1 METHOD AND SYSTEM USING A MEDIA GATEWAY FOR HANDOFF OF A MULTI-MODE MOBILE STATION
1. Field of the Invention
The present invention relates to telecommunications and, more particularly, to a method and system that uses a media gateway for handoff of a multi-mode mobile station from a first wireless network to a second wireless network.
2. Description of Related Art
There is an increased interest inusing more diverse types of wireless access technologies for mobile devices. Different wireless access technologies may be used to provide wireless coverage in different geographic areas. In addition, different wireless access technologies may be used to provide different capabilities for transmitting and receiving voice, data, and/or other media. For example, wireless wide area networks (WWANs), which often use wireless access technologies such as CDMA, TDMA, or GSM, typically provide wireless coverage in relatively large geographic areas. However, in many cases, WWANs do not provide good wireless coverage in buildings. In addition, many WWANs have a relatively limited bandwidth for transmitting and receiving media. However, wireless local area networks (WLANs), which may use wireless access technologies, such as IEEE 802.11, Bluetooth, HiperLAN, or HomeRF, have been used to provide wireless coverage in more limited areas, such as the inside of buildings. In addition, WLANs can often transmit and receive media at a higher rate than many WWANs.
With this increased interest in using diverse wireless access technologies to provide wireless coverage has come an increased interest in providing multi-mode mobile stations that can communicate using more than one type of wireless access technology. For example, a multi-mode mobile station may have one interface for communication with a WWAN, using a wireless access technology such as CDMA, and another interface for communication with a WLAN, using a wireless access technology such as IEEE 802.11. Although such multi-mode mobile stations can provide better wireless coverage in more areas by being able to communicate over different wireless networks, they do not necessarily change their network connectivity in a seamless mamrer. For example, while engaged in a call via a first wireless network, the multi-mode mobile station may move into an area in which the first wireless network no longer provides good wireless coverage but the second wireless network does. In that situation, it wouldbe desirable for the multi-mode mobile station to be able to continue the call via the second wireless network.
Accordingly, there is a need for methods and systems that can facilitate handoffs of multi-mode mobile stations, for example, from a WWAN to a WLAN or vice versa.
In a first principal aspect, an exemplary embodiment of the present invention provides a method for call handoff between a first wireless network and a second wireless network for a multi-mode mobile station. The multi-mode mobile station includes a first interface for wireless communication with the first wireless network and a second interface for wireless communication with the second wireless network. In accordance with the method, the multi-mode mobile station transmits a handoff request via the first interface while the multimode mobile station is engaged in a first communication
session with an endpoint via the first interface. The multimode mode mobile becomes engaged in a second communication session with the endpoint via the second interface and begins receiving media via the second interface. The multimode mobile station stores the media, thereby accumulating stored media. The multi-mode mobile station receives a handoff instruction via the first interface. In response to the handoff instruction, the multi-mode mobile station conveys the stored media to a user and drops the first communication session.
In a second principal aspect, an exemplary embodiment of the present invention provides a method for effecting a handoff of a multi-mode mobile station from a first wireless network to a second wireless network. The multi-mode mobile station has a first interface for wireless communication with the first wireless network and a second interface for wireless communication with the second wireless network. In accordance with the method, a call request is received that requests establishment of a call between the multi-mode mobile station and an endpoint. In response to the call request, a first call leg for the call is established between an anchor point and the multi-mode mobile station via the first wireless network. A handoff request from the multi-mode mobile station is received via the first wireless network. In response to the handoff request, a second call leg for the call is established between the anchor point and the multi-mode mobile station via the second wireless network and a handoff instruction is transmitted to the multi-mode mobile station via the first wireless network. The first call leg is dropped.
In a third principal aspect, an exemplary embodiment of the present invention provides a system for providing wireless telecommunications to a multi-mode mobile station. The multi-mode mobile station has a first interface for wireless communication with the first wireless network and a second interface for wireless communication with the second wireless network. The system comprises a media gateway that is comrnunicatively coupled to the first and second wireless networks and a call control system that is comrnunicatively coupled to the media gateway. The call control system routes calls to and from the multi-mode mobile station through the media gateway and controls handoffs of the calls between the first and second wireless networks.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified block diagram of a wireless telecommunications system, in accordance with an exemplary embodiment of the present invention;
FIG. 2 is a flow chart illustrating a method for establishing a call between an endpoint and a multi-mode mobile station via a WWAN, in accordance with an exemplary embodiment of the present invention;
FIG. 3 is a flow chart illustrating a method for handing off the call established in FIG. 2 from the WWAN to a WLAN, in accordance with an exemplary embodiment of the present invention;
FIG. 4 is a flow chart illustrating a method for establishing a call between a multi-mode mobile station and an endpoint via a WLAN, in accordance with an exemplary embodiment of the present invention; and
FIG. 5 is a flow chart illustrating a method for handing off the call established in FIG. 4 from the WLAN to a WWAN, in accordance with an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The present invention, in its preferred embodiments, facilitates call handoffs between a first wireless network and a second wireless network for multi-mode mobile stations. The first and second wireless networks use different wireless communication technologies. For example, the first wireless network could be a wireless local area network (WLAN) that uses a protocol such as IEEE 802.11x, HiperLAN, HomeRF, Bluetooth for wireless communication. The second wireless network could be a wireless wide area network (WWAN) that uses, for example, CDMA or GSM for wireless communication. Thus, a multi-mode mobile station may have at least a first interface for wireless communication with the first wireless network and a second interface for wireless communication with the second wireless network.
