WO2017162295A1

WO2017162295A1 - Method and node for handling re-selection of a serving node to serve a ue

Info

Publication number: WO2017162295A1
Application number: PCT/EP2016/056609
Authority: WO
Inventors: Yong Yang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-03-24
Filing date: 2016-03-24
Publication date: 2017-09-28

Abstract

The embodiments herein relate to a method performed by a re-selecting node (108) for handling selection of a serving EPC node (110a, 110b, 110c) to serve a UE (101). The re-selecting node (108) comprises EPC node information of EPC nodes (110a, 110b, 110c) in an EPC node domain that the re-selecting node (108) is responsible for. The re-selecting node (108) receives a request message associated with the UE (101). The request message comprises request message information. The re-selecting node (108) re-selects, based on the EPC node information and the request message information, a second EPC node (110b, 208e) as the serving EPC node among to serve the UE (101) instead of a first node (110a, 208a) currently selected to be the serving EPC node. The re-selecting node (108) forwards the request message together with forwarding information to the second EPC node (110b, 208e) as the re-selected serving EPC node.

Description

METHOD AND NODE FOR HANDLING RE-SELECTION OF A SERVING NODE TO SERVE A UE

TECHNICAL FIELD

Embodiments herein relate generally to a re-selecting node and a method performed by the re-selecting node. More particularly the embodiments herein relate to handling selection of a serving Evolved Packet Core (EPC) node to serve a User Equipment (UE).

BACKGROUND

The Third Generation Partnership Project (3GPP) has introduced Dedicated Core Network (DCN) concept as specified in sub clause 4.3.25 of 3GPP TS 23.401 V13.5.0 (2015-12). DCN enables an operator to deploy multiple DCNs within a Public Land

Mobile Network (PLMN) with each DCN consisting of one or multiple Core Network (CN) nodes. Each DCN may be dedicated to serve specific type(s) of subscriber. DCN may be deployed for one or multiple Radio Access Technologies (RATs) (e.g. GERAN, UTRAN and E-UTRAN). GERAN is short for GSM EDGE Radio Access Network, GSM is short for Global System for Mobile Communications, EDGE is short for Enhanced Data Rates for GSM Evolution, UTRAN is short for Universal Terrestrial Radio Access Network and E-UTRAN is short for Evolved-UTRAN.

A DCN may comprise one or more Mobility Management Entity/Serving General Packet Radio Services Support Node (MME/SGSNs) and one or more Serving

Gateways/Packet data network Gateways/Policy and Charging Rules Functions

(SGW/PGW/PCRFs). The DCN feature enables subscribers to be allocated to and served by a DCN based on subscription information ("UE Usage Type"). The feature requires no specific User Equipment (UE) functionality, i.e. it also works with UEs of earlier releases.

According to the 3GPP, the motivation for deploying the DCN concept may be for example "to provide DCNs with specific characteristics/functions or scaling, to isolate specific UEs or subscribers (e.g. M2M subscribers, subscribers belonging to a specific enterprise or separate administrative domain, etc.)". M2M is short for Machine to Machine. In the Fifth Generation (5G) Context, networks may be built in a flexible way so that speed, capacity and coverage can be allocated in logical slices to meet the specific demands of each use case. This may be referred to as network slicing. In addition to the DCN, in the 5G context, the network slicing concept has been introduced to address different use cases, such as e.g.:

· Mobile broadband experience everywhere with more video, higher speeds, and wide scale availability

• Massive Machine Type Communication (MTC) with transportation monitoring and control leading the list.

• Mass market personalized TV with big data analytics helping to shape the video experience.

• Critical MTC with remote operation putting both bandwidth and latency demands on the network.

Each use case will require a different configuration of requirements and parameters in the network. Each use case will require its own Network Slice.

For example, networks may be built in a flexible way so that speed, capacity and coverage can be allocated in logical slices to meet the specific demands of each use case.

A way to implement Network Slices is to use Service Provider SDN, NFV and network orchestration. There are commercial solutions using an SDN Controller to configure network service chains (Header Enrichment, DPI, Video Optimization, Parental Control) per user, service or other parameter. The SDN Service Chaining solution may build a Network Slice for each user or service. NFV solutions exist for virtual EPC and virtual IMS. In both cases, the flexibility inherent in NFV enables operators to set up services quickly, and move them around as virtual machines in response to network demands. It should also be possible via the OSS/BSS for third parties to configure, deploy and manage their own network slide, without intervention from the operator. All of these functions will scale and translate directly into the future cross-domain, integrated 5G network." Some of the abbreviations mentioned in the cited sections above will now be described. SDN is short for Software Defined Network. NFV is short for Network Function

Virtualization. DPI is short for Deep Packet Inspection. IMS is short for IP Multimedia Subsystem, where IP is short for Internet Protocol. OSS is short for Operations Support System, and BSS is short for Business Support System.

So, it is important, when a UE attaches to the network, how to make sure that an appropriate network slice, including different core network entities, is selected to serve the UE. Having said that 3GPP has agreed that there are UEs with distinct different traffic characteristics, e.g. Internet of Things (loT) Devices as studied in 3GPP TR 23.720 V1 .3.0 (2016-02), chapter 4.3, which are very cheap and disposable, and they will send only infrequent small data; while the existing devices using Mobile broadband service will expect high throughput and will generate large amount of signaling messages due to frequent mobility, on the other hand, other type of machine type devices, e.g. for an industry controlling device, which requires very low latency, so these various devices require network resources in different ways, and so that an EPC entity may be developed/implemented with the support of only a subset of features specifically ONLY for a certain type of UEs, where the software and hardware are constructed in the way to more efficient to support those features.

The term EPC entity used herein may be also referred to as an EPC node, an EPC unit, and EPC module, an EPC element, an EPC means etc. Examples of an EPC entity may be a MME, a SGW, a PGW, a PCRF, a Home Subscriber Server (HSS), evolved Packet Data Network Gateway (ePDG), SGSN, virtualized MME (vMME), virtualized SGW

(vSGW), virtualized PGW (vPGW), virtualized PCRF (vPCRF), virtualized HSS (vHSS) etc. Even though EPC is used as an example herein, the text is equally applicable to PC, in general. I.e. the text is not limited to EPC, and EPC is only used as an example. For example, loT devices may support certain power saving mechanism, e.g. extended Discontinuous Reception (eDRX) feature, to be able to use it, the network (i.e. EPC entities) must have corresponding functionalities, e.g. the SGW needs to support extended Downlink Data Buffering feature and the MME needs to support the eDRX feature, e.g. be able to calculate when the UE is reachable. However such functionalities does not need to be implemented for the EPC entities which are dedicated for the devices using Mobile Broadband, i.e. those devices may not use the eDRX feature and does not require SGW extended buffering.

So a dedicated core network is created to serve one or more dedicated type of UEs which require similar capabilities on the network resource. E.g. to support high latency communication, the SGW needs to be equipped with a large memory to buffer Downlink Data while having less Central Processing Unit (CPU) power since those UEs have much less mobility. Some other SGWs may be equipped with a faster CPU power, considering that they have to serve UEs having higher mobility (which triggers a large amount of network signaling).

Thus examples of different requirements on a SGW may be as follows:

• Less or more memory, e.g. for downlink user plane data buffering.

· A slower or faster CPU, or more or fewer parallel CPUs.

• Etc.

One of benefit for such DCN is that EPC entities are just required to support a subset of available 3GPP feature which are developed for a specific UE group. Such approach will be much more cost efficient, thus to save Operating Expenditures (OPEX) and Capital Expenditures (CAPEX) of the operator. If such dedicated core network is deployed, or at least some of EPC entities with support of only a subset of 3GPP features are deployed in the network, so the key issue here is to select a suitable/right EPC entity to serve a UE.

The current solution for selecting a suitable/right EPC entity includes:

1. Selection of a Mobility management node (during Packet Data Network (PDN) connection creation and idle mode mobility). a) Radio Access Network (RAN) (represented by e.g. an evolved NodeB (eNB) or a Radio Network controller (RNC)) tries to select a mobility management node per existing Non-Access Stratum (NAS) Node Selection Function (as specified in 3GPP TS 36.300 V13.2.0 (2015-12), 19.2.1.17); b) The selected mobility management node needs to determine if the selection performed by the RAN is correct or not. The decision is taken based on UE usage type, together serving network policies which also contain local configuration information. If the selection is not correct, the mobility management node triggers a NAS re-direction procedure as specified in 5.19.1 of 3GPP TS 23.401 V13.5.0 (2015-12). c) A new mobility management node may be selected.

