Patent Publication Number: US-2011051701-A1

Title: Ims deregistration of a dual mode device triggered through a legacy network

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention is related to the field of communications and, in particular, to de-registration of a dual mode device in an IMS network. 
     2. Statement of the Problem 
     One type of communication network gaining popularity is an IP Multimedia Subsystem (IMS) network. As set forth in the 3 rd  Generation Partnership Project (3GPP), the IMS is a core network that provides multimedia services to user equipment (UE) over an Internet Protocol (IP) network. The IMS network is able to communicate with UE through different types of access networks, such as a Wide Local Area Network (WLAN) (e.g., a WiFi or a WiMAX network), an Ethernet network, a High Rate Packet Data (HRPD) network, or another type of access network. Service providers are accepting the IMS architecture in next generation network evolution. 
     Before the UE receives service from IMS network, the UE attempts to register with the IMS network through the appropriate access network. To register according to 3GPP standards, the UE transmits a register request message, such as a Session Initiation Protocol (SIP) REGISTER message, to a Serving-Call Session Control Function (S-CSCF) in the IMS network. Responsive to receiving the register request message, the S-CSCF generates an authentication request message, such as a Diameter Multimedia Authentication Request (MAR) message, and transmits the authentication request message to a Home Subscriber Server (HSS). The HSS then authenticates the UE, such as through the Authentication and Key Agreement (AKA) authentication method. If the UE is authenticated, then the HSS updates the IMS registration status of the UE as “registered” in the subscriber profile for the UE. The S-CSCF then typically requests the subscriber profile of the UE by sending a Diameter Server Assignment Request (SAR) message to the HSS. In response, the HSS sends the subscriber profile for the UE to the S-CSCF in a Diameter Server Assignment Answer (SAA) message. The S-CSCF thus knows the UE is presently registered based on the IMS registration status in the subscriber profile. 
     The HSS maintains a SIP registration timer for the UE. In order to remain registered with the IMS network, the UE needs to re-register periodically before the SIP registration timer expires. If the UE fails to re-register in time, the HSS will automatically deregister the UE. 
     Wireless phone providers are developing dual mode devices that have the functionality for communicating with a legacy network (e.g., a cellular network) and other types of wireless data networks, such as an IMS network. The concept of the dual mode device is to allow a user the flexibility to communicate with either the legacy network or the IMS network. 
     When a dual mode device is in range of the legacy network, the dual mode device registers with the legacy network to receive communication access. Likewise, when the dual mode device is in range of the IMS access network, the dual mode device registers with IMS network as described above. During the registration process, network resources are reserved for the dual mode device. 
     After registration, the dual mode device may communicate over either network until such time as the dual mode device is deregistered and network resources are released for each respective network. The dual mode device may actively deregister with the IMS network while it is in range of the IMS network. When the dual mode device moves out of range of the IMS network, the status of the dual mode device within the IMS network remains “registered” until the SIP registration timer expires. 
     SUMMARY 
     Embodiments described herein deregister a dual mode device in an IMS network by sending messages over a legacy network, when the dual mode device loses communication with the IMS access network. Support of accurate IMS registration status for a dual mode device is typically difficult due the mobility of the device while accurate IMS registration status of the dual mode device is desirable in order to support smooth handover between the IMS network and the legacy network and to conserve network resources. For example, a problem arises when the dual mode device loses communication with the IMS access network, such as when the dual mode device moves out of the service area of the IMS access network. When communication with the IMS access network is lost, the dual mode device cannot actively deregister with the IMS network. Therefore, the status of the dual mode device within the IMS network remains “registered” until the SIP registration timer expires. If the IMS network were to receive a session initiation request (i.e., SIP INVITE) before the SIP registration timer expires, the S-CSCF that is serving the dual mode device may attempt to set up the call/session to the dual mode device because it is still indicated as registered even though the dual mode device has move out of range. As the dual mode device is no longer in range of the IMS access network, call set up over the IMS network will fail and the call set up will be redirected to the legacy network. This unfortunately delays set up time and wastes network resources. 
