US20060109819A1 - Method and apparatus for inter-system active handoff of a hybrid subscriber unit - Google Patents

Abstract

A communication system provides for an active handoff of a voice call between a packet switched network and a circuit switched network. An active handoff from the packet switched network to the circuit switched network is accomplished by multicasting the call over forward links of both networks during the handoff. An active handoff from the circuit switched network to the packet switched network is accomplished by multicasting the call over reverse links of both networks during the handoff. The former handoff further may be facilitated by routing the call for each network through a same packet data control switch, and the latter handoff further may be facilitated by routing the call for each network through a same mobile switching center. In order for a subscriber unit to operate concurrently in both networks, the subscriber unit may comprise multiple transceivers or a single transceiver that is rapidly switched between the networks.

Description

CROSS REFERENCE TO RELATED APPLICATION
• The present application claims priority from provisional application Ser. No. 60/629,960, entitled “METHOD AND APPARATUS FOR INTER-SYSTEM ACTIVE HANDOFF OF A HYBRID SUBSCRIBER UNIT,” filed Nov. 22, 2004, which is commonly owned and incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
• The present invention relates generally to wireless communication systems, and more specifically to handoff of a hybrid communication device between a Voice over Internet Protocol (VoIP) communication session and a conventional cellular communication session.
BACKGROUND OF THE INVENTION
• The evolution of cellular communications has resulted in a proliferation of networks of different technologies and corresponding different air interfaces. As a result, during the course of a single voice call, a wireless subscriber unit may roam among multiple networks, wherein each such network implements a different technology than the other networks of the multiple networks. Among the different network technologies are packet switched CDMA (Code Division Multiple Access) technologies, such as CDMA 2000 1XEV-DO (1X Evolution Data Only) or packet switched CDMA 1XRTT (1X Radio Transmission Technology), that are capable of providing Voice over Internet Protocol (VoIP) communication services, and conventional, or legacy, CDMA cellular communication technologies, such as a CDMA 1X, that provide circuit switched voice communication systems.
• As the subscriber unit roams among a packet switched CDMA communication network and a circuit switched CDMA communication network, it may be beneficial to system performance to handoff the subscriber unit from the former network to the latter network or from the latter network to the former network. For example, the channel conditions associated with one such network may be more favorable than the channel conditions associated with the other such network due to such factors as fading, adjacent and co-channel interference, and available power at a serving base station (BS) or radio access network (RAN). By way of another example, an operator of both a packet switched CDMA network and a circuit switched CDMA network may desire to move the subscriber unit from one such network to the other such network for purposes of balancing system loading.
• Currently, the only defined method for executing a handoff between a packet switched CDMA or WLAN network and a circuit switched CDMA network is an execution of a hard handoff, wherein a subscriber unit must drop a radio resource of a network of a first CDMA technology prior to acquiring a radio resource of a network of a second CDMA technology. A result is a brief period of time during which the subscriber unit is not actively engaged in a communication session with either network. Further, when executing a hard handoff there is no linkage between the two networks as the subscriber unit must drop the first network and acquire the second network without any assistance from the BS or RAN of either network. As a result, voice traffic may be lost during the handoff, resulting in poor system performance and efficiency and disgruntled end users.
• Therefore, a need exists for a method and apparatus for an active handoff of a voice call between a packet switched CDMA or WLAN network and a circuit switched CDMA network that assures that the subscriber unit is actively engaged in a communication session with at least one network at all times.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a block diagram of a wireless communication system in accordance with an embodiment of the present invention.
• FIG. 2 is a block diagram of a packet data control switch ofFIG. 1 in accordance with an embodiment of the present invention.
• FIG. 3 is a block diagram of a subscriber unit ofFIG. 1 in accordance with an embodiment of the present invention.
• FIG. 4 is a block diagram of a subscriber unit ofFIG. 1 in accordance with another embodiment of the present invention.
• FIG. 5 is a signal flow diagram illustrating a handoff of a voice call from a packet-based network ofFIG. 1 to a circuit switched network ofFIG. 1 in accordance with an embodiment of the present invention.
• FIG. 6 is a diagram of an exemplary SIP REFER message as modified in accordance with an embodiment of the present invention.
• FIG. 7 is a signal flow diagram illustrating a handoff of a voice call from a circuit switched network ofFIG. 1 to a packet-based network ofFIG. 1 in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• To address the need for a method and apparatus for an active handoff of a voice call between a packet switched CDMA or WLAN network and a circuit switched CDMA network that assures that the subscriber unit is actively engaged in a communication session with at least one network at all times, a communication system is provided that provides for an active handoff of a voice call between a packet switched network, such as a CDMA 2000 1XRTT network, a CDMA 2000 1XEV-DO network, or a WLAN network, and a circuit switched network, preferably a CDMA 1X network, by transmitting the call over both networks (herein referred to as multicasting) during the course of the handoffs. An active handoff from the packet switched network to the circuit switched network is accomplished by multicasting the call over forward links of both networks during the handoff. An active handoff from the circuit switched network to the packet switched network is accomplished by multicasting the call over reverse links of both networks during the handoff. The former handoff further may be facilitated by maintaining a packet data control switch of the packet switched network in the call even when the call is routed through the circuit switched network, and the latter handoff further may be facilitated by maintaining a mobile switching center of the circuit switched network in the call even when the call is routed through the packet switched network. In order for a hybrid subscriber unit to operate concurrently in both networks, the subscriber unit may comprise multiple transceivers. However, in another embodiment of the present invention, the hybrid subscriber unit may comprise a single transceiver that is rapidly switched between the networks to give the appearance of concurrent operation. In addition, when switching between networks, a vocoder in the single transceiver subscriber unit may be instructed by the processor to use a reduced rate that allows for the time for the rapid switching without severely degrading voice quality.
• Generally, an embodiment of the present invention encompasses a method for handoff of a voice call from a packet switched network having a packet data control switch to a circuit switched network. The method includes conveying forward link voice traffic to, and receiving reverse link voice traffic from, a subscriber unit via the packet switched network and receiving, by the packet switched network, a notification to hand off the call to the circuit switched network. The method further includes, in response to receiving the handoff notification, conveying forward link voice traffic to the subscriber unit via the packet switched network and via the packet data control switch and the circuit switched network, and concurrently receiving reverse link voice traffic only via the packet switched network. The method further includes, when conveying forward link voice traffic to the subscriber unit via each of the packet switched network and the circuit switched network, switching from the packet switched network to the packet data control switch and the circuit switched network for reception of reverse link voice traffic and, in response to switching from the packet switched network to the circuit switched network for reception of reverse link voice traffic, ceasing conveying forward link voice traffic to the subscriber unit via the packet data control switch and the packet switched network while continuing to convey forward link voice traffic to the subscriber unit via the packet data control switch and the circuit switched network.
