WO2015088540A1

WO2015088540A1 - Proxy-call session control function restoration for dual mode end devices

Info

Publication number: WO2015088540A1
Application number: PCT/US2013/074734
Authority: WO
Inventors: Frederic Nicholson
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2013-12-12
Filing date: 2013-12-12
Publication date: 2015-06-18
Anticipated expiration: 2016-06-12

Abstract

Various devices may benefit from Proxy-Call Session Control Function (P-CSCF) restoration. For example, dual mode end devices of an IP Multimedia Subsystem may benefit from P-CSCF restoration. A method can include selecting a preferred radio access type from a plurality of radio access types. The method can also include sending a first registration request to a network via the preferred radio access type to register with a first node of the network. The method can further include detecting whether a service was delivered by the preferred radio access type. When the service was not delivered by the preferred radio access type, the method can include sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

Description

TITLE:

Proxy-Call Session Control Function Restoration for Dual Mode End Devices

BACKGROUND:

Field:

[0001] Various devices may benefit from Proxy-Call Session Control Function (P-CSCF) restoration. For example, dual mode end devices of an IP Multimedia Subsystem (IMS) may benefit from P-CSCF restoration. In particular, dual mode end devices of the IMS as defined by the third generation partnership project (3GPP), and its usage for voice over Long-Term Evolution (LTE), may benefit from P-CSCF restoration.

Description of the Related Art:

[0002] Generally, IMS can be identified as a technological and architectural framework that can be capable of delivering internet protocol (IP) multimedia services to various IMS-enabled devices. For example, IMS can allow for the evolution of standardized person-to-person communication services from voice only, to multimedia, voice, text, pictures, videos, and the like, or a combination thereof.

[0003] Core components of an IMS framework may include a P-CSCF and a Serving-Call Session Control Function (S-CSCF), where the P-CSCF may function as the first point of contact of the IMS, and the S-CSCF may function as a registrar capable of authenticating users and storing the session initiation protocol (SIP) address of terminals (UEs). The P-CSCF and/or the S-CSCF in an IMS framework may sometimes fail. When these components fail, any originating or terminating activities and/or services from UEs may also fail. Thus, restoration of these components may be necessary so that activities and/or services between UEs may resume.

[0004] One aspect of P-CSCF restoration may involve the IMS registration establishing an association of a UE with the P-CSCF and the S-CSCF, which may be hosted on a different, or the same network element. If the network element fails, it can become difficult to reach the UE. Thus, IMS restoration procedures as defined in 3GPP TS 23.380 try to eliminate this issue. Potentially after restoration, the S-CSCF may be on a functional network element and working, but the P-CSCF may still experience failure.

[0005] For any originating activity from the UE, the UE may recognize that there is a failure, perform a P-CSCF reselection, register at a different functional P-CSCF, and then perform the originating activity. For example, originating activity can be the periodic re-registration with another P-CSCF, which can imply that the problematic states can last, at maximum, at least one registration period. However usual intervals here can be between one to two hours.

[0006] An issue with a failed P-CSCF often concerns terminating activities. Until re-registration has been completed, the UE receiving the service(s) cannot be reached, e.g. for a voice call. Moreover, the UE and, thus, the user may not even be aware of the failure, and, thus, not be aware that the UE and the user cannot be reached.

[0007] Chapter 5 of 3GPP TS 23.380 describes three approaches to P-CSCF restoration. In 5.1 and 5.2.2, a packet data network (PDN) gateway (PGW) or a gateway general packet radio service (GPRS) support node (GGSN) is continuously monitoring the state of the P-CSCF. Once the P-CSCF fails, it informs the UE in one way, or the other about the failure.

[0008] The PGW is a bearer level entity. Putting a control interface (i.e., SIP) on it to monitor the P-CSCF may contradict the principle of separation of bearer and signaling. It may also require an SIP protocol stack on the PGW. Also, the PGW has provided one or more P-CSCF addresses to the UE. However, there is no easy and well-defined mechanism for the PGW to monitor or know which UEs are actually registered at which P-CSCF. Thus, it would be difficult for the PGW to inform the affected UEs if the PGW does not know which UEs are registered to which P-CSCF. Further, if the PDN-GW informs all of the UEs shortly after a failure, they can all try to register at the same time at a different P-CSCF, resulting in a traffic burst in the network which may result in a significant overload.

