PATENT DOCUMENT

Publication Number: US-9538430-B2
Application Number: US-201414292733-A
Country: US
Kind Code: B2

Title: System and method for network selection to transfer call session

Abstract:
A method performed by stations to transfer call sessions between different access networks. The methods include transmitting, by a first station to a second station, an invite to join a voice call on a first radio access network (RAN), receiving, by the second station, the invite, generating, by the second station, a response to the invite, determining, by the second station, that the response cannot be successfully transmitted to the first station, associating, by the second station, with a second RAN, generating, by the second station, a message indicating the second station has associated with the second RAN, transmitting, by the second station, the message to the first station, retransmitting, by the first station, the invite to join the voice call, receiving, by the second station, the invite on the second RAN and setting up the voice call between the first station and the second station.

Claims:
What is claimed is: 
     
       1. A method, comprising:
 transmitting, by a first station to a second station, an invite to join a voice call on a first radio access network (RAN); 
 receiving, by the second station, the invite; 
 generating, by the second station, a response to the invite; 
 determining, by the second station, that the response cannot be successfully transmitted to the first station; 
 associating, by the second station, with a second RAN; 
 generating, by the second station, a message, for the first station, indicating the second station has associated with the second RAN; 
 transmitting, by the second station, the message to the first station; 
 determining whether the first station is to remain connected to the first RAN to perform the voice call or connect to the second RAN to perform the voice call; 
 connecting to the second RAN when it is determined the voice call is to be performed over the second RAN, wherein the voice call is performed as a VoLTE call by the first station when it is determined the first station is to remain connected to the first RAN; 
 retransmitting, by the first station, the invite to join the voice call; 
 receiving, by the second station, the invite on the second RAN; and 
 setting up the voice call between the first station and the second station. 
 
     
     
       2. The method of  claim 1 , wherein the first station participates in the voice call using one of the first RAN or the second RAN and the second station participates in the voice call using the second RAN. 
     
     
       3. The method of  claim 1 , wherein the first RAN is one of a Long Term Evolution radio access network (LTE-RAN) or a WiFi network. 
     
     
       4. The method of  claim 1 , wherein the second RAN performs voice calls as circuit switched calls. 
     
     
       5. The method of  claim 1 , wherein information required to join the voice call comprises a call setup procedure. 
     
     
       6. A method comprising:
 at a first station:
 receiving an invite for a setup procedure of a voice call from a second station, the first station being connected to a Long Term Evolution radio access network(LTE-RAN), the first station configured to perform the voice call using Voice over LTE (VoLTE); 
 determining the first station is incapable of transmitting a response to the invite to the second station using the LTE-RAN, wherein the determining includes:
 initiating a preset timer upon receiving the invite; and 
 determining the first station is incapable of transmitting a response when the preset timer lapses without a successful transmission of the response; 
 
 connecting the first station to a legacy RAN, wherein the legacy RAN performs voice calls as circuit switched calls; 
 generating a switch message upon connecting to the legacy RAN, the switch message including an indication the first station has associated with the legacy RAN; 
 transmitting the switch message to the second station; 
 receiving the invite for a setup procedure of a voice call from the second station, wherein the setup procedure is performed consistent with the legacy RAN; and 
 performing the voice call with the second station via the legacy RAN. 
 
 
     
     
       7. The method of  claim 6 , wherein the switch message includes an indication that the first station has switched from the LTE-RAN to the legacy RAN. 
     
     
       8. The method of  claim 6 , wherein the legacy RAN is one of a 2G RAN and a 3G RAN. 
     
     
       9. The method of  claim 6 , wherein the switch message is transmitted via a Short messaging Service (SMS) of the legacy RAN. 
     
     
       10. A method comprising:
 at a first station:
 transmitting an invite for a setup procedure of a voice call to a second station, the first station being connected to a Long Term Evolution radio access network(LTE-RAN), the first station configured to perform the voice call using Voice over LTE (VoLTE); 
 receiving a switch message from the second station, the switch message including an indication the second station has associated with a legacy RAN, wherein the legacy RAN performs voice calls as circuit switched calls; 
 determining whether the first station is to remain connected to the LTE-RAN to perform the voice call or connect to the legacy RAN to perform the voice call; 
 connecting to the legacy RAN when it is determined the voice call is to be performed over the legacy RAN, wherein the voice call is performed as a VoLTE call by the first station when it is determined the first station is to remain connected to the LTE-RAN; 
 re-transmitting the invite to the second station; 
 performing the setup procedure for the voice call; and 
 performing the voice call with the second station. 
 
 
     
     
       11. The method of  claim 10 , wherein the invite is a Session Initiation Protocol (SIP) invite when the first station is connected to the LTE-RAN. 
     
     
       12. The method of  claim 10 , wherein the re-transmitting the invite is performed without user interaction. 
     
     
       13. The method of  claim 10 , wherein the legacy network is one of a 2G network and a 3G network. 
     
     
       14. The method of  claim 10 , wherein the switch message further indicates that the second station has received the invite. 
     
