure 6, in some embodiments.

At step 15, the AMF provides an Nsmf_PDUSession_UpdateSMContext request to the SMF.

Between steps 14 and 15 is the first uplink data transmission from the UE to the

UPF.

At step 16a, the SMF provides an N4 session modification request to the UPF.

At step 16b, the UPF provides an N4 session modification response to the SMF. Between steps 16a and 16b is the first downlink data transmission from the UPF to the UE.

At step 17, the SMF provides an Nsmf_PDUSession_UpdateSMContext response to the AMF.

At step 18, the SMF provides an Nsmf_PDUSession_SMContextStatusNotify message to the AMF.

At step 19, the SMF provides to the UPF which in turns provides to the UE, IPv6 Address Configuration information.

At step 20, the SMF and UDM perform unsubscription/deregistration.

Figure 7 shows an example signalling diagram for inter NG-RAN node N2 based handover in the preparation phase. Figure 7 shows the signalling of Figure 4.9.1.3.2-1 of 3GPP TS 23.502. As shown in Figure 5, the N2 interface is the interface between the RAN and the AMF.

A decision to trigger a relocation via N2 will lead to step 1 , whereby a source RAN (S-RAN) will provide a handover required message to a source AMF (S-AMF). At step 2, the S-AMF will perform target AMF (T-AMF) selection.

At step 3, the S-AMF will provide a Nam f_communication_CreateUEContext request message to the T-AMF.

At step 4, the T-AMF will provide an N smf_PDUSession_UpdateSMContext request message to an SMF.

At step 5, the SMF will perform UPF selection.

At step 6a, the SMF will provide an N4 session establishment request to a target UPF (T-UPF).

At step 6b, the T-UPF will provide a N4 session establishment response to the SMF. At step 7, the SMF will provide an N smf_PDUSession_UpdateSMContext response to the T-AMF.

At step 8, the T-AMF performs PDU handover response supervision.

At step 9, the T-AMF provides a handover request message to a target RAN (T-

RAN).

At step 10, the T-RAN provides a handover request acknowledgment message to the T-AMF.

The message exchange (e.g. step 1 and step 2) of Figure 1 1 may use or replace the messages of steps 9 and 10 of Figure 7.

At step 1 1 a, the T-AMF provides an N smf_PDUSession_UpdateSMContext request message to the SMF.

At step 1 1 b, the SMF will provide an N4 Session modification request to the T-UPF. At step 1 1 c, the T-UPF will provide a N4 session modification response to the SMF. At step 1 1 d, the SMF will provide an N4 session modification request to a source

UPF

(S-UPF).

At step 1 1 e, the S-UPF will provide a N4 session modification response to the SMF. At step 1 1f, the SMF will provide a N smf_PDUSession_UpdateSMContext response message to the T-AMF.

At step 12, the T-AMF will provide a Namf_communication_CreateUEContext response message to the S-AMF.

This signalling of Figure 12 (e.g. step 1 ) may use or replace the message of step 12 of Figure 7.

Figure 8 shows an example signalling diagram for Inter NG-RAN node N2 based handover in the execution phase. Figure 8 follows on from the signalling shown in Figure 7. The signalling shown in Figure 8 is that of Figure 4.9.1 .3.3-1 of 3GPP TS 23.502.

At step 1 , the S-AMF provides a handover command message to the S-RAN.

The message exchange (e.g. step 1 and step 2) of Figure 12 may use or replace the message of step 1 of Figure 8. At step 2, the S-RAN provides a handover command message to the UE.

In step 3, uplink packets are sent from the T-RAN to the T-UPF and UPF PDU session anchor (PSA). Downlink packets are sent from the UPF (PSA) to the S-RAN via the S-UPF. The S-RAN should start the forwarding of downlink data from the S-RAN towards the T-RAN for quality of service (QoS) Flows subject to data forwarding. This may be either direct (step 3a) or indirect forwarding (step 3b). At this point the UE synchronises to the new cell (i.e. UE syncs to T-RAN).

At step 4, the UE provides a handover confirm message to the T-RAN. The handover confirm message will indicate that the handover has been successful.

At step 5, the T-RAN provides a handover notify message to the T-AMF.

At step 6a, the T-AMF provides an Namf_Communication_N2lnfoNotify message to the S-AMF.

At step 6b, the S-AMF provides an Namf_Communication_N2lnfoNotify acknowledgment message to the T-AMF.

At step 6c, the S-AMF provides an Nsmf_PDUSession_ReleaseSMContext request message to the SMF.

At step 7, the T-AMF provides an Nsmf_PDUSession_UpdateSMContext request message to the SMF.