2. Selection of gateway nodes and Mobility management node (only applicable for inter MME/SGSN handover procedure). a) As specified in sub clause 4.3.8 in TS 23.401 , v13.5.0, a number of DNS procedures are used to select a proper EPC entity. The detail of DNS procedures is specified in TS 29.303.

b) If DCN is deployed, the node performing a gateway selection function needs to support a new Domain Name System (DNS) procedure enhanced for DCN. The DNS Name Authority Pointer (NAPTR) record for a gateway belonging to a DCN is enhanced by that the corresponding field for the Service Parameter is appended with "+ue" with value(s) corresponding to the supported UE usage type(s).

The parameter UE usage type is part of subscription data, and describes the usage type of a particular UE 101 , e.g. the traffic characteristics of the UE 101. Different EPC nodes may support different UE usage types. For example, a certain SGW may support UE usage type 1 and 2 and another SGW may support UE usage type 3 and 4. The UE usage types are preconfigured in the DNS. The selection function in Core Network is to efficiently select an EPC node which is designated to serve a UE, where the capability (e.g. the support of various features, the manner of allocation of CPU and Memory) of the selected EPC node should match what the UE is expecting for the network, i.e. the selected EPC node should fit the UE traffic characteristics, UE subscription information, RAT type that UE is access from, UE radio capability and so on, in addition, the load sharing among EPC entities and potential overload situation should be also considered during a selection.

However, the existing solution relies on that the node performing the selection function, e.g. an MME, has to be equipped with knowledge of target node domain, e.g. SGW, which is as sufficient as possible. The finer information it has, the finer selection it can perform. Such knowledge may be obtained via a DNS procedure or by local

configuration. While provisioning sufficient information in the DNS server or local configuration can hardly be made dynamic, i.e. dynamically reflecting the current status of each of target EPC entities, which may be upgraded to support certain new feature. The data in the DNS or in a local configuration are semi-static. In addition, relying on the DNS configuration requires a lot of provisioning; it is error prone and not very flexible and not scalable. In addition, the node performing the selection function has to process and store a large quantity of information of each of target EPC node properties, so that it can select one of time, and such processing may increase the latency, e.g. causing delay in the PDN Connection Creation procedure.

SUMMARY

An objective of embodiments herein is therefore to obviate at least one of the above disadvantages and to provide improved selection of a serving EPC node to serve a UE.

According to a first aspect, the object is achieved by a method performed by a re- selecting node for handling selection of a serving EPC node to serve a UE. The re- selecting node comprises EPC node information for each EPC node of a plurality of EPC nodes in at least one EPC node domain that the re-selecting node is responsible for. The EPC node information indicates properties of the plurality of EPC nodes. The re- selecting node receives a request message associated with the UE. The request message comprises request message information enabling re-selection of a serving EPC node from the plurality of EPC nodes in the EPC node domain. The re-selecting node re-selects, based on the EPC node information and the received request message information, a second EPC node as the serving EPC node among the plurality of EPC nodes in the EPC node domain to serve the UE instead of a first node currently selected to be the serving EPC node. The re-selecting node forwards the request message together with forwarding information to the second EPC node as the re-selected serving EPC node to inform the re-selected serving EPC node that it should serve the UE.

According to a first aspect, the object is achieved by a re-selecting node for handling selection of a serving EPC node to serve UE. The re-selecting node comprises EPC node information for each EPC node of a plurality of EPC nodes in at least one EPC node domain that the re-selecting node is responsible for. The EPC node information indicates properties of the plurality of EPC nodes. The re-selecting node is adapted to receive a request message associated with the UE. The request message comprises request message information enabling re-selection of a serving EPC node from the plurality of EPC nodes in the EPC node domain. The re-selecting node is adapted to re- select, based on the EPC node information and the received request message information, a second EPC node as the serving EPC node among the plurality of EPC nodes in the EPC node domain to serve the UE instead of a first node currently selected to be the serving EPC node. The re-selecting node is adapted to forward the request message together with forwarding information to the second EPC node as the re- selected serving EPC node to inform the re-selected serving EPC node that it should serve the UE.

Since the re-selecting node re-selects the second EPC node as the serving EPC node to serve the UE instead of a first node currently selected to be the serving EPC node, improved selection of a serving EPC node to serve a UE since the second EPC node is more suitable to serve the UE instead of the first node.

Embodiments herein afford many advantages, of which a non-exhaustive list of examples follows: The re-selection of the serving EPC node is based on information comprised in the request message which is related to the UE context and on the EPC node information. This information is constantly updated to reflect the dynamic status of each EPC entities in the EPC node domain that the re-selecting node is responsible for. This can achieve a finer selection, in comparison to use DNS mechanism, where the information configured in the DNS is rather static, and limited. Thus, an advantage of the embodiments herein is that it is possible to perform finer selection than to use DNS. The embodiments herein are more flexible and scalable, and since there needs less DNS provision, so it reduces operational cost, not error prone.

The embodiments herein propose an improved alternative and a more realistic alternative to re-select a suitable EPC node to serve a UE in the 5G, when dedicated core is deployed. On the other hand, it reduces co-ordination of configuration effort, e.g. with DNS procedure enhanced for Dedicated Core Network, it is required all EPC entities have the same understanding for each of UE usage type.

Another advantage of the embodiments herein is that the DNS procedure becomes very simple with much less DNS records, and reducing the operation cost. For example, to select a SGW for a given Tracking Area Identity (TAI), only one SGW (e.g. the default SGW) needs to be defined in the DNS server, so that the MME always contact this one SGW.

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.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will now be further described in more detail in the following detailed description by reference to the appended drawings illustrating the embodiments and in which:

Fig. 1 is a schematic block diagram illustrating embodiments of a communications system.

Fig. 2 is a schematic block diagram illustrating embodiments of a communications system.

Fig. 3 is signaling diagram illustrating embodiments of a method.

Fig. 4 is a combined block diagram and flow chart illustrating embodiments of a

method.

Fig. 5 is flow chart illustrating embodiments of a method performed by the re-selecting node.

Fig. 6 is schematic block diagram illustrating embodiments of the re-selecting node.

The drawings are not necessarily to scale and the dimensions of certain features may have been exaggerated for the sake of clarity. Emphasis is instead placed upon

illustrating the principle of the embodiments herein.

DETAILED DESCRIPTION

Figure 1 depicts a communications system 100 in which embodiments herein may be implemented. The communications system 100 may in some embodiments apply to one or more radio access technologies such as for example 2G, 3G, 4G, 5G, or any other 3GPP Radio Access Technology (RAT) or other non-3GPP RATs such as Wireless

Local Area Network (WLAN). The communications system 100 may also be referred to as e.g. a wireless communications network, a wireless communications system, a communications network, a network or a system. The communications system 100 may comprise a DCN or an eDCN.

The communications system 100 comprises a plurality of UEs of which one UE 101 is illustrated. A RAN 103 may comprise a RAN node 105 which serves the UE 101. The RAN node 105 may be a base station such as a NodeB, an evolved NodeB (eNodeB, eNB), Radio Network Controller (RNC), Base Station Controller (BSC) or any other network unit capable to communicate over a radio carrier with the UE 101.

The UE 101 may 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 provide access, e.g. access to the Internet. The UE 101 may 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 (loT) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The UE 101 may 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 device or a server. The communications system 100 comprises a re-selecting node 108. In some embodiments, the re-selecting node 108 is a node which is dedicated to perform re-selection actions, e.g. re-selection of an EPC node, e.g. according to the context of a received request message. In other embodiments, the re-selecting node 108 is one of the EPC nodes 110 in an EPC domain. The properties and functions of the re-selecting node 108 will be described in more detail later. The re-selecting node 108 may be responsible for one or more EPC node domains.

The RAN 103 is connected to at least one an EPC node domain (the connection is not shown in fig. 1 ), and the EPC node domain comprises a plurality of EPC nodes 110. In figure 1 , the EPC node domain is exemplified to comprise EPC node 1 1 10a, EPC node 2 1 10b and EPC node n 1 10c, where n is a positive integer. I.e. the EPC node domain may comprise n number of EPC nodes 1 10. The EPC node 1 1 10a may be referred to as a first EPC node, the EPC node 2 100b may be referred to as a second EPC node etc. The EPC node domain may be described as a product domain where all nodes are of the same type or product. However, the different EPC nodes in a domain may be able to handle UEs 101 of different traffic

characteristics. For example, the EPC nodes 1 10 may be SGWs (i.e. the product is a SGW), and the EPC node domain may then be referred to as a SGW domain. In another example, the EPC nodes 1 10 may be PGWs (i.e. the product is a PGW), and then the EPC node domain may be referred to as a PGW domain. The EPC nodes 1 10 may be comprised in an eDCN. The EPC node domain may also be described as an EPC node group. The reference number 1 10 is used herein when referring to any of the EPC nodes 1 10 in the EPC domain.