     
       15. The method of  claim 10 , wherein the re-transmitting of the invite is performed without paging the second station on the legacy RAN. 
     
     
       16. The method of  claim 10 , wherein the receiving the switch message from the second station indicates that the voice call has not failed to establish.

Description:
BACKGROUND INFORMATION 
     A first station may be configured to communicate wirelessly with a second station. Specifically, the first station may transmit data to and receive data from the second station through a wireless communications network. The first and second stations may use the network to communicate using a variety of different applications. For example, the first station may be a mobile origination (MO) station while the second station may be a mobile terminating (MT) station for a voice call. The voice call may be performed in a variety of different manners. For example, when the MO or MT station is connected to a 2G or 3G network, the voice call may be performed using a circuit switched voice call. In another example, when the MO or MT station is connected to a Long Term Evolution (LTE) network, the voice call may be performed using a Voice over LTE (VoLTE) call. 
     When the VoLTE call is performed, the MO and MT stations may perform an initial setup procedure. In the initial setup procedure, the MO station may transmit an invitation to the MT station to participate in the VoLTE call. As a VoLTE call, the invitation is transmitted over the LTE network. The MT station may receive the invitation and provide a response, also over the LTE network. However, there may be a variety of reasons that prevent the MT station from responding to the invitation. For example, the MT station may be aware that there is an incoming call from the MO station but cannot provide the response to the invitation over the LTE network. In such a scenario, the call may fail to establish which is a very poor end user experience, particularly since the user of the MT station may have received the indication and manually responded to the invitation (e.g., a prompt). Furthermore, additional attempts for the VoLTE call may continue to fail until the MT station is capable of transmitting the response over the LTE network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary network arrangement for stations to perform a voice call. 
         FIG. 2  shows an exemplary station configured to perform the voice call. 
         FIG. 3  shows a first exemplary signaling diagram to perform a network selection to transfer a call session from a first network to a second network. 
         FIG. 4  shows a second exemplary signaling diagram to perform a network selection to transfer a call session from a first network to a second network. 
         FIG. 5  shows a first exemplary method for performing a voice call by a mobile terminating station over a first or second network. 
         FIG. 6  shows a second exemplary method for performing a voice call by a mobile originating station over a first or second network. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments describe a method that is performed by two stations. The method includes transmitting, by a first station to a second station, an invite to join a voice call on a first radio access network (RAN), receiving, by the second station, the invite, generating, by the second station, a response to the invite, determining, by the second station, that the response cannot be successfully transmitted to the first station, associating, by the second station, with a second RAN, generating, by the second station, a message indicating the second station has associated with the second RAN, transmitting, by the second station, the message to the first station, retransmitting, by the first station, the invite to join the voice call, receiving, by the second station, the invite on the second RAN and setting up the voice call between the first station and the second station. 
     The exemplary embodiments further describe a method performed by a first station, the method including receiving an invite for a setup procedure of a voice call from a second station, the first station being connected to a Long Term Evolution radio access network(LTE-RAN), the first station configured to perform the voice call using Voice over LTE (VoLTE), determining the first station is incapable of transmitting a response to the invite to the second station using the LTE-RAN, connecting the first station to a legacy RAN, wherein the legacy RAN performs voice calls as circuit switched calls, generating a switch message upon connecting to the legacy RAN, the switch message including an indication the first station has associated with the legacy RAN, transmitting the switch message to the second station, receiving the invite for a setup procedure of a voice call from the second station, wherein the setup procedure is performed consistent with the legacy RAN, and performing the voice call with the second station via the legacy RAN. 
     The exemplary embodiments also describe a method performed by a first station, the method including transmitting an invite for a setup procedure of a voice call to a second station, the first station being connected to a Long Term Evolution radio access network(LTE-RAN), the first station configured to perform the voice call using Voice over LTE (VoLTE), receiving a switch message from the second station, the switch message including an indication the second station has associated with a legacy RAN, wherein the legacy RAN performs voice calls as circuit switched calls, re-transmitting the invite to the second station, performing the setup procedure for the voice call and performing the voice call with the second station. 
     The exemplary embodiments may be further understood with reference to the following description and the related appended drawings, wherein like elements are provided with the same reference numerals. The exemplary embodiments are related to a system and method for network selection to transfer a call session. Specifically, the transfer relates to a setup procedure for a voice call for establishing the voice call. More specifically, a mobile originating (MO) station may invite a mobile terminating (MT) station to the voice call in which both MO and MT stations are connected to a Long Term Evolution radio access network (LTE-RAN). The MO and MT stations may perform the voice call using a Voice over LTE (VoLTE) call session. As such, data packets are transmitted between the MO and MT stations over the LTE-RAN during a setup procedure to establish the voice call. If the MT station is incapable of transmitting a response to an invitation for the voice call over the LTE-RAN, the MT station may provide a message to the MO station indicating that a different network is being selected that may be more reliable such as a legacy radio access network (RAN) (e.g., 2G network, 3G network, etc.). 