At step 8a, the SMF provides an N4 session modification request message to the T-

UPF.

At step 8b, the T-UPF provides an N4 session modification response message to the SMF.

At step 9a, the SMF provides an N4 session modification request message to the S-

UPF.

At step 9b, the S-UPF provides a N4 session modification response message to the

SMF.

At step 10a, the SMF provides an N4 session modification request message to the UPF (PSA).

At step 10b, the UPF (PSA) provides a N4 session modification response message to the SMF.

At step 1 1 , the SMF provides an Nsmf_PDUSession_UpdateSMContext response message to the T-AMF.

At step 12, the UE initiates a mobility registration update procedure.

At step 13a, the SMF provides a N4 session release request message to the S-UPF. At step 13b, the S-UPF provides an N4 session release response message to the

SMF.

At step 14a, the S-AMF provides a UE context release command message to the S-

RAN. At step 14b, the S-RAN provides a UE context release command complete message to the S-AMF.

At step 15a, the SMF provides an N4 session modification request message to the

T-UPF.

At step 15b, the T-UPF provides an N4 session modification response to the SMF. Figure 9 shows an example signalling diagram for an S1 -based handover. The signalling shown in Figure 9 is that of Figure 5.5.1.2.2-1 of 3GPP TS 23.401. An S1 interface based handover procedure is used when the X2-based handover (i.e. direct communication between the source base station and the target base station) cannot be used. The source eNodeB may initiate a handover by sending a handover required message over the S1 - MME reference point.

At step 1 , a source eNB (S-eNB) decides to trigger a relocation via an S1 handover. At step 2, the S-eNB provides a handover required message to a source MME (S-

MME).

At step 3, the S-MME provides a forward relocation request to a target MME (T-

MME).

At step 4, the T-MME provides a create session request to a target SGW (T-SGW). At step 4a, the T-SGW provides a create session response to the T-MME.

At step 5, the T-MME provides a handover request message to a target eNB (T- eNB).

At step 5a, the T-eNB provides a handover request acknowledgement to the T-MME. The message exchange (e.g. step 1 and step 2) of Figure 1 1 may use or replace the messages of steps 5a and 5b of Figure 7.

At step 6, the T-MME provides a create indirect data forwarding tunnel request to the T-SGW.

At step 6a, the T-SGW provides a create indirect data forwarding tunnel response to the T-MME.

At step 7, the T-MME provides a forward relocation response message to the S-

MME.

This signalling of Figure 12 (e.g. step S1 ) may use or replace the message of step 7 of Figure 9.

At step 8, the S-MME provides a create indirect data forwarding tunnel request to a source SGW (S-SGW).

At step 8a, the S-SGW provides create indirect data forwarding tunnel response to the S-MME.

At step 9, the S-MME provides a handover command message to the S-eNB.

The message exchange (e.g. step 1 and step 2) of Figure 12 may use or replace the message of step 9 of Figure 9. In step 9a, the S-eNB provides the handover command message to the UE.

In step 9b, the S-eNB provides a RAN usage data report to the S-MME.

In step 10, the S-eNB provides an eNB status transfer message to the S-MME.

At step 10a, the S-MME provides a forward access context notification to the T-

MME.

At step 10b, the T-MME provides a forward access context acknowledgment to the S-MME.

At step 10c, the T-MME provides an MME status transfer message to the T-eNB. Then the S-eNB starts the forwarding of downlink data from the S-eNB towards the T-eNB for bearers subject to data forwarding.

The forwarding is either direct from the S-eNB to the T-eNB as shown in step 11 a, or the forwarding is indirect as shown in step 1 1 b. Indirect forwarding is from the S-eNB to the S-SGW, then to the T-SGW, and finally to the T-eNB. At this point, the UE can detach from the S-eNB and synchronise to the T-eNB.

At step 12, the UE provides a handover confirm message to the T-eNB.

At step 13, the T-eNB provides a handover notify message to the T-MME.

At step 14, the T-MME provides a forward relocation complete notification to the S-

MME.

At step 14a, the S-MME provides a forward relocation complete acknowledgement to the T-MME.

At step 15, the T-MME provides a modify bearer request to the T-SGW.

At step 16, the T-SGW provides a modify bearer request to a PDN GW.

At step 16a, the PDN GW provides a modify bearer response to the T-SGW.

At step 17, the T-SGW provides a modify bearer response to the T-MME.

At step 18, the UE initiates a Tracking Area Update procedure.

At step 19a, the S-MME provides a UE context release command to the S-eNB.

