Patent Description:
Cellular phones have evolved from mobile voice transfer device to omnipotent computers. Wireless data transfer, particularly Internet use, require high data transfer capacity. This trend has driven the development of new cellular telecommunication standards from <NUM> with GSM towards the <NUM> that will have exceedingly fast data transfer and now also functions as services that communicate with each other.

Common to previous generations, also in the <NUM> the privacy and accountability of cellular telecommunications have remained essential. These have been safeguarded by use of cryptography to authenticate the subscriber, authorize telecommunications (and associated charging) and to protect the communications. These measures require signaling in both a core network that contains and manages the infrastructure of a cellular network and also over a radio interface between the mobile stations and the cellular network. All such signaling comes with a computation cost and use of limited signaling resources. The signaling resources are particularly valuable in the radio interface where every symbol used for anything else than transfer of user data reduces the capacity to transfer user data.

3GPP <NUM> will enhance wireless data transfer speeds also by reducing cell size, which inherently leaves more gaps between cells. The <NUM> technology will operate as a fallback to provide adequate data access where no <NUM> is available. At fringes of <NUM> cells, there may be repeated hand-overs between the <NUM> and <NUM> networks so signaling, both in the core network and in the radio access may be rapidly multiplied. In addition, emergency services may not be provided by the <NUM> network while the <NUM> network is capable of supporting emergency services especially during early phases of the <NUM> network deployment. In this case, it is desirable to use the <NUM> technology as a fallback.

<NPL>) discloses NAS security context handling during inter-system change from S1 mode (e-UTRA) to N1 mode (ng-RAN) and vice versa.

According to a first embodiment of the present invention, there is provided a method performed by a user equipment, UE, on idle mode inter-system change, while the UE is in a single registration mode, comprising:
deriving a cryptographic protection to a new initial non-access stratum, NAS, message for a target network from an existing security context during an idle mode inter-system change, if any one or more of following conditions are met:.

The method of the first example aspect may exclude any of following conditions: a); b); c); d); a) and b); a) and c); a) and d); b) and c); b) and d); a) and b) and c); a) and c) and d); b) and c) and d).

The S1 mode may be a mode of a UE allowing access to a <NUM> core network via a <NUM> access network. The N1 mode may be a mode of a UE allowing access to a <NUM> core network via a <NUM> access network.

The signaling channel between the mobility management entities of the source and target cellular networks may be an N26 interface. The mobility management entity in the <NUM> network may correspond to the access and mobility management function, AMF.

In case of condition a), the cryptographic protection may be integrity protecting (and partially ciphering, which can be optional) a REGISTRATIONREQUEST message with a <NUM> NAS security context mapped from current EPS security context. The indication defined in condition a) may be received from any of: the source cellular network; the target cellular network; or both the source cellular network and the target cellular network. The null integrity protection algorithm may be EIAO. The null ciphering algorithm may be EEA0.

In case of condition b), the cryptographic protection may be integrity protecting a TRACKING AREA UPDATE REQUEST message with current <NUM> NAS security context. The indication defined in condition b) may be received from any of: the source cellular network; the target cellular network; or both the source cellular network and the target cellular network.

In case of condition c), the cryptographic protection may be integrity protecting a TRACKING AREA UPDATE REQUEST message with current <NUM> NAS security context.

In case of condition d), the cryptographic protection may be integrity protecting an ATTACH REQUEST message with the valid native EPS security context. The indication defined in condition d) may be received from any of: the source cellular network; the target cellular network; or both the source cellular network and the target cellular network.

The ng-RAN may be compliant with 3GPP <NUM> release <NUM>.

According to a second embodiment of the present invention, there is provided a method performed by an Access and Mobility Management Function, AMF, for handling an idle mode inter-system change of User Equipment, UE, from an evolved universal terrestrial radio access network, e-UTRAN to a Next Generation Radio Access Network, ng-RAN, while the UE is in a single registration mode connection, comprising:
deriving a mapped <NUM> Non-Access Stratum, NAS, security context from a source cellular network that is an Evolved Packet System, EPS, security context maintained by a source Mobility Management Entity of the EPS, during an idle mode inter-system change, if any one or more of following conditions are met:.

The method may comprise, before the deriving of the mapped security context, receiving the REGISTRATION REQUEST message without integrity protection and encryption.

The method may further comprise that, after receiving the REGISTRATION REQUEST message without integrity protection and encryption, the AMF either creates a fresh mapped <NUM> NAS security context or trigger a primary authentication and key agreement procedure to create a fresh native <NUM> NAS security context. In particular, if conditions <NUM>) and <NUM>) are met, the AMF may choose between creating a fresh mapped <NUM> NAS security context and triggering a primary authentication and key agreement procedure to create a fresh native <NUM> NAS security context.

The method of the second example aspect may exclude any of following conditions: <NUM>); <NUM>); <NUM>); <NUM>); <NUM>) and <NUM>); <NUM>) and <NUM>); <NUM>) and <NUM>); <NUM>) and <NUM>); <NUM>) and <NUM>); <NUM>) and <NUM>) and <NUM>); <NUM>) and <NUM>) and <NUM>); <NUM>) and <NUM>) and <NUM>).

