Patent Application
20060268781
The present invention relates generally to the field of wireless communication networks and in particular to a system and method for handing off a call from a packet data wireless network to a circuit switched wireless network.
Early wireless communication networks were circuit switched, with a communication channel dedicated to each call. A network “channel” may comprise a particular transmission frequency, a time slot in a Time Division Multiple Access (TDMA) system, a unique spreading code in a Code Division Multiple Access (CDMA) system, or the like. Circuit switched wireless networks are widely deployed and extensively used, communicating both voice and digital data to and from mobile users using mobile terminals (MT).
With the rapid growth of the Internet, technological advances in packet data networks have yielded network architectures, protocols, and equipment that route data in autonomous units (“packets”) using shared channels with high speed, low latency, and high network resource utilization efficiency. Recently, dedicated packet data wireless communication networks have been developed and deployed that route packetized voice (such as Voice over IP, or VoIP) and data packets to and from mobile users using mobile access terminals (AT). The distinguishing characteristic of such packet data wireless networks, as opposed to circuit switched wireless networks with packet data transmission capabilities, is that packet data for multiple users is transmitted over one or more shared, high bandwidth channels, rather than a dedicated channel being assigned to each user (or call). One example of such a dedicated packet data wireless communication network is the CDMA 1xEV-DO standard. The development, deployment, and use of packet data a wireless networks is expected to increase.
As with any cellular wireless network, mobility management is required to maintain communications with mobile MTs or ATs as users move throughout different geographic areas. Mobile Assisted Hand-Off (MAHO) is a well-known element of mobility management. In MAHO, mobile terminals report channel conditions, desired data rates, pilot strengths signals from neighboring radio base stations, and the like to a serving base station, which, using this information as well as the relative loading among neighboring base stations, determines if, when, and to which base station to hand off a mobile terminal.
One problem with some deployed packet data wireless networks (such as 1xEV-DO) is that the shared packet data channels are transmitted in a different frequency band than are the dedicated traffic channels in a corresponding circuit switched wireless network, and a mobile unit cannot operate on both frequencies at the same time. It may be possible to handoff a VoIP call on a packet data wireless network to, e.g., the packet data services available on a circuit switched wireless network if the proper service options were set in the standards to support the required Quality of Service (QoS) needed for the voice call, and if the networks support concurrent voice/data services. Because these conditions are not generally met by deployed wireless networks, a need exists in the art for a system and method to facilitate handoff of a VoIP call in a packet data wireless network to a conventional circuit switched wireless network for hybrid mobile units (AT/MT) that are capable of communications with both networks (e.g., in both frequency bands).
A Handoff (HO) Function facilitates the handoff of a hybrid Access Terminal/Mobile Terminal (AT/MT) from a packet data wireless network to a circuit switched wireless network. The HO Function receives a handoff indication from the packet data wireless network, and generates and forwards to the circuit switched wireless network (such as to an MSC) an emulated circuit switched handoff request. The HO Function receives handoff radio parameters from the circuit switched wireless network, encapsulates the handoff radio parameters into packets, and forwards them to the packet data wireless network. The handoff parameters are transmitted to the hybrid AT/MT, allowing the hybrid AT/MT to tune to the frequency band of the circuit switched wireless network.
Additionally, the HO Function initiates the IMS network signaling necessary to route voice signals from the other party of the existing call, through the IMS network, and to the hybrid AT/MT on the circuit switched wireless network. The HO Function additionally controls a Media Gateway that translates call media between the packet data networks and the circuit switched network formats and protocols.
In one embodiment, the present invention relates to a method of facilitating the handoff of a hybrid Access Terminal/Mobile Terminal (AT/MT), engaged in a call with another party, from a packet data wireless network to a circuit switched wireless network. A handoff indication is received from the packet data network. An emulated circuit switched handoff request is generated in response to the handoff indication. The emulated circuit switched handoff request is forwarded to the circuit switched network. Handoff radio parameters are received from the circuit switched network. The handoff radio parameters are encapsulated into data packets, and the handoff radio parameters are forwarded to the packet data network.