At step 19b, the S-eNB provides a UE context release complete message to the S-

MME.

At step 19c, the S-MME provides a delete session request message to the S-SGW. At step 19d, the S-SGW provides a delete session response message to the S-

MME.

At step 20a, the S-MME provides a delete indirect data forwarding tunnel request to the S-SGW.

At step 20b, the S-SGW provides a delete indirect data forwarding tunnel response message to the S-MME.

At step 21 a, the T-MME provides a delete indirect data forwarding tunnel request message to the T-SGW. At step 21 b, the T-SGW provides a delete indirect data forwarding tunnel response message to the T-MME.

The steps, as shown in Figures 10 to 13, which may utilize the messaging exchanges as shown in figures 6 to 10, may be individually applied to Figures 6 to 10. Therefore, one or more steps may be omitted or changed. A subset of the signalling shown in Figures 10 to 13 may be used during a handover.

Network slicing is a form of virtual network architecture. Network slicing allows a plurality of virtual networks to be instantiated on top of a shared physical infrastructure. The benefit is that the virtual networks can be customised to the needs of a customer or an operator. For example, in 5G systems, a single physical network may be sliced into multiple virtual networks that can support different radio access networks (RANs), or different service types running across a single RAN. Network slicing may be used to partition the core network and/or it may also be implemented inside the RAN.

For example, in 3GPP TS 23. 501/23.502 there is one single AMF for a UE attached to multiple slices simultaneously, if multiple slices are allowed in the public land mobile network (PLMN) area. However, that means that only slices which are compatible with each other can be served by one single AMF hosting those multiple and compatible slices. Thus, in situations whereby slices of a network are incompatible with one another, for example, ultra-reliable low latency (URLLC) with high latency (e.g. internet browsing), there cannot be a single AMF serving the plurality of slices.

For example, in 3GPP TS 23.502 there may be a supervision timer in the AMF which supervises the response to be received from an SMF (for example, step 8 in Figure 7) which leads to termination of the handover (HO) at least for those protocol data unit (PDU) sessions which did not respond in time. The supervision timer may be governed by a lowest timer value of a maximum delay indication for the PDU sessions that are a candidate for HO. This means that if one high demanding slice expects a fast reaction time, other PDU session for other slices are not considered for HO.

This may mean that incompatible services cannot be served in two slices served by the same AMF. Therefore, these services would not be able to be run on two slices of the same physical network architecture.

In some embodiments, slices will declare if they are not compatible and do not support procedures such as set out previously. For example, an enhanced mobile broadband (eMBB) slice and URLLC slice are not compatible together and so they would declare that they are not compatible with one another in any suitable manner.

In some embodiments, if any of the participating network functions (NFs) including the RAN does not support the procedure of determining a time difference between the control plane and the user plane during handover and/or if the network already knows that the two slices are incompatible due to the specified behaviour (for example as set out in 3GPP TS 23.502 chapter 4.9.1.3.3) or because of any other relevant issue then the communication device is requested to set up a different PDU session via the data network name (DNN) approach.

As shown in Figure 14, at step 1 a UE may provide a PDU session establishment request to an AMF. In other examples, the UE may provide another suitable request format.

At step 2, the AMF may determine if the PDU session would be compatible with the current network slices. For example, the AMF may check whether the hosting base station (S-RAN) supports determining a time difference between the control plane and the user plane during handover. If not, the PDU session establishment may not be continued.

If the UE requests to setup a PDU session for single network slice selection assistance information (S-NSSAI) which is incompatible with one of the slices of the already established PDU session, then the AMF may return for this S-NSSAI an indication back to the communications device. The indication may be provided in a response message carrying a corresponding DNN to be used. The response message may be provided back to the UE as shown in step 3.

On receipt of the PDU Session Establishment response message at the UE, which may be an accept, or a reject or a similar response, the UE may set up a separate PDU session with the DNN received for that S-NSSAI. The AMF may be configured with a mapping from any S-NSSAI / Slice ID to its corresponding DNN. Alternatively, the corresponding mapping may be stored at the network slice selection function (NSSF) and may be retrieved by the AMF from the NSSF.

The example signalling diagrams of Figures 10 to 14 use 5G architecture, however, in other examples 4G architecture can perform the same signalling. For example, the AMF would be replaced with an MME, while the RAN would be replaced with an eNB. However, the RAN and the eNB and their corresponding control plane and user plane functions are just examples. It is not excluded that the same procedure can be applied for non-3GPP fixed access networks.

In other embodiments different entities may be used to provide the functions of one or more of the entities shown in Figures 10 to 14.

