PATENT DOCUMENT

Publication Number: US-10129808-B2
Application Number: US-201615136043-A
Country: US
Kind Code: B2

Title: Reducing communication silence when performing inter-technology handoff

Abstract:
To perform an inter-technology handoff, an indicator in a service request message is received by a mobile switching center (MSC). The indicator is to indicate to the MSC that an inter-technology handoff from a packet-data wireless access network to a circuit wireless access network has been requested. The behavior of the MSC is modified in response to the indicator to reduce the communication silence during the inter-technology handoff.

Claims:
What is claimed is: 
     
       1. A method of operating a node of a wireless communication system to reduce communication silence when handing off a mobile device between different types of wireless access network, the method comprising:
 receiving a request to hand off the mobile device; 
 determining that the received request is a request to hand off the mobile device from a packet data wireless access network to a circuit wireless access network; and 
 in response to the determining, converting the handoff request to a service request for sending to a mobile switching center (MSC) and adding an indicator to the service request to indicate that an inter-technology handoff from the packet-data wireless access network to the circuit wireless access network has been requested, wherein the indicator is configured to cause the MSC to delay handoff of the mobile device. 
 
     
     
       2. The method of  claim 1 , wherein the received request is a 1× call origination message. 
     
     
       3. The method of  claim 1 , further comprising, in response to determining that the received request is a request to hand off the mobile device from the packet data wireless access network to the circuit wireless access network, creating a message for sending to a receiver, the message indicating that an inter-technology handoff from a packet-data wireless access to a circuit wireless access network has been requested. 
     
     
       4. The method of  claim 3 , further comprising sending the service request to the MSC. 
     
     
       5. The method of  claim 4 , wherein the service request is a 1×CM Service Request comprising a packet data indicator. 
     
     
       6. The method of  claim 1 , further comprising sending a message that commands the packet-data wireless access network to send a handoff message to the mobile device after a predetermined trigger has occurred. 
     
     
       7. The method of  claim 6 , wherein the message comprises a HRPD handoff direction. 
     
     
       8. The method of  claim 6 , wherein the message comprises a 1× handoff direction. 
     
     
       9. The method of  claim 6 , wherein the predetermined trigger comprises one of:
 a mobile switching center (MSC) receiving an IP multimedia subsystem routing number (IMRN); 
 a MSC receiving an ISDN user part (ISUP) answer message (ANM); 
 a MSC sending an ISUP initial address message (IAM); 
 a MSC sending a session initiation protocol (SIP) INVITE message; 
 a MSC receiving an ISUP address complete message (ACM); 
 a MSC receiving a SIP 200 OK message; and 
 a MSC receiving a SIP 183 session progress message. 
 
     
     
       10. The method of  claim 9 , wherein the node comprises a high rate packet data (HRPD) access node (AN). 
     
     
       11. The method of  claim 9 , wherein the node comprises an 1×RTT base station and a interworking system (IWS). 
     
     
       12. A node comprising:
 communication circuitry; and 
 processing hardware coupled to the communication circuitry, wherein the processing hardware and the communication circuitry are configured to operate together to:
 receive a request to hand off a mobile device; 
 determine that the received request is a request to hand off the mobile device from a packet data wireless access network to a circuit wireless access network; and 
 in response to the determining, convert the handoff request to a service request for sending to a mobile switching center (MSC) and adding a packet data indicator to the service request to indicate that an inter-technology handoff from the packet-data wireless access network to the circuit wireless access network has been requested, wherein the indicator is configured to cause the MSC to delay handoff of the mobile device. 
 
 
     
     
       13. The node of  claim 12 , wherein the processing hardware and the communication circuitry are further configured to:
 in response the converting, forwarding the service request to the MSC. 
 
     
     
       14. The node of  claim 12 , wherein the node comprises a base station and an interworking system (IWS). 
     
     
       15. The node of  claim 12 , wherein the node comprises a high rate packet data (HRPD) access node (AN). 
     
     
       16. The node of  claim 12 , wherein the processing hardware and the communication circuitry are further configured to:
 subsequent to the converting the handoff request to the service request, receive an assignment request from the MSC; and 
 in response to receiving the assignment request, cause a handoff initiation message to be sent to the mobile device. 
 
     
     
       17. A non-transitory, computer accessible memory medium storing program instructions executable by a processor to:
 receive a request to hand off a mobile device; 
 determine that the received request is a request to hand off the mobile device from a packet data wireless access network to a circuit wireless access network; and 
 in response to the determining, convert the handoff request to a service request for sending to a mobile switching center (MSC) and adding, a packet data indicator to the service request to indicate that an inter-technology handoff from the packet-data wireless access network to the circuit wireless access network has been requested, wherein the indicator is configured to cause the MSC to delay handoff of the mobile device. 
 
