WO2022228685A1

WO2022228685A1 - Methods and apparatuses for enforcing fast connection re-establishment

Info

Publication number: WO2022228685A1
Application number: PCT/EP2021/061297
Authority: WO
Inventors: Markus Wimmer; Birger HÄTTY; Steffen Schulz
Original assignee: Nokia Technologies Oy
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2022-11-03

Abstract

Techniques for enforcing fast connection re-establishment are provided. For example, a method to be performed by a user equipment (UE) is provided. The UE has a connection to a first network such as a first Public Land Mobile Network. The method comprises: receiving, from the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication; and upon releasing the connection, performing an attach procedure according to the immediate re-attach indication to establish a connection to a second network such as a second Public Land Mobile Network. In some embodiments, the immediate re-attach indication indicates to start the attach procedure immediately after releasing the connection.

Description

METHODS AND APPARATUSES FOR ENFORCING FAST CONNECTION REESTABLISHMENT

FIELD

[0001] The subject disclosure generally relates to wireless communication systems and more particularly, to wireless communication systems enforcing fast connection re establishment. Yet more particularly, the subject disclosure provides methods and apparatuses for enforcing fast connection re-establishment of the user equipment (UE).

BACKGROUND

[0002] Border-crossing may be seamless for passengers. Mobile Network Operators (MNOs) typically however provide their services within the jurisdiction of one nation or region. As a user equipment (UE) such as a mobile phone is moved from one nation/region to another, the UE leaves the coverage of the mobile network the UE is connected to. If in an idle mode such as the RRC IDLE mode, several seconds to minutes pass until the UE has discovered the available national networks/regions and managed to get reconnected. If the UE is in a connected mode such as the RRC CONNECTED mode, i.e., if a call is taking place, while the border is crossed, a handover to an MNO providing services in the new country/region is typically not supported, resulting in a call drop. The reasons include different national regulatory requirements. Again, several seconds to minutes may pass until the UE has then detected the new networks providing wireless services and get attached to one of them.

[0003] The service interruption is especially critical for services which require a highly reliable and continuous data service availability, such as infrastructure assisted and automated driving or for transnational railway services. For high level of assisted and automated driving as promoted by Cooperative Intelligent Transport Systems (C-ITS) information services, messages need to be delivered within timescales of less than 100ms to be effective to fulfill their real-time and safety requirements. This condition is not fulfilled when UEs such as vehicles are crossing borders. For highly automated driving, latency below 100ms is expected, covered under the topic Ultra-Reliable Low Latency Communication (URLLC).

[0004] Seamless data service continuation in the cross-border case and consistent service provision for roaming UEs results in service degradation for assisted and automated driving and for railway services. If a handover between a serving mobile network to another available or preferred network is not supported, no radio access network (RAN) assisted solutions to switch a UE in a connected mode fast from the serving mobile network to another available or preferred network exist. In other words, there is a need for an accelerated method to terminate a connection such as an RRC connection of a UE in one network and re-establish a connection in another network.

SUMMARY

[0005] According to a first aspect of the subject disclosure, a method to be performed by a user equipment (UE) having a connection to a first network is provided. The method comprises: receiving, from the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication; and upon releasing the connection, performing an attach procedure according to the immediate re-attach indication to establish a connection to a second network.

[0006] In some embodiments of the method, the immediate re-attach indication indicates to start the attach procedure immediately after releasing the connection.

[0007] In some embodiments, the method further comprises: releasing one or more radio bearers to release the connection to the first network; and entering an idle mode.

[0008] In some embodiments, the method further comprises, upon releasing the connection, finding a cell of the second network that fulfils a cell selection criterion, wherein the attach procedure is performed to establish the connection to the cell of the second network that fulfills the cell selection criterion.

[0009] In some embodiments, the method further comprises, in response to performing the attach procedure, entering a connected mode with the second network.

[0010] In some embodiments of the method, the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network. The attach procedure is performed to establish the connection with the at least one cell.

[0011] In some embodiments of the method, the release message to release the connection further includes information about at least one cell of the second network. The attach procedure is performed to establish the connection with the at least one cell.

[0012] In some embodiments, the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells. The attach procedure is performed to establish the connection with one of the plurality of cells. In another embodiment, the list defines an order of priority and performing the attach procedure comprises selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell. [0013] In some embodiments of the method, the information about the at least one cell comprises an identifier of the at least one cell. In other embodiments, the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located. In yet other embodiments, the information further comprises one or more parameters to accelerate random access. As an example, the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention- free procedure using a dedicated RACH preamble.

[0014] In some embodiments of the method, the release message to release the connection includes information about at least one prioritized frequency. The attach procedure is performed in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency. As an example, the cell of the second network among the plurality of cells on any of the at least one prioritized frequency is determined to be different from a cell of the first network.

[0015] In some embodiments, the method further comprises: sending, to the first network, an indication that the UE supports a procedure according to the immediate re-attach indication. [0016] In some embodiments of the method, the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message. As an example, the release message comprises at least one information element including the immediate re-attach indication. [0017] In some embodiments of the method, the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

[0018] According to a second aspect of the subject disclosure, a method to be performed by a first network is provided. The method comprises: sending, to a user equipment (UE) having a connection to the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication. The immediate re attach indication instructs the UE to perform an attach procedure according to the immediate re-attach indication to establish a connection to a second network upon releasing the connection to the first network.

[0019] In some embodiments of the method, the immediate re-attach indication instructs the UE to start the attach procedure immediately after releasing the connection.

[0020] In some embodiments of the method, the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network. The immediate re-attach indication instructs the UE to perform the attach procedure to establish the connection with the at least one cell.

[0021] In some embodiments of the method, the release message to release the connection further includes information about at least one cell of the second network. The immediate re attach indication instructs the UE to perform the attach procedure to establish the connection with the at least one cell.

[0022] In some embodiments of the method, the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells. The immediate re-attach indication instructs the UE to perform the attach procedure to establish the connection with one of the plurality of cells.

[0023] In some embodiments of the method, the list defines an order of priority. The immediate re-attach indication instructs the UE to perform the attach procedure to establish the connection with the one of the plurality of cells by selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell. [0024] In some embodiments of the method, the information about the at least one cell comprises an identifier of the at least one cell. In other embodiments, the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located. In yet other embodiments, the information further comprises one or more parameters to accelerate random access. As an example, the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention- free procedure using a dedicated RACH preamble.

[0025] In some embodiments of the method, the release message to release the connection includes information about at least one prioritized frequency. The immediate re-attach indication instructs the UE to perform the attach procedure in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency.

[0026] In some embodiments, the method further comprises: receiving, from the UE, an indication that the UE supports a procedure according to the immediate re-attach indication. [0027] In some embodiments of the method, the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message. As an example, the release message comprises at least one information element including the immediate re-attach indication.

[0028] In some embodiments of the method, the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network. [0029] According to a third aspect of the subject disclosure, a user equipment (UE) in a first network is provided. The UE comprises: at least one processor; and at least one memory including computer program code. The computer program code causes the UE, when executed with the at least one processor, to at least: receive, from the first network, a release message to release a connection to the first network, the release message including an immediate re-attach indication; and upon releasing the connection, perform an attach procedure according to the immediate re-attach indication to establish a connection to a second network.

[0030] In some embodiments, the immediate re-attach indication indicates to start the attach procedure immediately after releasing the connection.

[0031] In some embodiments, the computer program code causes the UE, when executed with the at least one processor, to at least: release one or more radio bearers to release the connection to the first network; and enter an idle mode.

[0032] In some embodiments, the computer program code causes the UE, when executed with the at least one processor, to at least: upon releasing the connection, find a cell of the second network that fulfils a cell selection criterion. The attach procedure is performed to establish the connection to the cell of the second network that fulfills the cell selection criterion. [0033] In some embodiments, the computer program code causes the UE, when executed with the at least one processor, to at least: in response to performing the attach procedure, enter a connected mode with the second network.

[0034] In some embodiments, the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network. The attach procedure is performed to establish the connection with the at least one cell.

[0035] In some embodiments, the release message to release the connection further includes information about at least one cell of the second network. The attach procedure is performed to establish the connection with the at least one cell.

[0036] In some embodiments, the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells. The attach procedure is performed to establish the connection with one of the plurality of cells.

[0037] In some embodiments, the list defines an order of priority and performing the attach procedure comprises selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell.

[0038] In some embodiments, the information about the at least one cell comprises an identifier of the at least one cell. In other embodiments, the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located. In yet other embodiments, the information further comprises one or more parameters to accelerate random access. As an example, the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention-free procedure using a dedicated RACH preamble.

[0039] In some embodiments, the release message to release the connection includes information about at least one prioritized frequency. The attach procedure is performed in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency. As an example, the cell of the second network among the plurality of cells on any of the at least one prioritized frequency is determined to be different from a cell of the first network.

[0040] In some embodiments, the computer program code causes the UE, when executed with the at least one processor, to at least: send, to the first network, an indication that the UE supports a procedure according to the immediate re-attach indication.

[0041] In some embodiments, the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message. As an example, the release message comprises at least one information element including the immediate re-attach indication.