     For example, the dual mode device may send a deregistration SMS message to the IMS network through the legacy network, which causes the IMS network to deregister the dual mode device. Thus, even though the dual mode device cannot communicate directly with the IMS network, the dual mode device may trigger deregistration in the IMS network over the legacy network before the SIP registration timer expires. This advantageously reduces call initiation times, and saves network resources in the IMS network. 
     One embodiment comprises a dual mode device. The dual mode device includes a network interface operable to exchange wireless communications with an access network of an IMS network, and to exchange wireless communications with a legacy network, such as a cellular network. The dual mode device further includes a deregistration system operable to detect a loss of wireless communications with the access network of the IMS network. In response to detecting the loss of wireless communications, the deregistration system is further operable to generate a deregister request message (e.g., an SMS message) to deregister the device in the IMS network, and to transmit the deregister request message to the legacy network through the network interface for delivery to the IMS network. 
     Another embodiment comprises a network element in the IMS network. The network element includes an interface system operable to receive the deregister request message from the legacy network that was sent from the dual mode device. The network element further includes a registration system operable to update an IMS registration status of the dual mode device based on the deregister request message to indicate the dual mode device as deregistered. 
     In yet another embodiment, the network element further includes a notification system operable to identify one or more other network elements in the IMS network that maintains an IMS registration status for the dual mode device, and to send a deregistration notification message to the network element(s) indicating that the dual mode device is deregistered. 
     Other exemplary embodiments may be described below. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1  illustrates a communication network in an exemplary embodiment. 
         FIG. 2  illustrates a dual mode device in an exemplary embodiment. 
         FIG. 3  is a flow chart illustrating a method of operating a dual mode device to initiate deregistration in an IMS network in an exemplary embodiment. 
         FIG. 4  illustrates a network element of an IMS network in an exemplary embodiment. 
         FIG. 5  is a flow chart illustrating a method of deregistering a dual mode device in an IMS network in an exemplary embodiment. 
         FIG. 6  illustrates another communication network in an exemplary embodiment. 
         FIG. 7  is a message diagram illustrating deregistration of a dual mode device in an IMS network using a cellular network in an exemplary embodiment. 
         FIG. 8  is another message diagram illustrating deregistration of a dual mode device in an IMS network using a cellular network in another exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
       FIG. 1  illustrates a communication network  100  in an exemplary embodiment of the invention. Communication network  100  includes an IMS network  110  and access network  120  for IMS network  110 . IMS network  110  is a core network adapted to deliver Internet Protocol (IP) multimedia services. The IMS architecture allows for a variety of different access types for IMS devices. In this embodiment, access to IMS network  110  is provided through access network  120 . Access network  120  comprises any type of network adapted to communicate through wireless signals. Some examples of access network  120  include a WiFi network, a WiMAX network, an HRPD network, etc. 
     IMS network  110  is generally shown as including a plurality of network elements  112 - 114 . One of network elements  112 - 114  may represent a Serving-Call Session Control Function (S-CSCF). Likewise, one or more of network element  112 - 114  may represent application servers. One of network elements  112 - 114  may represent an IMS subscriber server that stores profiles for IMS subscribers, such as a Home Subscriber Server (HSS). The network elements  112 - 114  in IMS network  110  are labeled generally because the operations described in the following flow charts may be performed in different types of network elements. One common feature of network elements  112 - 114  is that they know or maintain an IMS registration status of IMS devices. For example, an HSS maintains subscriber profiles that indicate the IMS registration status of IMS devices. An S-CSCF maintains an IMS registration status of IMS devices that it is serving. Application servers provide services to IMS devices that are presently registered. 