• Another embodiment of the present invention encompasses a packet data control switch having a processor configured to, in association with a subscriber unit call, route forward link voice traffic and receive reverse link voice traffic via a packet switched network, receive a notification to hand off the call from the packet switched network to a circuit switched network, in response to receiving the handoff notification, route forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network and concurrently receive reverse link voice traffic only via the packet switched network, when conveying forward link voice traffic to the subscriber unit via each of the packet switched network and the circuit switched network, switch reception of reverse link voice traffic from the packet switched network to the circuit switched network, and in response to switching reception of reverse link voice traffic from the packet switched network to the circuit switched network, cease routing forward link voice traffic to the subscriber unit via the packet switched network while continuing to route forward link voice traffic to the subscriber unit via the circuit switched network.
• Yet another embodiment of the present invention encompasses a method for handoff of a voice call from a circuit switched network to a packet switched network. The method includes conveying forward link voice traffic to, and receiving reverse link voice traffic from, a subscriber unit via the circuit switched network and determining, by the circuit switched network, to hand off the call. The method further includes notifying the packet switched network, by the circuit switched network, of the need for a handoff and, in response to receiving the handoff notification, conveying, by the packet switched network of the subscriber unit, a request to perform a handoff and establishing a communication session between the packet switched network and the subscriber unit. The method further includes receiving reverse link voice traffic from the subscriber unit via the circuit switched network and via the packet switched network, and concurrently conveying forward link voice traffic to the subscriber unit only via the circuit switched network and, when receiving reverse link voice traffic via the packet switched network and the circuit switched network, switching from the circuit switched network to the packet switched network for conveyance of forward link voice traffic to the subscriber unit. The method further includes, in response to switching forward link voice traffic from the packet switched network to the circuit switched network, ceasing reception of reverse link voice traffic via the circuit switched network while continuing to receive reverse link voice traffic via the packet switched network.
• Still another embodiment of the present invention encompasses a communication system for inter-network handoff of a voice call from a circuit switched network to a packet switched network. The communication system includes a base station that transmits forward link voice traffic to a subscriber unit via a first forward link, receives reverse link voice traffic from the subscriber unit via a first reverse link from, and that determines to hand off the call. The communication system further includes a mobile switching center in communication with the base station that conveys the forward link voice traffic to the base station, receives the reverse link voice traffic from the base station, and that, in response to the determination to hand off the call, conveys a notification of the need for a handoff, and a packet data control switch that receives the handoff notification from the mobile switching center and, in response to receiving the handoff notification, requests that the subscriber unit perform a handoff. The communication system further includes an access network in communication with the packet data control switch that, in response to the request to perform a handoff, establishes a second forward link and a second reverse link with the subscriber unit. In response to the establishment of the second forward link and the second reverse link with the subscriber unit, each of the base station and the access network receives reverse link voice traffic from the subscriber unit while only the base station conveys forward link voice traffic to the subscriber unit. After each of the base station and the access network begins receiving reverse link voice traffic from the subscriber unit, conveyance of the forward link voice traffic to the subscriber unit is switched from the base station and the first forward link to the access network and the second forward link. In response to switching conveyance of forward link voice traffic from the base station and the first forward link to the access network and the second forward link, the base station ceases receiving reverse link voice traffic while the access network continues to receive reverse link voice traffic.
• Yet another embodiment of the present invention encompasses a method for handoff of a voice call from a packet switched network having a packet data control switch to a circuit switched network. The method includes communicating voice traffic via the packet switched network, receiving, by the packet switched network, a notification to hand off the call, wherein the notification to hand off identifies the circuit switched network as the network to hand off the call to, and in response to receiving the handoff notification, establishing communication via the circuit switched network and terminating communication via the packet switched network.
• Still another embodiment of the present invention encompasses a method for handoff of a voice call from a packet switched network having a packet data control switch to a circuit switched network. The method includes communicating voice traffic via the packet switched network, determining, by subscriber unit, to hand off the call, transmitting a notification to hand off the call, wherein the notification to hand off identifies the circuit switched network as the network to hand off the call to, and in response to transmitting the handoff notification, establishing communication via the circuit switched network and terminating communication via the packet switched network.
• Yet another embodiment of the present invention encompasses a method for emulating concurrent operation by a hybrid subscriber unit in each of a network associated with a first radio frequency (RF) technology and a network associated with a second RF technology. The method includes, when transmitting, alternating between transmission via a first air interface associated with the first RF technology and transmission via a second air interface associated with the second RF technology and, when receiving, alternating between reception via an air interface associated with the first RF technology and reception via an air interface associated with the second RF technology.
• Still another embodiment of the present invention encompasses a hybrid subscriber unit capable of operating in each of a network associated with a first RF technology and a network associated with a second RF technology. The subscriber unit includes a transceiver for transmitting and receiving RF communications and a processor in communication with to the transceiver. The processor, when transmitting, alternates between transmission via an air interface associated with the first RF technology and transmission via an air interface associated with the second RF technology and, when receiving, alternates between reception via a first air interface associated with the first RF technology and reception via a second air interface associated with the second RF technology.
• The present invention may be more fully described with reference toFIGS. 1-7.FIG. 1 is a block diagram of awireless communication system100 in accordance with an embodiment of the present invention.Communication system100 includes a wireless IP (Internet Protocol)-based packet switchednetwork110 and a wireless circuit switchednetwork120. Packet switchednetwork110 includes a packet data control switch (PDCS)118 that is in communication with a packet-based wireless Access Network (AN)114, such as a Radio Access Network (RAN) or a wireless local area network (WLAN) Access Point (AP), via a Packet Data Serving Node (PDSN)116. In one embodiment of the present invention, PDCS118 may comprise one or more of a Mobile Switching Center Evolution-Emulation (MSCe) and a Media Gateway (MGW). In other embodiments of the present invention, PDCS118 may further comprise, or be coupled to, one or more Session Initiation Protocol (SIP) Servers.PDCS118 further provides transcoding functionality with respect to transcoding between the vocoder formats provided bysubscriber unit102 and the 64 kbps Pulse Code Modulation (PCM) format (ITU-T G.711) transported byPSTN132. In still other embodiments of the present invention,PDCS118 may comprise one or more SoftSwitch(es), which is available from Motorola, Inc., of Schaumburg, Ill. and other suppliers.