[0042] In some embodiments, the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

[0043] According to a fourth aspect of the subject disclosure, a base station of a first network is provided. The base station comprises: at least one processor; and at least one memory including computer program code. The computer program code causes the base station, when executed with the at least one processor, to at least: send, to a user equipment (UE) having a connection to the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication. The immediate re-attach indication instructs the UE to perform an attach procedure according to the immediate re-attach indication to establish a connection to a second network upon releasing the connection to the first network.

[0044] In some embodiments, the immediate re-attach indication instructs the UE to start the attach procedure immediately after releasing the connection.

[0045] In some embodiments, the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network. The immediate re-attach indication instructs the UE to perform the attach procedure to establish the connection with the at least one cell.

[0046] In some embodiments, the release message to release the connection further includes information about at least one cell of the second network. The immediate re-attach indication instructs the UE to perform the attach procedure to establish the connection with the at least one cell.

[0047] In some embodiments, the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells. The immediate re-attach indication instructs the UE to perform the attach procedure to establish the connection with one of the plurality of cells.

[0048] In some embodiments, the list defines an order of priority and the immediate re attach indication instructs the UE to perform the attach procedure to establish the connection with the one of the plurality of cells by selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell.

[0049] In some embodiments, the information about the at least one cell comprises an identifier of the at least one cell. In other embodiments, the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located. In yet other embodiments, the information further comprises one or more parameters to accelerate random access. As an example, the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention-free procedure using a dedicated RACH preamble.

[0050] In some embodiments, the release message to release the connection includes information about at least one prioritized frequency. The immediate re-attach indication instructs the UE to perform the attach procedure in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency.

[0051] In some embodiments, the computer program code causes the base station, when executed with the at least one processor, to at least: receive, from the UE, an indication that the UE supports a procedure according to the immediate re-attach indication.

[0052] In some embodiments, the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message. As an example, the release message comprises at least one information element including the immediate re-attach indication. [0053] In some embodiments, the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

[0054] According to a fifth aspect of the subject disclosure, a computer program product comprises program instructions stored on a computer readable medium to execute steps according to any one of the embodiments of the methods outlined above when said program is executed on a computer.

[0055] The above-noted aspects and features may be implemented in systems, apparatuses, methods, articles and/or non-transitory computer-readable media depending on the desired configuration. The subject disclosure may be implemented in and/or used with a number of different types of devices, including but not limited to cellular phones, tablet computers, wearable computing devices, portable media players, and any of various other computing devices.

[0056] This summary is intended to provide a brief overview of some of the aspects and features according to the subject disclosure. Accordingly, it will be appreciated that the above- described features are merely examples and should not be construed to narrow the scope of the subject disclosure in any way. Other features, aspects, and advantages of the subject disclosure will become apparent from the following detailed description, drawings and claims.

LIST OF ABBREVIATIONS

[0057] In the subject disclosure, the following abbreviations are used and should be understood in accordance with the given definitions:

3 GPP 3^rd Generation Partnership Project

5G 5^th Generation (Mobile Communication Network)

AF Application Function

AMF Access and Mobility Function

AN Access Network

ARFCN Absolute Radio Frequency Carrier Number

BS Base Station

CDMA Code Division Multiple Access

CGI Cell Group Identifier

C-ITS Cooperative Intelligent Transport System

CN Core Network

CP Control Plane CSG Closed Subscriber Group

E-ARFCN E-UTRA Absolute Radio Frequency Carrier Number eNB Evolved NodeB

EPC Evolved Packet Core

EPLMN Equivalent PLMN

ETSI European Telecommunications Standards Institute

E-UTRAN Evolved UMTS Terrestrial Radio Access

HPLMN Home PLMN

HSS Home Subscriber Service

IE Information Element

IMSI International Mobile Subscriber Identity

IP Internet Protocol

GTP GPRS Tunnelling Protocol

LTE Long Term Evolution

MCC Mobile Country Code

MME Mobility Management Entity

MNC Mobile Network Code

MNO Mobile Network Operator

MOCN Multi-Operator Core Network

MORAN Multi-Operator Radio Access Network

NAS Non-Access Stratum

NR New Radio

PCF Policy Control Function

PCRF Policy Control and Charging Rules Function

PGW PDP Gateway

PDN Packet Data Network

PDP Packet Data Protocol

PGW PDN Gateway

PLMN Public Land Mobile Network

QCI QoS Class Identifier

QoS Quality of Service

RACH Random Access Channel

RAN Radio Access Network

RPLMN Registered PLMN WO 2022/228685 - 1° - PCT/EP2021/061297

RRC Radio Resource Control (Protocol)

SGW Serving Gateway

SIM Subscriber Identity Module

TS Technical Specification

UDM Unified Data Management

UE User Equipment

URLLC Ultra-Reliable Low Latency Communication

VPLMN Visited PLMN

BRIEF DESCRIPTION OF THE DRAWINGS [0058] A better understanding of the subj ect disclosure can be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0059] FIG. 1 shows a schematic diagram of an example communication system comprising a base station and a plurality of communication devices;

[0060] FIG. 2 shows a schematic diagram of an example mobile communication device;

[0061] FIG. 3 shows a schematic diagram of an example control apparatus;

[0062] FIGS. 4 and 5 illustrate flow charts of methods for enforcing fast connection re establishment according to some embodiments of the subject disclosure;

[0063] FIG. 6 illustrates a message flow in a method for enforcing fast connection re establishment according to some embodiments of the subject disclosure;

[0064] FIG. 7 shows the Dedicated Bearer Activation Procedure according to 3 GPP TS 23.401; and

[0065] FIG. 8 shows the non-roaming LTE architecture for 3 GPP access according to 3 GPP TS 23.401.

DETAILED DESCRIPTION

[0066] Before explaining the examples in detail, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to FIGS. 1 to 3 to assist in understanding the technology underlying the described examples. [0067] In a wireless communication system 100, such as that shown in FIG. 1, mobile communication devices or user equipment (UE) 102, 104, 105 are provided wireless access via at least one base station (e.g., next generation NB, gNB) or similar wireless transmitting and/or receiving node or point. Base stations may be controlled or assisted by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g., wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatuses. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller. In FIG. 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

[0068] In FIG. 1, base stations 106 and 107 are shown as connected to a wider communications network 113 via gateway 112. A further gateway function may be provided to connect to another network.

[0069] As used herein, the term "base station" has the full breadth of its ordinary meaning, and at least includes a wireless communication station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system. The communication area (or coverage area) of the base stations may be referred to as a "cell." The base stations and the UEs may be configured to communicate over the transmission medium using any of various radio access technologies (RATs), also referred to as wireless communication technologies, or telecommunication standards described hereinbelow. As illustrated in FIG. 1, while one of the base stations may act as a "serving cell" for UEs, each UE may also be capable of receiving signals from (and possibly within communication range of) one or more other cells (which might be provided by the base stations and/or any other base stations), which may be referred to as "neighboring cells".

[0070] The smaller base stations 116, 118 and 120 may also be connected to the network 113, for example by a separate gateway function and/or via the controllers of the macro level stations. The base stations 116, 118 and 120 may be pico or femto level base stations or the like. In the example, stations 116 and 118 are connected via a gateway 111 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided. Smaller base stations 116, 118 and 120 may be part of a second network, for example WLAN and may be WLAN APs. The communication devices 102, 104, 105 may access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other non-limiting examples comprise time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on.

[0071] An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE (LTE-A) employs a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence/Radio Link Control/Medium Access Control/Physical layer protocol (PD CP/RLC/M AC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system comprise those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). A base station can provide coverage for an entire cell or similar radio service area. Core network elements include Mobility Management Entity (MME), Serving Gateway (S-GW) and Packet Gateway (P-GW).

[0072] An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE Advanced. Base stations of NR systems may be known as next generation Node Bs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and finer QoS support, and some on-demand requirements for e.g. QoS levels to support QoE of user point of view. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple input-multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. [0073] Future networks may utilize network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0074] An example 5G core network (CN) comprises functional entities. The CN is connected to a UE via the radio access network (RAN). An UPF (User Plane Function) whose role is called PSA (PDU Session Anchor) may be responsible for forwarding frames back and forth between the DN (data network) and the tunnels established over the 5G towards the UE(s) exchanging traffic with the DN.

[0075] The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function). The CN may also include an AMF (Access & Mobility Function).

[0076] A possible mobile communication device will now be described in more detail with reference to FIG. 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a smart phone, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (e-mail), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

[0077] In an industrial application a communication device may be a modem integrated into an industrial actuator (e.g., a robot arm) and/or a modem acting as an Ethernet-hub that will act as a connection point for one or several connected Ethernet devices (which connection may be wired or unwired).

[0078] A mobile device is typically provided with at least one data processing entity 201, at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as keypad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

[0079] The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In FIG. 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

[0080] The mobile device 200 may also or alternatively be configured to communicate using one or more global navigational satellite systems (GNSS, e.g., GPS or GLONASS), one or more mobile television broadcasting standards (e.g., ATSC-M/H or DVB-H), and/or any other wireless communication protocol, if desired. Other combinations of wireless communication standards (including more than two wireless communication standards) are also possible.

