Hand-off technique for a wireless network

A technique that relates to use of a known messaging sequence, e.g., ISANSWER messaging in the IS-41 protocol, in a heretofore unknown manner to improve hand-off procedures that may be established between a serving (anchor or intermediate) mobile switching center and a target (or border) mobile switching center is provided. Specifically, the ISANSWER message is selectively sent from the serving mobile switching center to the target mobile switching center during the hand-off process. The transmission of the ISANSWER message in this manner allows the target mobile switching center to terminate ring back to a caller when the mobile station answers the call after the handoff has been started, but while the mobile station is still within a cell area of the serving mobile switching center.

BACKGROUND OF THE INVENTION

This invention relates to an improved hand-off technique for a wireless network. More particularly, the invention relates to use of a known messaging sequence, e.g., ISANSWER messaging in the IS-41 protocol, in a heretofore unknown manner to improve hand-off procedures that may be established between a serving (anchor or intermediate) Mobile Switching Center (MSC) and a target (or border) mobile switching center. That is, the ISANSWER message is selectively sent from the serving (anchor or intermediate) mobile switching center to the target (or border) mobile switching center during the hand-off process that may be induced during call termination to a mobile station. The transmission of the ISANSWER message in this manner allows the target (or border) mobile switching center to end ring back to a caller and to actually connect the call when the mobile station answers the call while it was still within a cell area of the serving (anchor or intermediate) mobile switching center.

While the invention is particularly directed to the art of hand-off techniques, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications.

By way of background, a variety of hand-off techniques are well known in the wireless industry. Many of these hand-off techniques are governed by the American National Standards Institute Standard 41 (ANSI41 or IS-41).

To illustrate one type of hand-off technique, referring toFIG. 1, a network10includes a first mobile switching center12and a corresponding cell site14. Also illustrated inFIG. 1are a second mobile switching center16and a second cell site18. It should be appreciated that the first mobile switching center12may also be referred to as the serving (anchor or intermediate) mobile switching center and the second mobile switching center16may also be referred to as the target (or border) mobile switching center. This nomenclature is useful because, as illustrated, a mobile device20migrates from an area of cell site14corresponding to the mobile switching center12to an area of cell site18corresponding to the mobile switching center16. The anchor MSC is the first to assign a traffic channel. In the examples, a simple scenario of a handoff from the serving MSC or anchor MSC is described. Nevertheless, note that the handoff, as well as the concept of using ISANSWER, may occur in other situations. For example, the handoff may also happen from an intermediary MSC (after handoff from anchor), still during a call termination. Also shown inFIG. 1is another communication device24which, for purposes of this example, may take a variety of forms and is operative to establish a call between itself and the mobile device20.

Using the example network ofFIG. 1, a hand-off procedure embodied in a call flow30is illustrated in an example inFIG. 2. The call flow30begins with a hard hand-off request being transmitted from the cell site14to the serving (anchor or intermediate) mobile switching center12(at line32). This occurs after a mobile device, such as the mobile device20, migrates from an area corresponding to, for example, the cell site14(and the signal there becomes weak) to an area corresponding to, for example, the cell site18.

The serving (anchor or intermediate) mobile switching center12then sends an invoke message, e.g., a Facility Directive (FACDIR2) message, to the target (or border) mobile switching center16(at line34). It should be understood that the functionality of providing ring back to a caller that may be calling the mobile device may be (and in many actual systems is) provided from the target (or border) mobile switching center after this message is received by this target (or border) MSC. So, from this point forward, ring back is provided by the target (or border) mobile switching center, not the serving (anchor or intermediate) mobile switching center.

The rationale for this transfer of ring back responsibility to the target (or border) mobile switching center is based on the fact that, when the mobile device is answered on the target (or border) MSC, the system can simply perform normal switching functions through, for example, a Digital Cellular Switch (DCS). The ring back function can then simply be discontinued. This discontinuation of ring back is immediate. Otherwise, if the serving (anchor or intermediate) mobile switching center were providing the ring back, there would be a delay between the actual answer on the target (or border) and the receipt and processing of the ISANSWER invoke message (conventionally only sent from the target (or border) mobile switching center to the serving (anchor or intermediate) mobile switching center). This delay could result in overlap of “talking” phase of the call and giving the ring back to the caller.

