Abstract:
A wireless device comprises a first wireless interface, a second wireless interface, and a power control module. The first wireless interface is configured to communicate with a first access network. The second wireless interface is configured to communicate with a second access network. One of the first and second wireless interfaces comprises a circuit-switched interface. The other one of the first and second wireless interfaces comprises a packet-switched interface. The power control module selectively disables the first wireless interface, provides registration information with respect to the first wireless interface to a remote system, and updates the registration information in the remote system prior to disabling the first wireless interface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/950,468, filed on Jul. 18, 2007. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to multiple network access interfaces and more particularly to power enhancements for multiple network access interfaces. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Referring now to  FIG. 1 , a functional block diagram of a communications system  102  is presented. User equipment (UE)  104  establishes connections with a 3rd generation partnership project (3GPP) network  106  and a non-3GPP network  108 . The non-3GPP network  108  maintains a communications link with the Internet  110 . The 3GPP network  106  may establish links with other user equipment and provide communication between various user equipment, including the user equipment  104 . 
     The 3GPP network  106  may maintain a link with the public switched telephone network (PSTN)  112  and/or other service providers  114 . The other service providers  114  may also maintain 3GPP networks. For example only, the user equipment  104  may include a mobile phone or a laptop with voice capability. The user equipment  104  may transmit and receive packet data to and from the Internet  110  via the non-3GPP network  108 . For example, the user equipment  104  can display web pages from the Internet  110  via the non-3GPP network  108 . The user equipment  104  transmits and receives circuit-switched voice data over the 3GPP network  106 . 
     SUMMARY 
     A wireless device comprises a first wireless interface, a second wireless interface, and a power control module. The first wireless interface is configured to communicate with a first access network. The second wireless interface is configured to communicate with a second access network. One of the first and second wireless interfaces comprises a circuit-switched interface. The other one of the first and second wireless interfaces comprises a packet-switched interface. The power control module selectively disables the first wireless interface, provides registration information with respect to the first wireless interface to a remote system, and updates the registration information in the remote system prior to disabling the first wireless interface. 
     The first wireless interface comprises a circuit-switched cellular interface. The second wireless interface comprises a packet-switched wireless local area network interface. The power control module performs the registration and the updating of the registration information via the first access network. The power control module disables the first wireless interface when the first wireless interface is unused for at least a predetermined period of time. 
     The predetermined period of time is adjustable based on a battery state of the wireless device. The power control module updates the registration information by replacing information corresponding to the first wireless interface with information corresponding to the second wireless interface. The power control module periodically enables the first wireless interface to maintain communication with the first access network. The power control module enables the first wireless interface when data for the first wireless interface is received over the second wireless interface. 
     The power control module provides registration information with respect to the second wireless interface to the remote system after communication between the second wireless interface and the second access network is established. The updating of the registration information causes the remote system to forward data destined for the first wireless interface to the second wireless interface. The power control module cancels the forwarding in the remote system when the power control module re-enables the first wireless interface. 
     A communication controller comprises a power control module configured to control a first wireless control module and a second wireless control module. The first and second wireless control modules are configured to communicate with a circuit-switched interface and a packet-switched interface respectively. The power control module is further configured to forward respective registration information associated with the circuit-switched interface and the packet-switched interface to a remote system. The circuit-switched interface and the packet-switched interface are used to communicate with a first access network and a second access network respectively. The power control module controls the first wireless control module to selectively disable the circuit-switched interface based on a level of communication activities between the first access network and the circuit-switched interface. When the circuit-switched interface is disabled, data destined for the circuit-switched interface is forwarded to the packet-switched interface. 
     The power control module is further configured to update the registration information for the circuit-switched interface in the remote system prior to the power control module disabling the circuit-switched interface via the first wireless control module. The registration information for the circuit-switched interface is updated with the registration information for the packet-switched interface. The power control module is further configured to perform the forwarding and the updating of the registration information with respect to the circuit-switched interface via the first access network. 
     The updating of the registration information with respect to the circuit-switched interface causes the remote system to forward data destined for the circuit-switched interface to the packet-switched interface. The power control module is further configured to cancel the forwarding in the remote system when the circuit-switched interface is re-enabled. The power control module is further configured to disable the circuit-switched interface via the first wireless control module when the level of communication activities is determined to be below a predetermined limit. The predetermined limit is adjustable based on a power state of a wireless device associated with the communication controller. 