     
     
       18. The non-transitory, computer accessible memory medium of  claim 17 , wherein the program instructions are further executable to:
 determining that the mobile device should be handed off from a packet data wireless access network to a circuit wireless access network. 
 
     
     
       19. The non-transitory, computer accessible memory medium of  claim 17 , wherein the program instructions are further executable to:
 in response the converting the handoff request to the service request, forward the service request to the MSC.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a continuation application of U.S. patent application Ser. No. 12/119,024, filed May 12, 2008, entitled “Reducing Communication Silence When Performing Inter-Technology Handoff”, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application Ser. No. 60/917,108, filed May 10, 2007, entitled “Voice Gap Reduction for Inter-Technology Hard Handoff (ITHHO) and Voice Call Continuity (VCC) Coordinated Voice Break,” the entirely of both of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to reducing communication silence during handoff of a mobile device between two different types of wireless access networks. 
     BACKGROUND 
     Mobile or wireless communications networks are capable of carrying circuit-switched and packet-data traffic (e.g., voice traffic, data traffic, etc.) between a mobile device and some other endpoint or endpoints. The endpoint can be another mobile device or a device connected to a network such as a public switched telephone network (PSTN) or a packet data network. Traditional wireless protocols provide for circuit-switched communications between devices, such as the circuit-switched protocol provided by 1×RTT, as defined by CDMA (code division multiple access) 2000. With circuit-switched communications, a dedicated circuit or channel is established between nodes and terminals to allow communication between endpoints. Each circuit or channel that is dedicated cannot be used by other users until the circuit or channel is released. 
     In contrast, with packet-data communications, data is split into packets, with the packets routed individually over one or more paths. A widely-used protocol for transporting packet-data communication information is Internet Protocol (IP). Examples of packet-data communications that are possible over packet-data networks include electronic mail, web browsing, file downloads, electronic commerce transactions, voice or other forms of real-time, interactive communications, and others. 
     To provide wireless access to a packet-data network, a wireless access network according to any of the following standards can be used: EV-DO or EV-DV (also referred to as HRPD or high rate packet data), as defined by the CDMA 2000 family of standards; WiFi; WiMax (Worldwide Interoperability for Microwave Access); and others. 
     It is common for circuit wireless access networks (such as those based on 1×RTT) to coexist with packet-data access networks within a communications network. Certain mobile devices are able to operate with both circuit wireless access networks and packet-data wireless access networks. Such mobile devices are referred to as multi-mode mobile devices. 
     Conventionally, when a multi-mode mobile device transitions from a packet-data wireless access network, such as an EvDO access network, to a circuit wireless access network, such as a 1×RTT access network, a relatively large voice gap can occur during the handoff. A “voice gap due to handoff” refers to a time duration during which voice bearer data is not being exchanged between the mobile device and some other endpoint as a result of the mobile device transitioning from one access network to a different access network. A long voice gap can be bothersome to the users involved in the call session, and sometimes may even result in the call being dropped by one of the users. 
     SUMMARY OF THE INVENTION 
     According to a preferred embodiment, a method of reducing communication silence when a mobile device hands off between different types of wireless access networks includes communicating a special indicator in a handoff request sent to a mobile switching center (MSC). The special indicator is used to indicate to the MSC/VLR (Visitor Location Register) that an inter-technology handoff from a packet-data wireless access network to a circuit wireless access network has been requested, such that the MSC/VLR can take action to reduce communication silence (e.g., voice gap) during the handover of the mobile device. 
     Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-3  are block diagrams to illustrate an inter-technology handoff according to preferred embodiments of the invention of a mobile device from a packet-data domain to a circuit-switched domain. 
         FIGS. 4 and 5  are message flow diagrams of processes of performing inter-technology handoffs of a mobile device from a packet-data domain to a circuit-switched domain, in accordance with preferred embodiments. 