Figure 1 illustrates only one EPC domain for the sake of simplicity, but the communication system 100 may comprise any other suitable number of EPC node domains, e.g. two, three etc. Examples of such other number of EPC domains will be given below.

The EPC nodes 1 10 in the EPC node domain may be described as being comprised in one or more (different) DCNs. The DCN may comprise more nodes in addition to the ones illustrated in figure 1.

It should be noted that the communication links in the communications system 100 may be of any suitable kind including either a wired or wireless link. The link may use any suitable protocol depending on type and level of layer (e.g. as indicated by the OSI model) as understood by the person skilled in the art.

Figure 2 illustrates an example of the communications system 100 in figure 1. Figure 2 illustrates the UE 101 and the RAN 103 as in figures 1. The RAN node 105 in figure 1 is represented by an eNB 205 in figure 2.

In figure 2, the communication system 100 comprises three EPC node domains, i.e. an MME domain, a SGW domain and a PGW domain. The MME domain may also be referred to as a mobility domain, the SGW domain may be referred to as a gateway domain (e.g. a first gateway domain) and the PGW domain may be referred to as a gateway domain (e.g. a second gateway domain).

The SGW domain in figure 2 is exemplified to comprise five SGWs 208, e.g. SGW1 208a, SGW2 208b, SGW3 208c, SGW4 208d and SGW5 208e. The reference number 208 used herein refers to any of the SGWs 208 in the SGW domain. Note that the number five is only an example and that any other suitable number of SGWs may be comprised in the SGW domain. The term gateway or first gateway may also be used when referring to the SGW 208. Note that the SGW 208 may be a dedicated SGW node, it may be a SGW function implemented in a node or a computer, it may be co-located with another node etc.

The MME domain in figure 2 is exemplified to comprise five MMEs 210, e.g. MME 1 210a, MME2 210b, MME3 210c, MME4 210d and MME5 210e. The reference number 210 used herein refers to any of the MMEs 210 in the MME domain. Note that the number five is only an example and that any other suitable number of MMEs may be comprised in the MME domain. An MME 210 may be referred to as a mobility node. When the term MME is used herein it refers to any of a MME, a SGSN, a combined MME/SGSN node, a S4-SGSN, a MME/S4- SGSN, a TWAN, an ePDG, a virtualized MME (vMME), a virtualized SGSN (vSGSN), a virtualized MME/SGSN (vMME/vSGSN), a virtualized S4-SGSN (S4-vSGSN), a virtualized MME/S4-SGSN (vMME/S4-vSGSN), a virtualized TWAN (vTWAN), a virtualized ePDG (vePDG) etc. Note that the MME 210 may be a dedicated MME node, it may be a MME function implemented in a node or a computer, it may be co-located with another node etc. The PGW domain in figure 2 is exemplified to comprise a five of PGWs 215, e.g. PGW1 215a, PGW2 215b, PGW3 215C, PGW4 215d and PGW 5 215e. The reference number 215 used herein refers to any of the PGWs 215 in the PGW domain. Note that the number five is only an example and that any other suitable number of PGWs may be comprised in the PGW domain. The term gateway or second gateway may also be used when referring to the PGW 215. Note that the PGW 215 may be a dedicated PGW node, it may be a PGW function implemented in a node or a computer, it may be co-located with another node etc.

The re-selecting node 108 of figure 1 is not explicitly illustrated in figure 2, but it may be also comprised in the communication system 100. The re-selecting node 108 may one of the SGWs 208, it may be one of the MMEs 210, one of the PGWs 215 or it may be a dedicated re- selecting node not comprised in any of the EPC domains.

The method for handling selection of a serving EPC node 1 10a, 1 10b, 1 10c to serve a UE 101 according to some embodiments will now be described with reference to the signaling diagram depicted in Figure 3 and with reference to the communication system 100 exemplified in figure 1 .

The re-selecting node 108 comprises EPC node information for each EPC node 1 10a, 1 10b, 1 10c of a plurality of EPC nodes 1 10a, 1 10b, 1 10c in at least one EPC node

domain that the re-selecting node (108) is responsible for. The EPC node information indicates properties of the plurality of EPC nodes 1 10a, 1 10b, 1 10c in the EPC node domain. The EPC node information may indicate at least one of: UE usage type served by each EPC node, IMSI series to be served by each EPC node, IMEI range to be serve by each EPC node, PDN Connection type to be served by the EPC node, UE radio

capability, current load status, current overload status, EPC node resilience level, the number of EPC nodes in the relevant EPC domain, the type of UEs 101 served by the various EPC nodes in the relevant domain (e.g. loT UEs, M2M UEs etc.), the available processing power and/or memory capacity of EPC nodes in question etc.

The EPC node information for each of the EPC nodes in a given EPC node domain comprises at least a list of functional features that the node supports, e.g. UE usage type that the node is serving, IMSI series to serve, IMEI range to serve, PDN Connection type to serve, UE radio capability (e.g. if UE support extended DRX). The EPC node information for each of EPC nodes in a given node domain may further comprise at least a list of non-functional features that the node supports, e.g. the current load status, the current overload status, the node resilience level (e.g. for an emergency session, a SGW with higher reliability should be selected).

The method exemplified in figure 3 comprises at least some of the following steps, which steps may as well be carried out in another suitable order than described below: Step 301

The re-selecting node 108 receives a request message associated with the UE 101. The request message comprises request message information enabling re-selection of a serving EPC node from the plurality of EPC nodes in the EPC node domain. The request message may be received from a request sending node (not illustrated), and the request sending node may be e.g. a RAN node 105, a MME 210, a SGW 208 or a PGW 215. The request message may be for example a General Packet Radio

Services (GPRS) Tunneling protocol version 2 (GTPv2) Create Session Request message or a GTPv2 Forward Relocation Request message or a S1 Application

Protocol (S1 AP) Initial UE message. S1 AP is associated with eNB selection of the MME.

The request message information may indicate at least one of: UE usage type information, UE radio capability, UE subscribed or Requested Access Point Name, APN, Radio Access Type, RAT, where the UE 101 is camping on, UE current Location Information, UE Close Subscriber Group, IMSI, MSISDN, IMEI, APN, Quality of Service Class Identifier (QCI), Address Resolution Protocol (ARP), Serving Network Operator Identifier, Packet Data Network, PDN, Connection type, UE time zone, Signaling Priority Indication, Charging Characteristics, a current procedure that the UE 101 is performing. The UE usage type information may be at least one of: a subscribed UE usage type information and mapped UE usage type information.

The request message information may indicate that the re-selecting node 108 is the first node currently selected to serve the UE 101. The request message may not comprise any information that explicit says that the first EPC node is selected. However, the request message may e.g. comprise the IP-address of the first EPC node and/or a TEID indicating the first EPC node. Such information may be an indication of that the first EPC node has been selected to serve the UE 101 in question.

At least one of the properties of the received request message may indicate that a first EPC node is currently selected as a serving EPC node. Such properties may be at least one of: the name of the request message, the interface on which the request message is received, the sender of the request message.

The currently selected serving EPC node may be referred to as a default serving EPC node or a default EPC node.

Step 302

The re-selecting node 108 may determine which type of EPC node the re-selected serving EPC node should be. The decision may be made based on the request message information comprised in the received request message in step 301 and the EPC node information. The re-selecting node 108 may also determine the purpose of the request message e.g. based on the request message information, and possibly also based on the EPC node information. The outcome of step 302 may be used in the re-selection step 303.

Step 303

Based on the EPC node information and the received request message information, the re-selecting node 108 re-selects a second EPC node 1 10b as the serving EPC node among the plurality of EPC nodes 1 10a, 1 10b, 1 10c in the EPC node domain to serve the UE 101 instead of a first node 110a currently selected to be the serving EPC node. The first node 1 10a may be selected by another node or by the re-selecting node 108. The re-selected serving EPC node 1 10b may be more suitable to serve the UE 101 than the currently selected EPC node 1 10a. The second EPC node 1 10b may be re-selected as the serving EPC node such that the second EPC node is of the determined node type, i.e. the type which may be determined in step 302. The second node 1 10b is re-selected because at least part of the EPC node information matches what is included in the request message information.