       FIG. 1  shows an exemplary network arrangement  100  for a MO station  105  to perform a voice call with a MT station  110 . Specifically, the MO station  105  may wirelessly communicate with the MT station  110  to perform the voice call. The network arrangement  100  may include an LTE-RAN  115 , a legacy RAN  120  and a cellular core network  125 . According to the exemplary embodiments, the MO station  105  and the MT station  110  may utilize both the LTE-RAN  115  and the legacy RAN  120 . As discussed above, when related to voice calls, the LTE-RAN  115  may be a substantially all-IP based network standard while the legacy RAN  120  may utilize a circuit switched protocol through a dedicated communications channel. While the exemplary embodiments are described with reference to an LTE-RAN and a legacy RAN (such as a 2G or 3G network), it is not required that the networks be these precise type of networks. For example, the first network could be any type of packet switched or IP based network and the legacy RAN may be any type of circuit switched network. For example, either network  115 ,  120 , may be a WiFi network such as defined under IEEE 802.11 a/b/g/n/ac. The WiFi network  105  may further represent any type of WiFi network such as a personal WiFi network, a home WiFi network, an enterprise WiFi network, a HotSpot, etc. In some cases, WiFi networks may be referred to as Wireless local area networks (WLANs). The networks  115 ,  120  may also include any network that is referred to as a WLAN. Thus, when it is described in the exemplary embodiments that the MO station  105  and the MT station  115  are connected to the LTE-RAN  115  or legacy RAN  120 , the MO station  105  and MT station  110  may, instead, be connected to a WiFi network. 
     The MO station  105  and the MT station  110  may represent any electronic device that performs the voice call. It may be considered that the MO station  105  and the MT station  110  have the required hardware and software configuration to perform VoLTE calls when connected to the LTE-RAN  115 . A voice call may be established between the MO station  105  and the MT station  110  using a variety of different applications. When the MO or MT station is connected to the legacy RAN  120 , the stations  105 ,  110  may participate in the voice call using a circuit switched voice call. With regard to voice transmissions, the legacy RAN  120  typically utilizes a dedicated communications channel to carry the voice calls, although this is not a requirement. 
     A VoLTE call relates to delivering the voice service as data flows over the LTE-RAN  115 . The VoLTE call may be performed as a substantially all-Internet Protocol (IP) based network standard without requiring the dedicated communications channel used in the legacy networks (e.g., legacy RAN  120 ). Therefore, the information used in the initial setup procedure and all voice information used during the VoLTE call are transmitted as data packets over the LTE-RAN  115 . 
     The VoLTE call may use an IP Multimedia Subsystem (IMS)  130  that is associated with the cellular core network  125  of the provider of the LTE-RAN  115 . The IMS  130  allows for multimedia access using a common IP interface. Using the IMS  130 , connections may be made over different protocols. Specifically, with the IMS  130 , a VoLTE call is able to inter-operate with circuit switched voice networks. For example, if the MO station  105  were connected to the LTE-RAN  115  and initiated a call to the MT station  110  that was connected to the legacy RAN  120 , the IMS  130  is used to interconnect the calls between the different networks. The IP interface of IMS  130  may also allow a VoLTE call to inter-operate with other voice networking technologies even when circuit switched networks are not available. Thus, the MO station  105  may be connected to the LTE-RAN  115 , but the MT station  110  is not required to be connected to the LTE-RAN  115  or vice versa for a voice call to be performed. Thus, when both the MO station  105  and the MT station  110  are connected to the LTE-RAN  115 , the VoLTE call may be performed by both stations  105 ,  110 . When only the MO station  105  is connected to the LTE-RAN  115  (or capable of using both the uplink and downlink transmissions thereof), the MO station  105  may perform the VoLTE call. However, the MT station  110  may not be connected to the LTE-RAN  115  such that the MT station  110  performs the circuit switched voice call. In this manner, the voice call between the MO station  105  and the MT station  110  is still established via the IMS  130 . 
     When establishing the voice call between the MO station  105  and MT station  110 , the legacy RAN  120  may be considered to be more reliable than the LTE-RAN  115  when considering the coverage area that the legacy RAN  120  provides. For example, a station may not have sufficient uplink transmission power to transmit a response to an invitation to a VoLTE call but may have sufficient uplink transmission power to respond to a call from the legacy RAN  120 . However, those skilled in the art will also understand that the LTE-RAN  115  may be preferred over the legacy RAN  120  when considering the potential data transfer rates. 