In another embodiment, the present invention relates to a Handoff (HO) Function with signaling connections to a packet data wireless network, a circuit switched wireless network, and at least one IP Multimedia Subsystem (IMS) network, and operative to facilitate the handoff of a hybrid Access Terminal/Mobile Terminal (AT/MT) from the packet data wireless network to the circuit switched wireless network. The HO Function includes a wireless network handoff translation module receiving a handoff indication from, and outputting packet-encapsulated handoff radio parameters to, the packet data wireless network, and outputting an emulated circuit switched handoff request to, and receiving handoff radio parameters from, the circuit switched wireless network. The HO Function additionally includes a IMS interface module exchanging SIP messages with a IMS network, and a Media Gateway Control Function (MGCF) controlling a Media Gateway (MGw).
In yet another embodiment, the present invention relates to a translation network operative to facilitate handoff of a hybrid Access Terminal/Mobile Terminal (AT/MT) from a packet data wireless network to a circuit switched wireless network. The translation network includes a Media Gateway (MGw) connected to the circuit switched wireless network via a dedicated handoff trunk and connected to one or more packet data networks by a packet data link, the MGw operative to translate media between packet data and circuit switched formats. The translation network also includes a Handoff (HO) Function controlling the MGw, the HO Function having signaling connections to the packet data wireless network, the circuit switched wireless network, and at least one IP Multimedia Subsystem (IMS) network.
In still another embodiment, the present invention relates to a method of facilitating the handoff of a hybrid Access Terminal/Mobile Terminal (AT/MT) from a packet data wireless network to a circuit switched wireless network by an Application Server (AS) having a sip:uri Public Service Identifier (PSI) in an IP Multimedia Subsystem (IMS) network, the PSI AS operative to handle inter-system handoffs and session transfer between IP connectivity points for a specific terminal. A SIP INVITE message directed to the PSI AS and indicating the hybrid AT/MT as the calling party is received. An ENUM conversion is performed on the hybrid AT/MT indicator to generate a SIP URI for the hybrid AT/MT. The called and calling party identifiers are swapped to generate a modified SIP INVITE message. The modified SIP INVITE message is sent to a Serving-Call Session Control Function (C-CSCF) in the IMS network.
The circuit switched wireless network 20 comprises a Mobile Switching Center (MSC) 22, connected to one or more circuit switched Base Station Controllers (CS BSC) 24 providing communication services to one or more mobile terminals (MT) 26. The MSC 22 routes voice and data over circuit switched network connections between the CS BSC 24 and numerous other network nodes (not shown) such as for example the Public Switched Telephone Network (PSTN). The CS BSC 24 includes or controls one or more radio base stations or base station transceivers (not shown) that include the transceiver resources necessary to support radio communication with MTs 26, such as modulators/demodulators, baseband processors, radio frequency (RF) power amplifiers, antennas, and the like.
The packet data wireless network 30 comprises a Packet Data Switching Node (PDSN) 32 connected to one or more packet data Base Station Controllers (PD BSC) 34 providing packet data communication services to one or more access terminals (AT) 36. The PDSN 32 routes data packets between the PD BSC 34 and other packet data networks, such as the IMS 40. The PD BSC 34 includes or controls one or more radio base stations similar to the CS BSC 24, but provides packet data communications on shared, high-bandwidth channels to ATs 36, and, as depicted in
The packet data wireless network 30 is connected to an IMS network 40. The IMS is a general-purpose, open industry standard for voice and multimedia communications over packet-based IP networks 40. The IMS network 40 includes one or more Application Servers (AS) providing various services (audio and video broadcast or streaming, push-to-talk, videoconferencing, games, filesharing, e-mail, and the like). In particular, a AS 42 maintains knowledge of all calls to and from the hybrid AT/MT 66. Another AS within the IMS 40 is a Public Service Identifier (PSI) AS 46. The PSI AS 46 is a generic AS that handles session transfer between IP connectivity points for a specific terminal. The PSI AS 46 handles inter-system handoffs within a system.
Communications between nodes within the IMS network 40 utilize the Session Initiation Protocol (SIP). SIP is a signaling protocol for Internet conferencing, telephony, presence, events notification, instant messaging, and the like. SIP uses a long-term stable identifier, the SIP Universal Resource Indicator (URI).
