CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a 35 U.S.C. § 371 National Stage of International Patent Application No. PCT/EP2017/080110, filed Nov. 22, 2017, designating the United States and claiming priority to U.S. provisional application no. 62/474,392, filed on Mar. 21, 2017. The above identified applications are incorporated by reference.

TECHNICAL FIELD

Embodiments herein relate generally to an Access and Mobility Management Function (AMF) and a method performed by the AMF. More particularly the embodiments herein relate to handling handover.

BACKGROUND

The Next Generation (NG) mobile wireless communication system, which is referred to as “5G,” will support a diverse set of use cases and a diverse set of deployment scenarios. 5G will encompass an evolution of today's 4G Long Term Evolution (LTE) networks. The terms 5G and 4G are short for fifth generation and fourth generation.

Reference point representation of the 5G architecture has been decided by the 3GPP. Two examples of this representation are provided inFIGS. 1 and 2.

FIG. 1illustrates a non-roaming architecture view for next generation (NG) networks. In other words,FIG. 1illustrates a non-roaming 5G system architecture in reference point representation.FIG. 1illustrates a UE102that is adapted to be connected to a (Radio) Access Network ((R)AN)104. The parenthesis in the (R)AN104indicates that the term refers to an AN or a RAN. The (R)AN may comprise an AN node, a RAN node, a (R)AN node etc. In the text herein, the terms (R)AN or RAN may be used when referring to the (R)AN node, AN node or RAN node. The (R)AN104in the NG network may also be referred to as a NG (R)AN or NG RAN. The (R)AN104is adapted to be connected to an AMF106via a N2 reference point. N14 is a reference between two AMFs106, however only one AMF106is illustrated inFIG. 1for the sake of simplicity. The UE102is adapted to be connected to the AMF106via a N1 reference point. The AMF106is adapted to be connected to a SMF108via a N11 reference point. The (R)AN104is adapted to be connected to a User Plane Function (UPF, UP function)110via a N3 reference point. Two UPFs110are adapted to be connected to each other via a N9 reference point, however only one UPF110is illustrated here for the sake of simplicity.

The UPF110is adapted to be connected to the SMF108via a N4 reference point. The SMF108is adapted to be connected to a Policy Control Function (PCF)113via a N7 reference point. The PCF113and the AMF106are adapted to be connected to each other via a N15 reference point. The PCF115is adapted to be connected to an Application Function (AF)115via a N5 reference point. The UPF110is adapted to be connected to a Data Network (DN)120via a N6 reference point. An Authentication Server Function (AUSF)122is adapted to be connected to the AMF106via a N12 reference point. The AUSF122is adapted to be connected to a Unified Data Management (UDM)123via a N13 reference point. The UDM123may also be referred to as a UDM node. The UDM123is adapted to be connected to the AMF106via a N8 reference point and to the SMF108via a N10 reference point.

When the term function is used herein, e.g. as in application function, policy control function etc., such function may be implemented in a node, entity etc. Consequently, the AF may be referred to as an AF node, the PCF may be referred to as a PCF node etc.

The UE102may be a device by which a subscriber may access services offered by an operator's network and services outside operator's network to which the operators radio access network and Core Network (CN) provide access, e.g. access to the Internet. The UE102may be any device, mobile or stationary, enabled to communicate in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device, Device to Device (D2D) device, Internet of Things (IoT) device or any type of consumer electronic, for instance but not limited to television, UE102, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The UE102may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another UE or a server.

The (R)AN104may be represented by a base station such as a NodeB, an evolved NodeB (eNodeB, eNB), gNodeB, gNB, Radio Network Controller (RNC), Base Station Controller (BSC), or any other network unit capable to communicate over a radio carrier with the UE102being served by the (R)AN104.

FIG. 2illustrates a roaming, e.g. home-routed, architecture view for next generation networks. In other words,FIG. 2illustrates a roaming 5G system architecture home routed scenario in reference point representation.FIG. 2illustrates a Home Public Land Mobile Network (HPLMN, H-PLMN)200aand a Visited PLMN (VPLMN, V-PLMN)200b. The letters a and b are used in reference numbers inFIG. 2in order to clarify whether the entity is located in the HPLMN200aor the VPLMN200b, where a indicates the HPLMN and b indicates the VPLMN200a. The vertical dotted line illustrates the division between the HPLMN200aand the VPLMN200a, i.e. the HPLMN200ais on the right side of the dotted line and the VPLMN200bis on the left side of the dotted line.