     If both the MO station  105  and MT station  110  are connected to the LTE-RAN  115  and registered for voice over IMS  130  when connected to the LTE-RAN  115 , both the MO station  105  and MT station  115  may have simultaneous data and voice over the LTE-RAN  115 , thereby providing the stations  105  and  110  with the option to perform a VoLTE call. When both the MO station  105  and MT station  110  are capable of utilizing the LTE-RAN  115 , the VoLTE call may be preferable over the circuit switched voice call for a variety of reasons from the user perspective and the network perspective. In fact, when the station is connected to the LTE-RAN  115 , the station may be configured to always use the VoLTE call to participate in the voice call. However, there may be a variety of scenarios in which the LTE-RAN  115  may not be utilized by one of the stations. For example, the MT station  110  may be incapable of using the uplink transmission in the LTE-RAN  115  during a setup procedure for the VoLTE call, resulting in the voice call failing to establish. In another example, if the station is not registered on the IMS  130 , the station may rely on the LTE-RAN  115  for data transfer and the legacy RAN  120  for voice calls. 
     The exemplary embodiments provide a seamless manner of transferring the call session to the legacy RAN  120  network in order to establish the voice call between the MO station  105  and MT station  110 . Specifically, when the MT station  110  is incapable of responding to an invitation for a VoLTE call, the MT station  110  may provide a switch message to the MO station  105  that indicates that the MT station  110  cannot utilize the LTE-RAN  115 . The switch message may also indicate to the MO station  105  that the MT station  110  intends to utilize the legacy RAN  120  for the voice call. The MO station  105  may perform different operations upon receiving the switch message from the MT station  110  for the voice call to be established. 
       FIG. 2  shows an exemplary station  200  configured to perform the voice call using the VoLTE call or the circuit switched voice call. Specifically, the station  200  may represent an electronic device such as the MO station  105  and the MT station  110 . The station  200  may be any electronic component configured to join a network such as a portable device (e.g., a cellular phone, a smartphone, a tablet, a phablet, a laptop, etc.) or a stationary device (e.g., a desktop computer). The station  200  may include a processor  205 , a memory arrangement  210 , a display device  215 , an input/output (I/O) device  220 , a transceiver  225 , and other components  230  such as a portable power supply, an audio I/O device, etc. 
     The processor  205  may be configured to execute a plurality of applications of the station  200 . The processor  205  may be an applications processor, a baseband processor or a combination thereof. The applications may include a web browser when connected to the LTE-RAN  115  or the legacy RAN  120  via the transceiver  225 . The web browser may represent a data-related application. 
     In another example, the applications may include a call application  235 . The call application  235  may represent a voice-related application that performs the voice call for the station  200 . When the station  200  is the MO station  105 , the call application  235  may generate the invitation for the voice call. When the station  200  is the MT station  110 , the call application  235  may receive the invitation for the voice call. The call application  235  may then generate a response to the invitation. This setup procedure for the voice call may be used to establish the voice call between the MO station  105  and the MT station  110 . When the voice call has been established, the call application  235  may perform the functionalities associated with transmitting and receiving voice information during the voice call. For example, the audio I/O device may receive raw voice from the user and convert the raw voice to data packets which may be transmitted via the transceiver  235  to the network. In a specific example, the voice data packets may be transmitted over the LTE-RAN  115  when the voice call is the VoLTE call. 
     The call application  235  may also determine the type of voice call that is to be performed by the station  200 . For example, when the station  200  is connected to the LTE-RAN  115 , the voice call may be the VoLTE call. In another example, when the station  200  is only connected to the legacy RAN  120 , the voice call may be the circuit switched voice call. It should be noted that the call application  235  may be configured to always perform the VoLTE call when connected to the LTE-RAN  115 . However, as will be described in further detail below, the exemplary embodiments provide a manner of using the legacy RAN  120  even when the station  200  is connected to the LTE-RAN  115 . 
     In a further example and according to the exemplary embodiments, the applications may include a network selection application  240 . As will be described in further detail below, the network selection application  240  may perform the transfer of the call session when the station  200  is experiencing conditions that prevent the voice call from being established. Specifically, when the station  200  (as the MT station  110 ) is incapable of responding to an invitation to the voice call using a VoLTE call, the network selection application  240  may use the legacy RAN  120  to establish the voice call. The network selection application  240  may also generate a switch message to be transmitted to the MO station  105  indicating that the MT station  110  is using the legacy RAN  120 . 
     It should be noted that the call application  235  and the network selection application  240  being an application (e.g., a program) executed by the processor  205  is only exemplary. The applications  235 - 240  may also be represented as a separate incorporated component of the station  200  or may be a modular component coupled to the station  200 . 
     The memory arrangement  210  may be a hardware component configured to store data related to operations performed by the station  200 . For example, the memory arrangement  210  may store a caller database associated with the call application  235 . The caller database may be, for example, a directory of people having associated contact information to be used by the call application  235  in a voice call with a corresponding station of a selected person. The memory arrangement  210  may also store further data such as measured network parameters for the LTE-RAN  115 . The display device  215  may be a hardware component configured to show data to a user while I/O device  220  may be a hardware component configured to receive inputs from the user and output corresponding data. The other components  230  may include a portable power supply (e.g., battery), a data acquisition device, ports to electrically connect the station  200  to other electronic devices, etc. 