The re-selection function in Core Network aims to efficiently re-select a serving EPC node which is designated to serve a UE 101 , where the capability (e.g. the support of various features, the manner of allocation of CPU and Memory) of the re-selected serving EPC node should match what the UE 101 is expecting for the network, i.e. the re-selected serving EPC node should fit the UE traffic characteristics, UE subscription information, RAT type that UE 101 is access from, UE radio capability and so on, in addition, the load sharing among EPC nodes and potential overload situation should be also considered during a selection. The re-selection may be further based on at least one of operator's policies and local configuration associated with the UE 101.

When receiving the request message, based on which interface the re-selecting node 108 receives the message, (in fact, based on the message content itself) it may know which node has sent the request message. On the same basis, the re-selecting node 108 may also know the purpose of the message. For example, both the MME and the SGW can send a Create session request. There are a few parameters in the request message, e.g. Sender's F-TEID, which can enable the receiver of the message to determine if the message is from a MME, or a SGSN or a SGW. If it is from the SGW, the re-selecting node 108 needs to select a PGW.

The re-selection of the serving EPC node may be based on:

a. Node properties of each of EPC nodes in the respective EPC node

domain for given interface where the request message is received.

b. UE related information included in the request message

c. Any local configuration (operator policies) which is applicable for the UE 101 (e.g. IMSI starting with 26202100 may be served by MME2, SGW3...lt is likely that operator allocates certain IMSI range for a specific UE group, e.g. Machine type UE.)

Step 304

The re-selecting nodes 108 forwards the request message together with forwarding information to the second EPC node 1 10b as the re-selected serving EPC node 1 10b to inform the re-selected serving EPC node that it should serve the UE 101. The forwarding information may be seen as being added to the request message. The term forwarding refers to that the same request message which was received in step 301 is sent or transmitted to the re-selected serving EPC node 1 10b.

The forwarding information enables the re-selected serving EPC node 1 10b to correctly respond to the request message. This will be described in more detail below. The

forwarding information may indicate a destination address of the currently selected

serving EPC node, a source address of a request sending node, and a UDP port of the request sending node.

The forwarded request message comprises one or more parameters of the request message information in the request message from step 301. The re-selected serving EPC node 1 10b receives the forwarded request message

together with the forwarding information from the re-selecting node 108.

Step 305

The re-selected serving EPC node 1 10b serves the UE 101. Based on the forwarding information received in step 304, the re-selected serving EPC node 1 10b may send a response message to the re-selecting node 108. The re-selected EPC node 1 10b should handle the request message.

Table 1 below illustrates some examples of the re-selecting node 108, the currently selected to be the serving EPC node and the re-selected serving EPC node. Table 1

The currently selected serving EPC node performs the forwarding of the request message. In the case of a dedicated re-selecting node 108, this node must be the first node to be selected as the serving EPC node.

The method for handling selection of a serving EPC node 1 10a, 1 10b, 1 10c to serve a UE 101 according to some embodiments will now be described with reference to the Figure 4 and with reference to the communication system 100 exemplified in figure 2. Figure 4 illustrates a procedure when a UE 101 performs an initial attach. A UE 101 performs an Initial Attach procedure, and activates a PDN connection for APN1. In figure 4, the request message is exemplified with a Create Session Request message.

The method in figure 4 comprises at least some of the following steps, which steps may as well be carried out in another suitable order than described below:

Step 400

The UE 101 sends a request message to the eNB 205 in RAN 1. The RAN 1 may be identified with a Tracking Area Identity (TAI) 1. The message sent in step 400 may be referred to as control plane signaling, i.e. a NAS/S1AP message is transmitted from the UE 101 to the eNB 205. Step 401

The eNB 205 selects the MME1 210a and forwards the NAS/S1AP message to the MME1 210a. Step 402

The MME1 210a performs the selection function as specified in the sub clause 4.3.8 of 3GPP TS 23.401 V13.5.0 (2015-12) by using an existing Fully Qualified Domain Name (FQDN), i.e. TAI1 FQDN for the selection of a SGW 208 and the APN1 FQDN for the selection of a PGW 215. As the outcome of this selection procedure in step 201 , the SGW1 208 and PGW1 215 are selected. The SGW1 208a and the PGW1 215a may be referred to as default SGW 208 and default PGW 215. Note that only the SGW1 208a and PGW1 215a for the TA11 /APN 1 are configured in the DNS. This implies that e.g. SGW2, 3, 4 and 5 and PGW2, 3, 4, and 5 are not present in the DNS configuration. The FQDN used in the selection is a domain name that specifies an exact location of a node in the DNS. A FQDN can only be interpreted in one way, and can therefore also be referred to as an absolute domain name. The FQDN may be e.g. a TAI FQDN or an APN FQDN In DNS, for TAI 1 FQDN only the SGW1 208a is configured as default SGW 208, to be selected by the MME 210, where the SGW1 208a is responsible to select a more suitable SGW 208 among SGW2,3, 4 and 5. Similarly, in DNS, for APN 1 FQDN, only PGW1 215a is configured as default PGW 215 to be selected by the MME1 210a, where the PGW1 215a is responsible to select a more suitable PGW 215 among PGW2,3, 4 and 5.

Step 403

This step corresponds to step 301 in figure 3. The MME1 210a sends a Create Session Request message (from the IP address IP 1 and source port number x) to the

SGW1 208a (destination IP address of this message is IP 2 from the SGW1 208a received from the DNS procedure). The Create Session Request message comprises request message information. Additional parameters in addition to the ones which already are comprised in the Create Session Request message which may help the SGW1 208a to re-select a more suitable SGW 208 may be included in the Create Session Request message. An example of such parameter may be the UE Usage Type. The MME1 210a may have previously received the UE Usage Type from a subscriber server such as e.g. a Home Subscriber Server (HSS) or a Home Location Register (HLR) or similar. The UE Usage Type received from the subscriber database may be a subscribed UE Usage Type, and the UE Usage Type parameter sent to the SGW1 208 may be a mapped Usage type. A subscribed UE Usage type is typically sent from the subscriber server to the MME1 210a. Then, the MME1 210a maps the subscribed UE Usage type based on e.g. RAT, to a mapped UE Usage type. In some embodiments, both the subscribed and mapped UE Usage Type parameters may be sent to the SGW1 208a.

The SGW1 208a receives the Create Session Request message from the MME1 210a. In step 402, the MME1 210a represents or is the request sending node and the

SGW1 208 represents or is the re-selecting node 108.

Step 404

This step corresponds to step 303 and step 304 in figure 3. The SGW1 208a re-selects SGW5 208e to serve the UE 101. In step 403, the SGW1 208a represents or is the re- selecting node 108 in figure 1 , the SGW1 208a represents or is the first EPC node currently selected to serve the UE 101 and the SGW5 208e represents or is the second EPC node which has been re-selected as the serving EPC node. The re-selection is preferably performed based on local information in the re-selecting SGW1 that indicates properties of the plurality of SGW nodes SGW2-SGW5, and the information included in the Create Session Request message for the UE, e.g. IMSI, MSISDN, IMEI, APN, QCI, ARP, Serving Network Operator Identifier, PDN Connection type, Radio Access Technology type, User Location Information, UE time zone, UE Close Subscriber Group, Signaling Priority Indication, Charging Characteristics, whether UE is performing a handover attach (from non-3GPP to 3GPP handover), whether Network Based IP Flow Mobility (NBIFOM) is supported etc. The operator's policies may be locally configured in the SGW1 208a. It is not suitable to use the DNS procedure to fetch the properties of the most suitable SGW 208 to be selected, since it is hard to keep the DNS server properly updated in a dynamic environment. However, updating the default SGW1 208a with the required information about the other SGWs 208 that may be selected is easier. I.e. is it not hard to keep the SGW1 208a properly updated with information about the other SGWs 208 in a dynamic environment.

The term re-selection is used since the SGW1 308 re-selects the SGW5 208e (the first selection was SGW1 308a performed by the MME1 210a in step 402).

The SGW1 208a is able to keep and use such a big list of EPC node information to determine which SGW 208 is best suited to serve the UE 101. Such information is increasing constantly with introducing more and more features in the communications system 100. On the other hand, is not possible or practical to configure this large list of information in the DNS server.