According to a embodiment, there is provided a method comprising the first and second example aspects.

According to a fourth embodiment, there is provided a user equipment, UE comprising means for performing:deriving a cryptographic protection to a new initial non-access stratum, NAS, message for a target network from an existing security context during an idle mode inter-system change, if any one or more of following conditions are met:condition a) the source cellular network is an evolved universal terrestrial radio access network, e-UTRAN; and the target cellular network is a Next Generation Radio Access Network, ng-RAN of a <NUM> system, 5GS; and the UE does not have a valid native <NUM> NAS security context; and the UE has a packet data network, PDN, connection for emergency bearer services; and the UE has a current Evolved Packet System, EPS, security context including NAS security algorithms set to a null integrity protection algorithm and null ciphering algorithm; and the UE has received an indication that the source cellular network does not support interworking with the target cellular network without a signaling channel between mobility management entities of the EPS and the 5GS;condition b) the source cellular network is the ng-RAN; and the target cellular network is the e-UTRAN; and the UE has received an indication that the source cellular network does not support interworking with the target cellular network without a signaling channel between mobility management entities of the EPS and the 5GS;condition c) the source cellular network is the ng-RAN; and the target cellular network is the e-UTRAN; and the UE does not support sending an ATTACH REQUEST message containing a PDN CONNECTIVITY REQUEST message with request type set to "handover" to transfer a Protocol Data Unit, PDU, session from N1 mode to S1 mode;condition d) the source cellular network is the ng-RAN; and the target cellular network is the e-UTRAN; and the UE has received an indication that the source cellular network supports interworking with the target cellular network without a signaling channel between mobility management entities of the EPS and the 5GS; and the UE supports sending an ATTACH REQUEST message containing a PDN CONNECTIVITY REQUEST message with request type set to "handover" to transfer a PDU session from N1 mode to S1 mode; and the UE has a valid native EPS security context.

According to a fifth embodiment, there is provided an Access and Mobility Management Function, AMF, configured to handle an idle mode inter-system change of User Equipment, UE, from an evolved universal terrestrial radio access network, e-UTRAN to a Next Generation Radio Access Network, ng-RAN, while the UE is in a single registration mode connection, the AMF comprising:.

According to a sixth example aspect of the present invention, there is provided a system comprising the UE of the fourth example aspect and the AMF of the fifth embodiment.

An example embodiment of the present invention and its potential advantages are understood by referring to <FIG> of the drawings. In this document, like reference signs denote like parts or steps.

<FIG> shows an architectural drawing of a system <NUM> of a claimed embodiment. <FIG> shows non-roaming architecture for interworking between 5GS and EPC/E-UTRAN, but suitably demonstrates various network parts and interfaces useful to explain some example embodiments. <FIG> shows corresponding parts of Evolved Packet System, EPS, <NUM> and of a fifth Generation System, 5GS, <NUM> that are related to EPS and 5GS interworking. It should be appreciated that in practice, the EPS and the 5GS need not comprise functionalities of each other, although it is also possible to implement shared functionalities by shared execution platform, for example.

In <FIG>, user equipment <NUM> are in radio access to respective cellular networks that comprise an evolved Universal Terrestrial Radio Access Network, e-UTRAN, <NUM> and a Next Generation Radio Access Network, ng-RAN, <NUM>. The EPS comprises the e-UTRAN <NUM> and Evolved Core Network, EPC, parts such as a Mobility Management Entity, MME, <NUM>.

The 5GS <NUM> comprises the ng-RAN <NUM> and a <NUM> core network that comprises, for example, an access and mobility management function, AMF <NUM>.

<FIG> shows a flow chart of a process <NUM> of a claimed embodiment in user equipment, UE, on idle mode inter-system change, while the UE is in a single registration mode, comprising:
deriving <NUM> a cryptographic protection to a new initial non-access stratum, NAS, message for a target network from an existing security context in an idle mode inter-system change, if any one or more of following conditions are met:.

<FIG> shows a flow chart of a process of a claimed embodiment in the AMF, for handling an idle mode inter-system change of the UE, from an e-UTRAN to an ng-RAN, while the UE is in a single registration mode connection, comprising:
deriving <NUM> a mapped <NUM> NAS security context from a source cellular network that is an EPS security context maintained by a source MME of the EPS, in an idle mode inter-system change, if any one or more of following conditions are met:.

The method may comprise, before the deriving of the mapped security context, receiving <NUM> the REGISTRATION REQUEST message without integrity protection and encryption.

<FIG> shows a block diagram of an apparatus <NUM> according to an embodiment of the invention.