The UE102is in the VPLMN200aand is adapted to be connected to the (R)AN104in the VPLMN200b. The (R)AN104is adapted to be connected to the UPF110in the VPLMN200bvia a N3 reference point. The UE102is adapted to be connected to the AMF106via the N1 reference point, and the (R)AN104is adapted to be connected to the AMF106via the N2 reference point. The UPF110is adapted to be connected to a visited-SMF (V-SMF, VSMF)108bvia a N4 reference point. The V-SMF108bis adapted to be connected to the AMF106via a N11 reference point. The AMF106is adapted to be connected to a Visited-PCF (V-PCF, VPCF)113bvia a N15 reference point. As mentioned above, the VPLMN200acomprises a UPF110.FIG. 2illustrates that the HPLMN200aalso comprises a UPF110. The UPF110in the VPLMN200ais adapted to be connected to the UPF110in the HPLMN200avia a N9 reference point. The UPF110in the HPLMN200ais adapted to be connected to the DN120via a N6 reference point. The UPF110in the HPLMN200ais adapted to be connected to a Home-SMF (H-SMF, HSMF)108avia a N4 reference point. The H-SMF108ain the HPLMN200ais adapted to be connected to the V-SMF1008bin the VPLMN200avia a N16 reference point. The H-SMF108ais adapted to be connected to a Home-PCF (H-PCF, HPCF)113ain the HPLMN200avia a N7 reference point. The H-PCF113ais adapted to be connected to an AF115via a N5 reference point. The H-SMF108ais adapted to be connected to the UDM123via a N10 reference point. The UDM123is adapted to be connected to the AUSF122via a N13 reference point. The H-PCF113ain the HPLMN200ais adapted to be connected to the V-PCF113bin the VPLMN200bvia an N7r reference point. The UDM123in the HPLMN200ais adapted to be connected to the AMF106in the VPLMN200avia a N8 reference point. The AMF106in the VPLMN200bis adapted to be connected to the AUSF122in the HPLMN200avia a N12 reference point.

As exemplified inFIG. 2, the HPLM200amay comprise the DN120, the UPF110, the AF115, the H-PCF113a, the H-SMF108a, the UDM and the AUSF. The VPLMN200bis exemplified to comprise the UPF110, the (R)AN104, the UE102, the V-SMF108b, the AMF106and the V-PCF113b. Note that the HPLMN200aand the VPLMN200bmay comprise other entities in addition to or instead of the ones exemplified inFIG. 2. For example, the HPLMN200amay comprise an AMF106in addition to the entities already illustrated inFIG. 2. An AMF106in the VPLMN200bmay be referred to as a Visited-AMF (V-AMF, VAMF)106b, and an AMF106in the HPLMN200amay be referred to as a Home-AMF (H-AMF, HAMF)106a.

Handover may be described as the procedure for when a UE102is leaving an area served by one (R)AN104, and moves to another area which is served by another (R)AN104. In other words, the UE102is handed over from one (R)AN to another (R)AN. The (R)AN which currently serves the UE102may be referred to as a serving or source (R)AN (S-RAN, SRAN) and the (R)AN to which the UE102is to be handed over to may be referred to as a target (R)AN (T-RAN, TRAN). The (R)AN104which currently serves the UE102may be in the HPLMN200aor the VPLMN200b. The terms source (S) and target (T) may be used herein with the same meaning for other entities in the network such as e.g. S-AMF, T-AMF etc. The letters t and s are used in reference numbers in order to indicate whether the entity is a source entity or a target entity, where s indicates the source and t indicates the target. When the reference numbers do not have any t or s, they refer to any entity regardless of whether they are target or source entities. A source entity may be in the HPLMN200aor in the VPLMN200b, and the target entity may be in the HPLMN200aor in the VPLMN200bin which the source entity is not located.

It should be noted that the communication links inFIGS. 1 and 2may be of any suitable kind including either a wired or wireless link. The links may use any suitable protocol depending on type and level of layer, e.g. as indicated by the Open Systems Interconnection (OSI) model.