[0009] The approach in section 5.3 relies on keep-alive between the UE and the network. This approach is applicable to fixed networks. However, the resulting load for the UE battery and air interface would not be acceptable for mobile networks.

[0010] Where applicable, these approaches may provide for P-CSCF restoration. Ideally, the UE is informed shortly after the UE failure, can register elsewhere and any negative impact to ongoing or outgoing calls or messages can be avoided.

SUMMARY:

[0011] According to certain embodiments, a method can include selecting a preferred radio access type from a plurality of radio access types. The method can also include sending a first registration request to a network via the preferred radio access type to register with a first node of the network. The method can further include detecting whether a service was delivered by the preferred radio access type. When the service was not delivered by the preferred radio access type, the method can include sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0012] In certain embodiments, a method can include providing a plurality of radio access types. The method can also include receiving a first registration request at a network via a preferred radio access type to register with a first node of the network. The method can further include delivering a service by a radio access type of the plurality of radio access types. When the service was not delivered by the preferred radio access type, the method can additionally include receiving a second registration request to the network via the preferred radio access type to register with a second node of the network. [0013] An apparatus according to certain embodiments can include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to select a preferred radio access type from a plurality of radio access types. The at least one memory and the computer program code can also be configured to send a first registration request to a network via the preferred radio access type to register with a first node of the network. The at least one memory and the computer program code can further be configured to detect whether a service was delivered by the preferred radio access type. When the service was not delivered by the preferred radio access type, the at least one memory and the computer program code can further be configured to cause the apparatus at least to send a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0014] An apparatus according to certain embodiments can include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to provide a plurality of radio access types. The at least one memory and the computer program code can also be configured to receive a first registration request at a network via a preferred radio access type to register with a first node of the network. The at least one memory and the computer program code can further be configured to deliver a service by a radio access type of the plurality of radio access types. When the service was not delivered by the preferred radio access type, the at least one memory and the computer program code can further be configured to cause the apparatus at least to receive a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0015] According to certain embodiments a non-transitory computer-readable medium can be encoded with instructions that, when executed in hardware, perform a process. The process can include selecting a preferred radio access type from a plurality of radio access types. The process can also include sending a first registration request to a network via the preferred radio access type to register with a first node of the network. The process can further include detecting whether a service was delivered by the preferred radio access type. When the service was not delivered by the preferred radio access type, the process can also include sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0016] In certain embodiments a non-transitory computer-readable medium can be encoded with instructions that, when executed in hardware, perform a process. The process can include providing a plurality of radio access types. The process can further include receiving a first registration request at a network via a preferred radio access type to register with a first node of the network. The process can additionally include delivering a service by a radio access type of the plurality of radio access types. When the service was not delivered by the preferred radio access type, the process can also include receiving a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0017] An apparatus according to certain embodiments can include means for selecting a preferred radio access type from a plurality of radio access types. The apparatus can also include means for sending a first registration request to a network via the preferred radio access type to register with a first node of the network. The apparatus can further include means for detecting whether a service was delivered by the preferred radio access type. When the service was not delivered by the preferred radio access type, the apparatus can include means for sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0018] An apparatus in certain embodiments can include means for providing a plurality of radio access types. The apparatus can also include means for receiving a first registration request at a network via a preferred radio access type to register with a first node of the network. The apparatus can further include means for delivering a service by a radio access type of the plurality of radio access types. When the service was not delivered by the preferred radio access type, the apparatus can include means for receiving a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0019] According to certain embodiments a computer program product can encode instructions for performing a process. The process can include selecting a preferred radio access type from a plurality of radio access types. The process can also include sending a first registration request to a network via the preferred radio access type to register with a first node of the network. The process can further include detecting whether a service was delivered by the preferred radio access type. When the service was not delivered by the preferred radio access type, the process can also include sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

[0020] In certain embodiments a computer program product can encode instructions for performing a process. The process can include providing a plurality of radio access types. The process can further include receiving a first registration request at a network via a preferred radio access type to register with a first node of the network. The process can additionally include delivering a service by a radio access type of the plurality of radio access types. When the service was not delivered by the preferred radio access type, the process can also include receiving a second registration request to the network via the preferred radio access type to register with a second node of the network.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0021] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0022] Figure 1 illustrates a signaling flow according to certain embodiments.

[0023] Figure 2 illustrates a method according to certain embodiments.

[0024] Figure 3 illustrates another method according to certain embodiments.