27 The AS 42 is connected to a Serving-Call Session Control Function (C-CSCF) 44. The C-CSCF 44 initiates, manages, and terminates multimedia sessions between IMS 40 terminals. In particular, the C-CSCF 44 is the registration server for the hybrid AT/MT 66. The C-CSCF 44 may be connected to an optional Interrogating-CSCF (I-CSCF) 48. The l-CSCF 48 is a SIP proxy located at the edge of an administrative domain. The I-CSCF (or C-CSCF if a l-CSCF is not present) is connected to a Proxy-CSCF (P-CSCF) 50. The P-CSCF is a SIP proxy that is the first point of contact to the IMS 40.
As depicted in
As the hybrid AT/MT 66 moves physically further from the radio transceiver resources of the PD BSC 34, the hybrid AT/MT 66 indicates poor channel conditions to the PD BSC 34, such as by requesting a lower data rate via a Data Rate Control (DRC) index. When the hybrid AT/MT 66 reports sufficiently poor channel conditions, the PD BSC 34 determines it must hand the hybrid AT/MT 66 off to another wireless network node.
If the packet data wireless network 30 is of limited geographic extent, and the hybrid AT/MT 66 is at the edge of its service area, it is likely that the hybrid AT/MT 66 may be served by a circuit switched wireless network 20, which are more widely deployed. However, the hybrid AT/MT 66 cannot simultaneously operate in the different frequency bands utilized by the packet data wireless network 30 and the circuit switched wireless network 20. CDMA soft handoff is thus impossible.
According to one or more embodiments of the present invention, the handoff of a hybrid AT/MT 66 from the packet data wireless network 30 to the circuit switched wireless network 20 is facilitated by a Handoff (HO) Function 62. The HO Function 62 is an inventive network node in the translation network 60 that resides between the packet data wireless network 30 and the circuit switched wireless network 20, as depicted in
When it determines that a handoff of the hybrid AT/MT 66 is necessary, the PD BSC 34 sends a handoff indication to the HO Function 62. The handoff indication is transmitted from the PD BSC 34 to the HO Function 62 over an Al p interface. The handoff indication includes a target MSC identifier and the International Mobile Subscriber Identity (IMSI) of the hybrid AT/MT 66 being handed off. Upon receipt of the handoff indication, the HO Function 62 generates an emulated circuit switched handoff request, and forwards the emulated circuit switched handoff request to the MSC 22. For example, the HO Function 62 may generate and send an IS-41 protocol FacilitiesDirective2 (FACDIR2) signal. The FACDIR2 includes a CircuitID perimeter indicating the dedicated trunk to which a Media Gateway 64 is connected (see below).
In one embodiment, the PD BSC 34 includes the ability to directly generate the emulated circuit switched handoff request (e.g., a FACDIR2 message) with the appropriate parameters, and encapsulate the HO Request in a packet data structure for transmission to the HO Function 62 as a handoff indication. In this embodiment, the HO Function 62 simply decapsulates the message and forwards it to the MSC 22. In another embodiment, the PD BSC 34 sends the HO Function 62 a handoff indication and the required parameters, and the HO Function 62 generates and forwards the emulated circuit switched handoff request.
The MSC 22 receives the HO Request, and queries the CS BSC 24 to obtain handoff radio parameters. The CS BSC 24 allocates a channel for the handoff, and provides the handoff radio parameters associated with the allocated channel to the MSC 22. The MSC 22 returns the radio parameters to the HO Function 62. The HO Function 62 encapsulates the returned message containing the handoff radio parameters into a packet data structure, and forwards the parameters to the PD BSC 34 across the A1p interface. The PD BSC 34 transmits them to the hybrid AT/MT 66 to be handed off. The hybrid AT/MT 66 may then tune to the frequency band of the CS BSC 24, and begin communication with the circuit switched wireless network 20, as depicted in
35 To route data from the packet data wireless network 30 to the MSC 22 and to translate between network protocols and data formats, the HO Function 62 selects a Media Gateway (MGw) 64 having a dedicated handoff trunk to the MSC 22. The HO Function 62, which includes a Media Gateway Control Function (MGCF), sets up the MGw 64 to translate the call between network protocols with a MEGACO or H.248 protocol Modify Request. The MGw 64 responds with a Modify Acknowledge, and activates the dedicated handoff trunk to the MSC 22. This sequence of transactions hands off the hybrid AT/MT 66 to the circuit switched wireless network 20, and provides for communications between the AT/MT 66 and the MGw 64.