The SGW1 208a forwards the Create Session Request message received from the MME1 210a to the re-selected SGW5 208e. At least some of the following information elements (the following information corresponds to the forwarding information in figure 3) may be transmitted together with the forwarded Create Session Request message.

• Source IP address: Indicating the IP address which originates the GTP Initial message, e.g. Create Session Request, i.e. source IP address. For example, the IP1 from the MME1 210a.

· Source UDP Port: Indicating the UDP port number used in the he GTP Initial message, e.g. Create Session Request. For example, the source port number x.

• Destination IP address: Indicating the IP address addressed by the GTP Initial message, e.g. Create Session Request. For example, the destination IP address IP2 of SGW1 208a.

Note that the above listed information may be used for step 408 described below only when the SGW5 208e sends a Create Session Response message back to the

MME1 210a. The forwarding may be done using GTP redirection.

The SGW5 208e receives the forwarded Create Session Request message form the SGW1 208a.

Step 405

This step corresponds to step 301 in figure 3. The SGW5 208e sends a Create Session Request message to the PGW1 215a. Thus, the SGW5 208e represent or is a request sending node and the PGW1 215a represents or is the re-selecting node 108.

Recall that the MME1 210a selects both the SGW1 208a and the PGW1 215a in step 402. Information about the selected PGW1 215a should be sent in step 403 to the SGW1 208a and in step 404 to the SGW5 208e, whereupon the SGW5 208e knows that the request message should be sent to the PGW1 215a.

Note, that the Create Session Request message in step 405 does not have the additional information as the message in step 404 (e.g. source IP address, Source UDP port etc.). Recall that the PGW1 215a (e.g. the default PGW1 215a) was selected by the MME1 210a in step 402.

The PGW1 215a receives the Create Session Request message from the SGW5 208a.

Step 406

This step corresponds to step 303 in figure 3. Similar to what the SGW1 208a performed in step 404, the PGW1 215a re-selects the PGW4 215d as being more suitable to serve the UE 101. The re-selection may be performed based on any available information included in the Create Session Request message and any local information in the re-selecting PGW1 215a. The PGW1 215a may represent or is the first EPC node currently selected to serve the UE 101 in the PGW node domain and the PGW4 215d may represent or is the second EPC node which is re-selected to serve the UE 101 instead of PGW1 215a. The PGW1 215a forwards the Create Session Request message from step 405 to the re-selected PGW4 215d, and may add at least some of the following forwarding information · Source IP address: Indicating the IP address originating the GTP Initial message, e.g. Create Session Request, i.e. source IP address. For example, the IP 3 from the SGW5 308.

• Source UDP Port: Indicating the UDP port number used in the he GTP Initial message, e.g. Create Session Request. For example, the source port number y. · Destination IP address: Indicating the IP address addressed by the GTP Initial message, e.g. Create Session Request. For example, the destination IP address IP4 of the PGW1 315.

Note the above forwarding information may be used for the step 407 only when the selected PGW4 215d sends a Create Session Response message to the SGW5 208e.

The forwarding may be done using GTP redirection.

The PGW4 215d receives the forwarded Create Session Request message from the PGW1 215a.

Step 407

The PGW4 215d sends a Create Session Response message to the SGW5 208e, from IP 4 (as source IP address of Create Session Response) towards the IP 3 (of the SGW5 208e as destination IP address) and UDP destination port number y.

The SGW5 208e receives the Create Session Response message from the PGW4 215d. The Create Session Response message is a response to the Create Session Request message in step 405. Step 408

The SGW5 208e sends a Create Session Response message to the MME1 210a, from IP 2 (as source IP address of Create Session Response) towards the IP 1 (of the MME1 210a as destination IP address) and UDP destination port number x.

The MME1 210a receives the Create Session Response message from the MME1 210a. The Create Session Response message is a response to the Create Session Request message in step 403. By responding with the addresses of the SGW1 208a and the PGW1 215a to the MME1 210a form which the request message in step 403 was received, any re-selection of the SGW5 208e and the PGW4 215d will be hidden. In other words, the MME1 210a perceives the response as coming from the SGW1 208a and the PGW1 215a originally selected by the MME1 210a. This means that a prior art legacy MME 210 can be used without any changes in the re-selecting procedure described herein.

The procedure exemplified in the PDN Connection creation procedure (for a selection of SGW/PGW) illustrated in the figure 4 can also be used for MME re-selection during a handover procedure. However, such handover procedure is not illustrated and described herein for the sake of simplicity. In the handover procedure, the request message may be a Forward Relocation Request message.

The method described above will now be described seen from the perspective of the re- selecting node 108. Figure 5 is a flowchart describing the present method performed by the re-selecting node 108 for handling selection of a serving EPC node 110a, 110b, 1 10c to serve a UE 101. The re-selecting node 108 comprises EPC node information for each EPC node 1 10a, 1 10b, 110c of a plurality of EPC nodes 1 10a, 1 10b, 1 10c in at least one EPC node domain that the re-selecting node 108 is responsible for. The EPC node information may indicate properties of the plurality of EPC nodes 1 10a, 1 10b, 1 10c. the EPC node information comprises at least one of: UE usage type served by each EPC node, International Mobile Subscriber Identity (IMSI) series to be served by each EPC node, International Mobile Equipment Identity (IMEI) range to be serve by each EPC node, Packet Data Network (PDN) Connection type to be served by the EPC node, whether the EPC node is optimized for certain UE radio capability, current load and overload status of each EPC node, resilience level of each of EPC node in in the EPC node domain.

The re-selecting node 108 may be one of the plurality of EPC nodes 1 10a, 1 10b, 1 10c in the EPC node domain.

The method comprises at least some of the following steps to be performed by the re- selecting node 108: Step 501

This step corresponds to step 301 in figure 3, and steps 403 and 405 in figure 4. The re- selecting node 108 receives a request message associated with the UE 101. The request message comprises request message information enabling re-selection of a serving EPC node from the plurality of EPC nodes in the EPC node domain. The EPC node domain may be referred to as a target EPC node domain.

The request message information may indicates at least one of: UE usage type information, UE radio capability, UE subscribed or Requested Access Point Name, APN, Radio Access Type, RAT, where the UE 101 is camping on, UE current Location Information, UE Close Subscriber Group, International Mobile Subscriber Identity (IMSI), Mobile Station International Subscriber Directory Number (MSISDN), International Mobile Equipment Identity (IMEI), APN, Quality of Service Class Identifier (QCI), Address Resolution Protocol (ARP), Serving Network Operator Identifier, Packet Data Network ( PDN) Connection type, UE time zone, Signaling Priority Indication, Charging Characteristics, a current procedure that the UE 101 is performing.

The UE usage type information may be at least one of: a subscribed UE usage type information and mapped UE usage type information. The request message may be received from an eNB 205, a MME 210, a SGW 208, a virtualized MME (vMME) or a virtualized SGW (vSGW). The request may be a General Packet Radio Services Tunneling protocol version 2 (GTPv2) Create Session Request message or a GTPv2 Forward Relocation Request message or a S1 Application Protocol (S1AP) Initial UE message. The request message information may indicate that the re-selecting node 108 is the first node currently selected to serve the UE 101.

Step 502

This step corresponds to step 302 in figure 3. The re-selecting node 108 may determine, based on the request message information and the EPC node information, which type of EPC node 1 10a, 1 1 0b, 1 10c the re-selected serving EPC node should be.

Step 503

This step corresponds to step 303 in figure 3 and steps 404 and 406 in figure 4. The re- selecting node 108 re-selects, based on the EPC node information and the received request message information, a second EPC node 1 10b, 208e as the serving EPC node among the plurality of EPC nodes 1 10a, 1 10b, 1 10c in the EPC node domain to serve the UE 101 instead of a first node 1 10a, 208a currently selected to be the serving EPC node.

The EPC node domain in which the second EPC node 1 10b, 208e is re-selected as the serving EPC node is in the same target EPC node domain as the first EPC node.

The re-selecting node 108 may re-select the second EPC node 1 10b such that the second EPC node is of the determined node type, the type determined in step 502.