[0081] Generally, the communication device 200 illustrated in FIG. 2 includes a set of components configured to perform core functions. For example, this set of components may be implemented as a system on chip (SOC), which may include portions for various purposes. Alternatively, this set of components may be implemented as separate components or groups of components for the various purposes. The set of components may be coupled (e.g., communicatively; directly or indirectly) to various other circuits of the communication device 200

[0082] The communication device 200 may include at least one antenna in communication with a transmitter and a receiver (e.g., the transceiver apparatus 206). Alternatively, transmit and receive antennas may be separate. The communication device 200 may also include a processor (e.g., the at least one data processing entity 201) configured to provide signals to and receive signals from the transmitter and receiver, respectively, and to control the functioning of the communication device 200. The processor may be configured to control the functioning of the transmitter and receiver by effecting control signaling via electrical leads to the transmitter and receiver. Likewise, the processor may be configured to control other elements of the communication device 200 by effecting control signaling via electrical leads connecting processor to the other elements, such as a display (e.g., display 208) or a memory (e.g., the at least one memory 202). The processor may, for example, be embodied in a variety of ways including circuitry, at least one processing core, one or more microprocessors with accompanying digital signal processor(s), one or more processor(s) without an accompanying digital signal processor, one or more coprocessors, one or more multi-core processors, one or more controllers, processing circuitry, one or more computers, various other processing elements including integrated circuits (for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and/or the like), or some combination thereof. Accordingly, in some examples, the processor may comprise a plurality of processors or processing cores.

[0083] The communication device 200 may be capable of operating with one or more air interface standards, communication protocols, modulation types, access types, and/or the like. Signals sent and received by the processor may include signaling information in accordance with an air interface standard of an applicable cellular system, and/or any number of different wireline or wireless networking techniques, comprising but not limited to Wi-Fi, wireless local access network (WLAN) techniques, such as Institute of Electrical and Electronics Engineers (IEEE) 802.11, 802.16, 802.3, ADSL, DOCSIS, and/or the like. In addition, these signals may include speech data, user generated data, user requested data, and/or the like.

[0084] For example, the communication device 200 and/or a cellular modem therein may be capable of operating in accordance with various first generation (1G) communication protocols, second generation (2G or 2.5G) communication protocols, third-generation (3G) communication protocols, fourth-generation (4G) communication protocols, fifth-generation (5G) communication protocols, Internet Protocol Multimedia Subsystem (IMS) communication protocols (for example, session initiation protocol (SIP) and/or the like. For example, the communication device 200 may be capable of operating in accordance with 2G wireless communication protocols IS-136, Time Division Multiple Access TDMA, Global System for Mobile communications, GSM, IS-95, Code Division Multiple Access, CDMA, and/or the like. In addition, for example, the UE 120 may be capable of operating in accordance with 2.5G wireless communication protocols General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), and/or the like. Further, for example, the communication device 200 may be capable of operating in accordance with 3G wireless communication protocols, such as Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA2000), Wideband Code Division Multiple Access (WCDMA), Time Division- Synchronous Code Division Multiple Access (TD-SCDMA), and/or the like. The communication device 200 may be additionally capable of operating in accordance with 3.9G wireless communication protocols, such as Long-Term Evolution (LTE), Evolved Universal Terrestrial Radio Access Network (E-UTRAN), and/or the like. Additionally, for example, the communication device 200 may be capable of operating in accordance with 4G wireless communication protocols, such as LTE Advanced, 5G, and/or the like as well as similar wireless communication protocols that may be subsequently developed.

[0085] It is understood that the processor may include circuitry for implementing audio/video and logic functions of the communication device 200. For example, the processor may comprise a digital signal processor device, a microprocessor device, an analog-to-digital converter, a digital-to-analog converter, and/or the like. Control and signal processing functions of the communication device 200 may be allocated between these devices according to their respective capabilities. The processor may additionally comprise an internal voice coder (VC), an internal data modem (DM), and/or the like. Further, the processor may include functionality to operate one or more software programs, which may be stored in memory. In general, the processor and stored software instructions may be configured to cause the communication device 200 to perform actions. For example, the processor may be capable of operating a connectivity program, such as a web browser. The connectivity program may allow the communication device 200 to transmit and receive web content, such as location-based content, according to a protocol, such as wireless application protocol (WAP), hypertext transfer protocol (HTTP), and/or the like.

[0086] The communication device 200 may also comprise a user interface including, for example, an earphone or speaker, a ringer, a microphone, a display, a user input interface, and/or the like, which may be operationally coupled to the processor. The display may, as noted above, include a touch sensitive display, where a user may touch and/or gesture to make selections, enter values, and/or the like. The processor may also include user interface circuitry configured to control at least some functions of one or more elements of the user interface, such as the speaker, the ringer, the microphone, the display, and/or the like. The processor and/or user interface circuitry comprising the processor may be configured to control one or more functions of one or more elements of the user interface through computer program instructions, for example, software and/or firmware, stored on a memory accessible to the processor, for example, volatile memory, non-volatile memory, and/or the like. The communication device 200 may include a battery for powering various circuits related to the mobile terminal, for example, a circuit to provide mechanical vibration as a detectable output. The user input interface may comprise devices allowing the communication device 200 to receive data, such as a keypad (e.g., keypad 206) and/or other input devices. The keypad can also be a virtual keyboard presented on display or an externally coupled keyboard.

[0087] The communication device 200 may also include one or more mechanisms for sharing and/or obtaining data. For example, the communication device 200 may include a short- range radio frequency (RF) transceiver and/or interrogator, so data may be shared with and/or obtained from electronic devices in accordance with RF techniques. The communication device 200 may include other short-range transceivers, such as an infrared (IR) transceiver, a Bluetooth™ (BT) transceiver operating using Bluetooth™ wireless technology, a wireless universal serial bus (USB) transceiver, a Bluetooth™ Low Energy transceiver, a ZigBee transceiver, an ANT transceiver, a cellular device-to-device transceiver, a wireless local area link transceiver, and/or any other short-range radio technology. The communication device 200 and, in particular, the short-range transceiver may be capable of transmitting data to and/or receiving data from electronic devices within the proximity of the apparatus, such as within 10 meters, for example. The communication device 200 including the Wi-Fi or wireless local area networking modem may also be capable of transmitting and/or receiving data from electronic devices according to various wireless networking techniques, including 6LoWpan, Wi-Fi, Wi Fi low power, WLAN techniques such as IEEE 802.11 techniques, IEEE 802.15 techniques, IEEE 802.16 techniques, and/or the like.

[0088] The communication device 200 may comprise memory, such as one or more Subscriber Identity Modules (SIM), one or more Universal Subscriber Identity Modules (USIM), one or more removable User Identity Modules (R-UIM), one or more eUICC, one or more UICC, and/or the like, which may store information elements related to a mobile subscriber. In addition, the communication device 200 may include other removable and/or fixed memory. The communication device 200 may include volatile memory and/or non volatile memory. For example, the volatile memory may include Random Access Memory (RAM) including dynamic and/or static RAM, on-chip or off-chip cache memory, and/or the like. The non-volatile memory, which may be embedded and/or removable, may include, for example, read-only memory, flash memory, magnetic storage devices, for example, hard disks, floppy disk drives, magnetic tape, optical disc drives and/or media, non-volatile random-access memory (NVRAM), and/or the like. Like volatile memory, the non-volatile memory may include a cache area for temporary storage of data. At least part of the volatile and/or non volatile memory may be embedded in the processor. The memories may store one or more software programs, instructions, pieces of information, data, and/or the like which may be used by the apparatus for performing operations disclosed herein.

[0089] The memories may comprise an identifier, such as an International Mobile Equipment Identification (IMEI) code, capable of uniquely identifying the communication device 200. The memories may comprise an identifier, such as an international mobile equipment identification (IMEI) code, capable of uniquely identifying the communication device 200. In the example embodiment, the processor may be configured using computer code stored at memory to cause the processor to perform operations disclosed herein.

[0090] Some of the embodiments disclosed herein may be implemented in software, hardware, application logic, or a combination of software, hardware, and application logic. The software, application logic, and/or hardware may reside on the memory, the processor, or electronic components, for example. In some example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer- readable media. In the context of this document, a "computer-readable medium" may be any non-transitory media that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer or data processor circuitry, with examples depicted at FIG. 2, computer-readable medium may comprise a non-transitory computer-readable storage medium that may be any media that can contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[0091] In some embodiments, the communication device 200 (i.e., a user equipment (UE) in a network) comprises the processor (e.g., the at least one data processing entity 201) and the memory (e.g., the at least one memory 202). The memory includes computer program code causing the communication device 200 to perform processing according to the methods described below with reference to FIG. 4. [0092] FIG. 3 shows an example embodiment of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a RAN node, e.g., a base station, eNB or gNB, a relay node or a core network node such as an MME or S-GW or P-GW, or a core network function such as AMF/SMF, or a server or host. The method may be implanted in a single control apparatus or across more than one control apparatus. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301, at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head.