     The power control module periodically enables the circuit-switched interface via the first wireless control module to maintain communication with the first access network. When the circuit-switched interface is in a disabled state, the power control module enables the circuit-switched interface via the first wireless control module when it is determined that data for the circuit-switched interface is received over the packet-switched interface. A wireless device incorporates the communication controller. 
     A wireless device comprises first wireless interface means, second wireless interface means, and power control means. The first wireless interface means is for communicating with a first access network. The second wireless interface means is for communicating with a second access network. One of the first and second wireless interfaces comprises a circuit-switched interface. The other one of the first and second wireless interfaces comprises a packet-switched interface. The power control means is for selectively disabling the first wireless interface means, for providing registration information with respect to the first wireless interface means to a remote system, and for updating the registration information in the remote system prior to disabling the first wireless interface means. 
     The first wireless interface means comprises a circuit-switched cellular interface. The second wireless interface means comprises a packet-switched wireless local area network interface. The power control means performs the registration and the updating of the registration information via the first access network. The power control means disables the first wireless interface means when the first wireless interface means is unused for at least a predetermined period of time. The predetermined period of time is adjustable based on a battery state of the wireless device. 
     The power control means updates the registration information by replacing information corresponding to the first wireless interface means with information corresponding to the second wireless interface means. The power control means periodically enables the first wireless interface means to maintain communication with the first access network. The power control means enables the first wireless interface means when data for the first wireless interface means is received over the second wireless interface means. 
     The power control means provides registration information with respect to the second wireless interface means to the remote system after communication between the second wireless interface means and the second access network is established. The updating of the registration information causes the remote system to forward data destined for the first wireless interface means to the second wireless interface means. The power control means cancels the forwarding in the remote system when the power control means re-enables the first wireless interface means. 
     A communication controller comprises power control means for controlling a first wireless control module and a second wireless control module. The first and second wireless control modules are configured to communicate with a circuit-switched interface and a packet-switched interface, respectively. The power control means is also for forwarding respective registration information associated with the circuit-switched interface and the packet-switched interface to a remote system. The circuit-switched interface and the packet-switched interface are used to communicate with a first access network and a second access network respectively. The power control means controls the first wireless control module to selectively disable the circuit-switched interface based on a level of communication activities between the first access network and the circuit-switched interface. When the circuit-switched interface is disabled, data destined for the circuit-switched interface is forwarded to the packet-switched interface. 
     The power control means is further configured to update the registration information for the circuit-switched interface in the remote system prior to the power control means disabling the circuit-switched interface via the first wireless control module. The registration information for the circuit-switched interface is updated with the registration information for the packet-switched interface. The power control means is further configured to perform the forwarding and the updating of the registration information with respect to the circuit-switched interface via the first access network. 
     The updating of the registration information with respect to the circuit-switched interface causes the remote system to forward data destined for the circuit-switched interface to the packet-switched interface. The power control means is further configured to cancel the forwarding in the remote system when the circuit-switched interface is re-enabled. The power control means is further configured to disable the circuit-switched interface via the first wireless control module when the level of communication activities is determined to be below a predetermined limit. The predetermined limit is adjustable based on a power state of a wireless device associated with the communication controller. 
     The power control means periodically enables the circuit-switched interface via the first wireless control module to maintain communication with the first access network. When the circuit-switched interface is in a disabled state, the power control means enables the circuit-switched interface via the first wireless control module when it is determined that data for the circuit-switched interface is received over the packet-switched interface. A wireless device incorporates the communication controller. 
     A method comprises selectively establishing wireless communication between a first wireless interface and a first access network; selectively establishing wireless communication between a second wireless interface and a second access network; providing registration information with respect to the first wireless interface to a remote system; selectively disabling the first wireless interface; and updating the registration information in the remote system prior to disabling the first wireless interface. One of the first and second wireless interfaces comprises a circuit-switched interface. The other one of the first and second wireless interfaces comprises a packet-switched interface 
     The first wireless interface comprises a circuit-switched cellular interface. The second wireless interface comprises a packet-switched wireless local area network interface. The method further comprises performing the providing and the updating of the registration information via the first access network. The method further comprises disabling the first wireless interface when the first wireless interface is unused for at least a predetermined period of time. The predetermined period of time is adjustable based on a battery state. 