         FIG. 6  is a block diagram of an exemplary network node that can be configured according to preferred embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     In the following description, numerous details are set forth to provide an understanding of some embodiments. However, it will be understood by those skilled in the art that some embodiments may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     According to preferred embodiments, a technique or mechanism is provided to reduce a voice gap (or other communication silence) during a communications session as a mobile device is being handed over from a packet-data wireless access network to a circuit wireless access network (an inter-technology handoff). A circuit wireless access network is a wireless network that established a fixed bandwidth channel or connectivity from the access device to the first network call control node. The channel is dedicated to the access device. A packet-data wireless access network is a wireless network that provides data connectivity between a packet-data network (typically a public or private internet) and an access terminal. The connectivity between the access terminal and the packet-data network is over a shared channel (or connection). Examples of a packet-data wireless access network include High-Speed Downlink Packet Access (HSDPA) and Evolution-Data Optimized (EV-DO). A “voice gap” refers to a time duration during which voice bearer data is not being exchanged between two devices which have established a communications dialog. A “voice gap due to handoff” refers to a time duration during which voice bearer data is not being exchanged between the mobile device and the other endpoint as a result of the mobile device handing off, or transitioning, from one access network to a different access network. A voice gap is one example of communication silence in which bearer data is not exchanged between the mobile device and the other endpoint of the established communications dialog. Other types of communication silence can include a break in video bearer data, or any other type of application bearer data. In the ensuing discussion, reference is made to reduction of voice gaps due to handoff. However, the same or similar techniques can be applied to reduction of other forms of communication silence during handoff. 
     The reason that a relatively large voice gap occurs in a conventional inter-technology handoff from a packet-data wireless access network (e.g., EvDO wireless access network) to a circuit wireless access network (e.g., 1×RTT wireless access network) is that the MSC/VLR is not aware that an inter-technology handoff is occurring. Without a preferred embodiment, the MSC/VLR is operating under the assumption that the mobile device is attempting a service request for the purpose of originating a voice call. This assumption results in the MSC/VLR commanding the packet-data wireless access network to instruct the mobile device to handoff to the circuit wireless access network relatively early. The MSC is a controller in the circuit-switched domain that sets up and releases an end-to-end call session, controls mobility and handover events during the call session, manages billing, and performs other tasks. The VLR is the location register used by an MSC to retrieve information for handling of calls to or from a visiting subscriber. The MSC/VLR may be capable of using packet-data call control messaging (e.g., SIP) and circuit-switched call control messaging (e.g., ISUP) or only be capable of using circuit-switched call control messaging. 
     In one example, the MSC/VLR commands the packet-data access network to send a handoff message to the mobile device for the purpose of detaching the mobile device from the packet-data wireless access network and attaching the mobile device to a circuit wireless access network. The handoff message is in the form of a traffic assignment message, e.g., Universal Handoff Direction Message (UHDM), which contains various radio parameters associated with a target circuit access network base station that the mobile device is to access and communicate with after the handoff is complete. Once the mobile device detaches from the packet-data wireless access network, a voice gap starts and continues until the other endpoint of the voice call is informed of the change and a new voice signaling path and voice bearer path is established between the other endpoint and the MSC/VLR. For a MSC/VLR that is only capable of using circuit-switched call control messaging, part of establishing a new voice bearer path implies that a media gateway (MGW) is used to exchange voice bearer data between the MSC/VLR and the packet-data network and that a media gateway control function (MGCF) is used to exchange voice signaling data being the MSC/VLR and the packet-data network. Signaling from the MSC/VLR passes through the MGCF as part of the process of informing the other endpoint that a change has occurred, and signaling passing through the MGCF to the MSC/VLR is used to inform the MSC/VLR that the other endpoint has established a new voice bearer path. 
     A MGCF performs call control protocol conversion between packet-data call control messaging and circuit-switched call control messaging, such as between Session Initiation Protocol (SIP) messaging and ISUP (ISDN User Part) messaging (which is part of the Signaling System No. 7 (SS7) protocol used to set up telephone calls in a circuit-switched domain). A version of SIP is described in Request for Comments (RFC) 3261, entitled “SIP: Session Initiation Protocol,” dated June 2002. The MGCF also controls the MGW, such as by using H.248 control messages. A version of H.248 is described ITU-T H.248.1, entitled “Gateway control protocol: Version 1”, dated March 2002. The MGW converts between voice bearer data in packet-data format and voice bearer data in circuit-switched format. 
     Conventionally, the voice gap during a inter-technology handoff can be relatively large, on the order of 2,000 to 3,000 milliseconds (ms). Such a relatively large voice gap may be irritating to users, and in some cases, may result in a voice call being dropped. 