• FIG. 2 is a block diagram ofPDCS118 in accordance with an embodiment of the present invention.PDCS118 includes aprocessor202, such as one or more microprocessors, microcontrollers, digital signal processors (DSPs), combinations thereof or such other devices known to those having ordinary skill in the art, which processor is configured to execute the functions described herein as being executed byPDCS118.PDCS118 further includes at least onememory device204 associated withprocessor202, such as random access memory (RAM), dynamic random access memory (DRAM), and/or read only memory (ROM) or equivalents thereof, that store data and programs that may be executed by the processor and that allow the PDCS to perform all functions necessary to operate incommunication system100.
• Circuit switchednetwork120 includes a Base Station (BS)124 that is in communication with a circuit switch-based Mobile Switching Center (MSC)126. With respect to circuit switchednetwork120,MSC126 is coupled to a respective Home Location Register (HLR) (not shown) and further is coupled to a respective Visited Location Register (VLR) (not shown) or is coupled to an Authentication, Authorization, and Accounting Server (AAA) (not shown). As is known in the art, the HLR and VLR or AAA associated withMSC126 includes mobility and provisioning information associated with each subscriber unit subscribed to and/or registered for the services of the PDCS's or MSC'srespective network110,120, such as a profile of the subscriber unit, including the capabilities of the subscriber unit, and an AN or BS currently serving the subscriber unit. With respect to packet switchednetwork110, when Mobile IP (Internet Protocol) is used, macro-mobility is handled by a Home Agent (HA) (not shown) and a Foreign Agent (FA) (not shown) associated withPDSN116 as is known in the art. When simple IP is used, there is no macro-mobility and micro-mobility is handled by a hierarchical arrangement of RANs, PSDNs, and PCFSs as is known in the art. AN114 andBS124 each provides wireless communication services to the subscriber units located in a coverage area of the AN or BS via arespective air interface112,122. Eachair interface112,122 includes a forward link that includes at least one forward link traffic channel and at least one forward link control channel. The forward link may or may not further include a paging channel. For example, in a CDMA 2000 1XEV-DO communication system the paging function is performed using a Route Update Protocol. Eachair interface112,122 further includes a reverse link that includes at least one reverse link traffic channel, at least one reverse link signaling channel, and an access channel.
• Packet switchednetwork110 and circuit switchednetwork120, and more particularly PDCS118 andMSC126, communicate with each other via anintermediate network130 that operates in accordance with well-known intersystem protocols and preferably the protocols described in the 3GPP2 (Third Generation Partnership Project 2) TIA-41 (Telecommunications Industry Association-41) standard, that is, 3GPP2 N.S0005. The TIA-41 standard provides standardized intersystem procedures for mobility management in cellular systems and prescribe messaging among Mobile Switching Centers, Home Location Registers (HLRs), Visited Location Registers (VLRs), Authentication Centers (ACs), and other core network elements of cellular systems in order to provide services to subscriber units when interaction is required between different cellular systems. Packet switchednetwork110 and circuit switchednetwork120, and more particularly PDCS118 andMSC126, are each further coupled to alandline network132, such as a Public Switched Telephone Network (PSTN) that includes SS7 signaling.
• Communication system100 further includes a wireless subscriber unit (SU)102, for example but not limited to a cellular telephone, a radiotelephone, or a Personal Digital Assistant (PDA), personal computer (PC), or laptop computer equipped for wireless voice communications. In various communications systems,subscriber unit102 may also be referred to as an access terminal (AT), a mobile station (MS), or a user's equipment (UE).Subscriber unit102 comprises a hybrid terminal that is capable of engaging in a Voice over Internet Protocol (VoIP) call with packet switchednetwork110 and is further capable of engaging in a conventional cellular call with circuit switchednetwork120, and more particularly is capable of communicating withPDCS118 via the SIP protocols and withMSC126 via the IS-2000 protocols.
• Referring now toFIG. 3, in one embodiment of the present invention, ahybrid subscriber unit300, such assubscriber unit102, capable of operating incommunication system100 may include multiple transceivers, that is, afirst transceiver302 for operation packet switchednetwork110 and asecond transceiver304 for operation in circuit switchednetwork120, thereby allowing the subscriber unit to concurrently transmit or receive in each of the two networks. Each transceiver is coupled to avocoder306 and aprocessor308, which processor is further coupled to an at least onememory device310.
• In another embodiment of the present invention, and referring now toFIG. 4, ahybrid subscriber unit400, such assubscriber unit102, capable of operating incommunication system100 may include asingle transceiver402 that emulates the operation of dual transceivers, such astransceivers302 and304.Transceiver402 is coupled to aprocessor404, which processor is further coupled to an at least onememory device406.Processor404 may causetransceiver402 to rapidly switch betweennetworks110 and120 to give the appearance of concurrent operation. Further,subscriber unit400 may maintain apriori information in at least onememory device406 that facilitates the switching between networks at optimum times. In addition, when switching between networks, avocoder408 coupled to a bus interconnecting each oftransceiver402,processor404, and at least onememory device406 may be instructed by the processor to use a reduced rate that allows for the time for the rapid switching without severely degrading voice quality.
• Each ofprocessors308 and404 may comprise one or more microprocessors, microcontrollers, digital signal processors (DSPs), combinations thereof or such other devices known to those having ordinary skill in the art, which processor is configured to execute the functions described herein as being executed bysubscriber unit102. Each of at least onememory devices310 and406 may comprise random access memory (RAM), dynamic random access memory (DRAM), and/or read only memory (ROM) or equivalents thereof, that store data and programs that may be executed by the associated processor and that allowsubscriber unit102 to perform all functions necessary to operate incommunication system100.
• In order forsubscriber unit102 to engaged in a voice call with adistant party134 vialandline network132 and one or more of packet switchednetwork110 and circuit switchednetwork120, each ofsubscriber unit102, packet switchednetwork110, and circuit switchednetwork120 operates in accordance with well-known wireless telecommunications protocols. Whiledistant party134 is depicted as being connected tolandline network132,distant party134 may be connected to any voice communication network, including packet switchednetwork110 and circuit switchednetwork120. Preferably, packet switchednetwork110 is a CDMA (Code Division Multiple Access) 2000 communication system that provides VoIP communication services to subscribers serviced by the network and that operates in accordance with the 3GPP2 and TIA/EIA (Telecommunications Industry Association/Electronic Industries Association) IS-856 and 3GPP2 C.S0024 standards, which provides a compatibility standard for CDMA 2000 1XEV-DO (1X Evolution Data Only) systems. Preferably, circuit switchednetwork120 is a CDMA 2000 communication system that provides circuit switched communication services to subscribers serviced by the network and that operates in accordance with the CDMA 1X standards.
• Further,air interface122, and correspondingly network120 andsubscriber unit102, preferably operates in accordance with the TIA/EIA (Telecommunications Industry Association/Electronic Industries Association) one or more of the IS-95 and TIA-2000 standards, or Inter Operability Specifications (IOSs), which provide a compatibility standard for cellular mobile telecommunications systems that operate as a CDMA 2000 system. In addition,air interface112, and correspondingly network110 and againsubscriber unit102, preferably operates in accordance with one or more of the IS-95, TIA-2000, TIA-2001 (3GPP2 A.S0011 to A.S0017), or TIA-878 and TIA-1878 (A.s0007 and A.S0008) standards, or Inter Operability Specifications (IOSs), which provide a compatibility standard for cellular mobile telecommunications systems that operate as a CDMA 2000 1XEV-DO, 1XEV-DV, or 1XRTT system. To ensure compatibility, radio system parameters and call processing procedures are specified by the standards, including call processing steps that are executed by an MS and a base station serving the MS and between the BS and associated infrastructure in order to establish a call or execute a handoff. However, those of ordinary skill in the art realize that packet switchednetwork110 may operate in accordance with any one of a variety of wireless packet data communication systems that provide VoIP communication services, such as a Wireless Local Area Network (WLAN) communication system as described by the IEEE (Institute of Electrical and Electronics Engineers) 802.xx standards, for example, the 802.11, 802.15, 802.16, or 802.20 standards, and that circuit switchednetwork120 may operate in accordance with any one of a variety of well-known conventional wireless telecommunication systems that provide circuit switched communication services.