     The method further comprises updating the registration information by replacing information corresponding to the first wireless interface with information corresponding to the second wireless interface. The method further comprises periodically enabling the first wireless interface to maintain communication with the first access network. The method further comprises enabling the first wireless interface when data for the first wireless interface is received over the second wireless interface. 
     The method further comprises providing registration information with respect to the second wireless interface to the remote system after communication between the second wireless interface and the second access network is established. The updating of the registration information causes the remote system to forward data destined for the first wireless interface to the second wireless interface. The method further comprises cancelling the forwarding in the remote system when the first wireless interface is re-enabled. 
     A method comprises controlling a first wireless control module and a second wireless control module, the first and second wireless control modules configured to communicate with a circuit-switched interface and a packet-switched interface respectively. The circuit-switched interface and the packet-switched interface are used to communicate with a first access network and a second access network respectively. The method further comprises forwarding respective registration information associated with the circuit-switched interface and the packet-switched interface to a remote system; controlling the first wireless control module to selectively disable the circuit-switched interface based on a level of communication activities between the first access network and the circuit-switched interface; and causing data destined for the circuit-switched interface to be forwarded to the packet-switched interface when the circuit-switched interface is disabled. 
     The method further comprises updating the registration information for the circuit-switched interface in the remote system prior to disabling the circuit-switched interface via the first wireless control module. The registration information for the circuit-switched interface is updated with the registration information for the packet-switched interface. The method further comprises performing the forwarding and the updating of the registration information with respect to the circuit-switched interface via the first access network. 
     The updating of the registration information with respect to the circuit-switched interface causes the remote system to forward data destined for the circuit-switched interface to the packet-switched interface. The method further comprises cancelling the forwarding in the remote system when the circuit-switched interface is re-enabled. The method further comprises disabling the circuit-switched interface via the first wireless control module when the level of communication activities is determined to be below a predetermined limit. 
     The predetermined limit is adjustable based on a power state of a battery. The method further comprises periodically enabling the circuit-switched interface via the first wireless control module to maintain communication with the first access network. The method further comprises, when the circuit-switched interface is in a disabled state, enabling the circuit-switched interface via the first wireless control module when it is determined that data for the circuit-switched interface is received over the packet-switched interface. 
     A computer program stored on a computer-readable medium for use by a processor comprises selectively establishing wireless communication between a first wireless interface and a first access network; selectively establishing wireless communication between a second wireless interface and a second access network; providing registration information with respect to the first wireless interface to a remote system; selectively disabling the first wireless interface; and updating the registration information in the remote system prior to disabling the first wireless interface. One of the first and second wireless interfaces comprises a circuit-switched interface. The other one of the first and second wireless interfaces comprises a packet-switched interface 
     The first wireless interface comprises a circuit-switched cellular interface. The second wireless interface comprises a packet-switched wireless local area network interface. The computer program further comprises performing the providing and the updating of the registration information via the first access network. The computer program further comprises disabling the first wireless interface when the first wireless interface is unused for at least a predetermined period of time. The predetermined period of time is adjustable based on a battery state. 
     The computer program further comprises updating the registration information by replacing information corresponding to the first wireless interface with information corresponding to the second wireless interface. The computer program further comprises periodically enabling the first wireless interface to maintain communication with the first access network. The computer program further comprises enabling the first wireless interface when data for the first wireless interface is received over the second wireless interface. 
     The computer program further comprises providing registration information with respect to the second wireless interface to the remote system after communication between the second wireless interface and the second access network is established. The updating of the registration information causes the remote system to forward data destined for the first wireless interface to the second wireless interface. The computer program further comprises cancelling the forwarding in the remote system when the first wireless interface is re-enabled. 