     Communication network  100  further includes a legacy network  130 . Legacy network  130  comprises any non-IMS mobile network adapted to provide mobile communication services. Examples of legacy network  130  include a Code Division Multiple Access (CDMA) network and a Global System for Mobile communications (GSM) network. “Legacy” is not intended to refer to only networks presently existing, but also to non-IMS networks that are developed in the future, such as new cellular networks. Although not shown, those skilled in the art will appreciate that legacy network  130  may include a Radio Access Network (RAN), a Mobile Switching Center (MSC), a Short Message Service Center (SMSC), a subscriber server (such as a Home Location Register (HLR)), etc. 
     The network clouds illustrating access network  120  and legacy network  130  are not being used to show the actual service areas of the networks, as the service areas may be separate or may overlap. IMS network  110  and legacy network  130  are separate networks, but both networks  110  and  130  may be managed or owned by a common service provider. 
     IMS network  110  and legacy network  130  are both adapted to provide communication services to a dual mode device  140 . Dual mode device  140  comprises any type of communication device adapted to communicate with both an IMS network and a legacy network. For example, dual mode device  140  may be SIP-enabled, and is able to communicate with IMS network  110  through a WiFi connection. At the same time, dual mode device  140  may be a CDMA device that is able to communicate with a CDMA network. 
     If dual mode device  140  is in range of access network  120 , then dual mode device  140  registers with IMS network  110  through access network  120 . When registered with IMS network  110 , dual mode device  140  is able to access services provided by IMS network  110 , such as voice calls, video downloads, audio downloads, gaming, etc. Similarly, if dual mode device  140  is in range of legacy network  130 , then dual mode device  140  registers with legacy network  130 . When registered with legacy network  130 , dual mode device  140  is able to access services provided by legacy network  130 , such as voice calls, SMS, etc. If dual mode device  140  is in range of both access network  120  and legacy network  130 , then dual mode device  140  may register with one or both of the networks depending on design preferences. 
     In  FIG. 1 , assume that dual mode device  140  is in range of access network  120  and is registered with IMS network  110 . At some point after registering with IMS network  110 , further assume that dual mode device  140  loses communication with access network  120 . When this occurs, dual mode device  140  is no longer able to communicate with IMS network  110 , but is still registered with IMS network  110 . This can be a problem as IMS network  110  may continue to attempt to connect calls to dual mode device  140  even though it is out of range of access network  120 . According to the embodiments described below, dual mode device  140  communicates with IMS network  110  over legacy network  130  to deregister itself in IMS network  110 . 
       FIG. 2  illustrates dual mode device  140  in an exemplary embodiment. In this embodiment, dual mode device  140  includes a network interface  202  and a deregistration system  204 . Network interface  202  comprises any device, component, or system adapted to exchange wireless communications with access network  120  of IMS network  110 , and to exchange wireless communications with legacy network  130 . Deregistration system  204  comprises any device, component, or system adapted to initiate a deregistration process to deregister dual mode device  140  in IMS network  110  by communicating over legacy network  130 . One exemplary operation of dual mode device  140  is illustrated in  FIG. 3 . 
       FIG. 3  is a flow chart illustrating a method  300  of operating dual mode device  140  to initiate deregistration in IMS network  110  in an exemplary embodiment. The steps of method  300  will be described with reference to communication network  100  in  FIG. 1  and dual mode device  140  in  FIG. 2 , but those skilled in the art will appreciate that method  300  may be performed in other networks and systems. Also, the steps of the flow charts described herein are not all inclusive and may include other steps not shown, and the steps may be performed in an alternative order. 