[0093] Generally, the control apparatus 300 has an antenna, which transmits and receives radio signals. A radio frequency (RF) transceiver module, coupled with the antenna, receives RF signals from antenna, converts them to baseband signals and sends them to processor (e.g., the at least one data processing unit 302, 303). RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in control apparatus 300. Memory (e.g., the at least one memory 301) stores program instructions and data to control the operations of the control apparatus 300. In the example of FIG. 3, the control apparatus 300 also includes protocol stack and a set of control functional modules and circuit. PDU session handling circuit handles PDU session establishment and modification procedures. Policy control module that configures policy rules for UE. Configuration and control circuit provides different parameters to configure and control UE of related functionalities including mobility management and session management. Suitable processors include, by way of example, a special purpose processor, a digital signal processor (DSP), a plurality of micro-processors, one or more micro-processor associated with a DSP core, a controller, a microcontroller, application specific integrated circuits (ASICs), file programmable gate array (FPGA) circuits, and other type of integrated circuits (ICs), and/or state machines. [0094] In some embodiments, the control apparatus 300 (i.e., the base station or the wireless transmitting and/or receiving point equipment) comprises the processor (e.g., the at least one data processing unit 302, 303) and the memory (e.g., the at least one memory 301). The memory includes computer program code causing the control apparatus 300 to perform processing according to the method described below with reference to FIG. 5.

[0095] Before referring to FIGS. 4 and 5 and describing the methods for enforcing fast connection re-establishment according to some embodiments of the subject disclosure, some background information and aspects related to the subject disclosure will be provided.

[0096] The subject disclosure described herein particularly refers to use cases such as automated driving where network service availability is critical. In these use cases, subscribers such as UE (e.g., a car, a train, or the like) is connected to the network (i.e., serving PLMN) and require a low latency communication with high reliability as data has frequently to be exchanged with a service platform (e.g., about every 100ms or less). For example, the UE is in the RRC CONNECTED mode. In other words, the subscribers use services which are highly sensible to long interruption times.

[0097] Within the coverage of the network, the services can be provided (and maintained) when the UE is connected to the network. However, a problem may arise when the UE is moving out-of-coverage of the serving PLMN and in-coverage of a non-serving PLMN. A typical example concerns the case at the border between countries where the UE has to change PLMNs. For example, when the UE leaves a first country and the serving PLMN of the first country is not available anymore, the UE has to change to a PLMN of a second country (i.e., the country which the UE entered). The process of changing from PLMN of the first country to the PLMN of the second country takes time - too much time for use cases such as automated driving.

[0098] Several techniques have been developed to allow to change (fast) in-between different PLMNs. Examples include “Equivalent PLMN” (EPLMN) and “inter-PLMN handover” (inter-PLMN HO).

[0099] According to EPLMN, a list of PLMNs is sent by the current serving Registered PLMN (RPLMN) to the UE over dedicated NAS signaling. When the UE receives the Equivalent PLMN list, the UE shall adjust the cell re-selection algorithm to consider both RPLMN cells and EPLMN cells as suitable cells for re-selection. For example, a Finnish operator may use EPLMN in a part of Finland where it is possible to cross the border to Sweden just by driving on a bridge across the border river and slowing down to allow control by the customs. In view of the Finnish operator, a short service gap in changing PLMN when coverage of the Home PLMN (HPLMN) gets lost soon after crossing the border may be found acceptable. The motivation of the Finnish operator is to ensure that the UE does not have any choice of other Visited PLMN (VPLMN) than a specific Swedish operator (such as the Swedish subsidiary of the Finnish operator). So, when approaching to border from one side in Finland, at the last Location Update (e.g., the Registration Update in 5G) the RPLMN informs the UE that the specific Swedish operator is equivalent to the Finnish operator. After that indication, the UE does not even lose service on the bridge, but the UE keeps selecting the best cell among all cells indicating either the Finnish operator or the specific Swedish operator (specifically, the identifiers of the cells). The service gap is limited because no PLMN selection takes place at all and the change of PLMN selection is just a cell re-selection followed by mobility update to new area. The EPLMN may be used if the UE is in idle mode. If the UE crossing the border is in the connected mode, the network may order a handover from the cell of the Finnish operator to a cell of the specific Swedish operator such that the change in-between different PLMNs is largely seamless. In this case, the UE just follows the handover command (e.g., HO COMMAND) even between the networks.

[0100] For the idle state of the UE, the EPLMN is an efficient technique for changing (fast) in-between different PLMNs in the same or different country. EPLMN may be used selectively, towards only those UEs that need EPLMN, and the use of EPLMN may be limited to only the border areas where EPLMN is needed.

[0101] In an example, the UE in the idle mode (e.g., RRC IDLE mode) may perform cell selection and reselection (e.g., in LTE according to 3GPP TS 36.304). If the UE is camping on a serving cell, then the cell provides the UE with a cell neighborhood list(s). This allows the UE to perform the cell selection process very quickly. The neighborhood list(s) may include cells of other PLMNs, which the UE can select if they are included in the EPLMN list. However, whether and how fast the UE performs the cell selection and reselection is not specified and left for UE implementation.

[0102] In an exemplary UE implementation, the cell selection and reselection process including a PLMN change may just be finished only after the UE has verified that a change of a PLMN cannot be avoided before offering connectivity to the subscriber, resulting in a long service interruption time.

[0103] Another UE implementation may choose the first detected suitable cell to provide network connection - and the first suitable cell (i.e., the cell fulfilling the S-criterion) may even be the cell the UE just got disconnected from because the radio connectivity was no longer reliable. [0104] For the connected state of the UE, the inter-PLMN HO is a technique that is efficient, but the inter-PLMN HO puts some pre-requisite requirements on the network coordination which might not be possible to use in all cases. In such case, re-establishment using inter-PLMN HO may give the UE an educated guess on where to re-establish next to get the connection restored fast. This requires some CN level coordination between the two networks, as the data path must be switched from the old RPLMN to the new RPLMN.

[0105] So, a handover (HO) between two Mobile Operators (PLMNs) may be possible. For use cases such as automated driving, which require very short service interruption times, the availability of inter-PLMN HO may be efficient, but inter-PLMN HOs are often not supported for a range of administrative and regulatory reasons.

[0106] The aforementioned techniques are not suitable in scenarios where: the UE requires a continuous service provision, i.e., mobile service interruption times have to be kept at a minimum; the UE is in a connected mode (e.g., RRC CONNECTED mode); and the UE is leaving the coverage area of its serving PLMN (i.e., cross-border case). In these scenarios, inter- PLMN HO may be not supported.

[0107] In accordance with the subject disclosure, the disadvantages of the existing techniques for changing in-between different networks (e.g., different PLMNs) such as EPLMN and inter-PLMN HO, especially in cases like automated driving where network service availability is critical, may be overcome by providing an immediate re-attach indication with a release message to release connection to the network. The immediate re-attach indication instructs the UE to re-establish a connection immediately after releasing the connection and entering an idle mode. As an example, a new Information Element (IE) may be provided in, e.g, the RRC CONNECTION RELEASE message in LTE (e.g., the RRC CONNECTION RELEASE message according to 3GPP TS 36.331) or in the RRC RELEASE message in 5G (e.g, the RRC RELEASE message according to 3GPP TS 38.331). With this new IE, the UE receives a notification that an RRC connection is to be re-established immediately after entering the RRC IDLE mode. The behaviour of the UE is thereby specified to select a suitable cell and enter the RRC CONNECTED mode quickly.

[0108] Now, the methods for enforcing fast connection re-establishment according to some embodiments of the subject disclosure will be described.

[0109] FIG. 4 illustrates a flow chart of a method for enforcing fast connection re establishment according to some embodiments. The method is performed by a user equipment (UE). For example, the UE may be represented by any one of the mobile communication devices 102, 104, 105 of the wireless communication system 100 as described above with reference to FIG. 1, or the communication device 200 as described above with reference to FIG. 2.

[0110] The UE has established a connection to a first network (such as a first PLMN). That is, the UE is located in the communication area or coverage area (i.e., the cell) of one of the base stations such as base stations 106, 107 shown in FIG. 2 and communicates with the base station. The base station with which the UE established the connection is referred to as the "serving cell" for the UE. In an example, the UE is in RRC CONNECTED mode and communicates with the first network. As discussed hereinbefore, the UE may use a service accessible via, or provided by, the first network and require a continuous provision of the service, i.e., interruption times of the service have to be kept at a minimum.

[0111] Prior to performing the operations shown in FIG. 4, the UE may indicate the capability of supporting the fast connection re-establishment to the first network. In an example, an indication that the UE supports the procedure according to the immediate re-attach indication may be sent to the first network, e.g., during establishment of the connection to the first network and/or in a message reporting capability of the UE.

[0112] If the UE is leaving the coverage area of the first network (i.e., the serving PLMN, the first PLMN) and thus communication with the first network may become interrupted, the UE is ordered into the idle mode. In an example, the idle mode is the RRC IDLE mode. That is, continuation of the service cannot be provided any longer within the UE’s serving PLMN. [0113] At block 410, the UE may receive from the first network a release message (e.g., RRC CONNECTION RELEASE in LTE, RRC RELEASE in 5G). In response to receiving the release message, the UE releases one or more (usually all) bearers and thus releases the connection to the first network (block 420) and enters the idle mode (block 430). That is, the first network triggers the UE to release the connection and the UE is sent into the idle mode. The UE may then perform cell selection and reselection. In an example, the cell selection and reselection in accordance with 3GPP TS 36.304 (for LTE) or any equivalent specification for other architectures standardized by 3GPP (e.g., 3GPP TS 38.304 for 5G) is performed. As already discussed above, the UE does not necessarily start the cell selection and reselection immediately and also the selection and reselection may take often more than a minute before the UE has selected a new network and registered in the new network. The details of the cell selection and reselection resulting in the selection of a new network is left to UE implementation. In order avoid the unpredictable behavior of the UE, especially in case of requiring continuous communication and service availability, the release message received from the first network in block 410 includes an immediate re-attach indication. According to the subject disclosure, the immediate re-attach indication is to instruct the UE to start the attach procedure (e.g., to start the cell selection and reselection) immediately after releasing the connection to the first network and entering the idle mode.