     A computer program stored on a computer-readable medium for use by a processor comprises controlling a first wireless control module and a second wireless control module, the first and second wireless control modules configured to communicate with a circuit-switched interface and a packet-switched interface respectively. The circuit-switched interface and the packet-switched interface are used to communicate with a first access network and a second access network respectively. The computer program further comprises forwarding respective registration information associated with the circuit-switched interface and the packet-switched interface to a remote system; controlling the first wireless control module to selectively disable the circuit-switched interface based on a level of communication activities between the first access network and the circuit-switched interface; and causing data destined for the circuit-switched interface to be forwarded to the packet-switched interface when the circuit-switched interface is disabled. 
     The computer program further comprises updating the registration information for the circuit-switched interface in the remote system prior to disabling the circuit-switched interface via the first wireless control module. The registration information for the circuit-switched interface is updated with the registration information for the packet-switched interface. The computer program further comprises performing the forwarding and the updating of the registration information with respect to the circuit-switched interface via the first access network. 
     The updating of the registration information with respect to the circuit-switched interface causes the remote system to forward data destined for the circuit-switched interface to the packet-switched interface. The computer program further comprises cancelling the forwarding in the remote system when the circuit-switched interface is re-enabled. The computer program further comprises disabling the circuit-switched interface via the first wireless control module when the level of communication activities is determined to be below a predetermined limit. 
     The predetermined limit is adjustable based on a power state of a battery. The computer program further comprises periodically enabling the circuit-switched interface via the first wireless control module to maintain communication with the first access network. The computer program further comprises, when the circuit-switched interface is in a disabled state, enabling the circuit-switched interface via the first wireless control module when it is determined that data for the circuit-switched interface is received over the packet-switched interface. 
     In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a computer readable medium such as but not limited to memory, nonvolatile data storage, and/or other suitable tangible storage mediums. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of a communications system according to the prior art; 
         FIG. 2  is a functional block diagram of an exemplary communications system according to the principles of the present disclosure; 
         FIG. 3  is a functional block diagram of an exemplary implementation of an internet protocol multimedia system according to the principles of the present disclosure; 
         FIG. 4  is a functional block diagram of an exemplary implementation of the user equipment according to the principles of the present disclosure; 
         FIGS. 5 and 6  are flowcharts depicting exemplary steps performed by the communications system of  FIG. 2  according to the principles of the present disclosure; and 
         FIG. 7  is a functional block diagram of a mobile phone according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 2 , a functional block diagram of an exemplary communications system  202  is presented. User equipment  204  includes a control module  206 , a circuit-switched interface  208 , and a packet-switched interface  210 . The circuit-switched interface  208  establishes a link with a circuit-switched network  220 . The circuit-switched network  220  may include, for example, a cellular network, a 3GPP network, and/or a Global System for Mobile communications (GSM) network. 
     The circuit-switched network  220  may include a mobile switching center (MSC)  222 , which communicates with the circuit-switched interface  208 . The MSC  222  may maintain registration information for user equipment associated with the circuit-switched network  220 , including the user equipment  204 . The MSC  222  may route calls between users associated with the circuit-switched network  220 . 
     For some or all associated user equipment, the MSC  222  may forward call requests to and receive instructions from an Internet protocol (IP) multimedia system (IMS) gateway  224 . The IMS gateway  224  communicates with an IMS  230 . The IMS  230  may coordinate calls and provision of other services over the circuit-switched network  220 . 
     In various implementations, the IMS gateway  224  may convert call set-up requests from the MSC  222  within the circuit-switched network  220  into IMS requests that are forwarded to the IMS  230 . In this way, the IMS  230  can coordinate some or all calls using the circuit-switched network  220 . 
     The IMS  230  may also service calls from the PSTN  112  and/or other IMS providers  240 . In addition, the IMS  230  may service calls via packet-switched networks, such as by using the Voice over Internet Protocol (VoIP). For example, VoIP communications may include calls from dedicated IP phones and calls from software-based phones running on computers, including applications such as Skype. The IMS  230  may communicate with the Internet  110  and with a packet-switched network  250 . In various implementations, the packet-switched network  250  and the Internet  110  may overlap, meaning that various resources within the packet-switched network  250  are part of the Internet  110 . 
     The packet-switched interface  210  of the user equipment  204  may establish a wireless link with an access point  252  of the packet-switched network  250 . For example only, this wireless link may include wireless local area networks (such as Wi-Fi or IEEE 802.11) and/or wireless metro area networks (such as WiMAX or IEEE 802.16). 