In other networks, one or more different entities may provide the functions of the entities of Figures 10 to 14.

In some embodiments, during a session establishment and with/after each service request and handover, the AMF or MME provides an estimation for the control plane delay between the AMF or MME and the base station or RAN.

Some embodiments may be used with a slicing concept, such as in 5G, where there is one single AMF for all slices. In some embodiments, the AMF, during the session establishment and with/after each service request and handover procedure, provides a new estimation, for each slice, for the control plane delay between the AMF and the RAN. For example, the AMF may provide a new estimation for the control plane delay for each PDU session in any slice in a 5G architecture. It should be appreciated that there may not be any network slices in a 4G architecture.

In another example, instead of one single MME/AMF at the centralized DC (data centre), distributed MMEs/AMFs are used for all slices and all UEs. This may mean that MMEs/AMFs may be relocated. This may be relatively frequently.

Thus, in some embodiments, by determining the time difference between control plane delays and user plane delays during a handover, user plane packets can be delayed by the determined time difference such that packet loss and/or additional buffering may be minimized at the target RAN.

It should be understood that each block of the flowchart of the Figures and any combination thereof may be implemented by various means or their combinations, such as hardware, software, firmware, one or more processors and/or circuitry.

It is noted that whilst embodiments have been described in relation to one example of a standalone 5G networks, similar principles maybe applied in relation to other examples of standalone 3G or LTE networks. It should be noted that other embodiments may be based on other cellular technology other than 5G or on variants of 5G. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

It should be understood that the apparatuses may comprise or be coupled to other units or modules. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. The embodiments of this invention may be implemented by computer software executable by a data processor, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non- transitory media.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1 . An apparatus comprising means for:

delaying transmission of at least one first user plane packet, a delay of said first user plane packet being dependent on a timing difference between a control plane path and a user plane path.

2. An apparatus as claimed in claim 1 , wherein the means is for causing a second user plane packet to be transmitted to a target base station and for determining a user plane path delay dependent on a time taken for a response to said second user plane packet to be received.

3. An apparatus as claimed in claim 1 , wherein the means is for receiving user plane path delay information providing a user plane path delay, said user plane path delay information being between a source base station and a target base station.

4. An apparatus as claimed in any preceding claim, wherein the means is for receiving information about a control plane path delay.

5. An apparatus comprising means for:

determining a control plane path delay; and

causing the control plane path delay to be provided to a base station.

6. An apparatus as claimed in claim 5, wherein the means is for causing the control plane path delay to be provided to a network entity in a handover command message.

7. An apparatus as claimed in claim 5 or claim 6, wherein the means is for causing a first request message to be transmitted to a source base station and for determining a first control plane delay, dependent on a time taken for a response message to said first request message to be received.

8. An apparatus as claimed in any of claims 5 to 7, wherein the means is for receiving a second control plane delay, the second control plane delay being dependent on a control plane delay between a target core network function and a target base station.

9. An apparatus as claimed in claim 8 when appended to claim 7, wherein the means is for determining the control plane path delay by combining one or more of the first control plane delay, which is dependent on the control plane path to source base station, the second control plane delay which is dependent on the control path between the target core network function and the target base station, and a third control plane delay which is dependent on a control plane delay to the target core network function.

10. An apparatus comprising means for:

causing a request message to be transmitted to a target base station and for determining a control plane delay, dependent on a time taken for an acknowledgment message to said request message to be received.

1 1 . An apparatus as claimed in claim 10, wherein the means is for causing the request message to be transmitted to the target base station in a handover request message.

12. An apparatus as claimed in claim 10 or claim 1 1 , wherein the means is for providing the determined control plane delay to a core network entity.

13. An apparatus comprising means for:

receiving a request message;

causing, in response to said request message, an acknowledgment message to be transmitted to a target core network node, such that the target core network node can determine a control plane delay, dependent on a time at which the acknowledgement message is received at the target core network node, after the target core network node had sent the request message.

14. An apparatus as claimed in claim 13, wherein the means is for causing the acknowledgment message to comprise an indication of whether the apparatus supports a procedure taking into account control plane and user plane delay.

15. An apparatus as claimed in claim 13 or claim 14, wherein the means is for receiving a user plane packet from a source base station and causing a response to be transmitted back to the source base station, such that the source base station can determine a user plane path delay.

16. A method comprising:

17. A method comprising:

determining a control plane path delay; and

causing the control plane path delay to be provided to a base station.

18. A method comprising:

19. A method comprising:

receiving a request message;

20. A computer program comprising computer executable code which when run causes the method of any of claims 15 to 19 to be performed.