The re-selection may be further based on operator's policies and local configuration associated with the UE 101. The re-selected serving EPC node 1 10b may be more suitable to serve the UE 101 than the currently selected EPC node 1 10a. The currently selected EPC node 1 10 may be selected by the request sending node. In some embodiments, the re-selecting node 108 is a first MME 210a and the re- selected EPC node 110b is a second MME 210b. In other embodiments, the re-selecting node 108 is a first SGW 208a and the re-selected serving EPC node 1 10b is a second SGW 208b. In yet further embodiments, the re-selecting node 108 is a first PGW 215a and the re-selected serving EPC node 1 10b is a second PGW 215b. In other embodiments, re-selecting node 108 is a node dedicated to re-selecting a serving EPC node 1 10b as the serving EPC node among the plurality of EPC nodes 1 10a, 1 10b, 1 10c in the EPC node domain to serve the UE 101 , and the re-selected EPC node 1 10b is one of: a second MME 210b, a second SGW 208b or a second PGW 215b.

The the first node 1 10a currently selected to be the serving EPC node may be a default serving EPC node.

The first node 1 10a currently selected to be the serving EPC node may have been selected by a RAN node 105, a MME 210, a SGSN, a Trusted Wireless Local Area Network (TWAN), or an Evolved Packet Data Gateway (ePDG).

Step 504

This step corresponds to step 304 in figure 3 and step 404 in figure 4. The re-selecting node 108 forwards the request message together with forwarding information to the second EPC node 1 10b, 208e as the re-selected serving EPC node 110b, 208e to inform the re-selected serving EPC node that it should serve the UE 101.

The forwarding information may enable the re-selecting node 108 to respond to the request message. The forwarding information may indicate a destination address of the currently selected serving EPC node, a source address of a request sending node, and a User Datagram Protocol (UDP) port of the request sending node.

To perform the method steps shown in figure 5 for handling selection of a serving EPC node 1 10a, 1 10b, 1 10c to serve a UE 101 , the re-selecting node 108 may comprise an arrangement as shown in Figure 6. The re-selecting node 108 comprises EPC node information for each EPC node 110a, 1 10b, 1 10c of a plurality of EPC nodes 1 10a, 1 10b, 1 10c in at least one EPC node domain that the re-selecting node is responsible for. The EPC node information indicates properties of the plurality of EPC nodes 1 10a, 1 10b, 1 10c. The EPC node information may comprise at least one of: UE usage type served by each EPC node, IMSI series to be served by each EPC node IMEI range to be serve by each EPC node, PDN Connection type to be served by the EPC node, whether the EPC node is optimized for certain UE radio capability, current load and overload status of each EPC node, resilience level of each of EPC node in in the EPC node

domain. The re-selecting node 108 may be one of the plurality of EPC nodes 1 10a,

1 10b, 1 10c in the EPC node domain. To perform the method steps shown in figure 5 for handling selection of a serving EPC node 1 10a, 1 10b, 1 10c to serve a UE 101 , the re-selecting node 108 is adapted to, e.g.

by means of a receiving module 601 , receive a request message associated with the UE 101. The request message comprises request message information enabling re- selection of a serving EPC node from the plurality of EPC nodes in the EPC node

domain. The request message information may indicate at least one of: UE usage type information, UE radio capability, UE subscribed or Requested APN, RAT where the UE 101 is camping on, UE current Location Information, UE Close Subscriber Group, IMSI, MSISDN, IMEI, APN, QCI, ARP, Serving Network Operator Identifier, PDN Connection type, UE time zone, Signaling Priority Indication, Charging Characteristics, a current procedure that the UE 101 is performing. The UE usage type information may be at least one of: a subscribed UE usage type information and mapped UE usage type information. The request message may be a GTPv2 Create Session Request message or a GTPv2 Forward Relocation Request message or a S1AP Initial UE message. The request message information may indicate that the re selecting node 108 is the first node

currently selected to serve the UE 101.

The receiving module 601 may also be referred to as a receiving unit, a receiving

means, a receiving circuit, means for receiving, input unit etc. The receiving module 601 may be a receiver, a transceiver etc. The receiving module 601 may be a wireless

receiver of the re-selecting node 108 of a wireless or fixed communications system.

The re-selecting node 108 is further adapted to, e.g. by means of a re-selecting module 603, re-select, based on the EPC node information and the received request message information, a second EPC node 1 10b as the serving EPC node among the plurality of EPC nodes 110a, 1 10b, 1 10c in the EPC node domain to serve the UE 101 instead of a first node 1 10a currently selected to be the serving EPC node. The re-selected serving EPC node 1 10b may be adapted to be more suitable to serve the UE 101 than the currently selected EPC node 1 10a. The first node 1 10a currently selected to be the serving EPC node may be a default serving EPC node. The first node 1 10a currently selected to be the serving EPC node may have been selected by a RAN node 105, a MME 210, a SGSN, a TWAN, or an ePDG. The re-selecting module 603 may also be referred to as a re-selecting unit, a re-selecting means, a re-selecting circuit, means for re-selecting etc. The re-selecting module 603 may be a processor 605 of the re-selecting node 108.

The re-selecting node 108 is further adapted to, e.g. by means of a forwarding module 608, forward the request message together with forwarding information to the second

EPC node 1 10b as the re-selected serving EPC node 1 10b to inform the re-selected serving EPC node that it should serve the UE 101. The forwarding information may enable the re-selecting node 108 to respond to the request message. The forwarding information may indicate a destination address of the currently selected serving EPC node, a source address of a request sending node, and a UDP port of the request

sending node.

The forwarding module 608 may also be referred to as a forwarding unit, a forwarding means, a forwarding circuit, means for forwarding etc. The forwarding module 608 may be the processor 605 of the re-selecting node 108. The re-selecting node 108 may be further adapted to, e.g. by means of a determining module 610, determine, based on the request message information and the EPC node information, which type of EPC node 110a, 11 0b, 1 10c the re-selected serving EPC node should be. The determining module 610 may also be referred to as a determining unit, a

determining means, a determining circuit, means for determining etc. The determining module 610 may be the processor 605 of the re-selecting node 108. The re-selecting node 108 may be further adapted to, e.g. by means of the re-selecting module 603, re-select the second EPC node 1 10b such that the second EPC node is of the determined node type. The re-selecting node 108 may be further adapted to, e.g. by means of the re-selecting module 603, to base the re-selection on operator's policies and local configuration

associated with the UE 101.

The re-selecting node 108 may be further adapted to, e.g. by means of the receiving module 601 , receive the request message from an eNB 205, a MME 210 or a SGW 208.

In some embodiments, the re-selecting node 108 is a first MME 210a and the re- selected EPC node 110b is a second MME 210b. In other embodiments, the re-selecting node 108 is a first SGW 208a and the re-selected serving EPC node 1 10b is a second SGW 208b. In yet other embodiments, the re-selecting node 108 is a first PGW 215a and the re-selected serving EPC node 1 10b is a second PGW 215b. In some

embodiments, the re-selecting node 108 is a node dedicated to re-selecting a serving

EPC node 1 10b as the serving EPC node among the plurality of EPC nodes 110a, 110b, 1 10c in the EPC node domain to serve the UE 101 , and the re-selected EPC node 1 10b is one of: a second MME 210b, a second SGW 208b or a second, PGW 215b.

The re-selecting node 108 may be adapted to, e.g. by means of a transmitting module 613, to transmit information, messages and data to other nodes in the communications system 100. The transmitting module 613 may be the same as the forwarding module 806. The transmitting module 613 may also be referred to as a transmitting unit, a transmitting means, a transmitting circuit, means for transmitting, output unit etc. The transmitting module 613 may be a transmitter, a transceiver etc. The transmitting module 613 may be a wireless transmitter of the re-selecting node 108 of a wireless or fixed communications system. In some embodiments, the EPC node 1 10 comprises the processor 605 and a memory 615. The memory 615 comprises instructions executable by the processor 605. The memory 615 comprises one or more memory units. The memory 615 is arranged to be used to store data, received data streams, power level measurements, request message, request message information, EPC node information, forwarding information, EPC node type, operator's policies, local configuration of the UE 101 , request sending node, first node currently selected to serve the UE 101 , the re-selected serving EPC node, threshold values, time periods, configurations, schedulings, and applications to perform the methods herein when being executed in the re-selecting node 108.

The present mechanism for handling selection of a serving EPC, node 110a, 110b, 1 10c to serve a UE 101 may be implemented through one or more processors, such as a processor 605 in the re-selecting node arrangement depicted in Figure 6, together with computer program code for performing the functions of the embodiments herein. The processor may be for example a Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC) processor, Field-programmable gate array (FPGA) processor or micro processor. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the EPC node 1 10. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code can furthermore be provided as pure program code on a server and downloaded to the re- selecting node 108.