     For example only, the user equipment  204  may normally use the circuit-switched network  220  for voice traffic and the packet-switched network  250  for data traffic. In order to reduce power consumption of the user equipment  204 , the circuit-switched interface  208  and/or the packet-switched interface  210  may be powered down. This may be especially important when the user equipment  204  is operating on battery power. 
     For example only, if no call has been made over the circuit-switched interface  208  for a predetermined period of time, the circuit-switched interface  208  may be powered down. Depending upon the requirements of the wireless link between the circuit-switched interface  208  and the circuit-switched network  220 , the circuit-switched interface  208  may need to be periodically powered on in order to preserve the registration of the user equipment  204  with the MSC  222 . 
     In addition, the circuit-switched interface  208  may need to be powered on to accommodate changes in position of the user equipment  204 . For example, as the signal from one base station gets weaker and the signal from another base station gets stronger, the circuit-switched interface  208  may cooperate in handing off the wireless link from one base station to the other. 
     When one of the interfaces  208  and  210  is powered down, registration information in the IMS  230  can be updated so that calls and/or other information can be provided to the interface that is still powered on. For example, the circuit-switched interface  208  may register with the IMS  230 . Before the circuit-switched interface  208  is powered down, registration with the IMS  230  can be updated to instead direct calls to the packet-switched interface  210 . 
     Alternatively, both the circuit-switched interface  208  and the packet-switched interface  210  may be registered with the IMS  230 . Then, before the circuit-switched interface  208  is powered down, call forwarding may be set up in the IMS  230  to forward the circuit-switched calls to the packet-switched network  250 . 
     When the circuit-switched interface  208  is powered down and a circuit-switched call is received over the packet-switched interface  210 , the control module  206  may power up the circuit-switched interface  208 . The call may then be forwarded from the IMS  230  to the circuit-switched interface  208 . Alternatively, once the circuit-switched interface  208  is powered up, the circuit-switched interface  208  may initiate a call to the IMS  230 , at which point the two calls are linked together. In order to allow this alternative option, the IMS  230  may transmit its network address to the packet-switched interface  210  along with the forwarded circuit-switched calls. 
     In either implementation, calls are still successfully routed and with minimum delay, even while reducing power consumption. In brief,  FIG. 3  depicts a functional block diagram of the IMS  230  and  FIG. 4  depicts a functional block diagram of the user equipment  204 .  FIGS. 5 and 6  depict exemplary operation of the communications system  202 . 
     Referring back to  FIG. 3 , a functional block diagram of an exemplary implementation of the IMS  230  is depicted. The IMS  230  includes a routing module  302 , a registration module  304 , a call session control module  306 , and a PSTN gateway  308 . The routing module  302  routes calls and other information between the circuit-switched network  220 , the packet-switched network  250 , the Internet  110 , the other IMS providers  240 , and the PSTN gateway  308 . 
     Additionally, the routing module  302  forwards IMS messages to the registration module  304  and the call session control module  306 . For example, registration requests from the circuit-switched network  220  and the packet-switched network  250  may be forwarded to the registration module  304 . The registration module  304  may include memory that stores information regarding registered devices. 
     As described above, the user equipment  204  of  FIG. 2  may be registered one or more times with the registration module  304 . For example only, the circuit-switched interface  208  may be registered with the registration module  304 , or both the circuit-switched interface  208  and the packet-switched interface  210  may be registered with the registration module  304 . 
     The call session control module  306  may coordinate receiving and forwarding calls based on information from the registration module  304 . For example only, the call session control module  306  may receive call requests from the circuit-switched network  220 . The call session control module  306  may configure the routing module  302  to route requested calls between various sources and the user equipment  204  of  FIG. 2 . 
     Alternatively, the call session control module  306  may send a control message to the circuit-switched network  220 . The circuit-switched network  220  may then perform routing of the call based upon the control message. The registration module  304  may also include information such as call forwarding information. For example, as described above, call forwarding may be established from the registration for the circuit-switched interface  208  to the registration for the packet-switched interface  210 . 