     To reduce the voice gap, an MSC/VLR configured according to preferred embodiments is able to delay commanding the packet-data wireless access network to send the handoff message (e.g., UHDM) to the mobile device until after a predetermined event has occurred. In one embodiment, the MSC/VLR delays commanding the packet-data wireless access network to send the handoff message until after the MSC/VLR receives a message indicating that the other endpoint is in the process of being informed that a new voice bearer path and new voices signal path is required. In one embodiment, the message providing such indication is an ISUP (ISDN User Part) address complete message (ACM) received by the MSC/VLR in response to an ISUP initial address message (IAM) sent by the MSC/VLR. In other words, the MSC/VLR delays commanding the packet-data wireless access network to send the handoff message until after the MSC/VLR has received the ISUP ACM (which is an indication that the voice bearer path at the other endpoint is about to break or has broken). 
     In another embodiment, instead of commanding the packet-data wireless access network to send the handoff message based on receipt of the ISUP ACM message by the MSC/VLR, the MSC/VLR can command the packet-data access network to send the handoff message based on receipt of the ISUP ANM message by the MSC/VLR. In other words, the MSC/VLR delays commanding the packet-data wireless access network to send the handoff message until after the MSC/VLR has received the ISUP ANM (which is an indication that the new voice bearer path from the other endpoint to the MSC/VLR has been established). 
     In another embodiment, instead of commanding the packet-data wireless access network to send the handoff message based on receipt of the ISUP ACM message by the MSC/VLR, the MSC/VLR can command the packet-data access network to send the handoff message anytime after receipt of a message containing routing information that identifies a node (e.g., voice call continuity application server, discussed further below) in the communications network responsible for re-establishing the call session during a inter-technology handoff. This routing information can be an IP multimedia subsystem routing number (IMRN) in some implementations. The routing information, such as IMRN, is used to establish a voice signaling path between the MSC/VLR and a node in the communications network responsible for re-establishing the call session during a inter-technology handoff. For a MSC/VLR that is only capable of using circuit-switched call control messaging the voice signaling path will be established through a MGCF. 
     In either case, the behavior of the MSC/VLR has been modified such that the MSC/VLR delays commanding the packet-data wireless access network to send the handoff message to the mobile device, such that the voice gap due to inter-technology handoff is reduced. Effectively, the start of the break in voice bearer data at the mobile device as a consequence of the mobile device handing off is delayed such that it is closer in time to the start of the break in voice bearer data at the other endpoint as a consequence of the other endpoint establishing a new voice bearer path, such the overall voice gap is reduced. In some implementations, the voice gap due to handoff can be reduced to less than 500 ms. 
     The behavior of the MSC/VLR is modified in response to a special indicator included in a handoff request sent from the mobile device to the MSC/VLR. The special indicator (referred to as a packet data (PD) indicator) is an indication to the MSC/VLR that an inter-technology handoff from a packet-data wireless access network to a circuit wireless access network has been requested by the mobile device. In some embodiments, the handoff request from the mobile device that is received by the MSC/VLR is a service request message (e.g., 1×CM Service Request message), which is triggered by the mobile device sending a handoff request message (e.g., 1× call origination message) to the packet-data access network controller. The access network controller, realizing the true nature of the request (e.g., the mobile device is requesting a handoff from the packet-data wireless access network to a circuit wireless access network, converts the handoff request to a service request and in turn adds the PD indicator into the service request message. The access network controller then forwards the service request message containing the PD indicator to the MSC/VLR. 
     In response to detecting the PD indicator, the MSC/VLR modifies its behavior when processing the service request message, and delays sending the message which will command the packet-data access network controller to instruct the mobile device to handoff until after the occurrence of a predetermined event (e.g., the MSC/VLR receives the ISUP ACM message, the MSC/VLR receives the ISUP ANM message, MSC/VLR receives a SIP 183 Session Progress message, the MSC/VLR receives a SIP 200 OK message, or any time after the MSC/VLR receiving the IMRN). 
       FIG. 1  illustrates an exemplary arrangement that includes a home network  100  (for a mobile device  104 ) that is attached to a visited network  102 . Dashed lines represent signaling paths, while solid lines represent bearer paths (for carrying voice bearer data or other types of bearer data). The mobile device  104  is a dual-mode mobile device that is capable of being connected to either a circuit wireless access network  107  (e.g., 1×RTT network) or a packet-data wireless access network  108  (e.g., EV-DO network, WiFi network, WiMax network, etc.) in the visited network  102 . EV-DO is also referred to as High Rate Packet Data (HRPD). In  FIG. 1 , the mobile device  104  is shown attached to the packet-data wireless access network  108 . 