To direct call data from the other party (in this case, the AT 36 on the packet data wireless network 30) to the MGw 64, the HO Function 62 sends a SIP INVITE message to the PSI AS 46, the IMS network 40 entity that handles handoff's for the system. The SIP INVITE message includes the IMSI of the hybrid AT/MT 66 in the P-Asserted ID header field of the SIP INVITE message. The P-Asserted ID header is functionally similar to the “From” header, but indicates that the address in the field has been validated. Upon receipt of the SIP INVITE message, the PSI AS 46 performs an ENUM conversion on the IMSI to convert it to a SIP URI, and swaps the contents of the “To” and P-Asserted ID header fields, i.e., the called and calling party identifiers. This swap transforms the SIP INVITE message into a call request from the PSI AS 46 to the SIP URI address of the hybrid AT/MT 66.
The PSI AS 46 sends the modified SIP INVITE message to the S-CSCF 44, which is the registration server for the hybrid AT/MT 66. Triggers in the S-CSCF 44 are set to include the AS 42 in the path for all calls terminating to the hybrid AT/MT 66. The modified SIP INVITE message is thus routed (via normal SIP routing procedures) to the AS 42. The AS 42 handles all calls for the hybrid AT/MT 66, and has knowledge of all existing calls. The AS 42 inspects the modified SIP INVITE message, detects the handoff (by recognizing the calling party), and establishes a dialogue between the AS 42 and the MGw 64. The AS 42 sends a SIP 200 OK signal to the S-CSCF 44, which is propagated back to the HO Function 62. The HO Function in turn sends a SIP ACK message back through the S-CSCF 44 to the AS 42, confirming the dialog establishment. The AS 42 then issues a SIP UPDATE message to the AS controlling call routing for the AT 36, to direct media (i.e., VoIP packets) transfer between the AT 36 and the MGw 64.
40 Another network 70, to which the other party of the VoIP call is connected, comprises a AS 72, a S-CSCF 74, an optional I-CSCF 76, a P-CSCF 78, a PDSN 80, and a PD BSC 82, with functionality as previously described. The flow of VoIP packets from the other party is indicated by heavy lines. Voice packets are routed from the AT 36 to the PD BSC 82, through the PDSN 80 and to the PDSN 32, as EVRC over an RTP or IP link. The voice packets are then routed to the PD BSC 34, and transmitted to the hybrid AT/MT 66. Voice packets in the opposite direction follow the reverse path.
As the user of the hybrid AT/MT 66 moves further from the radio transceivers of the PD BSC 34, the PD BSC 34 determines a handoff is required. If the user is moving to a geographic area served by the circuit switched wireless network 20 but not by another packet data wireless network, the PD BSC 34 may utilize the HO Function 62 to facilitate handing off the hybrid AT/MT 66 to the circuit switched wireless network 20.
42 Similarly to the non-roaming case describe above with reference to
The HO Function 62 also generates a SIP INVITE message “To” the PSI AS 46 and “From” (P-asserted ID) the hybrid AT/MT 66 and forwards the SIP INVITE message to the home area network 68. The INVITE is routed to the PSI AS 46, which swaps the called and calling party identifiers and forwards the message to the S-CSCF 44, which routes it to the AS 42 that controls calls for the hybrid AT/MT 66. The AS 42 detects the handoff, and sets up a dialog between the AS 42 and the MGw 64. The AS 42 additionally sends a SIP UPDATE message to the AS 72 that controls calls for the other party, directing its data stream to the MGw 64.
Initially, a VoIP call exists between an AT 36 or MGw 88 (connecting to the PSTN 86) and the PDSN 32, as indicated in the call diagram of
Referring to
At this point, the network activity may be logically divided into two parallel flows, as indicated in the flow diagram of
Considering flow 1 first (beginning with
The MSC 22 queries the SC BSC 24 for handoff radio parameters (block 106). The SC BSC 24 allocates a channel for the hybrid AT/MT 66 (block 108). The SC BSC 24 sends the handoff radio parameters to the MSC 22 (block 110). The MSC 22 sends the handoff radio parameters received from the SC BSC 24 to the HO Function 62 (block 112).