• Incommunication system100,subscriber unit102 may roam through the system when the subscriber unit is engaged in a voice call. As a result of the roaming, situations may arise where it is desirable to hand offsubscriber unit102 from packet switchednetwork110 to circuit switchednetwork120 or from circuit switchednetwork120 to packet switchednetwork110. For example and as is known in the art, while roaming incommunication system100 and being serviced by AN114,subscriber unit102 may receive a stronger signal fromBS124 or, while being serviced byBS124,subscriber unit102 may receive a stronger signal from AN114. Typically signal strengths are determined by a subscriber unit, such assubscriber unit102, measuring a pilot channel associated with the AN or BS. When a pilot channel of a serving AN or BS is weaker than a threshold value and a pilot channel of another AN or BS, that typically indicates a desirability of a handoff.
• By way of another example, the costs associated with operatingsubscriber unit102 on packet switchednetwork110 may be different from the costs associated with operatingsubscriber unit102 on circuit switchednetwork120. In turn, an operator (or operators) ofnetworks110 and120 may charge a different fee for use of each network. As a result, a user ofsubscriber unit102 may program into the subscriber a directive to operate on the lower cost network whenever the subscriber unit is able to obtain a traffic channel in the lower cost network. Whensubscriber unit102 is engaged in a voice call in a higher cost network and is able to obtain a traffic channel in the lower cost network, the subscriber unit, or the user of the subscriber unit if the user is informed of the availability of a traffic channel in the lower cost network, may initiate a handoff to the lower cost network.
• By way of yet another example, it may be desirable to move a subscriber unit, such assubscriber unit102, that is actively engaged in a voice call in circuit switchednetwork120 to packet switchednetwork110 when the user ofsubscriber unit102 prefers to use video telephony service rather than a voice call, and packet switchednetwork110 supports video telephony but circuit switchednetwork120 does not.
• By way of yet another example, for load leveling purposes, for network cost consideration purposes, or due to a need to clear traffic channels in a coverage area in order to facilitate emergency communications, an operator of a communication system such ascommunication system100 may find it desirable to move a subscriber unit, such assubscriber unit102, that is actively engaged in a voice call in a first network, such as packet switchednetwork110 or circuit switchednetwork120, to the other network.
• In order to facilitate a handoff of a subscriber unit such assubscriber unit102,communication system100 provides a method and apparatus for an active handoff ofsubscriber unit102 from packet switchednetwork110 to circuit switchednetwork120 or from circuit switchednetwork120 to packet switchednetwork110 when the subscriber unit is actively engaged in a voice call. By providing for an active handoff of a voice call between a packet switched CDMA network and a circuit switched CDMA network,communication system100 assures thatsubscriber unit102 is actively engaged in a communication session with at least one ofnetworks110 and120 at all times, thereby minimizing the likelihood that voice traffic may be lost during the handoff.
• FIG. 5 is a signal flow diagram500 of a handoff executed bycommunication system100 in handing off a voice call from packet switchednetwork110 to circuit switchednetwork120 in accordance with an embodiment of the present invention. Signal flow diagram500 begins whensubscriber unit102 is actively engaged in a VoIP call withdistant party134 via packet switchednetwork110 andlandline network132. In order to participate in a VoIP call via packet switchednetwork110,subscriber unit102 must already be registered with the packet switched network. As part of the call, a SIP session and a Real Time Protocol (RTP) session are active betweensubscriber unit102 andPDCS118. WhenPDCS118 comprises an MSCe and an MGW, the SIP session is active betweensubscriber unit102 and the MSCe and the RTP session is active between the subscriber unit and the MGW. SIP is described in Internet Engineering Task Force (IETF) Request for Comment (RFC) 3261, which RFC is hereby incorporated herein in its entirety.Subscriber unit102 conveys502 reverse link frames comprising voice information to PDCS118 via a reverse link traffic channel ofair interface112, AN114, andPDSN116, (referred to herein as a reverse link unicast) for routing tolandline network132 anddistant party134. Further, whenPDCS118 receives voice traffic fromlandline network132, and more particularly fromdistant party134, and intended forsubscriber unit102, thePDCS routes504 the voice information to AN114 viaPDSN116 and the AN conveys forward link frames comprising the voice information tosubscriber unit102 via a forward link traffic channel of air interface112 (referred to herein as a forward link unicast).
• Prior to or during the course of the VoIP call,subscriber unit102further registers506 with circuit switchednetwork120, and more particularly withMSC126 viaBS124. For example,subscriber unit102 may roam from the coverage area serviced by AN114 to the coverage area serviced byBS124, that is, by circuit switchednetwork120, and upon roaming into the coverage area of the circuit switched network registers with the circuit switched network. By way of another example,subscriber unit102 may initially activate in an area of coverage of bothAN114 andBS124. At activation,subscriber unit102 may register with both packet switchednetwork110 and circuit switchednetwork120, and more particularly withPDCS118 via AN114 andPDSN116 and withMSC126 viaBS124. Such registration procedures are well-known in the art and will not be described in detail herein except to note that when a subscriber unit registers with a network, the network stores in a respective HLR or VLR an identification of an AN or BS associated with the network and serving the subscriber unit. Registration ofsubscriber unit102 with each ofnetworks110 and120 facilitates the network's ability to locate the subscriber unit and to determine an AN or BS to use when paging the subscriber unit. In response to registering with each ofnetworks110 and120,subscriber unit102 tunes to the forward link paging channel or paging function of thenetwork120.
• At some point in time during the course of the VoIP call,subscriber unit102 determines that the call should be handed off from AN114 and packet switchednetwork110 toBS124 and circuit switchednetwork120. As noted above, this determination may be made based on, among other considerations, any one or more of signal strength measurements, network cost/load considerations, or a directive of a user of the subscriber unit. In response to determining that the call should be handed off,subscriber unit102 notifies508 AN114 of the subscriber unit's desire to initiate a handoff. AN114forwards510 the notification to PDSN116 and, in turn, the PDSN forwards512 the notification toPDCS118. Typically, SIP messages are transparent to network elements such as AN114 andPDSN116. Preferably, the notification ofPDCS118 bysubscriber unit102 of the desire for a handoff is accomplished by use of SIP messaging, and more particularly by use of a modified version of a SIP REFER message (RFC 3515) that is transmitted by the subscriber unit and forwarded to the PDCS, which SIP REFER message is modified to identify a target network, that is, circuit switchednetwork120, for a handoff of the identified subscriber unit.