       FIG. 3  shows a first exemplary signaling diagram  300  to perform a network selection to transfer a call session from the LTE-RAN  115  to the legacy RAN  120 . Specifically, the signaling diagram  300  relates to a scenario where the MO station  105  remains on the LTE-RAN  115  after receiving a switch message form the MT station  110  indicating the MT station  110  is switching to the legacy RAN  120 . 
     As illustrated, the MO station  105  may transmit a session invite  305  to the MT station  110 . Specifically when the voice call is performed by the MO station  105  as a VoLTE call (e.g., the MO station  105  is connected to the LTE-RAN  115 ), the session invite  305  may be transmitted to a component of the LTE-RAN  115  (e.g., an enhanced Node B (eNB)). When the call is a VoLTE call, the session invite  310  may be a session initiation protocol (SIP) invite. Since both the MO station  105  and the MT station  110  are connected to the LTE-RAN  115 , the LTE-RAN  115  will then forward the session invite  310  to the MT station  110 . Those skilled in the art will understand that there may be additional signaling within the LTE-RAN  115  to ensure that the session invite  310  is transmitted to the MT station  110 . However, the signaling diagram  300  is only meant to be a simplified overview of the signaling process and does not show each and every signal that is transmitted to complete the voice call. 
     The MT station  110  may be connected to and capable of decoding the downlink of the LTE-RAN  115  such that the session invite  310  is received. The MT station  110 , when in receipt of the session invite  310 , may determine various parameters included in the session invite  310  such as the identity of the MO station  105 . In a specific example, upon receiving the SIP invite, the MT station  110  may have been paged for IMS  130  as well as establish a Radio Resource Control (RRC) connection. The MT station  110  may generate a session response  315  to the session invite  310  to establish the voice call. In this example, it is considered that the session response  315  does not reach the LTE-RAN  115 . However, for the purpose of providing a complete discussion, if the session response  315  was received by the LTE-RAN  115  and forwarded to the MO station  105 , a VoLTE call may be setup between the MO station  105  and MT station  110 . 
     In addition to generating the session response  315 , the network selection application  240  of the MT station  110 , upon receiving the session invite  310 , may initiate a timer  320 . In a first example, the timer  320  may be related to consecutive “out of sync” indications. The “out of sync” indications will be describe in greater detail below. In a second example, a preset timer may be selected to avoid reselecting systems too aggressively. Thus, this preset timer may be used as a threshold to determine when a network selection is to be performed by the network selection application  240 . The preset timer may be, for example, from 1 second to 3 seconds. 
     During the period of the timer  320 , the call application  235  of the MT station  110  may attempt to respond to the session invite  310  by transmitting the session response  315 , which may be in the form of a SIP response. However, as shown in  FIG. 3 , the MT station  110  may be incapable of transmitting the session response  315  to the MO station  105  using the LTE-RAN  115 . There may be any number of conditions that prevent the MT station  110  from providing the session response  315  to the LTE-RAN  115 , some examples being provided below. 
     In a first example, the MT station  110  may be in an uplink limited condition in the LTE-RAN  115  while still capable of decoding the downlink in the LTE-RAN  115 . The MT station  110  may therefore receive the session invite  310  transmitted through the LTE-RAN  115  from the MO station  105 , but is unable to respond. The uplink limited condition may result in the MT station  110  transmitting the session response  315 , but the session response  315  never reaching the destination, namely the LTE-RAN  115  or MO station  105 . 
     In a second example, the MT station  110  may determine a radio link failure (RLF) event. The RLF event may be a break in the physical (PHY) layer. The RLF event may be caused by a variety of different scenarios as would be understood by one skilled in the art. For example, there may be a consecutive number of “out of sync” indications (e.g., N 310 ) from the PHY layer. After a predetermined time of this occurring (e.g., T 311 ), the RLF event may be determined. In another example, the RLF event may be assumed to have occurred by the station  200  when the measured Reference Signal Received Power (RSRP) or the measured Reference Signal Received Quality (RSRQ) is below a predetermined threshold, when a Physical Downlink Control Channel (PDCCH) failed to decode due to power signal quality (e.g., low RSRP or RSRQ), when a Physical Downlink Shared Channel (PDSCH) failed to decode due to power signal quality, etc. In yet another example, the RLF event may be assumed to have occurred by an Evolved NodeB (eNB) of the LTE-RAN  115  when the Signal-to-Interference-plus-Noise Ratio (SINR) from the station  200  is significantly lower than the configuration of the eNB, when the eNB is incapable of detecting an Acknowledgement (ACK) or a negative ACK (NACK) from the station  200  for a PDSCH, etc. 
     Once the timer  320  has lapsed, the network selection application  240  determines that the MT station  110  is incapable of responding  325 . For example, when the above noted conditions are present on the MT station  110  (e.g., uplink limited scenario, RLF event, etc.), the network selection application  240  may determine that the MT station  110  may not be capable of performing the voice call as a VoLTE call via the LTE-RAN  115 . 