Referring back toFIG. 2, the target (or border) mobile switching center16then sends a (FACDIR2) return result to the serving (anchor or intermediate) mobile switching center12(at line36). The mobile switching center12consequently sends a message to the mobile device20through cell site14to start the handoff process, like, if applicable, to retune to an appropriate frequency so that the hand-off can be successfully completed (at line38).

During a successful hand-off, the cell site18will ultimately send a hand-off confirmation message to the target (or border) mobile switching center16(at line40). Then, the mobile switching center16completes the hand-off procedure by sending a mobile-on-channel message to the serving (anchor or intermediate) mobile switching center12(at line42).

If the mobile device20is called by another communication device (such as the communication device24inFIG. 1) during hand-off, and the mobile device20is answered while in the area of cell site18, then the cell site18sends an answer message to the target (or border) mobile switching center (at line44). The target (or border) mobile switching center16then sends an ISANSWER invoke message to the serving (anchor or intermediate) mobile switching center (at line46) to indicate that the call has been answered. Of course, the target (or border) mobile switching center14also ends the ring back to the caller at this point in time and connects the call by connecting the traffic channel from (the mobile and) the target cell to the inter-vendor trunk between target and serving MSCs.

The network as illustratively shown inFIG. 1does not, however, address the situation where the mobile device20is answered after FACDIR2 invoke is sent while still in the area of the cell site14during the hand-off procedure. At present, if this situation occurs, the ring back will continue to be provided by the target (or border) mobile switching center16and the caller using communication device24will continue to receive a ring back, as opposed to being connected to the mobile device20. This is, of course, not a desirable situation.

In particular, during the handoff process from the serving (anchor or intermediate) mobile switching center to the target (or border) mobile switching center, there is a “time window” of interest. This time window begins when the FACDIR2 invoke message is sent from the serving (anchor or intermediate) mobile switching center to the target (or border) mobile switching center. The time window ends when the mobile device actually re-tunes from the cell site associated with the serving (anchor or intermediate) mobile switching center to the cell site associated with the target (or border) mobile switching center. The time window is of a significant, non-zero, length. During this time window, two IS-41 messages are typically received at the serving (anchor or intermediate) mobile switching center from the target (or border) mobile switching center. In this scenario, however, there is no message sent from the serving (anchor or intermediate) mobile switching center to the target (or border) mobile switching center after the FACDIR2 invoke message. Therefore, there is no mechanism that is able to direct the target (or border) mobile switching center to stop the ring back (and switch the call), if the mobile device answers within the area of the serving (anchor or intermediate) mobile switching center (i.e., within the area of cell site14) during the “time window” specified above. Thus, the target (or border) mobile switching center will keep ringing back towards the caller, even after the called mobile device answers. Plus, the appropriate switching action on the target (or border) MSC connecting the mobile to the trunk between the target (or border) and the serving (anchor or intermediate) MSCs may not happen. This is clearly unacceptable, as this would interfere with the conversation that could otherwise start at this point.

The present invention contemplates a new and improved hand-off technique for a wireless network that resolves the above-referenced difficulties and others.

SUMMARY OF THE INVENTION

A method and apparatus for improved hand-off procedures are provided.

In one aspect of the invention, the method comprises initiating a hand-off procedure for a mobile device migrating between a first mobile switching center and a second mobile switching center, determining that a communication device is attempting to terminate a call to the mobile device during the hand-off procedure (or thereafter), determining that the mobile device answers the call during the hand-off procedure, the mobile device being within a geographic area corresponding to the first mobile switching center and sending a message (like ISANSWER invoke) from the first mobile switching center to the second mobile switching center, the message indicating that the call was answered.

In another aspect of the invention, the initiating of the hand-off procedure includes providing the second mobile switching center with responsibility for providing ring back to the communication device.

In another aspect of the invention, the method further comprises receiving a return result in response to the (e.g., ISANSWER) invoke message.

In another aspect of the invention, the method further comprises completing the hand-off procedure.

In another aspect of the invention, the message comprises a facility directive (2) message.

In another aspect of the invention, the method further comprises receiving the message.

In another aspect of the invention, the method further comprises terminating ring back based on the message.