• FIG. 6 is a diagram of an exemplary modified SIP REFERmessage600 that may be transmitted bysubscriber unit102 in order to initiate a handoff in accordance with an embodiment of the present invention. As depicted byFIG. 6, SIP REFERmessage600 includes a first data field602, that is, a message-type data field, that indicates that this is a SIP REFER message. SIP REFERmessage600 further includes asecond data field604, that is, a destination data field, that identifiessubscriber unit102 as the destination of the message, and athird data field606, an origination data field, that further identifiessubscriber unit102 as the originator of the message. By identifying the same subscriber unit, that is,subscriber unit102, as the originator and target of the message, the SIP REFER message indicates that a handoff is being requested. In addition, unlike SIP REFER messages of the prior art, SIP REFERmessage600 has been modified to further include a fourth data field608, a target network indicator data field, that identifies a target network for a handoff of the identified subscriber unit. For example, as depicted inFIG. 6, target network indicator data field is named “P-Access-Network-Info” and the target network for handoff is a 3GPP2 1XRTT network such as packet switchednetwork110.
• In response to being notified bysubscriber unit102 of the desire for a handoff and based on the target network identified by the notification, that is, circuit switchednetwork120,PDCS118 determines the target MSC, that is,MSC126, by reference to at least one of the HLR and VLR and a pre-provisioned database (not shown) included in or coupled to thePDCS118. In response to determining the target MSC, that is,MSC126,PDCS118 notifies514MSC126 viaintermediate network130 of the need for a handoff and further identifies the subscriber unit, that is,subscriber unit102, requesting the handoff. Preferably,PDCS118 notifiesMSC126 of the need for a handoff and the requesting subscriber unit by conveying a TIA-41 FACDIR2 (Facilities Directive No. 2) INVOKE message to the MSC. In response to receiving the handoff notification fromPDCS118,MSC126 determines the target BS, that is,BS124, by reference to at least one of the HLR and VLR included in or coupled to the MSC.MSC126 then notifies516target BS124 of the need for a handoff ofsubscriber unit102, preferably by conveying a HANDOFF REQUEST message as described in detail in the IOS, to the BS.
• In response to receiving the handoff notification fromMSC126,BS124pages518subscriber unit102.BS124 may further convey518ahandoff request message to the subscriber unit via the at least one forward link control channel of the air interface and may negotiate a vocoder format with the subscriber unit. In addition,BS124 preferably sets up a communication session withsubscriber unit102 by allocating a forward link traffic channel and a reverse link traffic channel to the subscriber unit and further establishes a bearer path between the subscriber unit andMSC126 in accordance with well-known techniques. For example,BS124 may directsubscriber unit102 to a traffic channel immediately following the page by performing an early traffic channel assignment or the BS may convey a channel assignment message (CAM) to force the subscriber unit to a traffic channel.BS124 then initiates the establishment of a bearer path with the subscriber unit by conveying520 null frames to the subscriber unit via the allocated forward link traffic channel.BS124 further informssubscriber unit102 of the allocated reverse link traffic channel via one of the allocated forward link traffic channel and the at least one forward link signaling channel.
• Further, in response to receiving the handoff notification fromMSC126,BS124 acknowledges522 the notification received fromMSC126 of the need for a handoff by conveying an acknowledgement, preferably a HANDOFF REQUEST ACK as described in detail in the IOS, back to the MSC. In response to receiving the acknowledgement fromBS124,MSC126 acknowledges524 the handoff notification514 received by the MSC fromPDCS118 by conveying a handoff notification acknowledgement to the PDCS. Preferably, the handoff notification acknowledgement comprises a TIA-41 FACDIR2 RESPONSE message toPDCS118.
• At this point in signal flow diagram500, forward link traffic channels are established withsubscriber unit102 in each ofair interfaces112 and122. In response to receiving the handoff notification acknowledgement fromMSC126,PDCS118 begins to multicast526,530 voice traffic tosubscriber unit102. That is, whenPDCS118 receives voice traffic fromdistant party134, the PDCS conveys526 the voice traffic tosubscriber unit102 via each of packet switchednetwork110 and circuit switchednetwork120. More particularly, whenPDCS118 receives voice traffic fromdistant party134, the PDCS routes a first copy of the voice traffic to AN114 viaPDSN116 and the AN transmits a first set of forward link frames comprising the voice traffic tosubscriber unit102 via the forward link traffic channel established inair interface112. In addition,PDCS118 routes a second copy of the voice traffic toBS124 viaintermediate network130 andMSC126 and the BS transmits a second set of forward link frames comprising the voice traffic tosubscriber unit102 via the forward link traffic channel established inair interface122. As noted above, reception of frames bysubscriber unit102 from both ofnetworks110 and120 may be implemented by dual receivers, such as receivers associated with each oftransceivers302 and304 of a subscriber unit, or may be implemented by a single receiver, such as a receiver associated withtransceiver402 of a subscriber unit, that is directed by a processor, such asprocessor404 of the subscriber unit, to rapidly alternate between the networks. To facilitate the latter,PDCS118 may force a vocoder in, or associated with,distant party134 to a lower frame rate, such as ⅛ rate vocoder frames instead of full-rate vocoder frames. By receiving reduced rate frames,subscriber unit102 has more time to alternate betweennetworks110 and102 without complete loss of vocoder frames or the need for dual receivers.Subscriber unit102 may implement methods well known in the art to eliminate duplicate processing of voice frames.
• PDCS118 acts as the anchor for the call, that is, as the gateway forlandline network132 into each ofnetworks110 and120, and remains in the path of the call for the duration of the call, even after the call is handed off from packet switchednetwork110 to circuit switchednetwork120. By providing for multicasting before the forward link is switched from packet switchednetwork110 to circuit switchednetwork120, any potential gap in the voice traffic received bysubscriber unit102 that may result from a “break and make” hard handoff is minimized. However, in order to assure proper synchronization of the forward link frames,subscriber unit102 may add a delay to the frames received from one of packet switchednetwork110 and circuit switchednetwork120.
• At this point in signal flow diagram500,subscriber unit102 continues to unicast528 reverse link frames comprising voice traffic tolandline network132, and more particularly toPDCS118, via packet switchednetwork110. That is,subscriber unit102 conveys reverse link frames comprising voice traffic only to AN114 via the reverse link traffic channel ofair interface112, and via the AN toPDCS118.
• In addition, in response to receiving the handoff notification acknowledgement fromMSC126,PDCS118 informs532subscriber unit102 that the handoff is proceeding via the at least one forward link channel ofair interface112. In packet switchednetwork110, this messaging may be handled via SIP messages. Preferably, the handoff notification acknowledgement fromPDCS118 comprises a SIP REFER “202 Accepted” message tosubscriber unit102 as described in IETF RFC 3515, Section 4.1, which RFC is hereby incorporated herein in its entirety. Again, AN114 andPDSN116 typically are transparent to SIP messages and there are no PDCS-to-PDSN or PDSN-to-AN messages as one would find in circuit switchednetwork120.
• In response to being informed that the handoff is proceeding,subscriber unit102 switches fromunicasting528 reverse link frames of voice information to PDCS118 via packet switchednetwork110 tounicasting542 reverse link frames of voice information to PDCS118 via circuit switchednetwork120. That is, while continuing to receive538,540 forward link frames comprising voice information via each of AN114 andBS124 and the respective forward link traffic channels ofair interfaces112 and122,subscriber unit102 switches from transmitting reverse link frames of voice information via packet switchednetwork110 and the reverse link traffic channel ofair interface112 to transmitting reverse link frames of voice information to circuit switchednetwork120 via the reverse link traffic channel ofair interface122. The switch of reverse link paths preferably occurs at a frame boundary, thereby providing for switching without any loss of a voice frame.
• In response to switching from the reverse link traffic channel ofair interface112 to the reverse link traffic channel ofair interface122,subscriber unit102 notifies544BS124 that the subscriber unit has completed the handoff. Preferably,subscriber unit102 notifiesBS124 that the handoff is complete by conveying a first HANDOFF COMPLETE message as described in the IOS. In response to being informed thatsubscriber unit102 has completed the handoff,BS124 informs546MSC126 that the subscriber unit has completed the handoff, preferably by conveying a second HANDOFF COMPLETE message as described in the IOS, to the MSC. In turn,MSC126 conveys548 a message toPDCS118 informing thatsubscriber unit102 has switched to the reverse link ofair interface122, preferably by conveying a TIA-41 MSONCH message to the PDCS viaintermediate network130. Based on the message received fromMSC126,PDCS118 determines that the subscriber unit has completed the handoff.