Referring toFIGS. 1 and 2, the AMF106and SMF108represents the Control Plane (CP) of the core network and has the same functionality as the control plane parts of a Serving General Packet Radio Services (GPRS) Support Node (SGSN), MME, Gateway GPRS Support Node (GGSN), Serving Gateway (SGW) and Packet Data Network (PDN) Gateway (PGW) in Global System for Mobile communications (GSM) Enhanced Data rates for GSM Evolution (EDGE) Radio Access Network (GERAN), UTRAN and E-UTRAN. The PCF113is a similar function as the Policy and Charging Rules Function (PCRF) used for GERAN, UTRAN and E-UTRAN. The UDM123is the subscription information storage including all information for the subscribers of the operator. When a subscriber connects to the network, subscription information is retrieved from the UDM123. In a roaming scenario such as inFIG. 2, the serving operator retrieves subscription information located in the home operator's network. The UDM123can be seen as similar to Home Subscriber Server (HSS) or Home Location Register (HLR), the first used for LTE/Evolved Packet System (EPS) and the second used for GERAN and UTRAN. Note that GERAN and UTRAN is not supported in 5G.

4G LTE uses an S1-based handover. This S1-based handover is described in 3GPP TS 23.401 v15.3.0 (March 2017), see e.g., clause 5.5.1.2.2S1-based handover, normal. Work on the specification for handover procedures for the 5G network has begun.

Currently, there is no N2 based handover included in the 5G specifications, e.g. 3GPP TS 23.501 and 23.502. N2 is a reference point between the Radio Access Network (RAN) and the Access and Mobility Management Function (AMF). Using 4G S1 handover as model for N2 based handover may work to some extent, but changes are needed due to several new concepts included in 5G that are not included in 4G (such as, for example, Mobility Management-Session Management (MM-SM) split, the possibility to have only some of the sessions as active, compared with Third Generation (3G), the possibility to use several network slices for a User Equipment (UE), and use of Session and Service Continuity (SSC) mode 2). Also the new low latency requirements for certain use cases puts new demands upon the handling of handover. The 51 mentioned above is a reference point between the Evolved-Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) and the Mobility Management Entity MME in 4G. Therefore, there is a need to at least mitigate or solve this issue.

SUMMARY

An objective of embodiments herein is therefore to obviate at least one of the above disadvantages and to optimize handling of handover.

According to a first aspect, the object is achieved by a method performed by an AMF for handling handover. The AMF receives one of: a handover required message and a first request message. The handover required message is transmitted by a Source-Radio Access Network (S-RAN). The first request message is transmitted by another AMF in response to the handover required message transmitted by the S-RAN. The AMF sends a set of one or more first Protocol Data Unit (PDU) request messages to a SMF and activates a timer. The AMF determines whether at least one of the following is true: a certain amount of time has elapsed since the timer was activated and the AMF has received a first PDU response message for each one of the first PDU request messages sent to the SMF. The AMF transmits a handover request message to a Target-Radio Access Network (T-RAN) as a result of determining that at least one of the conditions is true.

According to a second aspect, the object is achieved by an AMF for handling handover. The AMF is adapted to receive one of: a handover required message and a first request message. The handover required message is transmitted by an S-RAN, and the first request message is transmitted by another AMF in response to the handover required message transmitted by the S-RAN. The AMF is adapted to send a set of one or more first PDU request messages to a SMF, and to activate a timer. The AMF is adapted to determine whether at least one of the following is true: a certain amount of time has elapsed since the timer was activated and the AMF has received a first PDU response message for each one of the first PDU request messages sent to the SMF. The AMF is adapted to transmit a handover request message to a T-RAN, as a result of determining that at least one of the conditions is true.

Thanks to the timer and the received first PDU response message, handling of handover is optimized in that a N2 based handover is enabled.

Embodiments herein afford many advantages, of which a non-exhaustive list of examples follows:

One advantage of the embodiments herein is that the introduction of a time budget, i.e. the timer activation, enables the network to limit the execution time for a handover, which is important for network slices that have very strict latency requirements.

Another advantage of the embodiments herein is that a mechanism is introduced for handling PDU sessions supporting SSC mode 2 with UPF relocation during handover. In this way the T-RAN does not need to allocate resources for PDU sessions that do not need to be set up. In a worst case, the T-RAN lacks these resources whereby there is a risk that a whole load based handover is canceled by the S-RAN.

The embodiments herein are not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