     Through the packet-data wireless access network  108 , the mobile device  104  is able to communicate with the other endpoint  110  through a packet data serving node (PDSN)  109  and a packet data network  112  (e.g., the Internet, local area network, wide area network, etc.). The other endpoint  110  can be another mobile device, a desktop computer, a portable computer, and so forth. 
     As depicted in  FIG. 1 , the circuit wireless access network  107  includes a 1×RTT base station and an IWS (interworking system) which is connected to an MSC/VLR  114 . The IWS is shown as part of  107  yet in some arrangements can be part of  108 . The IWS performs message translation between packet-data wireless access messages and circuit wireless access messages (e.g., as described in 3GPP2 A.S0008-C v1.0, dated July 2007). The visited network  102  also includes a P-CSCF (proxy call session control function)  116 , which is the first packet-data call control contact point for a terminal, such as the mobile device  104 , connected to a packet-data access network. The P-CSCF is shown as part of  102  yet in some arrangements can be part of  100 . The P-CSCF further communicates packet-data call control signaling, such as SIP messages, with another CSCF, such as a serving CSCF (S-CSCF)  118 , which is in the home network  100 . SIP messages are used for establishing, releasing, or otherwise controlling packet-data communications sessions. 
     The home network  100  also includes an interrogating CSCF (I-CSCF)  120  and a voice call continuity (VCC) application server (AS)  124 . The VCC AS  124  supports the continuity of a communications session when a mobile device is being handed off between a packet-data domain and a circuit-switched domain. The VCC AS functionality is described in 3GPP TS 23.206 and 3GPP TS 24.206 for when a mobile device is connected to a 3GPP packet-data wireless access network or in 3GPP2 X.S0042 for when a mobile device is connected to a 3GPP2 packet-data wireless access network (e.g., HRPD). As discussed further below, the VCC AS  124  according to an embodiment is configured to control the synchronization of certain communication messages during the inter-technology handoff of the mobile device  104 . In accordance with preferred embodiments, the MSC/VLR  114  is provided with communication messages that allow the MSC/VLR  114  to synchronized the voice gap that occurs as mobile device  104  disconnects from the HRPD AN  108  and connects to the circuit wireless access network  107  to the voice gap that occurs due to the establishment of a new voice bearer path between the other endpoint  110  and the MSC/VLR  114 . 
       FIG. 1  also shows circuit-switched domain entities in the home network  100 , including a home location register (HLR)  126  and a WIN SCP (wireless intelligent network service control point)  128 . The HLR  126  is the central database used for the circuit-switched domain that contains details of each mobile device subscriber that is authorized to use the circuit-switched service domain. The WIN SCP  128  controls service delivery to subscribers, and allows certain high-level services to be moved away from the MSC/VLR  114  and be controlled at the WIN SCP  128 . As discussed further below, in the context of one exemplary embodiment, the WIN SCP  128  is used to supply routing information, such as the IMRN, to the MSC/VLR  114  during handoff of the mobile device  104  from the packet-data wireless access network  108  to the circuit wireless access network  107 . 
     In  FIG. 1 , the following entities in the home and visited networks  100  and  102  are part of the circuit-switched domain: circuit wireless access network  107 , MSC/VLR  114 , HLR  126 , and WIN SCP  128 . The following entities are part of the packet-data domain: packet-data wireless access network  108 , PDSN  109 , P-CSCF  116 , S-CSCF  118 , and VCC AS  124 . 
       FIG. 2  shows entities that are involved in a handoff of the mobile device  104  from the packet-data domain to the circuit-switched domain.  FIG. 2  assumes that the MSC/VLR  114  is only capable of using circuit-switched call control messaging (e.g., ISUP). If a handoff trigger is detected (such as a detection that the strength of the RF signals communicated between the mobile device  104  and the packet-data wireless access network  108  have dropped below a predetermined level and that and the strength of the RF signals communicated between the mobile device  104  and the circuit wireless access network  107  are above a predetermined level), a handoff procedure is initiated (either by the mobile device  104  or the packet-data wireless access network  108 ). In response to initiation of the handoff procedure, the mobile device  104  sends a handoff request (e.g., in the form of a 1× call origination message) to the packet-data wireless access network  108 . The packet-data wireless access network  108  forwards the request to the IWS, which is shown associated with the circuit wireless access network  107 . Since in this arrangement the IWS is in part of the circuit wireless access network  107  the 1× call origination message is forwarded over an interface (e.g., A21 interface shown in  FIG. 2 ). The A21 interface is defined in 3GPP2 A.S0008 and 3GPP2 A.S0009 and is used to pass air interface signaling messages between the HRPD AN  108  and a standalone IWS or the IWS-1×BS. 
     In accordance with a preferred embodiment, the IWS, upon receipt of the 1× call origination message from the mobile device  104 , translates it into a CM Service Request message with a PD indicator, and then forwards the CM Service Request message to the MSC/VLR  114 . 