[0114] At block 450, the UE performs the attach procedure to establish a connection to a second network (i.e., the target PLMN, the second PLMN) immediately after releasing the connection to the first network (block 420) and entering the UE mode (block 430). That is, upon releasing the connection, the UE performs the attach procedure (block 450). As will be described with reference to some examples hereinbelow, the attach procedure is performed in accordance with the immediate re-attach indication, i.e., with information of the immediate re attach indication. In an example, the UE enters the connected mode (e.g., RRC CONNECTED mode) in response to performing the attach procedure. Establishing the connection with the second network and ordering the UE in the connected mode minimizes the interruption time and allows continuous communication and service availability.

[0115] In an example, as shown in FIG. 4, the UE may start to find one or more cells of the second network and determines whether one of the cells fulfills a cell selection criterion, at block 440. The cell selection criterion may, for example, correspond to the cell selection criterion (so-called S-criterion) according to 3GPP TS 36.304. To limit the time for determining the cell of the second network to be connected in the attach procedure, the UE may stop whether found cells fulfil the cell selection criterion when a first cell that fulfils the cell selection criterion is found. In other examples, the UE may determine all cells among the found cells that fulfil the cell selection criterion and select the best or most optimal cell. The cell is selected by the UE and then used in performing the attach procedure (block 450) in order to establish a connection with the selected cell of the second network.

[0116] In some examples, the release message received at block 410 includes information about at least one cell of the second network. The presence of the information about the at least one cell of the second network instructs the UE to perform the attach procedure (block 450) upon releasing the connection. That is, the presence of the information about the at least one cell of the second network represents the immediate re-attach indication. In this example, the immediate re-attach indication is implicitly provided by the release message. The information about the at least one cell is used in the attach procedure (block 450) to establish a connection with the at least one cell.

[0117] In other examples, the release message received at block 410 comprises the immediate re-attach indication and information about at least one cell of the second network. In this case, the immediate re-attach indication indicates to the UE to perform the attach procedure (block 450) upon releasing the connection to the first network. The information about the at least one cell is used in the attach procedure (block 450) to enable establishing a connection with the at least one cell of the second network. In one example, the immediate re attach indication may be represented by a flag in the release message such as a bit value. If the bit value corresponds to a first value (e.g., “1”), the immediate re-attach indication indicates to start the attach procedure immediately after releasing the connection to the first network. Otherwise, if the bit value corresponds to a second value (e.g., “0”), the immediate re-attach indication indicates that there is no need for starting the attach procedure immediately. In this case, the UE may start the attach procedure in response to the cell selection and reselection in accordance with the UE implementation. If, in this case, the information about at least one cell of the second network is also included in the release message, the information may be ignored or used by the UE in the cell selection and reselection. In examples in which no immediate re attach indication is to be made, the immediate re-attach indication may be not included in the release message. That is, the absence of the immediate re-attach indication indicates no need for starting the attach procedure immediately.

[0118] In the above examples, the information may include information about a plurality of cells of the second network. Here, the cells may also be cells of a plurality of networks. This case may occur in a tri-border or multi-border area where networks of three or more different networks are present. The information about the plurality of cells may be included in the release message in the form of a list. The UE may select one cell among the list of cells based on certain criteria. Examples of such criteria include a preferred MNO serving the second network, that MNOs of the cell of the first network and of the cell of the second network are the same, that the cell fulfils the cell selection criterion (S -criterion). The selected cell is used in the attach procedure (block 450) to establish the connection with the selected cell.

[0119] In some examples, the list of cells may define an order of priority. That is, the first cell in the list may be the cell with highest priority and the UE uses the cell with the highest priority in the attach procedure (block 450). If for any reason the UE cannot select the cell with the highest priority or cannot establish the connection with that cell, the UE uses the next cell in the list having the second highest priority and establishes the connection with that cell. Thus, the UE uses the cells in the order defined by the list and tries to establish the connection with one of the cells. If for any reason no connection can be established with one of the cells in the list, the UE may find a cell that fulfils the cell selection criterion (block 440) as described above. [0120] Exemplary information about the at least one cell includes an identifier of the at least one cell. In the example with the list of the plurality of cells, an identifier for each of the plurality of cells may be included. In an example, the identifier may be the physical cell id (PCI) of the cell or the cell global identity (CGI).

[0121] In addition to the identifier, the information may further comprise one of more of: an Absolute Radio Frequency Carrier Number (ARFCN) of the at least one cell, a radio technology of the at least one cell (e.g., CDMA), and a band in which the at least one cell is located. In some examples, the information may further include one or more parameters to accelerate random access procedure performed, at least in part, to establish the connection to the second network. The one or more parameters may be used to accelerate accessing the cell via Random Access Channel (RACH) using a dedicated RACH preamble. The access via RACH may follow a contention-free procedure.

[0122] Additionally, or alternatively in some other examples, the release message received by the UE in block 410 may include information about at least one prioritized frequency. The attach procedure is performed by the UE in block 450 on the at least one prioritized frequency in order to establish the connection to a cell of the second network which is on the at least one prioritized frequency. In case the release message includes information about a plurality of prioritized frequencies, the UE may find cells corresponding to said prioritized frequencies and may then perform the attach procedure to establish the connection with one of these cells. In order to avoid that the UE selects the cell of the first network again, the UE may use cells on which to perform the attach procedure which are determined to be different from the cell of the first network even if this cell uses one of the prioritized frequencies.

[0123] As described above, the release message may correspond to the RRC CONNECTION RELEASE message in LTE or the RRC RELEASE message in 5G. The immediate re-attach indication and/or the information about the at least one cell of the second network may be included in at least one Information Element (IE) of the release message. In one example, the IE may be called ImmediateRe Attach.

[0124] The method shown in FIG. 4 has been described in view of first and second networks. In one example, the first network may be a first Public Land Mobile Network (PLMN) which is the serving PLMN of the UE. The second network which is not limited to only one second network but is to be understood to encompass one or more second networks may be a second Public Land Mobile Network (PLMN) which is the target PLMN. As regards the cross-border case, it is to be understood that the first and second networks are different. In other examples, the first and second networks may also represent network slices of one or more networks. [0125] The method for enforcing fast connection re-establishment according to some embodiments allows to change the UE behaviour to perform a fast switch between two MNOs, thereby minimizing the service interruption time when a handover between MNOs is not supported. The method according to some embodiments achieves this advantage by extending the release message of existing standards such as the RRC CONNECTION RELEASE message in LTE or the RRC RELEASE message in 5G with a new Information Element (IE) including the immediate re-attach indication.

[0126] FIG. 5 illustrates a flow chart of a method for enforcing fast connection re establishment according to some embodiments. The method is performed by the network (also referred to as the first or serving network). More specifically, the method may be performed by a base station such as the base station represented by the control apparatus 300 as described above with reference to FIG. 3. The base station may be a serving base station, or a gNB or a transmission/reception point (TRP) in a 5G system. Generally, the method may be performed at a core network function such as AMF.

[0127] Within the coverage area of the base station (i.e., in the cell provided by the base station), a user equipment (UE) such as one of the mobile communication devices 102, 104, 105 of the wireless communication system 100 as described above with reference to FIG. 1, or the communication device 200 as described above with reference to FIG. 2. The UE has established a connection to the serving network (e.g., a first PLMN). In an example, the UE may be in RRC CONNECTED mode and communicates with the serving network via the base station. As discussed hereinbefore, the UE may use a service accessed via, or provided by, the serving network and require a continuous provision of the service, i.e., interruption times of the service have to be kept at a minimum.

[0128] For ease of understanding, FIG. 5 shows operations performed prior to sending a release message to release the connection to the serving network. Such operations may include, among others, receiving a capability of supporting the fast connection re-establishment from the UE (block 510). In an example, an indication that the UE supports the procedure according to the immediate re-attach indication may be received from the UE, e.g., during establishment of the connection and/or in a message reporting capability of the UE. Further, in response to receiving the indication that the UE supports the fast connection re-establishment, the serving network configures the release message to be sent to the UE (block 520). Also, the serving network decides whether and when to instruct the UE to release the connection (block 530). For example, in case the serving network is informed or derives, based on information provided by the UE, that the UE is leaving the coverage area of the serving network (i.e., the coverage area of the serving base station) such that the communication with the serving network may become interrupted and the UE may enter the idle mode (e.g., the RRC IDLE mode), thereby contradicting with the requirement for continuity of the service the EE uses. In an example, the idle mode is the RRC IDLE mode.

[0129] At block 540, the serving network may send to the UE the release message (e.g., RRC CONNECTION RELEASE in LTE, RRC RELEASE in 5G), for example, based on the determination that the UE is leaving the coverage area of the serving network and the connection may become interrupted. The release message instructs the UE to release one or more (usually all) bearers to release the connection to the serving network. The UE is also ordered into the idle mode after releasing the connection to the serving network. The UE may then perform cell selection and reselection. For example, the UE may perform the cell selection and reselection in accordance with 3GPP TS 36.304 or equivalent specifications. However, as already discussed above, the time when the UE starts the cell selection and reselection depends on the UE implementation. The cell selection and reselection may also take some time, leading in sum to an unpredictable time period during which the UE cannot communicate and during which the service is not available. In order to achieve continuous communication and service availability, or at least limit the service interruption time to a minimum, the release message sent to the UE in block 540 is configured by the serving network to include an immediate re attach indication.