     In step  302 , deregistration system  204  detects a loss of wireless communications with access network  120  of IMS network  110 . The loss of wireless communications may be due to a failure of an access point in access network  120 , due to dual mode device  140  moving out of the coverage area of access network  120 , etc. In response to detecting the loss of wireless communications, deregistration system  204  generates a deregister request message to deregister dual mode device  140  in IMS network  110  in step  304 . A deregister request message comprises any message that instructs or causes IMS network  110  to terminate registration for a device. Deregistration system  204  may format the deregister request message with a teleservice ID, a service type, a content type, or some other parameter requesting deregistration in IMS network  110 . The deregister request message is in a protocol for transmission over legacy network  130  instead of over IMS network  110 . For example, deregistration system  204  may generate a Short Message Service (SMS) message in a signaling protocol used for transmission over legacy network  130 . In step  306 , deregistration system  204  transmits the deregister request message to legacy network  130  through network interface  202  for delivery to IMS network  110 . 
     In  FIG. 1 , legacy network  130  receives the deregister request message from dual mode device  140 , and delivers the deregister request message to IMS network  110  so that the IMS registration status of dual mode device  140  can be updated to “not registered”. Those skilled in the art will appreciate that legacy network  130  may alter or change the deregister request message that was initially sent by dual mode device  140 . For example, if dual mode device  140  sent an SMS message, legacy network  130  may change the SMS message to a Short Message Point-to-Point (SMPP) message, a Lightweight Directory Access Protocol (LDAP) message, etc. 
     One of network elements  112 - 114  will receive the deregister request message that was delivered over legacy network  130 , such as network element  112 .  FIG. 4  illustrates network element  112  in an exemplary embodiment. Network element  112  may represent an HSS in IMS network  110 , an application server in IMS network  110 , or another type of network element. In this embodiment, network element  112  includes an interface system  402 , a registration system  404 , and a notification system  406 . Interface system  402  comprises any device, component, or system adapted to receive messages from legacy network  130 . For example, interface system  402  may comprise an SMPP interface, an LDAP interface, etc. Registration system  404  comprises any device, component, or system adapted to maintain an IMS registration status of dual mode device  140 , such as “registered” or “not registered”. Notification system  406  comprises any device, component, or system adapted to notify other network elements in IMS network  110  of a change to the IMS registration status of dual mode device  140 . One exemplary operation of network element  112  is illustrated in  FIG. 5 . 
       FIG. 5  is a flow chart illustrating a method  500  of deregistering dual mode device  140  in IMS network  110  in an exemplary embodiment. The steps of method  500  will be described with reference to communication network  100  in  FIG. 1  and network element  112  in  FIG. 4 , but those skilled in the art will appreciate that method  500  may be performed in other networks and systems. 
     In step  502 , interface system  402  receives the deregister request message from legacy network  130 . The deregister request message received from legacy network  130  may comprise an SMPP message, an LDAP message, etc. The deregister request message includes a parameter or code instructing dual mode device  140  to be deregistered in IMS network  110 , such as a service type parameter, a content type parameter (in SIP), etc. The parameter may be inserted in the deregister request message by dual mode device  140  or legacy network  130 , such as by an SMSC in legacy network  130 . In step  504 , registration system  404  updates the IMS registration status for dual mode device  140  based on the deregister request message to indicate dual mode device  140  as deregistered or not registered. For example, registration system  404  may process the service type parameter or content type parameter to update the IMS registration status. 
     There may be other network elements  113 - 114  in IMS network  110  that are serving dual mode device  140 , and thus also maintain an IMS registration status for dual mode device  140 . Thus, in response to the update to the IMS registration status, notification system  406  may identify one or more other network elements  113 - 114  that maintain an IMS registration status for dual mode device  140  in step  506 . Notification system  406  may then send a deregistration notification message to the other network element(s)  113 - 114  in IMS network  110  indicating that dual mode device  140  is deregistered in step  508 . The network element(s)  113 - 114  receiving the deregistration notification message can likewise update the IMS registration status for dual mode device  140 . The goal is that each network element in IMS network  110  that is/was serving dual mode device  140  knows that dual mode device  140  is now deregistered so that they do not waste network resources in setting up a call to dual mode device  140  or providing some other unneeded service. 