In an exemplary embodiment, a media gateway that is communicatively coupled to the first wireless network and to the second wireless network is used as an anchor point for call handoffs for multi-mode mobile stations. The media gateway may be controlled by a softswitch or other call control system, which may route all calls to and from a multi-mode mobile station through the media gateway. Thus, when the call control system establishes a call between the multi-mode mobile station and an endpoint via the first wireless network, the call includes a call leg that extends from the media gateway to the multi-mode mobile station via the first wireless network. Similarly, when the call control system establishes a call between the multi-mode mobile station and an endpoint via the second wireless network, the call includes a call leg that extends from the media gateway to the multi-mode mobile station via the second wireless network.
The call control system may also control call handoffs between the first and second wireless networks for multimode mobile stations. In an exemplary embodiment, the multi-mode mobile station initiates the handoffs. For example, while a multi-mode mobile station is involved in a call with an endpoint via its first interface, so that the call includes a first call leg extending from the media gateway to the multi-mode mobile station via the first wireless network, the multi-mode mobile station may detennine that the second wireless network is available and preferred. This may occur, for example, when the multi-mode mobile station is moving out of the coverage area of the first wireless network and into the coverage area of the second wireless network.
In response to this determination, the multi-mode mobile station may use its second interface to register with the second wireless network and may use its first interface to transmit a handoff request to the first wireless network. The call control system receives the handoff request and responsively attempts to establish a second call leg that extends from the media gateway to the multi-mode mobile station via the second wireless network. To establish the second call leg, the second wireless network may transmit an incoming call request that includes a caller identification that identifies the multi-mode mobile station. The multi-mode mobile station may recognize from this caller identification that the incoming call request is part of the handoff process and, as a result, may answer it automatically.
Once the second call leg is established, the multi-mode mobile station may begin receiving voice or other media (e. g., from the endpoint involved in the call) via its second interface. The multi-mode mobile station may store this media, thereby accumulating stored media, until instructed to convey
it to the user by the call control system. In this regard, the call control system may wait until it receives signaling that confinns that the second call leg has been successfully established. When the call control system receives this confinnation, it may transmit a handoff instruction to the multi-mode mobile station via the first wireless network.
When the multi-mode mobile station receives the handoff instruction, the multi-mode mobile station may responsively (i) convey the stored media to the user, (ii) drop the first call leg, and (iii) continue the call using the second call leg. In this way, a call handoff from the first wireless network to the second wireless network is effected. In addition, because the second call leg is established before the first call leg is dropped, this approach can beneficially effect a “soft” handoff between the first and second wireless networks.
2. Exemplary Network Architecture
FIG. 1 is a simplified block diagram of an exemplary wireless telecommunications system 10. In FIG. 1, connections that carry primarily voice or other media are shown as solid lines and connections that cany primarily signaling are shown as dashed lines.
Wireless telecommunications system 10 includes network elements that function together as a wireless local area network (WLAN) 12 and network elements that function together as a wireless local area network (WWAN) 14. WLAN 12 may provide wireless coverage in a relatively limited area, such as in a building or part of a building. In addition, WLAN 12 may use one or more unlicensed frequency bands, such as the unlicensed frequency band in the 2.4 GHz range. For example, WLAN 12 may use IEEE 802.11a, IEEE 802.11b, IEEE 802.11e, IEEE 802.11g, or IEEE 802.1 1h (wherein these and other members of the IEEE 802.11 family of specifications are referred to generically herein as “802.1 1x”), or variations thereof, for wireless communication. These 802.1 1x standards are incorporated herein by reference. Altematively or additionally, WLAN 12 may use IEEE 802.16, Bluetooth, HomeRF, HiperLAN, a Multichannel Multipoint Distribution Service (MMDS), or some other wireless protocol or fonnat for wireless comrnunication.
WWAN 14 may provide wireless coverage in a relatively large geographic area, such as an entire city, often by using a plurality of contiguous wireless coverage areas, such as cells or sectors. The wireless communication in WWAN 14 may occur in an analog format, such as the Advanced Mobile Phone Service (AMPS), or in a digital fonnat, such as code division multiple access (CDMA), time division multiple access (TDMA), or Global System for Mobile communication (GSM), and it may occur in licensed frequency bands, such as the 1.9 GHz PCS bands.
A multi-mode mobile station 16 has a first interface for wireless communication with WLAN 12 and a second interface for wireless communication with WWAN 14. Thus, multi-mode mobile station 16 is able to communicate with WLAN 12 when operating in an area served by WLAN 12 and is able to communicate with WWAN 14 when operating in an area served by WWAN 14. In some areas, the wireless coverage of WLAN 12 and WWAN 14 may be overlapping, and multi-mode mobile station 16 may use an arbitration method to detennine whether to communicate with WLAN 12 or with WWAN 14.
Multi-mode mobile station 16 may be a wireless telephone, wirelessly-equipped personal digital assistant (PDA), wirelessly-equipped laptop computer, or other type of wireless communication device. The first and second interfaces of
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