The apparatus <NUM> comprises a memory <NUM> including a persistent computer program code <NUM>. The apparatus <NUM> further comprises a processor <NUM> for controlling the operation of the apparatus <NUM> using the computer program code <NUM>, a communication unit <NUM> for communicating with other nodes. The communication unit <NUM> comprises, for example, a local area network (LAN) port; a wireless local area network (WLAN) unit; Bluetooth unit; cellular data communication unit; or satellite data communication unit. The processor <NUM> comprises, for example, any one or more of: a master control unit (MCU); a microprocessor; a digital signal processor (DSP); an application specific integrated circuit (ASIC); a field programmable gate array; and a microcontroller. The apparatus may further comprise a user interface (U/I) <NUM>.

Some non-limiting example use cases are next described in context of 3GPP TS <NUM> V15. <NUM> section <NUM>. <NUM>, Establishment of secure exchange of NAS messages Secure exchange of NAS messages via a NAS signaling connection is usually established by the AMF during the registration procedure by initiating a security mode control procedure. After successful completion of the security mode control procedure, all NAS messages exchanged between the UE and the AMF are sent integrity protected using the current <NUM> security algorithms, and except for the messages such as REGISTRATION REQUEST and SECURITY MODE COMMAND messages, all NAS messages exchanged between the UE and the AMF are sent ciphered using the current <NUM> security algorithms.

During inter-system change from S1 mode to N1 mode in SGMM-CONNECTED mode, secure exchange of NAS messages is established between the AMF and the UE by:.

During inter-system change from S1 mode to N1 mode in SGMM-IDLE mode, if the UE is operating in single-registration mode and:.

After receiving the REGISTRATION REQUEST message without integrity protection and encryption:.

During inter-system change from N1 mode to S1 mode in SGMM-CONNECTED mode, secure exchange of NAS messages is established between the MME and the UE by:.

During inter-system change from N1 mode to S1 mode in SGMM-IDLE mode, if the UE is operating in the single-registration mode and:.

After receiving the ATTACH REQUEST message, the MME shall proceed with the attach procedure.

During an N1 mode to N1 mode handover, secure exchange of NAS messages is established between the AMF and the UE by:.

The secure exchange of NAS messages shall be continued after N1 mode to N1 mode handover. It is terminated after inter-system change from N1 mode to S1 mode in SGMM-CONNECTED mode or when the NAS signaling connection is released. When a UE in SGMM-IDLE mode establishes a new NAS signaling connection and has a valid current <NUM> NAS security context, the UE shall transmit the initial NAS message integrity protected with the current <NUM> NAS security context, but unciphered. The UE shall include the ngKSI indicating the current <NUM> NAS security context value in the initial NAS message. The AMF shall check whether the ngKSI included in the initial NAS message belongs to a <NUM> NAS security context available in the AMF, and shall verify the MAC of the NAS message. If the verification is successful, the AMF may reestablish the secure exchange of NAS messages:.

Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein is that it may be possible to avoid unnecessary 5GMM procedures being initiated which results in worsening user experience for a critical call. Another technical effect of one or more of the example embodiments disclosed herein is that radio interface and/or core network signaling may be reduced. Yet another technical effect of one or more of the example embodiments disclosed herein is that security may be improved by increasing use of previously established security contexts so that clear text transmission of data may be reduced over radio interface and/or in one or more core networks.

Embodiments of the present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic In an 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 or means 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, with one example of a computer described and depicted in <FIG>. A computer-readable medium may comprise a computer-readable storage medium that may be any media or means 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.

Claim 1:
A method performed by user equipment, UE, during idle mode inter-system change, while the UE is in a single registration mode, comprising:
deriving a cryptographic protection to a new initial non-access stratum, NAS, message for a target network from an existing security context in an idle mode inter-system change, if any one or more of following conditions are met:
condition a) the source cellular network is an evolved universal terrestrial radio access network, e-UTRAN; and the target cellular network is a Next Generation Radio Access Network, ng-RAN of a <NUM> system, 5GS; and the UE does not have a valid native <NUM> NAS security context; and the UE has a packet data network, PDN, connection for emergency bearer services; and the UE has a current Evolved Packet System, EPS, security context including NAS security algorithms set to a null integrity protection algorithm and null ciphering algorithm; and the UE has received an indication that the source cellular network does not support interworking with the target cellular network without a signaling channel between mobility management entities of the EPS and the 5GS;
condition b) the source cellular network is the ng-RAN; and the target cellular network is the e-UTRAN; and the UE has received an indication that the source cellular network does not support interworking with the target cellular network without a signaling channel between mobility management entities of the EPS and the 5GS;
condition c) the source cellular network is the ng-RAN; and the target cellular network is the e-UTRAN; and the UE does not support sending an ATTACH REQUEST message containing a PDN CONNECTIVITY REQUEST message with request type set to "handover" to transfer a Protocol Data Unit, PDU, session from N1 mode to S1 mode;
condition d) the source cellular network is the ng-RAN; and the target cellular network is the e-UTRAN; and the UE has received an indication that the source cellular network supports interworking with the target cellular network without a signaling channel between mobility management entities of the EPS and the 5GS; and the UE supports sending an ATTACH REQUEST message containing a PDN CONNECTIVITY REQUEST message with request type set to "handover" to transfer a PDU session from N1 mode to S1 mode; and the UE has a valid native EPS security context.