• In addition, in response to switching from the reverse link traffic channel ofair interface112 to the reverse link traffic channel ofair interface122,subscriber unit102 notifies550PDCS118 that the handoff is complete. Preferably, the handoff complete message fromsubscriber unit102 toPDCS118 comprises a SIP REFER “200 OK” message as described in IETF RFC 3515, Section 4.1.Subscriber unit102 may then go dormant or disconnect altogether with respect to packet switchednetwork110.PDCS118 then terminates the RTP session betweensubscriber unit102 and packet switchednetwork110 and ceases conveying forward link frames to the subscriber unit via the packet switched network, thereby converting556 the call to a unicast forward link call viaPDCS118, circuit switchednetwork120, and the allocated forward link traffic channel ofair interface122. As noted above, the call has already been converted to a unicast reverse link call via circuit switchednetwork120 and the allocated reverse link traffic channel ofair interface122. However, the call continues as a circuit switched call viaair interface122, circuit switchednetwork120,intermediate network130, andPDCS118. Signal flow diagram500 then ends.
• FIG. 7 is a signal flow diagram700 of a handoff executed bycommunication system100 in handing off a legacy voice call communicated via circuit switchednetwork120 to a VoIP voice call communicated via packet switchednetwork110 in accordance with an embodiment of the present invention. Signal flow diagram700 begins whensubscriber unit102 is actively engaged in a legacy, or conventional, cellular call withdistant party134 via circuit switchednetwork120 andlandline network132. In order to participate in the call,subscriber unit102 must already be registered with the circuit switched network. As part of the call,distant party134 communicates702 withBS124 vialandline network132 andMSC126 using a G.711 protocol (64 kbps Pulse Code Modulation (PCM)).BS124 transcodes the received communications to a vocoder format compatible withsubscriber unit102 and transmits702 the transcoded information tosubscriber unit102 via a forward link traffic channel ofair interface122. Further,BS124 receives704 vocoded information fromsubscriber unit102 via a reverse link traffic channel ofair interface122, transcodes the vocoded information to 64 kbps PCM (G.711), and conveys704 the transcoded information todistant party134 viaMSC126 andlandline network132.
• Prior to or during the course of the call,subscriber unit102further registers706 with packet switchednetwork110, and more particularly with AN114 andPDCS118, and establishes a PPP (Point-to-Point Protocol) communication session withPDSN116 in accordance with well known techniques. A connection between theAN114,PDSN116, andPDCS118 is established on packet switchednetwork110 such thatsubscriber unit102 andPDCS118 are able to communicate with each other. For example,subscriber unit102 may roam from the coverage area serviced byBS124 to the coverage area serviced by AN114, that is, by packet switchednetwork110 and register with the packet switched network. By way of another example,subscriber unit102 may initially activate in an area of coverage of bothAN114 andBS124 and upon activation register with both packet switchednetwork110 and circuit switchednetwork120, and more particularly withPDCS118 andMSC126.
• At some point in time during the course of the call,BS124 determines that a handoff is required. As noted above, this determination may be made based on, among other considerations, any one or more of signal strength measurements, network cost considerations, or a network operator directive. In another embodiment of the invention,subscriber unit102 may notifyBS124 thatsubscriber unit102 needs to handoff to packet switchednetwork110, for example, via a modified IS-2000 signaling message. This may be initiated via user action orsubscriber unit102 may determine the need to handoff, for example, when the user initiates an email downloading session via the subscriber unit. In response to determining that the call should be handed off,BS124 notifies708MSC126 of the need to initiate a handoff. Preferably, this notification includes an indication of the target network, such as a WLAN network or a CDMA 2000 1XEV-DO network. In response to being notified byBS124 of the need for a handoff,MSC126 determines a target switching center, that is,target PDCS118, by reference to at least one of the HLR and VLR and the pre-provisioned database included in or coupled toMSC126.
• In response to determining target a target switching center,MSC126 notifies710 the target switching center, that is,PDCS118, viaintermediate network130 of the need for a handoff and further identifies the subscriber unit, that is,subscriber unit102, to be handed off. Preferably,MSC126 notifiesPDCS118 of the need to handoff the associated subscriber unit by conveying a TIA-41 FACDIR2 INVOKE message to the PDCS. In response to receiving the handoff notification fromMSC126,PDCS118requests subscriber unit102 to perform a handoff of the call from the conventional cellular communication system to a VoIP communication session with the PDCS. Assubscriber unit102 is already registered on packet switchednetwork110, the packet switched network can determine the appropriate routing and there is no need at this time to determine a target AN.
• PDCS118 then requests714 thatsubscriber unit102 perform a handoff, preferably by conveying a SIP INVITE request or a SIP REFER message to the subscriber unit. In response to receiving the SIP INVITE request,subscriber unit102 negotiates forward link and reverse link traffic channels with AN114 inair interface112 and AN114 establishes a corresponding bearer path between the subscriber unit andPDSN116 in accordance with well-known techniques.Subscriber unit102 further conveys716 a message, preferably aSIP 180 RINGING message, toPDCS118 indicating that the subscriber unit is proceeding to activate the connection withPDCS118.
• Whensubscriber unit102 has negotiated a traffic channel with AN114 and a bearer path has been established withPDSN116,subscriber unit102 begins multicasting718,722 reverse link voice information toMSC126 via each of the packet switchednetwork110 and circuit switchednetwork120. That is,subscriber unit102 continues to convey722 a first set of reverse link frames comprising vocoded information toBS124 via the reverse link traffic channel ofair interface122, which voice information is then routed toMSC126, and further conveys a second set of reverse link frames comprising the vocoded information to AN114 via the reverse link traffic channel established inair interface112, which voice information is also routed toMSC126. In one embodiment of the present invention, in order to assure synchronization of the multicast reverse link frames,subscriber unit102 may add delay to frames transmitted to one of packet switchednetwork110 and circuit switchednetwork120. For example, a delay may be determined based on prior handoffs of the subscriber unit between the networks, whereinPDCS118 may calculate a delay value and convey the delay value to the subscriber unit. However, in another embodiment of the present invention, the delay may be added in the networks, for example, byMSC126. In various embodiments of the present invention,subscriber unit102 may concurrently transmit (718,722) via the reverse links ofair interfaces122 and112 by using a transmitter associated with each link, such as transmitters associated with each oftransceivers302 and304 of a subscriber unit, or may emulate concurrent transmission (718,722) via the reverse links ofair interfaces122 and112 by rapidly alternating transmission via a single transmitter, such as a transmitter associated withtransceiver402 of a subscriber unit, over a reverse link of a first air interface, that is, the reverse link ofair interface122, and over a reverse link of a second air interface that is, the reverse link ofair interface112. The process of alternating transmission paths may be further enhanced by a processor of the subscriber unit, such asprocessor404, forcing a vocoder of the subscriber unit, such asvocoder408, to vocode speech at a reduced rate when transmitting over the two air interfaces. For example, by using only ⅛ rate vocoder frames instead of full-rate vocoder frames, time becomes available to rapidly switch between paths without needing to use multiple transmitters.