     As depicted in  FIG. 2 , to perform the inter-technology handoff from the packet-data domain to the circuit-switched domain, communication signaling is exchanged through a MGCF  130 , which is associated with MGW  132 . If the MSC/VLR  114  is capable of using packet-data call control messaging (e.g., SIP) the use of MGCF  130  and MGW  132  would not be necessary. In this case, the Mg interface would be between MSC/VLR  114  and I-CSCF  120  and IP instead of PCM/TCM would be the voice bearer output of the MSC/VLR  114 . 
       FIG. 3  shows the various signaling and data paths once the inter-technology handoff procedure has completed. As in  FIG. 2 ,  FIG. 3  assumes that the MSC/VLR  114  is only capable of using circuit-switched call control messaging (e.g., ISUP). In  FIG. 3 , the mobile device  104  is attached to the circuit wireless access network  107 , rather than the packet-data wireless access network  108  depicted in  FIG. 1 . Also, for the call in the circuit-switched domain, the new voice bearer data path extends through the circuit wireless access network  107 , the MSC/VLR  114 , the MGW  132 , the packet data network  112  to the other endpoint  110 , instead of extending through the packet-data wireless access network  108 , the PDSN  109 , the packet data network  112 , to the other endpoint  110  as shown in  FIG. 1 . If the MSC/VLR  114  is capable of using packet-data control call messaging (e.g., SIP) the use of MGCF  130  and MGW  132  would not be necessary. In this case, the Mg interface would be between MSC/VLR  114  and I-CSCF  120  and IP instead of PCM/TCM would be the voice bearer output of the MSC/VLR  114  to the packet data network  112 . 
       FIG. 4  shows an exemplary message flow diagram that depicts a inter-technology handoff procedure from the packet-data wireless access network  108  to the circuit wireless access network  107 , according to a preferred embodiment. A voice path  202  through a packet-data domain has been established between the mobile device  104  and the other endpoint  110 . 
     In response to a handoff stimulus ( 204 ), the mobile device sends (at  206 ) a handoff request (e.g., 1× call origination message) to a HRPD AN  108 . The call origination message includes a VDN (VCC Domain Transfer Directory Number), which is the directory number associated with the VCC AS  124 . The HRPD AN  108  forwards the handoff request to the IWS. The IWS translates the handoff request to a Service Request (e.g., 1×CM Service Request as defined in 3GPP2 A.S0014-C v2.0). The IWS then adds a PD indicator into the 1×CM Service Request. Note that the handoff could continue without the IWS adding the PD indicator to the 1×CM Service Request yet MSC/VLR  114  would assume that the Service Request was a request to originate a call. The IWS then forwards (at  208 ) the Service Request (with the PD indicator) to the MSC/VLR  114 . 
     The MSC/VLR  114  detects the PD indicator in the 1×CM Service Request, and knows that the Service Request is not a request for a call origination but is for an inter-technology handoff. The PD indicator allows MSC/VLR  114  to modify its behavior such that the message (e.g., 1× Assignment Request) to command the HRPD AN  108  to instruct the mobile device  104  to hand off (e.g., HRPD 1× Handoff Direction message) to the mobile device is not sent after processing  208  but instead is delayed to reduce the voice gap due to inter-technology handoff. In response to the Service Request message, the MSC  114 /VLR sends (at  210 ) an ANSI-41 ORREQ (as defined in 3GPP2 X.S0004-550) message to the WIN SCP  128  (or alternatively, to the HLR  126 ) to obtain routing information for the inter-technology domain transfer. The ORREQ message contains the Calling Party Number (MDN) of the mobile device  104  and the Called Party Number (VDN of the VCC AS  124 ) obtained from the 1×CM Service Request message. The WIN SCP  128  (or HLR  126 ) forwards (at  212 ) the ORREQ message to the VCC AS  124 . Alternatively, the MSC/VLR  114  may send the ORREQ message directly to the VCC AS  124  that has an integrated WIN SCP function. 
     The VCC AS  124  determines that the ORREQ is a request of an inter-technology domain transfer scenario for mobile device  104  based on the VDN in the Called Party Number (CdPN) and the MDN in the Calling Party Number (CgPN) in the ORREQ message. As a result, the VCC AS  124  allocates an IMRN, which is a temporary routing number associated with this inter-technology domain transfer. The VCC AS  124  then sends back (at  214 ) a responsive orreq message (containing the IMRN) to the WIN SCP  128  (or HLR  126 ), which returns (at  216 ) the orreq message to the MSC/VLR  114 . Alternatively, the VCC AS  124  that has an integrated WIN SCP function can send the orreq message directly to the MSC/VLR  114 . 
     After receiving the IMRN, the MSC/VLR  114  creates an ISUP IAM message that includes a CdPN and a CgPN. The CgPN is set to the MDN of the mobile device  104 . In this inter-technology handoff context, the CdPN is set to the IMRN from the orreq message received at  216 . The translation of CdPN performed by the MSC/VLR  114  results in the ISUP IAM message being routed (at  220 ) to the MGCF  130 . 
     The MGCF  130  next requests the MGW  132  to create two terminations: (1) the first termination is a TDM (time-division multiplexing) connection between the MGW  132  and the MSC/VLR  114  (the circuit-switched call leg); and (2) the second termination is an RTP/UDP/IP termination between the MGW  132  and the other endpoint  110  (packet-data call leg). RTP stands for Real-Time Protocol and is defined by IETF RFC 3550, and UDP stands for User Datagram Protocol and is defined by IETF RFC 0768. 