[0025] Figure 4 illustrates a system according to certain embodiments.

DETAILED DESCRIPTION:

[0026] Certain embodiments provide, among other things, various ways to address S-CSCF restoration while considering P-CSCF failure. Certain embodiments may focus on the terminating services only.

[0027] End devices, such as, for example, a UE, may use different radio access types of an IMS. These radio access types may include, for example, LTE, Global System for Mobile Communications (GSM), Code Division Multiple Access (IxRTT/CDMA), and the like, for services. In certain embodiments, services for a UE may include calls, short message service(s) (SMS), and the like. If more than one access type is accessible at the same time, the IMS/LTE delivery can be selected as the preferred method.

[0028] If, however, the network fails to deliver a terminating service to a UE via the IMS infrastructure, the network may deliver the service via a different technology. The different technology can be any radio access type that is different from a preferred radio access technology or type. For example, if the preferred radio access type is set as IMS via LTE, a different technology may include IMS via GSM, or IMS via IxRTT/CDMA, and the like. In certain embodiments, this implementation can be achieved via the ability of the UE to quickly toggle between the radio access types.

[0029] Once the UE detects that the service was not delivered via its own preferred radio access type (in this example, IMS via LTE), the UE can conclude that the network detected a problem with the IMS registration. As a result, this triggers the UE to register in the network at a new P-CSCF. Once the registration at the new P-CSCF has been completed, the UE can now be reachable again before the IMS registration would detect and correct the failure.

[0030] According to certain embodiments, the examples discussed above may be applicable in LTE/CDMA or LTE GMS networks, where voice is provided via IMS or CDMA/GSM.

[0031] In certain embodiments, upon receipt of the service by another technology, a stale IMS registration can be triggered in the UE. Under a stale registration, the UE assumes that it is still registered, but in reality, it is no longer reachable because the P-CSCF is not able to send any SIP traffic towards the UE. The UE may then be triggered to re-initiate the registration process to register the UE at a new P-CSCF in the network so that the UE can be reachable before the IMS registration detects and corrects the failure.

[0032] In certain embodiments, after the UE has detected that the network failed to deliver a terminating service via the preferred radio access type IMS/LTE, the UE may first attempt to re-register at the original P-CSCF (failed P-CSCF) of the preferred radio access type IMS/LTE before registering at a new P-CSCF in the network. If the re-registration process at the original P-CSCF is unsuccessful, the UE may select a new P-CSCF within the network, and register there.

[0033] Figure 1 illustrates a signaling flow according to certain embodiments. Figure 1 more particularly illustrates an exemplary signaling flow for UE registration with a P-CSCF of an IMS network via a radio access type.

[0034] At 1 , the UE may detect a radio access type of an IMS network. As discussed above, the radio access type may include LTE, GSM, CDMA, and the like. The radio access type may also include any other suitable radio access method for different services, including the transfer of data, voice, and the like.

[0035] At 2, the UE may send a first registration request via a selected or preferred radio access type to register at a node of the IMS network. The node may be represented by a P-CSCF of the IMS network. Upon successful registration at the node, at 3, the preferred radio access type may provide an indication to the UE that the registration was successful.

[0036] At 4, the UE and the preferred radio access type may negotiate a registration time between the UE and the node of the preferred radio access type. Upon a successful negotiation, the UE may store the registration for the negotiated registration time, at 5. At 6, it is possible that the UE may become idle. In such a case, there is no outgoing SIP traffic from the UE. Thus, while the registration time on the UE and the S-CSCF has not yet expired, the P- CSCF used for the registration may become non-operational.

[0037] At 7, in light of the P-CSCF's non-operational state, the IMS network may deliver a service to the UE via a different radio access type. At 8, after receiving the service at the UE, the UE may detect that the service was not delivered via its own preferred radio access type, and conclude that the network detected a problem with the IMS registration. At 9, the delivery of the service by another radio access type may also trigger a stale IMS registration to the UE, which may subsequently trigger a registration in the IMS network.