     If dual mode device  140  is again able to exchange wireless communications with access network  120  of IMS network  110 , then dual mode device  140  may again register with IMS network  110 . Each time dual mode device  140  detects a loss of wireless communications with access network  120 , dual mode device  140  may initiate the deregistration process with IMS network  110  over legacy network  130 . 
     EXAMPLE 
       FIG. 6  illustrates another communication network  600  in an exemplary embodiment. Like  FIG. 1 , communication network  600  includes an IMS network  610  and access network  620  operable to provide communication service to a dual mode device  640 . Communication network  600  also includes a cellular network  630  operable to provide communication service to dual mode device  640 . 
     In this embodiment, IMS network  110  includes a Serving-Call Session Control Function (S-CSCF)  612 , a deregistration application server (D-AS)  614 , a Home Subscriber Server (HSS)  616 , and application servers (AS)  618 - 619 . S-CSCF  612  is adapted to set up and maintain calls/sessions involving dual mode device  640  over IMS network  610 . Deregistration application server  614  is a specialized server designated for deregistering devices based on messages received over cellular network  630  (or another type of legacy network). Deregistration application server  614  is optional is this embodiment, which will be shown in more detail below. HSS  616  is adapted to store a subscriber profile for dual mode device  640 . The subscriber profile for dual mode device  640  includes a variety of information for dual mode device  640 , such as service subscriptions and billing, and an IMS registration status. The IMS registration status for dual mode device  640  may indicate “registered” or “not registered”. Application servers  618 - 619  are adapted to provide services or features to dual mode device  640 , such as voice mail, call forwarding, video downloads, gaming, etc. 
     Cellular network  630  may comprise a CDMA network, a GSM/UMTS network, or some other cellular network. Cellular network  630  is one example of a “legacy network” described in  FIG. 1 . In this embodiment, cellular network  630  includes a Radio Access Network (RAN)  632 , a Mobile Switching Center (MSC)  634 , and a Short Message Service Center (SMSC)  636 . 
     During any given time, multiple network elements in IMS network  610  may maintain an IMS registration status for dual mode device  640 . For example, S-CSCF  612  needs to know whether or not dual mode device  640  is registered. Likewise, if application server  618  is providing a service to dual mode device  640 , then application server  618  needs to know whether or not dual mode device  640  is registered. Not all network elements in IMS network  610  may store an internal record of the IMS registration status as does HSS  616 . For example, application servers  618 - 619  may subscribe to HSS  616  to be notified if dual mode device  640  deregisters, but do not store their own IMS registration status record. However, each network element that needs to know whether or not dual mode device  640  is registered is generally referred to herein as “maintaining” an IMS registration status. 
     Assume for this example that dual mode device  640  registers with IMS network  610 . Thus, the subscriber profile stored in HSS  616  indicates that dual mode device  640  is “registered”. At some point after registering with IMS network  610 , further assume that dual mode device  640  loses communication with access network  620 . When this occurs, dual mode device  640  is no longer able to communicate with IMS network  610 , but is still registered with IMS network  610 . According to the example described below, dual mode device  640  communicates with IMS network  610  over cellular network  630  to deregister itself in IMS network  610 . 
       FIG. 7  is a message diagram illustrating deregistration of dual mode device  640  in IMS network  610  using cellular network  630  in an exemplary embodiment. Dual mode device (DMD)  640  detects the loss of wireless communications with access network  620 . In response to detecting the loss of wireless communications, dual mode device  640  generates a “deregistration” SMS message for deregistering itself in IMS network  610 . Dual mode device  640  identifies a teleservice ID (e.g., 4242) that instructs or indicates deregistration, and inserts the teleservice ID in a parameter of the SMS message. Dual mode device  640  may also identify a routing address for the destination of the SMS message, which may be the directory number of deregistration application server (D-AS)  614 , and insert the routing address in the SMS message. Dual mode device  640  then sends the SMS message to cellular network  630  in the proper signaling message. 