In another aspect of the invention, the methods are implemented using suitable means.

In another aspect of the invention, the system comprises a first MSC operative to initiate a hand-off procedure for a mobile device migrating out of a geographic area corresponding to the first MSC, determine that a communication device is attempting to establish a call with the mobile device during the hand-off procedure, determine that the mobile device answers the call during the hand-off procedure, even after the handoff attempt has already been indicated from the first MSC to the second MSC while the mobile device is still within the geographic area corresponding to the first MSC and transmit a message indicating that the call was answered and a second MSC operative to receive the message and end ring back (and switch the call, i.e., make sure to establish the connection between the mobile and the trunk from the second MSC to the first MSC) based on the message.

In another aspect of the invention, the first MSC is operative to provide the second MSC with responsibility for providing ring back to the communication device.

In another aspect of the invention, the message comprises a facility directive (2) message.

In another aspect of the invention, the method and/or system may be applied to other hand-off procedures such as hand-back and “hand-off to third” situations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Sending an ISANSWER invoke message from the serving (anchor or intermediate) mobile switching center to the target (or border) mobile switching center is not covered by the ANSI41 standard, particularly with respect to the contemplated use for call terminations to the mobile herein. In accordance with this invention, however, a well timed provision of the ISANSWER message to the target (or border) mobile switching center provides a resolution of the difficulty noted above relating to appropriate discontinuation of the ring back that the target (or border) mobile switching center will be giving to the caller, as well as relating to appropriate connecting of the call on the target (or mobile) MSC. Therefore, implementation of the presently described embodiments resolves the noted difficulties.

Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same,FIG. 3provides a view of a network into which the present invention may be implemented. As shown, an exemplary network100is illustrated. The network includes a first, or serving (anchor or intermediate), mobile switching center112having a software module112-1for implementing and/or storing software routines to implement features of the present invention and other functionality. Also included in the network is a cell site114operative to communicate with a mobile device120. The cell site114has a corresponding geographic area for which it provides service.

The network100includes a second, or target (or border), mobile switching center116. The target (or border) mobile switching center116likewise includes a software module116-1for implementation and/or storage of software routines to carry out features of the present invention and other functionality. The mobile switching center116is operative to communicate with a cell site118that, once the hand-off procedures are complete, will be able to fully communicate with the mobile device120. The cell site118has a corresponding geographic area for which it provides service. Also shown in the network is another communication device124that, in this scenario, is operative to terminate the call to and communicate with the mobile device120.

As noted, the mobile switching centers provide software routines in, for example, the software modules112-1and116-1, that will implement the present invention. The software routines may be included within conventional call processing software that is stored within the mobile switching center or any other software that performs suitable functions according to applicable standards such as IS-41. It will be understood by those of skill in the art that the software routines may be implemented in a variety of manners and may invoke the use of a variety of hardware configurations to carry out functionality of the wireless network, including functionality described in connection with the present invention.

It should also be understood that the mobile switching centers may take a variety of forms and typically will include appropriate hardware and software routines to perform other functionality that is not described herein, for ease of explanation. The present invention is particularly applicable to the situation where the serving (anchor or intermediate) mobile switching center is manufactured by a different vendor than the target (or border) mobile switching center.

Those of skill in the art will also understand that any primary switching module in a wireless network may be used as an alternative to the mobile switching centers. For example, other such switching modules may be implemented in other generations of wireless technology.

The cell sites114and118may also take a variety of forms that are known in the field. Again, the exact form thereof may be a function of the generation of technology that is implemented. Likewise, the communication device124may take numerous forms including a landline phone, a wireless phone, a personal digital assistant, personal computer, . . . etc. As shown, the mobile device120may take a variety of wireless forms including that of a wireless phone, a personal digital assistant, a personal computer with wireless communication capability, . . . etc.

As alluded to above, the invention relates to use of a known messaging sequence, e.g., ISANSWER messaging in the IS-41 protocol, in a heretofore unknown manner to improve hand-off procedures that may be established between the serving (anchor or intermediate) mobile switching center112and the target (or border) mobile switching center116. That is, the ISANSWER message is selectively sent from the serving (anchor or intermediate) mobile switching center112to the target (or border) mobile switching center116during the hand-off process and a termination to the mobile. The transmission of the ISANSWER message in this manner allows the target (or border) mobile switching center116to end ring back to a caller when the mobile station120answers the call while it is still within a cell area of the serving (anchor or intermediate) mobile switching center, e.g., the area corresponding to the cell site114.