     Once this determination is made, the network selection application  240  of the MT station  110  may select  330  the legacy RAN  120  over the LTE network  115 , e.g., the network selection application  240  may determine that a circuit switched voice call should be performed over the legacy RAN  120 . The network selection application  240  may indicate to the call application  235  that the voice call is to be performed over the legacy RAN  120 . If the call application  235  is configured to always use the LTE-RAN  115  when available, this indication may override this configuration. The network selection application  240  may also constructively indicate that the LTE-RAN  115  is unavailable such that the legacy RAN  120  is to be selected for use in the voice call by the call application  235 . In this manner, the configuration to use the VoLTE call when the LTE-RAN  115  is available is not be violated. The MT station  110  may perform an association functionality to connect to a base station of the legacy RAN  120 . This association functionality is not shown in the signaling diagram and should be understood the be the association procedure that is used for the network type of the legacy RAN  120  (e.g., 3G, 2G, etc.). 
     Since the legacy RAN  120  may be more reliable in the uplink transmission (e.g., when the SIP response failed due to the uplink limited scenario in the LTE-RAN  115 ), the network selection application  240  may utilize the legacy RAN  120  for any uplink transmissions. By moving to the legacy RAN  120 , the MT station  110  may perform several operations based upon the communications standard being used. For example, in 3GPP2, the MT station  110  may register for short messaging service (SMS) over IMS only on Enhanced High Rate Packet Data (eHRPD) (e.g., Enhanced Voice-Data Optimized (1x EV-DO)) and voice over 1x. In another example, in 3GPP, the MT station  110  may register for SMS over IMS and voice over Wideband Code Division Multiple Access (WCDMA). In this manner, the MT station  110  may move to the legacy RAN  120  from the LTE-RAN  115 . As will be described in greater detail below, the MT station registers for SMS because this functionality is used to transmit information to the MO station to continue with the voice call. 
     After the association with the legacy RAN  120 , the network selection application  240  may generate a switch message  335  to be transmitted to the MO station  105 . As described above, this message may be transmitted via SMS. However, if the MO station  105  and MT station  110  have another manner of transmitting messages between the stations (e.g., a proprietary messaging system), this other type of messaging system may also be used. In other words, the functionality that is of concern is that the MT station  110  transmits a message that reaches the MO station  105 . In this example, the switch message  335  may be transmitted via SMS from the MT station  120  via the legacy RAN  120  which forwards the switch message  340  to the MO station  105 . 
     The network selection application  240  of the MO station  105  may receive the switch message  340  from the MT station  110 . It should be noted that when the switch message  340  is in the form of an SMS message, it may be formatted such that the user of the MO station  105  is not aware that the message has been received. That is, the network selection application  240  may receive the switch message  340  and perform the described functionality without any input from the user of the MO station  105 . The receiving of the switch message  340  may indicate to the MO station  105  that the call has not failed to establish, e.g., the MT station  110  has received the session invite  310 , but cannot respond to the session invite  310  because of limited RF scenario and the MT station  110  has moved to the legacy RAN  120 . It should be noted that from a network perspective, the switch message  340  may be used so that there is no re-page from the MO station  105  to the MT station  110  over the legacy RAN  120 . 
     The MO station  105  may remain connected to the LTE-RAN  115  and participate in the voice call using the VoLTE call while the MT station  110  participates in the voice call using the legacy RAN  120 . Upon receipt of the switch message  340 , the MO station  105  may be configured to re-initiate the voice call transparently to the MT station  110 . Specifically, the MO station  105  may again transmit a session invite  345  to the LTE-RAN  115  indicating that a call should be placed to the MT station  110 . However, since the MT station  110  is no longer connected to the LTE-RAN  115 , a call setup procedure  350  involving the LTE-RAN  115 , legacy RAN  120 , cellular core network  125  and IMS  130  is performed to connect the MO station  105  with the MT station  110 . It should again be noted that the IMS  130  provides the functionality for VoLTE call to inter-operate with the circuit switched voice call. Once this setup procedure  350  has been completed, the voice call  355  may be performed. 
       FIG. 4  shows a second exemplary signaling diagram  400  to perform a network selection to transfer a call session from the LTE network  115  to the 3G network  120 . Specifically, the signaling diagram  400  relates to an example of the MO station  105  also switching to the legacy RAN  120  after receiving the switch message. The signaling diagram  400  may include substantially similar processes as the signaling diagram  300  such as until the switch message is received by the MO station  105 . Specifically, the steps of the session invites  305 ,  310 , session response  315 , timer  320 , cannot respond  325 , select legacy RAN  330  and switch messages  335 ,  340  may be performed in a substantially similar as described above with reference to the signaling diagram  300  of  FIG. 3 . 
     As illustrated in the signaling diagram  400 , when the network selection application  240  of the MO station  105  receives the switch message  340 , the network selection application  240  of the MO station  105  determines that the MO station  105  is also to select  445  the legacy RAN  120 . In this example, the MO station  105  moves to the legacy RAN  120  autonomously upon receiving the switch message  340  from the MT station  110 . Thus, the MO station  105  also associates with a base station of the legacy RAN  120  and connects to the legacy RAN  120 . Upon connecting to the legacy RAN  120 , the call application  235  of the MO station  105  may determine that the VoLTE call is unavailable and therefore use the circuit switched voice call. The call application  235  may re-initiate the voice call with the MT station  110  using the call setup procedure  450  of the legacy RAN  120 . Since neither the MO station  105  nor the MT station  110  are using the LTE-RAN  120 , the LTE-RAN  120  and the IMS  130  are not involved in this setup procedure  450 . Once this setup procedure  450  has completed, the voice call  455  may be performed. 