     Referring now to  FIG. 4 , a functional block diagram of an exemplary implementation of the user equipment  204  is presented. The circuit-switched interface  208  may transmit and receive data using a first antenna  402 . The packet-switched interface  210  may transmit and receive data using a second antenna  404 . In various implementations, the first and second antennas  402  and  404  may be combined. Communication may then be multiplexed between the circuit-switched interface  208  and the packet-switched interface  210 . 
     The circuit-switched interface  208  is controlled by a circuit-switched controller  410 . The packet-switched interface  210  is controlled by a packet-switched controller  412 . A power control module  414  selectively transmits a powerdown signal to the circuit-switched controller  410  and/or the packet-switched controller  412 . The circuit-switched controller  410  and the packet-switched controller  412  power down the circuit-switched interface  208  and the packet-switched interface  210  based upon the respective powerdown signals from the power control module  414 . 
     The power control module  414  may track the usage of the circuit-switched controller  410  and the packet-switched controller  412 . If a call has not been placed through the circuit-switched controller  410  for a predetermined period of time, the power control module  414  may transmit a powerdown signal to the circuit-switched controller  410 . The power control module  414  may also transmit a powerdown signal to the packet-switched controller  412  when no packets have been passed through the packet-switched interface  210 . During normal operation, the power control module  414  may avoid transmitting the powerdown signal to both the circuit-switched and packet-switched controllers  410  and  412 . 
     The control module  206  may include an IMS stack  420 , a circuit-switched stack  422 , and an IP stack  424 . The IMS stack  420 , the circuit-switched stack  422 , and the IP stack  424  may communicate with the circuit-switched controller  410  and the packet-switched controller  412  via a data routing module  430 . Before the power control module  414  shuts down the circuit-switched controller  410 , the power control module  414  may instruct the IMS stack  420  to send a message to the IMS  230 . As described above, this message may change the registration of the user equipment  204  or may establish call forwarding from the circuit-switched registration to the packet-switched registration. 
     The circuit-switched stack  422  may establish a link with the circuit-switched network  220  of  FIG. 2 . The circuit-switched stack  422  may periodically instruct the power control module  414  to power up the circuit-switched controller  410  to maintain the link with the circuit-switched network  220 . The IP stack  424  may transmit and receive packet data via the packet-switched interface  210 . Web browsing and other application-layer functionality (not shown) of the user equipment  204  may use the IP stack  424  to provide these services. A user interface application (not shown) may communicate with the IMS stack  420  and the circuit-switched stack  422  to establish calls requested by a user of the user equipment  204  and to receive incoming calls. 
     Referring now to  FIG. 5 , a flowchart depicts exemplary steps performed by the communications system  202  of  FIG. 2 . Control begins in step  502  when the user equipment  204  is powered on or otherwise activated. In step  502 , the user equipment  204  connects to the packet-switched network  240  for the transmission or reception of data traffic. Control continues in step  504 , where the user equipment  204  registers with the circuit-switched network  220 . 
     Control continues in step  506 , where the user equipment  204  registers with the IMS  230 , which will control calls over the circuit-switched network  220 . For example only, the registration in step  504  may be with a mobile switching center of a GSM network, while the registration in step  506  may be with an IMS that will provide instructions to the mobile switching center  222 . 
     Control continues in step  508 , where control determines whether a call has been received for the user equipment  204  by the IMS  230 . If so, control transfers to step  510 ; otherwise, control transfers to step  512 . In step  510 , the IMS  230  forwards the call based on the registration information. For example, the registration information may indicate that calls should be sent to the circuit-switched interface  208  of the user equipment  204 . Alternatively, the registration may have been amended to transmit calls over the packet-switched interface  210 . Control then continues in step  514 . 
     In step  512 , control determines whether a call has been received for the user equipment  204  over the circuit-switched network  220 . If so, control transfers to step  516 ; otherwise, control transfers to step  518 . In step  516 , the circuit-switched network  220  translates the received call into an IMS request. The IMS request is forwarded to the IMS  230  and control continues in step  510 . 
     In step  518 , control determines whether an outgoing call is requested by the user equipment  204 . If so, control transfers to step  520 ; otherwise, control transfers to step  522 . In step  522 , control determines whether the circuit-switched interface  208  of the user equipment  204  is unused. If so, control transfers to step  524 ; otherwise, control returns to step  508 . 