     MSC  634  receives the SMS message (through RAN  632  in  FIG. 6 ), and forwards the SMS message to SMSC  636  (i.e., in an SMDPP message, a MAP message, etc). SMSC  636  processes the SMS message to identify the teleservice ID and the routing address, and converts the teleservice ID to a service type (e.g., service_type=dereg). SMSC  636  then generates an SMPP message, and inserts the service type in a parameter of the SMPP message. With the message properly formatted, SMSC  636  sends the SMPP message to deregistration application server  614  based on the routing address. 
     Deregistration application server  614  receives the SMPP message, and processes the service type parameter in the SMPP message. Because the service type parameter represents an instruction to deregister dual mode device  640 , deregistration application server  614  generates an LDAP update message with an instruction to update the IMS registration status to “not registered”. Deregistration application server  614  then sends the LDAP update message to HSS  616 . Upon receiving the LDAP update message, HSS  616  updates the IMS registration status in the subscriber profile of dual mode device  640  to indicate “not registered”. 
     HSS  616  also notifies other network elements in IMS network  610  that dual mode device  640  is no longer registered. To do so, HSS  616  identifies the other network elements that maintain an IMS registration status for dual mode device  640 . As an example, S-CSCF  612  and application server  618  may subscribe to HSS  616  (such as with a SIP SUBSCRIBE) to be notified of a change to the registration status of dual mode device  640 . Thus, HSS  616  sends a Diameter Cx Registration Termination Request (RTR) message to S-CSCF  612  indicating that dual mode device  140  is deregistered. HSS  616  also sends a Diameter Sh Push Notification Request (PNR) to application server  618  indicating that dual mode device  140  is deregistered. The remaining messages in  FIG. 7  are response messages that do not need further explanation. 
     As is evident in  FIG. 7 , dual mode device  640  is advantageously able to update its IMS registration status in HSS  616  by sending an SMS message to IMS network  610  through cellular network  630 . HSS  616  is then able to notify other network elements in IMS network  610  that dual mode device  640  is not registered. Advantageously, S-CSCF  612 , application server  618 , and other network elements know that dual mode device  640  is no longer registered so that they do not waste network resources in attempting to set up a call to dual mode device  640  or provide other services. 
       FIG. 8  is another message diagram illustrating deregistration of dual mode device  640  in IMS network  610  using cellular network  630  in an exemplary embodiment. In this example, SMSC  636  contacts HSS  616  directly to update the IMS registration status of dual mode device  640 .  FIG. 8  is similar to  FIG. 7  until SMSC  636  receives SMS message from MSC  634 . 
     In response to receiving the SMS message, SMSC  636  processes the SMS message to identify the teleservice ID and the routing address, and converts the teleservice ID to a service type (e.g., service_type=dereg). In this embodiment, the routing address indicates that HSS  616  is the intended recipient of the SMS message. Thus, SMSC  636  generates an LDAP update message with an instruction to update the IMS registration status to “not registered”. SMSC  636  then sends the LDAP update message to HSS  616  based on the routing address. Upon receiving the LDAP update message, HSS  616  updates the IMS registration status in the subscriber profile of dual mode device  640  to indicate “not registered”. HSS  616  also notifies other network elements in IMS network  610  that dual mode device  640  is no longer registered similar to  FIG. 7 . 
     Any of the various elements shown in the figures or described herein may be implemented as hardware, software, firmware, or some combination of these. For example, an element may be implemented as dedicated hardware. Dedicated hardware elements may be referred to as “processors”, “controllers”, or some similar terminology. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, a network processor, application specific integrated circuit (ASIC) or other circuitry, field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), non volatile storage, logic, or some other physical hardware component or module. 
     Also, an element may be implemented as instructions executable by a processor or a computer to perform the functions of the element. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to perform the functions of the element. The instructions may be stored on storage devices that are readable by the processor. Some examples of the storage devices are digital or solid-state memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. 
     Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.