[0038] Once the UE is triggered to register again to the original P-CSCF via the preferred radio access type, at 10, the UE may resend the first registration request to the IMS network via the preferred radio access type in an effort to re -register at the old or previous P-CSCF. At 11, upon receipt of the first registration request, the IMS network may deny the registration (e.g., UE failed to reach the P-CSCF). At 12, failure to reach the old or previous P- CSCF may trigger the UE to send a second request to the IMS network via the preferred radio access type to register at a new P-CSCF in the IMS network. Registration at a new P-CSCF may then allow the UE to become reachable again before the IMS registration would detect and correct the failure. Finally, at 13, the UE may dynamically update this information. [0039] Figure 2 illustrates a method according to certain embodiments. Figure 2 more specifically illustrates a registration process between a UE and an IMS network, according to certain embodiments. The method of Figure 2 may be performed by, for example, a terminal or user equipment (UE), such as a device configured for device to device communication. The terminal may be, for example, a mobile phone, personal computer, personal digital assistant, laptop, tablet, mini-tablet, sensor, smart meter, or any other terminal device.

[0040] As shown in Figure 2, the method may include, at 205, detecting at least one radio access type of a plurality of radio access types. As discussed above, the radio access type may include, for example, LTE 210, GSM 215, CDMA 220, and the like. The radio access type may also include any other suitable radio access method for different services, including the transfer of data, voice, and the like.

[0041] The method may further include, at 225, sending a first registration request to the IMS network via the preferred radio access type selected by the UE to register at a P-CSCF of the IMS network. Upon successful registration at the P-CSCF of the IMS network, the method may further include, at 230, negotiating a registration time with the preferred radio access type. After the negotiation, the UE may store the registration time, at 235. When the UE goes idle, at 240, there is no outgoing SIP traffic from the UE. During this time, and while the registration time on the UE and the S-CSCF is not yet expired, the P- CSCF used for the registration becomes non-operational due to the UE's idling state.

[0042] As a result of the idling state of the UE, the service delivered to the UE from the IMS network may be accomplished by a different radio access type. For example, if the preferred radio access type is LTE, then the IMS network may deliver the service to the UE via a different radio access type, such as, for example, GSM, CDMA, or the like. At 245, the UE is able to detect that the service was not delivered via its own preferred radio access type, and therefore can conclude that the network detected a problem with the IMS. [0043] In certain embodiments, the sending of the service via a different radio access type of the IMS network may trigger a stale IMS registration, at 250, in the UE, in which the UE may assume that it is still registered, but in reality, it is no longer reachable because the P-CSCF is not able to send any SIP traffic towards the UE. At 255, the stale IMS registration may further trigger the UE to attempt to re-register at the original P-CSCF by resending the first registration request to the original P-CSCF of the IMS network via the preferred radio access type. If the re-registration is successful, the registration process may end. However, if the re-registration fails, the UE may, at 260 send a second registration request to another (new) P-CSCF in the IMS network via the preferred radio access type.

[0044] Figure 3 illustrates another method according to certain embodiments. The method of Figure 3 may be performed by a controlling node such as, for example, at least one P-CSCF within an IMS network. At 305, the IMS network may receive a first registration request via LTE at the P-CSCF. If it is determined that the registration is successful, the IMS network, at 310, can send an indication of successful registration to the UE. Further, at 315, the IMS network may send a negotiated registration time to the UE. The method may further include, at 320, delivering service from a radio access type of the IMS network that is different from the preferred radio access type selected by the UE. At 325, the IMS network may receive the first registration request again for registering at the originally selected P-CSCF. If the registration is successful, the method may end. However, if the registration with the original or old P-CSCF is not successful, at 330, the IMS network may receive a second registration request from the UE requesting to register at a new P- CSCF of the of the IMS network via the preferred radio access type.

[0045] Figure 4 illustrates a system according to certain embodiments of present invention. In one embodiment, a system may include multiple devices, such as, for example, at least one UE 410, at least one IMS networking device 420, at least one P-CSCF 430, and at least one new P-CSCF 440. In certain systems, UE 410, IMS networking device 420, P-CSCF 430, and new P-CSCF 440 may be present. Other configurations are also possible.

[0046] The UE 410 can be any terminal device, such as a cell phone, a smart phone, a personal digital assistant, a tabletop computer, a personal computer, a laptop computer, a mini-tablet computer, a tablet computer, or the like.

[0047] Each of these devices may include at least one processor, respectively indicated as 414, 424, 434, and 444. At least one memory may be provided in each device, as indicated at 415, 425, 435, and 445, respectively. The memory may include computer program instructions or computer code contained therein. The processors 414, 424, 434, and 444 and memories 415, 425, 435, and 445, or a subset thereof, can be configured to provide means corresponding to the various blocks of Figures 2 and 3. Although not shown the UE may also include positioning hardware, such as a global positioning system (GPS) or micro electrical mechanical system (MEMS) hardware, which can be used to determine a location of the device. Other sensors are also permitted and can be included to determine location, elevation, orientation, and so forth, such as barometers, compasses, and the like.