• MSC126 acts as the anchor for the call, that is, as the gateway forlandline network132 into each ofnetworks110 and120, and remains in the path of the call for the duration of the call, even after the call is handed off from circuit switchednetwork120 to packet switchednetwork110. By providing for multicasting before the reverse link is switched from circuit switchednetwork120 to packet switchednetwork110, any potential gap in the voice traffic received bynetworks110 and120 that may result from a “break and make” hard handoff is minimized. WhenMSC126 receives voice frames via each of packet switchednetwork110 and circuit switchednetwork120,MSC126 may perform buffering and may eliminate duplicate voice frames by selecting one voice frame from each of the packet switched network and the circuit switched network.
• At this point in signal flow diagram700, forward link frames of vocoded information continue to be unicast tosubscriber unit102, that is,MSC126 conveys724 forward link frames comprising vocoded information to the subscriber unit only viaBS124 and the forward link traffic channel ofair interface122. However,PDCS118 may begin conveying720 null frames tosubscriber unit102 via the established forward link traffic channel inair interface112.
• Further, in response to establishing a communication path withsubscriber unit102 via AN114 andair interface112,PDCS118 informs726MSC126 that a handoff ofsubscriber unit102 is progressing by conveying a handoff notification to the MSC. Preferably, the handoff notification comprises a TIA-41 FACDIR2 RESPONSE message.PDCS118 further acknowledges728 the message received fromsubscriber unit102 indicating that the subscriber unit is proceeding to activate the connection withPDCS118, that is, theSIP 180 RINGING message. Preferably,PDCS118 acknowledges the message by conveying a SIP PRACK (Provisional Acknowledgement) message to the subscriber unit. In response to receiving the acknowledgement fromPDCS118,subscriber unit102 acknowledges730 the acknowledgement, preferably by conveying a SIP OK (RINGING) message to the PDCS.
• In response to receiving the handoff notification fromPDCS118,MSC126 switches the forward link unicast of voice information tosubscriber unit102 from circuit switchednetwork120 to packet switchednetwork110. That is,MSC126 begins conveying732 voice information received fromdistant party134 and intended forsubscriber unit102 to AN114 viaintermediate network130,PDCS118, andPDSN116, and the AN transmits forward link frames comprising vocoded information to the subscriber unit via the forward link traffic channel established inair interface112. Meanwhile,MSC126 ceases conveying736 the voice information to the subscriber unit viaBS124 and the forward link traffic channel ofair interface122. However,subscriber unit102 continues to multicast734,738 reverse link frames of vocoded information via each of circuit switchednetwork120 and packet switchednetwork110. That is,subscriber unit102 continues to convey a first set of frames comprising the vocoded information toMSC126 viaBS124 and the reverse link traffic channel ofair interface122 and a second set of frames comprising the vocoded information toMSC126 viaPDCS118,PDSN116, AN114 and the reverse link traffic channel ofair interface112. As noted above,subscriber unit102 may concurrently transmit via the reverse links ofair interfaces112 and122 by using a transmitter associated with each link, such as a transmitter associated with each oftransceivers302 and304, or may emulate concurrent transmission via the reverse links ofair interfaces112 and122 by rapidly alternating between transmission via a single transceiver, such astransceiver402, over the reverse link ofair interface112 and over the reverse link ofair interface122, which process of alternating transmission paths may be further enhanced by forcing a vocoder, such asvocoder408, of the subscriber unit to vocode speech to a reduced rate.
• MSC126 further instructs740BS124 to complete the handoff, that is, to instructsubscriber unit102 to cease sending reverse link frames toBS124. In response to receiving the instruction,BS124 then instructs742subscriber unit102 to cease sending reverse link frames to the BS. In response to receiving the instruction fromBS124, subscriber unit ceases sending reverse link frames to the BS, leaving the subscriber unit in a bi-directional unicast mode withMSC126 and packet switchednetwork110. In other words, voice information is conveyed744 tosubscriber unit102 only viaMSC126,PDCS118,PDSN116, AN114 and the forward link traffic channel ofair interface112, andsubscriber unit102 conveys746 voice information toMSC126 only viaPDCS118,PDSN116, AN114, and the reverse link traffic channel ofair interface112.
• Further, in response to switching from the reverse link ofair interface122 to the reverse link ofair interface112,subscriber unit102 notifies748BS124 that the handoff is completed, that is, that the subscriber unit is now engaged in a bi-directional unicast with packet switchednetwork110, that is, AN114 andPDCS118. Preferably,subscriber unit102 notifiesBS124 that the handoff is completed by conveying a MS ACK ORDER message to the BS.
• In response to being informed that the handoff is completed,BS124 informs750MSC126 that the handoff has commenced. In addition, in response to receiving the instruction to cease sending reverse link frames toBS124,subscriber unit102 informs752PDCS118 that the request to perform a handoff received by the subscriber unit from the PDCS, that is, the SIP INVITE request, has been successfully executed, preferably by conveying aSIP 200 OK message to the PDCS.
• In response to being informed that the request to perform a handoff has been successfully executed,PDCS118 acknowledges754 the successful execution message, preferably by conveying a SIP ACK tosubscriber unit102.PDCS118 further informs756MSC126 that the subscriber unit is successfully exchanging voice frames on a bi-directional basis with packet switchednetwork110, that is, with AN114 andPDCS118, preferably by conveying a TIA-41 MSONCH message to the MSC viaintermediate network130. Based on the message received fromPDCS118,MSC126 determines thatsubscriber unit102 has completed the handoff and so informs758BS124, preferably by conveying a CLEAR COMMAND message to the BS. In response to being informed thatsubscriber unit102 has completed the handoff,BS124 terminates the legacy call, that is, the circuit switched network call, with the subscriber unit. Upon terminating the legacy call,BS124 informs760MSC126 that the legacy call has been terminated, preferably by conveying a CLEAR COMPLETE message to the MSC. Signal flow diagram700 then ends.
• In summarization,communication system100 provides for an active handoff of a voice call between packet switchednetwork110, preferably a CDMA 2000 1XRTT network, a CDMA 2000 1XEV-DO network, or a WLAN network, and circuit switchednetwork120, preferably a CDMA 1X network, by multicasting the call over both networks during the course of the handoffs. An active handoff from packet switchednetwork110 to circuit switched network is accomplished by multicasting the call over forward links of both networks during the handoff. An active handoff from the circuit switched network to the packet switched network is accomplished by multicasting the call over reverse links of both networks during the handoff. The former handoff further may be facilitated by maintainingPDCS118 in the call even when the call is routed through circuit switchednetwork120, and the latter handoff further may be facilitated by maintainingMSC126 in the call even when the call is routed through packet switchednetwork110. In order forhybrid subscriber unit102 to operate concurrently in bothnetwork110 andnetwork120, the subscriber unit may comprise multiple transceivers. However, in another embodiment of the present invention,subscriber unit102 may comprise a single transceiver that is rapidly switched betweennetworks110 and120 to give the appearance of concurrent operation. In addition, when switching between networks, avocoder408 in the singletransceiver subscriber unit102 may be instructed by the processor to use a reduced rate that allows for the time for the rapid switching without severely degrading voice quality.
• While the present invention has been particularly shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention as set forth in the claims below. Furthermore, one of ordinary skill in the art realizes that the components and operations of the transmitting communication device and receiving communication device detailed herein are not intended to be exhaustive but are merely provided to enhance an understanding and appreciation for the inventive principles and advantages of the present invention, rather than to limit in any manner the invention. Accordingly, the specification and figures are to be regarded in an illustrative rather then a restrictive sense, and all such changes and substitutions are intended to be included within the scope of the present invention.
• Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims. As used herein, the terms “comprises,” “comprising,” or any variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, unless otherwise indicated herein, the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