Those skilled in the art will also appreciate that the receiving module 601 , the re- selecting module 603, the forwarding module 608, the determining module 610 and the transmitting module 613 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processor 605 perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

In some embodiments, a computer program may comprise instructions which, when executed on at least one processor, cause the at least one processor to carry out at least some of the method steps 301 -305 in figure 3, steps 400-408 in figure 4 and steps 501-504 in figure 5. A carrier may comprise the computer program, and the carrier is one of an electronic signal, optical signal, radio signal or computer readable storage medium. Summarized, the embodiments herein relate to selecting a suitable PEC entity by enabling the redirection of a request message, e.g. a GTP initial message.

The node in the same product domain has the best knowledge about which individual entity in that domain is best suitable to serve a given UE 101. A node in another product domain does not have this type of information, e.g. a SGW has information about all

SGWs 208 in the SGW domain, but a MME 210 (in an MME domain) does not have any information about the SGW domain and is therefore not suitable to select which SGW

208 that is most suitable to serve a certain UE 101 . For example, for a PDN Connection creation procedure, it is not efficient to require the MME 210 to have an overview of the SGW product domain. If the MME 210 should have such knowledge of the SGW product domain, it needs to either be based on the local configuration, or based on DNS records for each of the candidate SGWs 208 in the SGW domain during a DNS procedure. The information in the DNS is rather static and thus not scalable and flexible. Thus, such approach where the MME 210 selects a SGW 208 does especially not fit to Network

Function Virtualization (NFV), where the EPC nodes are dynamically deployed on the cloud platform. It is difficult and maybe even impossible to add/update the DNS record for each of the dynamically created EPC node's instance in NFV. Therefore, it is

impossible to let the MME 210 which performs the selection function to have the full knowledge of the SGW 208 nodes.

The embodiments herein define a default node for each product domain, e.g. a default SGW 210 for a group of SGWs, a default PGW 215 for a group of PGWs, a default MME 210 for a group of MMEs etc. Each node in the group may support a different subset of features. The default node is equipped with full knowledge of the rest of the nodes in the group. Such default node is also responsible for the load sharing and overload control amongst the nodes in the group, e.g. load node software on a piece of hardware to form a new node when there is a need. With the embodiments herein, the DNS procedure becomes very simple, and less DNS records are needed. They also reduce the operation cost. For example, to select a SGW 208 for a given TAI, only the default SGW 208 is defined in the DNS server, so that the MME 210 always contacts the default SGW 208.

After the default SGW 208 receives PDN connection creation message, it then needs to allocate a suitable SGW 208 for the UE 101. The allocation is performed based on UE context information, e.g. access from Narrow Band-Internet of Things (NB-loT), using the APN and so on.

To be able to forward the request message to the selected more suitable node, the protocol for transmitting messages between the nodes may also needs to be updated. For example, to be able to forward the PDN connection creation message to the more suitable SGW 208, the GTPv2/GTP protocol may also need to be updated.

In chapter 4.2.2.1 of 3GPP TS 29.274 V13.4.0 (2015-12), there is a limitation for such forwarding. The following requirement is applicable to a triggered message, e.g. Create Session Response message:

" The IP Destination Address of a GTPv2 Triggered message and for a Triggered Reply message shall be copied from the IP Source Address of the message to which this GTPv2 entity is replying, except in the case of the SGSN pool scenario.

The IP Source Address of a GTPv2 Triggered message and for a Triggered Reply message shall be copied from the IP destination address of the message to which this GTPv2 entity is replying, except in the case of SGSN pool scenario. "

With respect to steps 403 and 408 in figure 4, the above citation from 3GPP TS 29.274 V13.4.0 (2015-12) implies that the MME1 210a sends (step 403) a Create Session Request to the default SGW1 208a and thus expects a response from the same

SGW1 208a, but it receives the response (step 408) from a "unknown" SGW5 208e that was re-selected by SGW1 208a. It is therefore a need for a protocol mechanism to allow it, so that the sending node, e.g. the MME 210 sending the Create Session Request message, is not aware at all (thus not impacted) that the SGW 208 is reselected by the default SGW 208. At least some of the following information elements may be added in a number GTP initial message, at least in the Create Session Request message when the default EPC node which forwards the message to a selected specific EPC node in its group:

• Source IP address: Indicating the IP address of the node at which the GTP Initial message, e.g. Create Session Request, originates from.

• Source UDP Port: Indicating the UDP port number used in the GTP Initial

message, e.g. Create Session Request.

• Destination IP address: Indicating the IP address addressed by the GTP Initial message, e.g. Create Session Request.

The destination UDP Port may be set to 2123. The UDP port number for an initial message is well-known, 2123.

The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the embodiments, which is defined by the appending claims.

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It should also be noted that the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements.

The term "configured to" used herein may also be referred to as "arranged to", "adapted to", "capable of or "operative to". It should also be emphasised that the steps of the methods defined in the appended claims may, without departing from the embodiments herein, be performed in another order than the order in which they appear in the claims.

Claims

1. A method performed by a re-selecting node (108) for handling selection of a serving Evolved Packet Core, EPC, node (1 10a, 1 10b, 110c) to serve a User Equipment, UE (101 ),

wherein the re-selecting node (108) comprises EPC node information for each EPC node (110a, 110b, 1 10c) of a plurality of EPC nodes (1 10a, 1 10b, 1 10c) in at least one EPC node domain that the re-selecting node (108) is responsible for,

wherein the EPC node information indicates properties of the plurality of EPC nodes (1 10a, 1 10b, 1 10c),

the method comprising:

receiving (301 , 403, 405, 501 ) a request message associated with the UE (101 ), wherein the request message comprises request message information enabling re- selection of a serving EPC node from the plurality of EPC nodes in the EPC node domain;

re-selecting (303, 404, 406, 503), based on the EPC node information and the received request message information, a second EPC node (1 10b, 208e) as the serving EPC node among the plurality of EPC nodes (1 10a, 1 10b, 1 10c) in the EPC node domain to serve the UE (101 ) instead of a first node (110a, 208a) currently selected to be the serving EPC node; and

forwarding (304, 404, 504) the request message together with forwarding information to the second EPC node (1 10b, 208e) as the re-selected serving EPC node (1 10b, 208e) to inform the re-selected serving EPC node that it should serve the UE (101 ).

2. The method according to claim 1 , further comprising:

determining (302, 502), based on at least one of: the request message information and the EPC node information, which type of EPC node (1 10a, 1 1 0b, 110c) the re-selected serving EPC node should be; and

re-selecting (303, 404, 406, 503) the second EPC node (1 10b) such that the second EPC node is of the determined node type.

3. The method according to any one of claims 1-2, wherein the request message information indicates at least one of: UE usage type information, UE radio capability, UE subscribed or Requested Access Point Name, APN, Radio Access Type, RAT, where the UE (101 ) is camping on, UE current Location Information, UE Close Subscriber Group, International Mobile Subscriber Identity, IMSI, Mobile Station International

Subscriber Directory Number, MSISDN, International Mobile Equipment Identity, IMEI, APN, Quality of Service Class Identifier, QCI, Address Resolution Protocol, ARP, Serving Network Operator Identifier, Packet Data Network, PDN, Connection type, UE time zone, Signaling Priority Indication, Charging Characteristics, a current procedure that the UE (101 ) is performing.

4. The method according to claim 3, wherein the UE usage type information is at least one of: a subscribed UE usage type information and mapped UE usage type information.

5. The method according to any one of claims 1 -4, wherein the re-selection is further based on operator's policies and local configuration associated with the UE (101 ).

6. The method according to any one of claims 1 -5, wherein the EPC node information indicates at least one of: UE usage type served by each EPC node, International Mobile Subscriber Identity, IMSI, series to be served by each EPC node, International Mobile Equipment Identity, IMEI, range to be serve by each EPC node, Packet Data Network, PDN, Connection type to be served by the EPC node, whether the EPC node is optimized for certain UE radio capability, current load and overload status of each EPC node, resilience level of each of EPC node in in the EPC node domain.

7. The method according to any one of claims 1-6, wherein the request message is received from an evolved Node B, eNB, (205), a Mobility Management Entity, MME, (210) or a Serving Gateway, SGW (208).

8. The method according to any one of claims 1-7, wherein the forwarding information enables the re-selection node (108) to respond to the request message, and wherein the forwarding information indicates a destination address of the currently selected serving EPC node, a source address of a request sending node, and a User Datagram Protocol, UDP, port of the request sending node.