[0130] According to the subject disclosure, the immediate re-attach indication is to instruct the UE to start the attach procedure (e.g., to start the cell selection and reselection) immediately after releasing the connection to the serving network and entering the idle mode. In other words, the UE is instructed to release the connection to the serving network and enter the idle mode based on the release message, and to immediately start - after releasing and entering the idle mode - the attach procedure to establish a connection with another network (e.g., a second or target network) in case the release message includes the immediate re-attach indication. In some examples, the target network may be a second PLMN different from the first PLMN from which the connection was released. In some examples, the UE is instructed by the immediate re-attach indication to perform the attach procedure in accordance with the immediate re-attach indication, i.e., with information of the immediate re-attach indication, upon releasing the connection to the serving network. The UE may also be instructed to enter the connected mode (e.g., RRC CONNECTED mode) in response to performing the attach procedure, thereby allowing the UE to communicate and use the service via the target network (i.e., access the service via the target network). The interruption time can be minimized, and continuous communication and service availability is achieved by including the immediate re-attach indication in the release message.

[0131] In some examples, the release message sent to the UE at block 540 may include information about at least one cell of the target network. The presence of the information about the at least one cell of the target network instructs the UE to perform the attach procedure upon releasing the connection. That is, the presence of the information about the at least one cell of the target network represents the immediate re-attach indication. In this example, the immediate re-attach indication is implicitly provided with the release message. The information about the at least one cell is used by the UE in the attach procedure to establish a connection with the at least one cell of the target network.

[0132] In other examples, the release message sent to the UE at block 540 comprises the immediate re-attach indication and information about at least one cell of the target network. In this case, the immediate re-attach indication instructs the UE to perform the attach procedure upon releasing the connection to the serving network and entering the idle mode. The information about the at least one cell is used by the UE in the attach procedure to establish a connection with the at least one cell of the target network. In one example, the immediate re attach indication may be represented by a flag in the release message such as a bit value set by the serving network. If the bit value is set by the serving network to a first value (e.g., “1”), the immediate re-attach indication instructs the UE to start the attach procedure immediately after releasing the connection to the serving network. Otherwise, if the bit value is set by the serving network to a second value (e.g., “0”), the immediate re-attach indication instructs the UE that there is no need for starting the attach procedure immediately. In this case, the UE may start the attach procedure in response to the cell selection and reselection in accordance with the UE implementation.

[0133] In the above examples, the information may include information about a plurality of cells of the target network. Here, the cells may also be cells of a plurality of networks. The information about the plurality of cells may be included in the release message in the form of a list. The list may instruct the UE to select one cell among the list of cells based on certain criteria (e.g., the cell selection criterion). The selected cell is used by the UE in the attach procedure to establish the connection with the selected cell.

[0134] In some examples, the list of cells may define an order of priority. That is, the first cell in the list may be the cell with highest priority and the UE is instructed to use the cell with the highest priority in the attach procedure. If for any reason the UE cannot select the cell with the highest priority or cannot establish the connection with that cell, the UE is instructed based on the list to perform the attach procedure to establish a connection with any other cell of the cells in the list in the order of priority.

[0135] Exemplary information about the at least one cell includes an identifier of the at least one cell. In the example with the list of the plurality of cells, an identifier for each of the plurality of cells may be included. In an example, the identifier may be the physical cell id (PCI) of the cell. In addition to the identifier, the information may further comprise one of more of: an Absolute Radio Frequency Carrier Number (ARFCN) of the at least one cell, a radio technology of the at least one cell (e.g., CDMA), and a band in which the at least one cell is located. In some examples, the information may further include one or more parameters to accelerate random access procedure performed, at least in part, to establish the connection to the target network. The one or more parameters may be used by the UE to accelerate accessing the cell via Random Access Channel (RACH) following a contention-free procedure using a dedicated RACH preamble.

[0136] Additionally, or alternatively in some other examples, the release message sent to the UE in block 540 may include information about at least one prioritized frequency. The information instructs the UE to perform the attach procedure on the at least one prioritized frequency. In case the release message includes information about a plurality of prioritized frequencies, the UE is instructed to find cells corresponding to said prioritized frequencies and to perform the attach procedure to establish the connection with one of these cells.

[0137] As described above, the release message may correspond to the RRC CONNECTION RELEASE message in LTE or the RRC RELEASE message in 5G. The immediate re-attach indication and/or the information about the at least one cell of the target network may be included in at least one Information Element (IE) of the release message. In one example, the IE may be called ImmediateRe Attach.

[0138] FIG. 6 illustrates a message flow in a method for enforcing fast connection re establishment according to some embodiments of the subject disclosure. The message flow shown in FIG. 6 is similar to the flow chart shown in FIG. 4. The method may be performed in the wireless communication system 100 of FIG. 1 with one of the mobile communication devices 102, 104, 105 as the user equipment (UE) 610 and one of the base stations 106, 108 as serving base station 620 of a first network and target base station 630 of a second network. That is, the serving base station 620 provides the serving cell 625 and the target base station 630 provides the target cell 635.

[0139] The UE 610 is connected to the serving cell 625 of the first network and communication with the serving base station 620. The UE may use a service accessible via, or provided by, the first network and require a continuous provision of the service, i.e., interruption times of the service have to be kept at a minimum. If the UE 610 is leaving the coverage area of the serving base station 620 (i.e., the serving cell 625) and thus communication with the first network may become interrupted, the UE 610 is ordered into the idle mode such as the RRC IDLE mode. That is, continuation of the service cannot be provided any longer within the serving cell.

[0140] In this case, the UE 610 receives from the serving base station 620 the RRC CONNECTION RELEASE message in LTE (other examples include the RRC RELEASE message in 5G) (arrow 640). In response to receiving the RRC CONNECTION RELEASE message, the UE 610 releases all radio bearers and the UE 610 is sent in the RRC IDLE mode (block 650). As described above, the RRC CONNECTION RELEASE message is extended by an Information Element (IE) that informs the UE 610 that immediately after finding the first suitable cell which fulfils the cell selection criterion (S-criterion) and which is not a cell of the first network (blocks 670), the UE 610 has to use the cell to start immediately the attach procedure (arrow 680). In an example, the IE may be called ImmediateRe Attach.

[0141] In some examples as will be described in more detail below, the RRC CONNECTION RELEASE message according to 3GPP TS 36.331 is extended by an optional Information Element (IE) which contains information of a cell or a list of cells on which the UE shall camp on, if the cell or at least one cell in the list of cells is suitable and fulfils the cell selection criterion (S-criterion) according to 3GPP TS 36.304. For each cell, one or more of the following information may be provided: the physical cell id (PCI) of the target cell, which is the minimum which has to be provided; the ARFCN of the cell; the radio technology of the cell (e.g., CDMA); the band, in which the cell is located; and optionally other parameters which accelerate the random access, i.e., access the target cell (i.e., the target cell 635 of FIG. 6) via RACH following a contention-free procedure using a dedicated RACH preamble according to 3 GPP TS 36.304.

[0142] The following behavior of the UE 610 is proposed if the RRC CONNECTION RELEASE message contains the new IE, which signals to the UE 610 that the UE 610 has to start immediately the attach procedure (arrow 680).

[0143] If the RRC CONNECTION RELEASE message used to send the UE 610 in the RRC IDLE mode additionally provides the UE 610 with a unique cell identity as a cell to prioritize to camp-on after state transition to the RRC IDLE mode, and if the cell is suitable and fulfils the cell selection criterion (S-criterion) (block 670), then the UE 610 shall use this cell to start immediately the attach procedure (arrow 680). [0144] Otherwise, if the RRC CONNECTION RELEASE message used to send the UE 610 in the RRC IDLE mode additionally provides the UE 610 with a list of cells (characterized for instance by the GCI, E-ARFCN, etc.) as cells to prioritize to camp-on after state transition to the RRC IDLE mode, and if a cell is suitable and fulfils the cell selection criterion (S- criterion)(block 670), then the UE 610 shall use this cell for the attach procedure (arrow 680). [0145] Alternatively, in other examples, the UE 610 can choose the cell which fulfils best the S-criterion for an immediately following attach procedure; however, finding the best cell may take more time than choosing the first suitable cell which fulfils the S-criterion.

[0146] Otherwise, if the RRC CONNECTION RELEASE message used to send the UE 610 in the RRC IDLE mode additionally provides the UE 610 with a prioritized frequency to camp-on after state transition to the RRC IDLE mode, then the UE 610 shall start the attach procedure (arrow 680) immediately in the first suitable cell on the prioritized frequency which fulfils the cell-selection criterion (S-criterion) (block 670) and whose PLMN-id differs from the PLMN-id of the network from which the RRC CONNECTION RELEASE message was received (i.e., the serving cell 625 in FIG. 6).

[0147] Alternatively, in other examples, the UE 610 can choose the cell which fulfils best the S-criterion on the frequency for an immediately following attach procedure; however, finding the best cell will lead to delays, which limits the advantages of the subject disclosure to minimize the connection interruption time. In this case, only a flag indicating that an immediate attach in the prioritized frequency band is required as addition in the RRC CONNECTION RELEASE message.