Claims (25)

1. A method for handoff of a voice call from a packet switched network having a packet data control switch to a circuit switched network, the method comprising:

conveying forward link voice traffic to, and receiving reverse link voice traffic from, a subscriber unit via the packet switched network;

receiving, by the packet switched network, a notification to hand off the call to the circuit switched network;

in response to receiving the handoff notification, conveying forward link voice traffic to the subscriber unit via the packet switched network and via the packet data control switch and the circuit switched network, and concurrently receiving reverse link voice traffic only via the packet switched network;

when conveying forward link voice traffic to the subscriber unit via each of the packet switched network and the circuit switched network, switching from the packet switched network to the packet data control switch and the circuit switched network for reception of reverse link voice traffic; and

in response to switching from the packet switched network to the circuit switched network for reception of reverse link voice traffic, ceasing conveying forward link voice traffic to the subscriber unit via the packet data control switch and the packet switched network while continuing to convey forward link voice traffic to the subscriber unit via the packet data control switch and the circuit switched network.

2. The method ofclaim 1, wherein conveying forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network comprises conveying, by the packet data control switch, forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network

3. The method ofclaim 2, wherein receiving a notification to hand off the call from the packet switched network to the circuit switched network comprises receiving, by the packet data control switch from the subscriber unit, a message identifying the circuit switched network as a target of the handoff and wherein conveying forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network comprises, conveying, by the packet data control switch based on the message identifying the circuit switched network, forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network.

4. The method ofclaim 3, wherein the message identifying the circuit switched network as a target of the handoff comprises a Session Initiation Protocol message.

5. The method ofclaim 1, wherein the notification to hand off the call from the packet switched network to the circuit switched network identifies the circuit switched network as a target of a handoff and wherein conveying forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network comprises:

notifying the circuit switched network, by the packet switched network, of the need for a handoff of the subscriber unit; and

in response to the notification of the circuit switched network, establishing a bearer path between the circuit switched network and the subscriber unit and conveying forward link voice traffic to the subscriber unit via the established bearer path.

6. The method ofclaim 5, wherein notifying the circuit switched network of the need for a handoff of the subscriber unit comprises conveying a TIA-41 FACDIR2 INVOKE message to the circuit switched network.

7. The method ofclaim 5, further comprising acknowledging the notification of the circuit switched network.

8. The method ofclaim 5, wherein establishing a bearer path between the circuit switched network and the subscriber unit comprises, in response to notification of the circuit switched network of the need for a handoff:

conveying, by the circuit switched network to the subscriber unit, a handoff request message; and

in response to conveying the handoff request message, establishing a bearer path between the circuit switched network and the subscriber unit.

9. The method ofclaim 1, wherein switching reception of reverse link voice traffic from the packet switched network to the circuit switched network comprises:

informing the subscriber unit that the handoff is preceding; and

in response to informing the subscriber unit that the handoff is preceding, switching reception of reverse link voice traffic from the packet data control switch and the packet switched network to the packet data control switch and circuit switched network.

10. The method ofclaim 9, further comprising:

receiving, by the circuit switched network from the subscriber unit, notification that the handoff is complete; and

informing, by the circuit switched network of the packet switched network, that the subscriber unit has completed the handoff.

11. The method ofclaim 9, wherein ceasing conveying forward link frames to the subscriber unit via the packet switched network comprises:

receiving, by the packet switched network from the subscriber unit, notification that the handoff is complete; and

in response to receiving notification that the handoff is complete, ceasing conveyance of forward link voice traffic to the subscriber unit via the packet data control switch and the packet switched network while continuing to convey forward link voice traffic to the subscriber unit via the packet data control switch and the circuit switched network.

12. A packet data control switch having a processor configured to, in association with a subscriber unit call, route forward link voice traffic and receive reverse link voice traffic via a packet switched network, receive a notification to hand off the call from the packet switched network to a circuit switched network, in response to receiving the handoff notification, route forward link voice traffic to the subscriber unit via both the packet switched network and the circuit switched network and concurrently receive reverse link voice traffic only via the packet switched network, when conveying forward link voice traffic to the subscriber unit via each of the packet switched network and the circuit switched network, switch reception of reverse link voice traffic from the packet switched network to the circuit switched network, and in response to switching reception of reverse link voice traffic from the packet switched network to the circuit switched network, cease routing forward link voice traffic to the subscriber unit via the packet switched network while continuing to route forward link voice traffic to the subscriber unit via the circuit switched network.

13. The packet data control switch ofclaim 12, wherein the notification comprises a Session Initiation Protocol message that identifies the circuit switched network as a target of the handoff.

14. The packet data control switch ofclaim 12, wherein the notification that the call should be handed off identifies the circuit switched network as a target of the handoff and wherein, in response to receiving the notification, the processor notifies the circuit switched network of the need for a handoff of the subscriber unit.

15. The packet data control switch ofclaim 14, wherein the processor notifies the circuit switched network of the need for a handoff of the subscriber unit by conveying a TIA-41 FACDIR2 INVOKE message to the circuit switched network.

16. The packet data control switch ofclaim 14, wherein the processor further receives an acknowledgement of the notification of the circuit switched network.

17. The packet data control switch ofclaim 12, wherein the processor switches receiving reverse link frames from the packet switched network to the circuit switched network by informing the subscriber unit that the handoff is preceding and, in response to informing the subscriber unit that the handoff is preceding, receives reverse link voice traffic from the subscriber unit via the circuit switched network instead of the packet switched network.

18. The packet data control switch ofclaim 17, wherein the processor further is informed by the circuit switched network that the subscriber unit has completed the handoff.

19. The packet data control switch ofclaim 17, wherein the processor ceases conveying forward link voice traffic to the subscriber unit via the packet switched network by receiving from the subscriber unit notification that the handoff is complete and, in response to receiving notification that the handoff is complete, ceasing conveying forward link voice traffic to the subscriber unit via the packet switched network.

20-33. (canceled)

34. A method for handoff of a voice call from a packet switched network having a packet data control switch to a circuit switched network, the method comprising:

communicating voice traffic via the packet switched network;

receiving, by the packet switched network, a notification to hand off the call, wherein the notification to hand off identifies the circuit switched network as the network to hand off the call to; and

in response to receiving the handoff notification, establishing communication via the circuit switched network and terminating communication via the packet switched network.

35. The method ofclaim 34, wherein the step of establishing communication via the circuit switched network includes paging the subscriber unit via the circuit switched network and receiving a response to the page message from the subscriber unit.

36. A method for handoff of a voice call from a packet switched network having a packet data control switch to a circuit switched network, the method comprising:

communicating voice traffic via the packet switched network;

determining, by a subscriber unit, to hand off the call;

transmitting a notification to hand off the call, wherein the notification to hand off identifies the circuit switched network as the network to hand off the call to; and

in response to transmitting the handoff notification, establishing communication via the circuit switched network and terminating communication via the packet switched network.

37. The method ofclaim 36, wherein the step of establishing communication via the circuit switched network includes receiving a paging message at the subscriber unit via the circuit switched network and transmitting a response to the page message from the subscriber unit.

38-41. (canceled)

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