9. The method according to any one of claims 1-8, wherein the re-selected serving EPC node (1 10b) is more suitable to serve the UE (101 ) than the currently selected EPC node

(1 10a).

10. The method according to any one of claims 1 -9, wherein the request message is a General Packet Radio Services Tunneling protocol version 2, GTPv2, Create Session Request message or a GTPv2 Forward Relocation Request message or a S1

Application Protocol, S1AP, Initial UE message.

1 1 . The method according to any one of claims 1 -10, wherein the re-selecting node (108) is a first Mobility Management Entity, MME, (210a) and the re-selected EPC node (1 10b) is a second MME (210b).

12. The method according to any one of claims 1 -10, wherein the re-selecting node (108) is a first Serving Gateway, SGW, (208a) and the re-selected serving EPC node (1 10b) is a second SGW (208b).

13. The method according to any one of claims 1 -10, wherein the re-selecting node (108) is a first Packet Data Network Gateway, PGW, (215a) and the re-selected serving EPC node (1 10b) is a second PGW (215b).

14. The method according to any one of claims 1 -10, wherein the re-selecting node

(108) is a node dedicated to re-selecting a serving EPC node (110b) as the serving EPC node among the plurality of EPC nodes (1 10a, 1 10b, 1 10c) in the EPC node domain to serve the UE (101 ), and wherein the re-selected EPC node (1 10b) is one of: a second Mobility Management Entity, MME (210b), a second Serving Gateway, SGW (208b) or a second Packet Data Network Gateway, PGW (215b).

15. The method according to any one of claims 1 -14, wherein the the first node (1 10a) currently selected to be the serving EPC node is a default serving EPC node.

16. The method according to any one of claims 1 -15, wherein the first node (1 10a) currently selected to be the serving EPC node has been selected by a Radio Access Node, RAN, node (105), a Mobility Management Entity, MME (210), a Serving General Packet Radio Services Support Node, SGSN, a Trusted Wireless Local Area Network, TWAN, or an Evolved Packet Data Gateway, ePDG.

17. The method according to any one of claims 1 -16, wherein the re-selecting node

(108) is one of the plurality of EPC nodes (1 10a, 1 10b, 1 10c) in the EPC node domain.

18. The method according to any one of claims 1 -16, wherein the request message information indicates that the re-selecting node (108) is the first node currently selected to serve the UE (101 ).

19. A re-selecting node (108) for handling selection of a serving Evolved Packet Core, EPC, node (1 10a, 1 10b, 1 10c) to serve a User Equipment, UE (101 ),

wherein the re-selecting node (108) comprises EPC node information for each EPC node (1 10a, 1 10b, 1 10c) of a plurality of EPC nodes (1 10a, 1 10b, 1 10c) in at least one EPC node domain that the re-selecting node is responsible for,

the re-selecting node (108) being adapted to:

receive a request message associated with the UE (101 ), wherein the request message comprises request message information enabling re-selection of a serving EPC node from the plurality of EPC nodes in the EPC node domain;

re-select, based on the EPC node information and the received request message information, a second EPC node (1 10b) as the serving EPC node among the plurality of

EPC nodes (1 10a, 1 10b, 1 10c) in the EPC node domain to serve the UE (101 ) instead of a first node (1 10a) currently selected to be the serving EPC node; and to

forward the request message together with forwarding information to the second

EPC node (1 10b) as the re-selected serving EPC node (110b) to inform the re-selected serving EPC node that it should serve the UE (101 ).

20. The re-selecting node (108) according to claim 19, being further adapted to:

determine, based on at least one of: the request message information and the EPC node information, which type of EPC node (1 10a, 1 1 0b, 1 10c) the re-selected serving EPC node should be; and to

re-select the second EPC node (110b) such that the second EPC node is of the determined node type.

21 . The re-selecting node (108) according to any one of claims 19-20, wherein the request message information indicates at least one of: UE usage type information, UE radio capability, UE subscribed or Requested Access Point Name, APN, Radio Access Type, RAT, where the UE (101 ) is camping on, UE current Location Information, UE Close Subscriber Group, International Mobile Subscriber Identity, IMSI, Mobile Station International Subscriber Directory Number, MSISDN, International Mobile Equipment Identity, IMEI, APN, Quality of Service Class Identifier, QCI, Address Resolution Protocol, ARP, Serving Network Operator Identifier, Packet Data Network, PDN,

Connection type, UE time zone, Signaling Priority Indication, Charging Characteristics, a current procedure that the UE (101 ) is performing.

22. The re-selecting node (108) according to claim 21 , wherein the UE usage type information is at least one of: a subscribed UE usage type information and mapped UE usage type information.

23. The re-selecting node (108) according to any one of claims 19-22, wherein the re- selection node (108) is further adapted to base the re-selection on operator's policies and local configuration associated with the UE (101 ).

24. The re-selecting node (108) according to any one of claims 19-23, wherein the EPC node information indicates at least one of: UE usage type served by each EPC node, International Mobile Subscriber Identity, IMSI, series to be served by each EPC node, International Mobile Equipment Identity, IMEI, range to be serve by each EPC node,

Packet Data Network, PDN, Connection type to be served by the EPC node, whether the EPC node is optimized for certain UE radio capability, current load and overload status of each EPC node, resilience level of each of EPC node in in the EPC node domain.

25. The re-selecting node (108) according to any one of claims 19-24, being further adapted to receive the request message from an evolved Node B, eNB, (205), a Mobility Management Entity, MME, (210) or a Serving Gateway, SGW (208).

26. The re-selecting node (108) according to any one of claims 19-25, wherein the forwarding information enables the re-selection node (108) to respond to the request message, and wherein the forwarding information indicates a destination address of the currently selected serving EPC node, a source address of a request sending node, and a User Datagram Protocol, UDP, port of the request sending node.

27. The re-selecting node (108) according to any one of claims 19-26, wherein the re- selected serving EPC node (1 10b) is adapted to be more suitable to serve the UE (101 ) than the currently selected EPC node (1 10a).

28. The re-selecting node (108) according to any one of claims 19-27, wherein the request message is a General Packet Radio Services Tunneling protocol version 2, GTPv2, Create Session Request message or a GTPv2 Forward Relocation Request message or a S1 Application Protocol, S1AP, Initial UE message.

29. The re-selecting node (108) according to any one of claims 19-28, wherein the re- selecting node (108) is a first Mobility Management Entity, MME, (210a) and the re- selected EPC node (1 10b) is a second MME (210b).

30. The re-selecting node (108) according to any one of claims 19-29, wherein the re- selecting node (108) is a first Serving Gateway, SGW, (208a) and the re-selected serving EPC node (1 10b) is a second SGW (208b).

31 . The re-selecting node (108) according to any one of claims 19-30, wherein the re- selecting node (108) is a first Packet Data Network Gateway, PGW, (215a) and the re- selected serving EPC node (1 10b) is a second PGW (215b).

32. The re-selecting node (108) according to any one of claims 19-31 , wherein the re- selecting node (108) is a node dedicated to re-selecting a serving EPC node (1 10b) as the serving EPC node among the plurality of EPC nodes (1 10a, 1 10b, 1 10c) in the EPC node domain to serve the UE (101 ), and wherein the re-selected EPC node (1 10b) is one of: a second Mobility Management Entity, MME (210b), a second Serving Gateway, SGW (208b) or a second Packet Data Network Gateway, PGW (215b).

33. The re-selecting node (108) according to any one of claims 19-32, wherein the the first node (110a) currently selected to be the serving EPC node is a default serving EPC node.

34. The re-selecting node (108) according to any one of claims 19-33, wherein the first node (1 10a) currently selected to be the serving EPC node has been selected by a Radio Access Node, RAN, node (105), a Mobility Management Entity, MME (210), a Serving General Packet Radio Services Support Node, SGSN, a Trusted Wireless Local Area Network, TWAN, or an Evolved Packet Data Gateway, ePDG.

35. The re-selecting node (108) according to any one of claims 19-34, wherein the re- selecting node (108) is one of the plurality of EPC nodes (1 10a, 1 10b, 1 10c) in the EPC node domain.

36. The re-selecting node (108) according to any one of claims 19-35, wherein the request message information indicates that the re-selecting node (108) is the first node currently selected to serve the UE (101 ).

37. A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of claims 1 -18.

38. A carrier comprising the computer program of claim 37, wherein the carrier is one of an electronic signal, optical signal, radio signal or computer readable storage medium.