[0048] As shown in Figure 4, transceivers 416, 426, 436, and 446 may be provided, and each device may also include at least one antenna, respectively illustrated as 417, 427, 437, and 447. The devices may have many antennas, such as an array of antennas configured for multiple input multiple out (MIMO) communications, or multiple antennas for multiple radio access technologies. Other configurations of these devices, for example, may be provided. For example, UE 410 may additionally be configured for wired communication, and in such a case, antenna 417 would also illustrate any form of communication hardware, without requiring a conventional antenna.

[0049] Transceivers 416, 426, 436, and 446 may each, independently, be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that is configured both for transmission and reception. [0050] Processors 414, 424, 434, and 444 may be embodied by any computational or data processing device, such as a central processing unit (CPU), application specific integrated circuit (ASIC), or comparable device. The processors 414, 424, 434, and 444 can be implemented as a single controller, or a plurality of controllers or processors according to other embodiments. The processors 414, 424, 434, and 444 can be any type of general or specific-purpose processor. Processors 414, 424, 434, and 444 may also include one or more of general-purpose computers, special-purpose computers, microprocessors, digital signal processors (DSPs), field- programmable gate arrays (FPGAs), ASICs, and/or processors based on a multi-core processor architecture, as examples.

[0051] Memories 415, 425, 435, and 445 may independently be any suitable storage device, such as a non-transitory computer-readable medium. The memories 415, 425, 435, and 445 may include computer program instructions or computer code. The memories 415, 425, 435, and 445 can be one or more memories of any type suitable to the local application environment, and can be implemented using any suitable volatile or nonvolatile data storage technology such as semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memories 415, 425, 435, and 445 may include any combination of random access memory (RAM), read only memory (ROM), flash memory, static storage such as magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media. The instructions stored in memories 415, 425, 435, and 445 may include program instructions or computer program code that, when executed by processors 414, 424, 434, and 444, enable the devices to perform tasks as described herein. Alternatively, certain embodiments may be performed entirely in hardware. Furthermore, the computer program instructions stored in the memory and which may be processed by the processors can be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language.

[0052] Additionally, although Figure 4 illustrates a system including a UE 410, IMS networking device 420, P-CSCF 430, and new P-CSCF 440, embodiments of the invention may be applicable to other configurations, and configurations involving additional elements.

[0053] One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.

[0054] Glossary

[0055] 3 GPP Third Generation Partnership Project

[0056] ASIC Application Specific Integrated Circuit

[0057] CDMA Code Division Multiple Access

[0058] CPU Central Processing Unit

[0059] DSP Digital Signal Processor

[0060] FPGA Field-Programmable Gate Arrays

[0061] GGSN Gateway General Packet Radio Service Support Node

[0062] GPS Global Positioning System

[0063] GSM Global System for Mobile Communications

[0064] HDD Hard Disk Drive

[0065] IMS IP Multimedia Subsystem

[0066] IP Internet Protocol

[0067] LTE Long-term Evolution

[0068] MEMS Micro Electrical Mechanical System [0069] P-CSCF Proxy-Call Session Control Function [0070] PGW Public Data Network Gateway

[0071] RAM Random Access Memory

[0072] ROM Read Only Memory

[0073] SIP Session Initiation Protocol

[0074] SMS Short Message Service

Claims

WE CLAIM:

1. A method comprising:

selecting a preferred radio access type from a plurality of radio access types;

sending a first registration request to a network via the preferred radio access type to register with a first node of the network;

detecting whether a service was delivered by the preferred radio access type; and

when the service was not delivered by the preferred radio access type, sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

2. The method of claim 1, further comprising detecting an error when the service was not delivered by the preferred radio access type.

3. The method of claim 1 or claim 2, further comprising resending the first registration request to the network via the preferred radio access type to re-register with the first node if the service was not delivered by the preferred radio access type.

4. The method of claim 3, further comprising sending the second registration request to the network via the preferred radio access type to register with the second node of the preferred radio access type when the re- registration with the first node fails.

5. The method of any of claims 1-4, further comprising triggering a stale registration when the service was not delivered by the preferred radio access type.