     In response to the IAM received at  220 , the MGCF  130  sends (at  222 ) a SIP INVITE message via the I-CSCF  120  ( FIG. 1 ) to the VCC AS  124 , where the SIP INVITE message is used to establish a call session. The SIP INVITE message contains the IMRN as the Request-URI of the INVITE message, where the Request-URI identifies the entity that the INVITE message is being addressed to (in this case the VCC AS  124 ), a P-Asserted-Identity set to the MDN and a SDP (Session Description Protocol as defined by RFC 4566) offer based on the RTP/UDP/IP termination created by MGW  132 . 
     The VCC AS  124  uses the P-Asserted-Identity in the INVITE message to determine which established voice call requires modification. The VCC AS  124  in response to the INVITE message, sends (at  224 ) a re-INVITE message to the other endpoint  110  to notify the other endpoint  110  of the change of IP address and UDP Port Number (from the IP address/UDP Port number used by the mobile device  104  to the IP address/UDP Port Number of the MGW  132 ). The re-INVITE message (at  224 ) forces the other endpoint  110  to establish a new voice bearer path to MGW  132 . 
     In the preferred embodiment, in response to the INVITE message received at  222 , the VCC AS  124  has to send (at  226 ) a SIP 183 Session Progress to the MGCF  130 . The 183 Session Progress message is used to convey information back to the MSC/VLR  114  about the progress of the call. 
     In response to the 183 Session Progress message, the MGCF  130  sends (at  228 ) an ISUP ACM message (as defined in 3GPP2 X.S0050) to the MSC/VLR  114 . The ACM message indicates to the MSC/VLR  114  that the VCC AS  124  has received the request to re-establish the call session in the circuit-switched domain, and that the VCC AS  124  has forwarded new information to the other endpoint  110  to enable the establishment of a new voice bearer path. 
     The VCC AS  124  is configured to send  224  and  226  at the earliest opportunity. The VCC AS is also configured to manipulate the sending of  224  and  226  such that  224  reaches the other endpoint  110  as compared to when  228  reached the MSC/VLR  114  is within some defined interval metric (e.g., the time differential that  224  reaches the other endpoint  110  as compared to  228  reaching the MSC/VLR  114  is +/−200 milliseconds). 
     In one exemplary embodiment, as depicted in  FIG. 4 , the SIP 183 Session Progress message ( 226 ) results in an ACM message ( 228 ) that triggers the MSC/VLR  114  to send (at  230 ) a 1× Assignment Request message to the IWS. The IWS translates and forwards the request to the HRPD AN  108 . The HRPD AN  108  converts the request into a handoff initiation message (e.g., a 1× Handoff Direction Message) that is sent (at  231 ) to the mobile device  104 . The handoff initiation message is an instruction to the mobile device  104  to perform the handoff and acquire the circuit traffic channel (e.g., 1×RTT traffic channel). The circuit base station  107  then acquires the reverse traffic channel of the mobile device  104  and a voice bearer path is established (at  232 ) between the mobile device  104  and the MSC/VLR  114 . 
     The mobile device  104  acknowledges the handoff initiation message ( 231 ) by sending (at  233 ) a handoff done message (e.g., a 1× Handoff Completion Message) to the 1×BS  107 . The 1×BS in return sends (at  235 ) a 1× Assignment Complete message to the MSC/VLR  114 . Also, the other endpoint  110  acknowledges the re-INVITE message (sent at  224  from the VCC AS  124 ) by returning (at  234 ) a SIP 200 OK message containing the IP address and UDP Port Number (e.g., OEP SDP) of the other endpoint  110  to the VCC AS  124  and by initiating a new voice bearer path to the MGW IP address and UDP Port number received in  224  (e.g., in the MGW SDP). The VCC AS  124  forwards the 200 OK message (at  236 ) to the MGCF  130  via the I-CSCF  120 . The MGCF  130 , upon receiving the SIP 200 OK message, requests modification of the MGW  132  termination using the other endpoint  110 , SDP (Session Description Protocol) information contained in the SIP 200 OK message, and instructs the MGW  132  to reserve/commit resources for the call. Also, the MGCF  130  sends (at  238 ) an ISUP ANM (answer message) to the MSC/VLR  114 , which is an indication that the other endpoint  110  has modified the call and that the new voice bearer path from the other endpoint  110  to the MSC/VLR  114  has been established. 
     The MGCF  130  acknowledges the SIP 200 OK message ( 236 ) by sending an SIP ACK message (at  242 ) to the VCC AS  124 . In turn, the VCC AS  124  forwards (at  244 ) the SIP ACK message to the other endpoint  110 . 
     Note that anytime after the VCC AS  124  has received (at  234 ) the SIP 200 OK message from the other endpoint  110 , the VCC AS  124  sends (at  240 ) a SIP BYE message to the mobile device via the S-CSCF  118  to release SIP call dialog that was initially established between the mobile device  104  and the VCC AS  124 . The SIP BYE message is not acknowledged, since when the mobile device  104  is now attached to the circuit wireless access network  107  and thus the mobile device  104  never receives it. 
     After the procedure depicted in  FIG. 4 , a voice call is re-established (at  246 ) between the mobile device  104  and the other endpoint  110  via the circuit-switched domain. 