     The MO station  105  also moving to the legacy RAN  120  may provide a more efficient response in handling the switch message, particularly from a network perspective. For example, there may be network delays in handling the event and re-routing a new call from the MO station  105  to the MT station  110  from the LTE-RAN  115  to the legacy RAN  120 . In another example, there may be network delays in releasing the previous call context from the LTE-RAN  115  for the MT station  110 . 
     Using the above manners of addressing the failure of establishing a voice call using VoLTE by the MT station  110 , the voice call may still be maintained and performed between the MO station  105  and the MT station  110  in a seamless manner. That is, the call session may be transferred to the legacy RAN  120  in the setup procedure of the voice call for either the MT station  110  or both the MO station  105  and the MT station  110 . Accordingly, when the setup procedure for the voice call would otherwise fail due to the MT station  110  being incapable of successfully transmitting the SIP response to the LTE-RAN  115 , the network selection application  240  may provide a mechanism to still enable the voice call to be performed although the MT station  110  would not utilize VoLTE to participate in the voice call. 
       FIG. 5  shows a first exemplary method  500  for performing a voice call by the MT station  110 . That is, the method  500  is from the perspective of the MT station  110  when the MT station  110  and MT station  105  implement the functionality described above for the network selection application  240  and the call application  235 . It may be considered that the MT station  110  is connected to the LTE-RAN  115  prior to the method  500  starting. The method  500  will be described with regard to the network arrangement  100  of  FIG. 1 , the station  200  of  FIG. 2  and the signaling diagrams  300 ,  400  of  FIGS. 3 and 4 , respectively. 
     In step  505 , the call application  235  of the MT station  105  receives the session invite  310  over the downlink of the LTE-RAN  115 . In step  510 , the network selection application  240  of the MT station  105  determines whether the MT station  105  is capable of responding to the session invite. For example, the network selection application  240  may receive information on network parameters such as an available uplink transmission power. 
     If an immediate determination is made by the network selection application  240  that the MT station  110  is incapable of responding to the session invite  310 , the method  500  continues to step  540 , which will be described in further detail below. However, if the network selection application  240  determines that the MT station  110  is capable of using the LTE-RAN  115  or otherwise able to transmit a response, the method  500  continues to step  515 . 
     In step  515 , the network selection application  240  of the MT station  110  initiates the preset timer  320 . In step  520 , the call application  235  transmits a session response  315  over the uplink of the LTE-RAN  115 . The call application  235  may transmit the session response until successful or until the duration of the timer lapses. In step  525 , the network selection application  240  of the MT station  110  determines whether the session response  315  was successfully transmitted to the MO station  105 . If successful, the method  500  continues to step  530 . In step  530 , the MT station  110  performs the voice call with the MO station  105 . Specifically, the MT station  110  performs the voice call with the MO station using VoLTE. 
     Returning to step  525 , if the attempt to transmit the session response is determined to be unsuccessful, the method  500  continues to step  535 . In step  535 , the network selection application  240  of the MT station  110  determines whether the timer  320  has lapsed. If the timer  320  is still running, the method  500  returns to step  520 . However, if the timer  320  has lapsed, the network selection application  240  may determine that the LTE-RAN  115  cannot be used for a VoLTE call. Therefore, the method  500  continues to step  540 . 
     In step  540 , the network selection application  240  of the MT station  110  selects the legacy RAN  120 . As discussed above, this may entail registering for SMS over the IMS  130  as well as registering for voice on lx in 3GPP2 or on WCDMA in 3GPP. Thus, the MT station  110  is now connected to the legacy RAN  120 . In step  545 , the network selection application  240  of the MT station  110  transmits the switch message  335  over, for example, SMS. In step  550 , the call application  235  of the MT station  110  receives the re-transmitted information to perform a call setup procedure for the voice call using the legacy RAN  120 . 
     After performing steps  540 - 550 , the method  500  continues to step  530  where the voice call is performed by the MT station  110  using the legacy RAN. The voice call is performed by the call application  235  of the MT station  110  as a circuit switched voice call since the legacy RAN  120  is being used. 
       FIG. 6  shows a second exemplary method  600  for performing a voice call by the MO station  110 . That is, the method  600  is from the perspective of the MO station  105  when the MO station  105  and MT station  110  implement the functionality described above for the network selection application  240  and the call application  235 . It may be considered that the MO station  110  is connected to the LTE-RAN  115  prior to the method  600  starting. The method  500  will be described with regard to the network arrangement  100  of  FIG. 1 , the station  200  of  FIG. 2  and the signaling diagrams  300 ,  400  of  FIGS. 3 and 4 , respectively. 