[0148] In some examples, the prioritized carrier may include cells of the network currently serving the UE 610 (e.g., the serving cell 625). Within a network, a handover can typically be realized to continue the service. In an inter-operator scenario, in which a handover is not an option or not possible, a fast switch between PLMNs is essential for service continuation. To avoid that the UE 610 quickly re-attaches to the current network, it is essential to specify that the PLMN-id (= MCC + MNC) has to differ when a fast re-attach is required. If PLMN-ids are signaled, the RAN should ensure that only cells of other operators are included in the list. [0149] Otherwise, if the RRC CONNECTION RELEASE message used to send the UE 610 in the RRC IDLE mode additionally provides the UE 610 with a set of prioritized frequency to camp-on after state transition to the RRC IDLE mode, then the UE 610 shall start the attach procedure (arrow 680) in the first suitable cell on any prioritized frequency which fulfils the cell-selection criterion (S-criterion)(block 670), and whose PLMN-id differs from the PLMN-id of the network from which the RRC CONNECTION RELEASE message was received (i.e., the serving cell 625 in FIG. 6).

[0150] Alternatively, in other examples, the UE 610 can choose the cell which fulfils best the S-criterion on the set of frequency for an immediately following attach procedure, and whose PLMN-id differs from the PLMN-id of the network from which the RRC CONNECTION RELEASE message was received (i.e., the serving cell 625 in FIG. 6); however, finding the best cell will lead to delays, which limits the advantages of the subject disclosure to minimize the connection interruption time.

[0151] Otherwise, if the RRC CONNECTION RELEASE message used to send the UE 610 in the RRC IDLE mode does not provide prioritized frequencies/carriers or cells, then the UE 610 shall immediately start the attach procedure (arrow 680) after finding the first suitable cell which fulfills the S-criterion (block 670), and whose PLMN-id differs from the PLMN-id of the network from which the RRC CONNECTION RELEASE message was received (i.e., the serving cell 625 in FIG. 6).

[0152] The methods for enforcing fast connection re-establishment according to some embodiments of the subject disclosure are described with reference to FIGS. 4 to 6. The methods describe the procedure to re-connect the UE fast with a new network after the RRC CONNECTION RELEASE message was received. The triggers to initiate the RRC CONNECTION RELEASE message may be defined in the standards or left to implementation. So, a procedure may be needed that defines how and when the RAN becomes aware that a fast inter-PLMN RRC CONNECTION re-establishment is required.

[0153] The following examples describes how the RAN may be informed that fast inter- PLMN RRC CONNECTION re-establishment (i.e., the methods in accordance with some embodiments of the subject disclosure) should be supported.

[0154] The UE capability indicates that the UE supports the fast inter-PLMN RRC CONNECTION re-establishment. If additionally, the UE is served in a cell with neighboring cross-border cells then these cells can be included in the list of cells on which the UE has to provide measurement report. Examples are cells at a national border, where users travel from one country into another. Only for those cells, the fast inter-PLMN RRC CONNECTION re establishment may be offered.

[0155] In some examples, the UE capability to support the fast inter-PLMN RRC CONNECTION re-establishment may be deduced either from an IE added to the list of UE capabilities, or e.g. deduced from 3GPP release version the UE supports. [0156] Additionally, or alternatively, a Packet Data Protocol (PDP) context lists the properties a packet data connection over which the UE and the network can exchange data packets. The context includes the IP address of the UE, IMSI and additional parameters to properly route data to and from the network. A PDP context is provided by the HSS to the MME (e.g., in LTE). For services requiring a fast interruption time, the associated PDP context can be extended with a flag, which indicates the need for the fast inter-PLMN RRC CONNECTION re-establishment. During dedicated bearer establishment, the information must be provided if the fast inter-PLMN RRC CONNECTION re-establishment is to be offered. [0157] FIG. 7 illustrates the dedicated bearer activation procedure in accordance with Figure 2 of sub-clause 5.4.1 in 3GPP TS 23.401. The Rx-interface between the PCRF and the Application Function (AF) is not shown in the FIG. 7.

[0158] FIG. 8 illustrates the non-roaming LTE architecture for 3GPP access in accordance with Figure 3 of sub-clause 4.2.1 in 3GPP TS 23.401. In some examples, messages used on the following interfaces of FIG. 8 may be extended to provide the information that fast inter-PLMN RRC CONNECTION re-establishment is required: a. Rx between PCRF and AF b. Gx between PCRF and PGW c. S5 (non-roaming) and S8 (roaming) between SGW and PGW d. SI 1 between SGW and MME e. S 10 between MME f. SI -MME between MME and the eNB g. S6a between HSS and MME

The message flow of FIG. 8 does not show all potentially impacted interfaces, which could provide this information. In some examples, the HSS may be involved in case of an HSS Initiated Subscribed QoS Modification.

[0159] In 5G, analogue to LTE, messages involved in bearer management used on following reference point require a field to indicate the need for the fast inter-PLMN RRC CONNECTION re-establishment: N5 (AF-PCF), N15 (PCF-AMF), N14 (inter-AMF), N8 (AMF-UDM), N2 (AMF-5G AN), and N26 (AMF-MME).

[0160] The following examples describe how the RAN may determine that the fast inter- PLMN RRC CONNECTION re-establishment is to be triggered, given that the inter-PLMN RRC CONNECTION re-establishment is supported by the UE and configured in the network. The RAN may take the following factors into consideration in the determining: [0161] The measurement reports of the UE indicate that a cell by another operator exceeds the reported quality of the UE’s serving cell by an operator set threshold. No other higher priority CS call takes place, e.g., an emergency call.

[0162] If such conditions are fulfilled, the RAN may trigger the procedure to release the UE’s connection in accordance with the methods of some embodiments described herein. [0163] As the connection release may take place without any knowledge how the connection release may affect the application (e.g., the application at the UE which uses the service of the network), the methods according to some embodiments of the subject disclosure include notifying the application about the situation on the radio side.

[0164] In some examples, the RAN notifies the Application Function (AF) that on the radio side, conditions are fulfilled which require release of the connection. The application can decide whether currently the release of the connection can be done without risk (e.g., whether any critical task is currently performed by the application which requires to continuously communicate with the network and thus the connection to the network). For instance, an automated vehicle may notify the driver to take over, thus ending the need for a continuous connectivity. The application may then signal to the AF that a connectivity break is acceptable. The information exchange between the RAN and the AF has to be realized via multiple network function or network elements described above.

[0165] In other words, the AF may indicate to the UE a point in time when releasing the connection to the first network and re-attaching to the second network shall be made (i.e., an optimal time when to release and re-attach).

[0166] In some of the examples described above, RAN (e.g., the RRC entity in the eNB in LTE) has to decide whether to include neighbouring cells of another operator in the neighbourhood list of the UE, particularly of the UE is in RRC-CONNECTED mode. For example, with the RRC CONNECTION RECONFIGURATION message, UE measurements and measurement reporting can be configured. The UE can be configured to provide periodically or on-request measurement reports on the strongest neighbouring cells. A list of neighbouring cells to be measured can be included in the RRC CONNECTION RECONFIGURATION message. The list of cells can include both the operator’s own cell as well as cells of other operators. If cells of other operators are included in the neighbourhood list, the cells have to be known as neighbours of the UE’s serving cell, e.g., by inter-operator agreements. The current 3GPP standards allow listing cells of other MNOs in the neighbourhood list provided to the UE. The decision of the RAN may be based on the UE capabilities; user subscription profile or profile of a currently supported bearer; and/or the QoS required for the service. The UE capabilities may include, for example, whether the UE supports RRC release directed to a cell or a list of cells as described above with respect to the IE in the release message (i.e., the immediate re-attach indication). As part of the subscriber profile, the requirement of continuous cross-operator service provisioning can be stored in the HSS - for instance as a flag. When a bearer for a service such as autonomous driving is requested, then the requirement of continuous cross-operator service provisioning has to be provided to the MME (e.g., via S6a shown in FIG. 8) and to the eNB (via SI -CP). The QoS may require, for example, that operators agree to reserve one QCI value for autonomously driving cars. The QoS Class Identifier (QCI) identifies requirements such as latency, reliability, traffic priority, etc. in accordance with 3GPP TS 23.203. Given specific QCI for services such as autonomous driving, the eNB and the RRC entity of the eNB can directly decide whether to direct the UE directly a specific cell or a specific list of cells with an RRC CONNECTION RELEASE message, to enable a fast RRC CONNECTION re-establishment as described above.

[0167] It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0168] It is noted that whilst embodiments have been described in relation to LTE and 5G NR, similar principles can be applied in relation to other networks and communication systems where enforcing fast connection re-establishment is required. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

[0169] It is also noted herein that while the above describes exemplary embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the subject disclosure.

[0170] In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the subject disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the subject disclosure is not limited thereto. While various aspects of the subject disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0171] Example embodiments of the subject disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0172] Further in this regard it should be noted that any blocks of the logic flow as in the figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media. [0173] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

[0174] Example embodiments of the subject disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0175] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of the subject disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of the subject disclosure as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1. A method to be performed by a user equipment (UE) having a connection to a first network, the method comprising: receiving, from the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication; and upon releasing the connection, performing an attach procedure according to the immediate re-attach indication to establish a connection to a second network.