The HO Function 62 encapsulates the radio handoff parameters in a packet data format and a sends the radio parameters and a handoff command to the PD BSC 34 (block 114). The PD BSC 34 sends the encapsulated handoff radio parameters to the hybrid AT/MT 66 (block 116). The hybrid AT/MT 66 acknowledges receipt of the radio handoff parameters (block 118), and proceeds to tune to the SC BSC 24 frequency (as indicated at 119 in the call flow diagram of
The hybrid AT/MT 66 sends a handoff complete message to the SC BSC 24 after turning to the appropriate frequency (block 122). The SC BSC 24 sends a handoff complete message to the MSC 22 (block 124). This establishes a (dormant) link comprising PCM over A2 between the MSC 22 and the SC BSC 24, as indicated in the call flow diagram of
Considering flow 2 in
The S-CSCF 44, which is the registration server for the hybrid AT/MT 66, includes triggers that include the AS 42 in the path for all calls terminating to the hybrid AT/MT 66. Accordingly, the S-CSCF 44 forwards the modified SIP INVITE message to the AS 42 (block 136). The AS 42, seeing a call from the PSI AS 46 to the hybrid AT/MT 66, detects the handoff, performs an ENUM conversion on the MDN, and establishes a dialog between the AS 42 and the MGw 64 (block 138). The AS 42 then sends a SIP 200 OK to the S-CSCF 44 including the Session Description Protocol (SDP) parameters for the other party, thus establishing the dialog (block 140). The S-CSCF 44 forwards the SIP 200 OK message to the HO Function 62 (block 142).
The HO Function 62 sends a Modify Request to the MGw 64 having a dedicated trunk to the MSC 22 (block 144). The MGw 64 response with a Modified Acknowledge (block 146). This activates a PCM data link over the dedicated trunk between the MGw 64 and the MSC 22, as indicated in the call flow diagram of
Upon receiving the acknowledgment, the AS 42 modifies the existing dialog with the other party, by sending a SIP UPDATE to the network entity controlling the other party (e.g., the S-CSCF 72 and AS 72 of
When both flows 1 and 2 of
Inventive network elements of the present invention include the HO Function 62 as described above; in one embodiment a modified PD BSC 34 operative to create and packet-encapsulate a circuit switched handoff request; a hybrid AT/MT 66 with the ability to handle sending and receiving circuit switched handoff messages on the packet data bearer; and a PSI AS 46 function of swapping calling and called party identifiers in a SIP INVITE message, as well as the methods of network operation described herein.
A functional block diagram of one embodiment of the HO Function 62 is depicted in
The wireless network handoff translation module 62A is connected, on the packet data side, to the PD BSC 34. On the circuit switched side, the wireless network handoff translation module 62A is connected to the MSC 22. The wireless network handoff translation module 62A receives a handoff indication 98 (see
The IMS interface 62B generates and outputs a SIP INVITE message 132 to the C-CSCF 44. The SIP INVITE is directed “To” the PSI AS 46, and includes the IMSI in the P-Asserted ID header field. The IMS interface 62B receives a SIP 200 OK message 142 from the C-CSCF 44, indicating that a modified SIP INVITE (from the PSI AS 46 and “To” the AT/MT 66) was accepted by the AS 42 controlling the hybrid AT/MT 66. Upon receipt of the SIP 200 OK, the IMS interface 62B outputs a SIP ACK 150A to the C-CSCF 44, which is propagated to the AS 42.
In response to both the wireless network handoff translation module 62A and the IMS interface 62B, the MGCF 62C generates and outputs MEGACO or H.248 protocol Modify Request signals 100, 146 to the MGw 64, to set up the MGw 64 and activate its dedicated trunk line connection to the MSC 22. The MGCF 62C additionally receives Modify Acknowledge signals 102, 148 from the MGw 64, and reports these signals to the IMS interface 62B and a wireless network handoff translation module 62A.
Although the present invention has been described herein with respect to particular features, aspects and embodiments thereof, it will be apparent that numerous variations, modifications, and other embodiments are possible within the broad scope of the present invention, and accordingly, all variations, modifications and embodiments are to be regarded as being within the scope of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
This application claims the benefit of U.S. Provisional Patent Application 60/676,790 filed May 2, 2005, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60676790 | May 2005 | US |