     In step  605 , the call application  235  of the MO station  105  transmits a session invite  305  over the uplink of the LTE-RAN  115 . Using the LTE-RAN  115 , the session invite  305  may be a SIP invite. In step  610 , the call application  235  of the MO station  105  determines whether a session response (e.g., SIP response) has been received. As discussed above in the method  500 , this may be when the MT station  110  successfully transmits the session response  315  using the uplink of the LTE-RAN  115 . If the call application  235  receives the session response, the method  600  continues to step  615 . In step  615 , the voice call is performed. Specifically, given these circumstances, the call application  235  of the MO station  105  performs the voice call as a VoLTE call over the LTE-RAN  115 . 
     Returning to step  610 , if the session response is not received, the method  600  continues to step  620 . In step  620 , the network selection application  240  of the MO station  105  determines whether a switch message  340  has been received from the MT station  110 , e.g., via SMS. If no switch message  340  has been received, the method  600  returns to step  610 . It is noted that this process may continue until either the session response  315  or the switch message  340  is received, or a timeout period has expired when neither has been received and the call is discontinued. 
     If the switch message  340  is received in step  620 , the method  600  continues to step  625 . In step  625 , the network selection application  240  of the MO station  105  determines whether the legacy RAN  120  is also to be used by the MO station  105 . It should be noted that the determination of using the legacy RAN  120  may be predetermined. In a first example, the legacy RAN  120  selection may be a user input that may be toggled. In a second example, the legacy RAN  120  selection may be set by an administrator. In a third example, the network selection application  240  may dynamically determine when the legacy RAN  120  is to be used. 
     If the legacy RAN  120  is not to be used and the connection to the LTE network  115  is maintained, the method  600  continues to step  630 . This branch of the method  600  refers to the process that is described in the signaling diagram  300 , where the MO station does not switch to the legacy RAN  120 . In step  630 , the call application  235  of the MO station  105  transparently re-initiates the voice call by re-transmitting the session invite  345  over the uplink of the LTE-RAN  115 . Subsequently, the method  600  continues to step  640 , which will be described in further detail below. 
     Returning to step  625 , if the legacy RAN  120  is to be used by the MO station  105 , the method  600  continues to step  635 . In step  635 , the network selection application  235  of the MO station  105  selects the legacy RAN  120  and performs the corresponding operations to connect to the legacy RAN  120 . This branch of the method  600  refers to the process that is described in the signaling diagram  400 , where the MO station  105  switches to the legacy RAN  120  to perform the voice call. 
     In step  640 , the call application  235  of the MO station  105  performs the call setup procedure for either the LTE-RAN  115  or the legacy RAN  120  depending upon the current connection of the MO station  105 . As described above, the call setup procedure involves the MO station  105  transparently re-initiating the voice call to the MT station  110 . In step  645 , the call application  235  of the MO station  105  receives the session response from the MT station  110 . The method  600  then continues to step  615  where the voice call is performed. 
     It should be noted that when step  630  is used and the connection to the LTE-RAN is maintained, the MO station  105  may participate in the voice call using a VoLTE call while the MT station  110  participates in the voice call using the circuit switched voice call. Furthermore, when steps  635  are used and the connection to the legacy RAN is used, the MO station  105  may participate in the voice call using the circuit switched voice call similar to the MT station  110 . 
     The exemplary embodiments provide a system and method for transferring a call session by selecting a network that enables the voice call to be performed. Specifically, a MO station may invite a MT station to a voice call in which both MO and MT stations are connected to a LTE-RAN. Thus, both the MO and MT stations may participate in the voice call using a VoLTE call. For a variety of reasons, the MT station may be incapable of responding to the invitation. Since the VoLTE call is to be used and due to this incapability, the voice call would normally fail to establish. However, a network selection application of the MT station may provide a functionality to select a legacy RAN for the voice call. By providing the MO station with a switch message that impliedly indicates that the voice call has not failed and requests for a re-initiation thereof, the voice call may be established transparently. 
     Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software or hardware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Mac platform and MAC OS, a mobile device executing the iOS, Android or other operating system. In a further example, the exemplary embodiments of the above described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor. 
     It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or the scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalent.

Metadata:
Filing Date: 20140530
Publication Date: 20170103
Grant Date: 20170103
Priority Date: 20140530
Inventors: KHAY-IBBAT SAMY
VANGALA SARMA V.
BALAKRISHNAN SWAMINATHAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W36/305", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0066", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0066", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W4/16", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W48/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W48/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W48/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W76/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0066", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0022", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/00224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/305", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/00224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/00224", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 54481711