2. The method of claim 1, wherein the immediate re-attach indication indicates to start the attach procedure immediately after releasing the connection.

3. The method of claim 1 or 2, further comprising: releasing one or more radio bearers to release the connection to the first network; and entering an idle mode.

4. The method of any of claims 1 to 3, further comprising, upon releasing the connection, finding a cell of the second network that fulfils a cell selection criterion, and wherein the attach procedure is performed to establish the connection to the cell of the second network that fulfills the cell selection criterion.

5. The method of any of claims 1 to 4, further comprising, in response to performing the attach procedure, entering a connected mode with the second network.

6. The method of any of claims 1 to 5, wherein the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network, and wherein the attach procedure is performed to establish the connection with the at least one cell.

7. The method of any of claims 1 to 5, wherein the release message to release the connection further includes information about at least one cell of the second network, and wherein the attach procedure is performed to establish the connection with the at least one cell.

8. The method of claim 6 or 7, wherein the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells, and wherein the attach procedure is performed to establish the connection with one of the plurality of cells.

9. The method of claim 8, wherein the list defines an order of priority, and wherein performing the attach procedure comprises selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell.

10. The method of any of claims 6 to 9, wherein the information about the at least one cell comprises an identifier of the at least one cell.

11. The method of claim 10, wherein the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located.

12. The method of claim 10 or 11, wherein the information further comprises one or more parameters to accelerate random access.

13. The method of claim 12, wherein the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention- free procedure using a dedicated RACH preamble.

14. The method of any of claims 1 to 5, wherein the release message to release the connection includes information about at least one prioritized frequency, and wherein the attach procedure is performed in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency.

15. The method of claim 14, wherein the cell of the second network among the plurality of cells on any of the at least one prioritized frequency is determined to be different from a cell of the first network.

16. The method of any of claims 1 to 15, further comprising: sending, to the first network, an indication that the UE supports a procedure according to the immediate re-attach indication.

17. The method of any of claims 1 to 16, wherein the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message.

18. The method of any of claims 1 to 17, wherein the release message comprises at least one information element including the immediate re-attach indication.

19. The method of any of claims 1 to 18, wherein the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

20. A method to be performed by a first network, comprising: sending, to a user equipment (UE) having a connection to the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication, wherein the immediate re-attach indication is to instruct the UE to perform an attach procedure according to the immediate re-attach indication to establish a connection to a second network upon releasing the connection to the first network.

21. The method of claim 20, wherein the immediate re-attach indication is to instruct the UE to start the attach procedure immediately after releasing the connection.

22. The method of claim 20 or 21, wherein the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with the at least one cell.

23. The method of claim 20 or 21, wherein the release message to release the connection further includes information about at least one cell of the second network, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with the at least one cell.

24. The method of claim 22 or 23, wherein the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with one of the plurality of cells.

25. The method of claim 24, wherein the list defines an order of priority, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with the one of the plurality of cells by selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell.

26. The method of any of claims 22 to 25, wherein the information about the at least one cell comprises an identifier of the at least one cell.

27. The method of claim 26, wherein the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located.

28. The method of claim 26 or 27, wherein the information further comprises one or more parameters to accelerate random access.

29. The method of claim 28, wherein the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention- free procedure using a dedicated RACH preamble.

30. The method of claim 20 or 21, wherein the release message to release the connection includes information about at least one prioritized frequency, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency.

31. The method of any of claims 20 to 30, further comprising: receiving, from the UE, an indication that the UE supports a procedure according to the immediate re-attach indication.

32. The method of any of claims 20 to 31, wherein the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message.

33. The method of any of claims 20 to 32, wherein the release message comprises at least one information element including the immediate re-attach indication.

34. The method of any of claims 20 to 33, wherein the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

35. A user equipment (UE) in a first network, comprising: at least one processor; and at least one memory including computer program code, wherein the computer program code causes the UE, when executed with the at least one processor, to at least: receive, from the first network, a release message to release a connection to the first network, the release message including an immediate re-attach indication; and upon releasing the connection, perform an attach procedure according to the immediate re-attach indication to establish a connection to a second network.

36. The UE of claim 35, wherein the immediate re-attach indication indicates to start the attach procedure immediately after releasing the connection.

37. The UE of claim 35 or 36, wherein the computer program code causes the UE, when executed with the at least one processor, to at least: release one or more radio bearers to release the connection to the first network; and enter an idle mode.

38. The UE of any of claims 35 to 37, wherein the computer program code causes the UE, when executed with the at least one processor, to at least: upon releasing the connection, find a cell of the second network that fulfils a cell selection criterion, and wherein the attach procedure is performed to establish the connection to the cell of the second network that fulfills the cell selection criterion.

39. The UE of any of claims 35 to 38, wherein the computer program code causes the UE, when executed with the at least one processor, to at least: in response to performing the attach procedure, enter a connected mode with the second network.

40. The UE of any of claims 35 to 39, wherein the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network, and wherein the attach procedure is performed to establish the connection with the at least one cell.

41. The UE of any of claims 35 to 39, wherein the release message to release the connection further includes information about at least one cell of the second network, and wherein the attach procedure is performed to establish the connection with the at least one cell.

42. The UE of claim 40 or 41, wherein the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells, and wherein the attach procedure is performed to establish the connection with one of the plurality of cells.

43. The UE of claim 42, wherein the list defines an order of priority, and wherein performing the attach procedure comprises selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell.

44. The UE of any of claims 40 to 43, wherein the information about the at least one cell comprises an identifier of the at least one cell.

45. The UE of claim 44, wherein the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located.

46. The UE of claim 44 or 45, wherein the information further comprises one or more parameters to accelerate random access.

47. The UE of claim 46, wherein the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention- free procedure using a dedicated RACH preamble.

48. The UE of any of claims 35 to 39, wherein the release message to release the connection includes information about at least one prioritized frequency, and wherein the attach procedure is performed in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency.

49. The UE of claim 48, wherein the cell of the second network among the plurality of cells on any of the at least one prioritized frequency is determined to be different from a cell of the first network.

50. The UE of any of claims 35 to 49, wherein the computer program code causes the UE, when executed with the at least one processor, to at least: send, to the first network, an indication that the UE supports a procedure according to the immediate re-attach indication.

51. The UE of any of claims 35 to 50, wherein the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message.

52. The UE of any of claims 35 to 51, wherein the release message comprises at least one information element including the immediate re-attach indication.

53. The UE of any of claims 35 to 52, wherein the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

54. A base station of a first network, comprising: at least one processor; and at least one memory including computer program code, wherein the computer program code causes the base station, when executed with the at least one processor, to at least: send, to a user equipment (UE) having a connection to the first network, a release message to release the connection to the first network, the release message including an immediate re-attach indication, wherein the immediate re-attach indication is to instruct the UE to perform an attach procedure according to the immediate re-attach indication to establish a connection to a second network upon releasing the connection to the first network.

55. The base station of claim 54, wherein the immediate re-attach indication is to instruct the UE to start the attach procedure immediately after releasing the connection.

56. The base station of claim 54 or 55, wherein the release message to release the connection includes, as the immediate re-attach indication, information about at least one cell of the second network, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with the at least one cell.

57. The base station of claim 54 or 55, wherein the release message to release the connection further includes information about at least one cell of the second network, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with the at least one cell.

58. The base station of claim 54 or 55, wherein the at least one cell comprises a plurality of cells of the second network and the release message to release the connection includes a list comprising the plurality of cells, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with one of the plurality of cells.

59. The base station of claim 58, wherein the list defines an order of priority, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure to establish the connection with the one of the plurality of cells by selecting a cell from the list in the order of priority and performing the attach procedure to establish the connection to the selected cell.

60. The base station of any of claims 56 to 59, wherein the information about the at least one cell comprises an identifier of the at least one cell.

61. The base station of claim 60, wherein the information further comprises one or more of: an Absolute Radio Frequency Carrier Number of the at least one cell, a radio technology of the at least one cell, and a band in which the at least one cell is located.

62. The base station of claim 60 or 61, wherein the information further comprises one or more parameters to accelerate random access.

63. The base station of claim 62, wherein the one or more parameters are to accelerate accessing the at least one cell via Random Access Channel (RACH) following a contention-free procedure using a dedicated RACH preamble.

64. The base station of claim 54 or 55, wherein the release message to release the connection includes information about at least one prioritized frequency, and wherein the immediate re-attach indication is to instruct the UE to perform the attach procedure in a cell of the second network among a plurality of cells on any of the at least one prioritized frequency.

65. The base station of any of claims 54 to 64, wherein the computer program code causes the base station, when executed with the at least one processor, to at least: receive, from the UE, an indication that the UE supports a procedure according to the immediate re-attach indication.

66. The base station of any of claims 54 to 65, wherein the release message is a RRC CONNECTION RELEASE message or a RRC RELEASE message.

67. The base station of any of claims 54 to 66, wherein the release message comprises at least one information element including the immediate re-attach indication.

68. The base station of any of claims 54 to 67, wherein the first network is a first Public Land Mobile Network and the second network is a second Public Land Mobile Network different from the first Public Land Mobile Network.

69. A computer program product comprising program instructions stored on a computer readable medium to execute the method of any of claims 1 to 34 when said program is executed on a computer.