     The determination of whether the circuit-switched interface  208  is unused may be based on the amount of time since a data transfer, such as a call, was last performed over the circuit-switched interface  208 . If the amount of time is greater than a predetermined limit, the circuit-switched interface  208  may be considered unused. This predetermined limit may be adjusted as battery power available to the user equipment  204  decreases. 
     In step  524 , the IMS registration is changed from the circuit-switched network  220  to the packet-switched network  240 . This means that the IMS  230  will forward its calls to the packet-switched network  250  in step  510  instead of the circuit-switched network  220 . For example, the IP address for the circuit-switched interface  208  may be replaced by the IP address for the packet-switched interface  210 . Control continues in step  526 , where the circuit-switched interface  208  of the user equipment  204  is powered down. Control then returns to step  508 . 
     In step  514 , control determines whether the user equipment  204  has received a call on the packet-switched interface  210 . If so, this is an indication that the circuit-switched interface  208  is powered down, and control continues in step  528 . Otherwise, the call is handled normally by the circuit-switched interface  208  and control returns to step  508 . In step  528 , the user equipment  204  powers up the circuit-switched interface  208  and control continues in step  530 . In step  530 , the IMS registration is changed back to a circuit-switched network  220 . 
     Control continues in step  532 , where the IMS  230  transfers the call to the circuit-switched network  220 . For example only, two ways of transferring the call to the circuit-switched network  220  have been described. The IMS  230  may route the call over the circuit-switched network  220  to the circuit-switched interface  208 . Alternatively, the circuit-switched interface  208  may initiate a call to the IMS  230  over the circuit-switched network  220 . The two calls are then joined by the IMS. Once the circuit-switched interface  208  has handled the call, control returns to step  508 . 
     In step  520 , when an outgoing call is initiated, control determines whether the circuit-switched interface  208  is powered down. If so, control transfers to step  534 ; otherwise, control transfers to step  536 . In step  534 , control powers up the circuit-switched interface  208 . Control then continues in step  538 , where the IMS registration is changed to route calls to the circuit-switched network  220 . Control continues in step  536 , where the user equipment  204  transmits a call request to the circuit-switched network  220 . As described above, the circuit-switched network  220  translates this request into an IMS request, which the IMS  230  uses to establish a call with the user equipment  204 . Control then returns to step  508 . 
     Referring now to  FIG. 6 , a flowchart depicts alternative exemplary operation of the communications system  202  of  FIG. 2 . Steps  506 ,  524 ,  530 , and  538  have been replaced with steps  606 ,  624 ,  630 , and  638 , respectively. In step  606 , the user equipment  204  registers both the circuit-switched interface  208  and the packet-switched interface  210  with the IMS  230 . In step  624 , prior to the circuit-switched interface  208  being powered down, the IMS  230  is instructed to forward calls originally directed to the circuit-switched network  220  to the packet-switched network  250 . In steps  630  and  638 , that call forwarding is cancelled. 
     Referring now to  FIG. 7 , the teachings of the disclosure can be implemented in a network interface  768  of a mobile phone  758 . The mobile phone  758  includes a phone control module  760 , a power supply  762 , memory  764 , a storage device  766 , and a network interface  767 . The mobile phone  758  may include the network interface  768 , a microphone  770 , an audio output  772  such as a speaker and/or output jack, a display  774 , and a user input device  776  such as a keypad and/or pointing device. The network interface  768  may include multiple physical layer interfaces, including cellular and wireless local area network. Because the network interface  768  includes a wireless interface, one or more antennas (not shown) may be included. 
     The phone control module  760  may receive input signals from the network interface  767 , the network interface  768 , the microphone  770 , and/or the user input device  776 . The phone control module  760  may process signals, including encoding, decoding, filtering, and/or formatting, and generate output signals. The output signals may be communicated to one or more of memory  764 , the storage device  766 , the network interface  767 , the network interface  768 , and the audio output  772 . 
     Memory  764  may include random access memory (RAM) and/or nonvolatile memory. Nonvolatile memory may include any suitable type of semiconductor or solid-state memory, such as flash memory (including NAND and NOR flash memory), phase change memory, magnetic RAM, and multi-state memory, in which each memory cell has more than two states. The storage device  766  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The power supply  762  provides power to the components of the mobile phone  758 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.