6. A method comprising: providing a plurality of radio access types;

receiving a first registration request at a network via a preferred radio access type to register with a first node of the network;

delivering a service by a radio access type of the plurality of radio access types; and

when the service was not delivered by the preferred radio access type, receiving a second registration request to the network via the preferred radio access type to register with a second node of the network.

7. The method of claim 6, wherein if the service was not delivered by the preferred radio access type, the service is delivered by a different radio access type of the plurality of radio access types.

8. The method of claim 6 or claim 7, further comprising receiving the first registration request again at the network via the preferred radio access type to re-register with the first node, if the service was not delivered by the preferred radio access type.

9. The method of any of claims 6-8, further comprising receiving the second registration request at the network via the preferred radio access type to register with the second node of the preferred radio access type when the re-registration with the first node fails.

10. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to select a preferred radio access type from a plurality of radio access types; send a first registration request to a network via the preferred radio access type to register with a first node of the network;

detect whether a service was delivered by the preferred radio access type; and

when the service was not delivered by the preferred radio access type, send a second registration request to the network via the preferred radio access type to register with a second node of the network.

11. The apparatus of claim 10, wherein if the service was not delivered by the preferred radio access type, the service is delivered by a different radio access type of the plurality of radio access types.

12. The apparatus of claim 10 or claim 11, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to resend the first registration request to the network via the preferred radio access type to re-register with the first node.

13. The apparatus of claim 12, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to send the second registration request to the network via the preferred radio access type to register with the second node of the preferred radio access type when there-registration with the first node fails.

14. The apparatus of any of claims 10-13, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to trigger a stale registration when the service was not delivered by the preferred radio access type.

15. An apparatus, comprising: at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to provide a plurality of radio access types;

receive a first registration request at a network via a preferred radio access type to register with a first node of the network;

deliver a service by a radio access type of the plurality of radio access types; and

16. The apparatus of claim 15, wherein if the service was not delivered by the preferred radio access type, the service is delivered by a different radio access type of the plurality of radio access types.

17. The apparatus of claim 15 or claim 16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to receive the first registration request again at the network via the preferred radio access type to re-register with the first node, if the service was not delivered by the preferred radio access type.

18. The apparatus of any of claims 15-17, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to receive the second registration request at the network via the preferred radio access type to register with the second node of the preferred radio access type when the re-registration with the first node fails.

19. An apparatus comprising:

means for selecting a preferred radio access type from a plurality of radio access types;

means for sending a first registration request to a network via the preferred radio access type to register with a first node of the network;

means for detecting whether a service was delivered by the preferred radio access type; and

means for, when the service was not delivered by the preferred radio access type, sending a second registration request to the network via the preferred radio access type to register with a second node of the network.

20. The apparatus of claim 19, further comprising means for detecting an error when the service was not delivered by the preferred radio access type.

21. The apparatus of claim 19 or claim 20, further comprising means for resending the first registration request to the network via the preferred radio access type to re-register with the first node if the service was not delivered by the preferred radio access type.

22. The apparatus of claim 21, further comprising means for sending the second registration request to the network via the preferred radio access type to register with the second node of the preferred radio access type when the re-registration with the first node fails.

23. The apparatus of any of claims 19-22, further comprising means for triggering a stale registration when the service was not delivered by the preferred radio access type.

24. An apparatus comprising:

means for providing a plurality of radio access types;

means for receiving a first registration request at a network via a preferred radio access type to register with a first node of the network;

means for delivering a service by a radio access type of the plurality of radio access types; and

means for, when the service was not delivered by the preferred radio access type, receiving a second registration request to the network via the preferred radio access type to register with a second node of the network.

25. The apparatus of claim 24, wherein if the service was not delivered by the preferred radio access type, the service is delivered by a different radio access type of the plurality of radio access types.

26. The apparatus of claim 24 or claim 25, further comprising receiving the first registration request again at the network via the preferred radio access type to re-register with the first node, if the service was not delivered by the preferred radio access type.

27. The apparatus of any of claims 24-26, further comprising receiving the second registration request at the network via the preferred radio access type to register with the second node of the preferred radio access type when the re-registration with the first node fails.

28. A non-transitory computer-readable medium encoded with instructions that, when executed in hardware, perform a process, the process comprising the method according to any of claims 1-9.

29. A computer program product encoding instructions for performing a process, the process comprising the method according to any of claims 1-9.