     A break in the voice bearer data starts either when the mobile device  104  detaches from the packet-data wireless access network  108  (after  231 ) or when the other endpoint  110  stops sending voice bearer data to the IP address/UDP Port Number of mobile device  104  and initiates a new voice bearer path to MGW  132  (after receiving  224 ). The break in the voice bearer data will continue until the other endpoint  110  establishes the new voice bearer path (after MGCF receives step  236 ) and the mobile device  104  attached to the circuit wireless access network  107 . 
     A “P2C” time interval is defined as the time interval of the MSC/VLR  114  sending a 1× Assignment Request ( 230 ) until a 1× Assignment Complete ( 233 ) is received by the MSC/VLR  114 . The P2C time interval varies for each set of MSC/VLR  114 , HRPD AN  108 , and circuit wireless access network  107 . For some sets the P2C time interval might be short (e.g., 300 milliseconds) whereas for other sets the P2C time interval might be long (e.g., 2000 milliseconds). Usually the P2C time interval for the set is known and in the preferred embodiment the MSC/VLR can use this additional information to determine an appropriate trigger for sending  230 . 
     In the message flow of  FIG. 4 , as part of the preferred embodiment, the VCC AS  124  provides feedback ( 226 ) to the MSC/VLR  114  as to the progress of the establishing the new voice bearer path. A mentioned the VCC AS  124  manipulates the sending of  224  and  226  such that  224  to reach the other endpoint  110  within so time interval (e.g., +/−200 milliseconds) of  228  reaching the MSC/VLR  114 . As discussed above, in an alternative embodiment, if the P2C time interval is long, the MSC/VLR  114  might send  230  upon receiving  216  or sending  220 . If the P2C time interval is extremely short the MSC/VLR  114  might send  230  after receiving  238 . 
       FIG. 5  shows a variation of the  FIG. 4  flow in which the MSC/VLR  114  is assumed to be capable of using both packet-data control call messaging (e.g., SIP) and circuit-switched control signaling (e.g., ISUP). In this case, the MGCF  130  and MGW  132  can be omitted, and the messages of  FIG. 4  exchanged with the MGCF can be omitted. For example, the SIP 183 Session Progress message is sent (at  226 ) from the VCC AS  134  to the MSC/VLR  114  instead of the MGCF (note that the ISUP ACM message ( 228 ) of  FIG. 4  has been omitted in  FIG. 5 ). In this example, the 183 Session Progress message triggers sending ( 230 ) of the 1× Assignment Request from the MSC/VLR  114  to the IWS. 
     Also, the VCC AS  124  can send (at  236 ) the SIP 200 OK message to the MSC/VLR  114 , instead of the MGCF. As a result, the ISUP ANM message ( 238 ) of  FIG. 4  can be omitted. 
     The remaining parts of the flow of  FIG. 5  are similar to the flow of  FIG. 4 . 
       FIG. 6  generically shows a network node  500  that can represent any one of a base station (e.g., base station in the packet-data wireless access network  108  or in the circuit wireless access network  107  of  FIG. 1 ), the MSC/VLR  114 , and the VCC AS  124 , as configured according to preferred embodiments. The network node  500  includes software  502  that is executable on one or more central processing units (CPUs  504 ), which is (are) connected to a computer-readable storage  506  (e.g., memory, disk drive, etc.). The network node  500  also include protocol layers  508  and a network interface  510  to enable communication with another network node (e.g., between a mobile device  104  and base station, between a base station and the MSC/VLR  114 , between the VCC AS  124  and the other endpoint  110  or MGCF  130 , and so forth). 
     A CPU  504  can include any type of processor, such as microprocessors, microcontrollers, processor modules or subsystems (including one or more microprocessors or microcontrollers), or other control or computing devices. A “processor” can refer to a single component or to plural components. 
     Data and instructions (of the software) are stored in respective storage devices, which are implemented as one or more computer-readable or computer-usable storage media. The storage media include different forms of memory including semiconductor memory devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and flash memories; magnetic disks such as fixed, floppy and removable disks; other magnetic media including tape; and optical media such as compact disks (CDs) or digital video disks (DVDs). 
     In the foregoing description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details. While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.

Metadata:
Filing Date: 20160422
Publication Date: 20181113
Grant Date: 20181113
Priority Date: 20070510
Inventors: STEGALL, MARK A.
BIENN, MARVIN
CHEN, JING
STEPHENS, GARY
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W36/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W88/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W60/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0066", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0022", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/144", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/304", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0066", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W60/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W88/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0066", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/144", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/304", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 45990870