From the perspective of the serving (anchor or intermediate) (or intermediate; in general, serving MSC) mobile switching center, such as the mobile switching center112, a method of the present invention is described in connection withFIG. 4. This method may be embodied in the software module112-1, as noted above. As shown, a method300is initiated upon commencement of hand-off procedures (at302). The initiation of these procedures may include the provision of a facility directive invoke message (e.g., FACDIR2) from the serving (anchor or intermediate) mobile switching center112to, for example, a target (or border) mobile switching center116. This facility directive message will typically provide data needed by the target (or border) mobile switching center116to perform the handoff. Also, in some actual widely used implementations, the data the facility directive invoke contains will imply (for the call which is being terminated to the mobile device120and which is also, at the same time, being handed off) that the target (or border) MSC should take responsibility for ring back functions. Therefore, the target (or border) mobile switching center116will provide ring back to any device, such as communication device124, attempting to communicate with (specifically, terminate the call to) the mobile device120during a hand-off procedure.

The method of the present invention checks whether a ring back is actually in progress (at304). If no ring back is in progress, normal processing to complete the hand-off is accomplished (at306).

If it is determined that a ring back is in progress, then the serving MSC not only expects and processes the (FACDIR2) Return Result and Mobile on Channel IS-41 messages, but also needs to monitor whether the mobile device120answered the call while still within the area of the serving (anchor or intermediate) mobile switching center112, or the area corresponding to the cell site114, prior to (or close to) the mobile-on-channel message being received (at308). If not, normal processing to complete the hand-off is completed (at310). A check is then made as to whether hand-off is finished (at311). If so, the hand-off procedures are completed (at314) as is known. If not, the process returns to308.

If, however, the mobile device120answers the call while still within the area of the cell site114and prior or close to receipt of the mobile-on-channel message, then the mobile switching center112sends an ISANSWER message invoke to the target (or border) mobile switching center116(at312). If the transaction is successful, the mobile switching center112then receives the return result for the ISANSWER invoke (ISANSWER RR) from the target (or border) mobile switching center116and the hand-off procedures are then completed (at314).

Implementation of this process will allow the target (or border) mobile switching center116to appropriately terminate the ring back to the caller, e.g., the caller using communication device124, to allow for (full) communication between the caller and the called party. In this regard, from the perspective of the target (or border) mobile switching center116,FIG. 5illustrates an example procedure. This procedure or method may be embodied in the software module116-1, as noted above.

As shown, the method400includes the commencement of hand-off procedures (at402) which may, as noted above, include the receipt of the ring back functionality that is necessary to provide to calling parties to indicate an attempt to connect to a mobile device, such as mobile device120(i.e., terminate the call to mobile device120). Implementation of ring back may be realized in any number of known manners. This method allows for the determination of whether an ISANSWER invoke message is received by the target (or border) mobile switching center116from the serving (anchor or intermediate) mobile switching center112during the ring back process (at404). If no such ISANSWER invoke message is received, normal processing to complete the hand-off is conducted (at406and then, eventually,410). As shown, a check is made to determine if hand-off is finished (at407). If so, the procedures are completed (at410). If not, the process returns to404. This, of course, provides monitoring as to whether the ISANSWER message is received. If an ISANSWER invoke message is eventually received by the target (or border) mobile switching center116, the target (or border) mobile switching center116ends the ring back to the calling party (i.e., to communication device124) (at408). Ending the ring back to the calling party may be accomplished using a variety of known techniques. Thus, also, appropriate communication can then be established between the communication device124and the mobile device120. The hand-off procedures are also completed (at410).

It is to be appreciated that the methods described herein may be implemented in a variety of manners and in a variety of different networks. In addition, a variety of different call flows may result depending on the precise circumstances of the hand-off. For example, the call flows may depend on whether the mobile device120is in the process of being contacted by another communication device during the hand-off procedure. Moreover, the time at which the mobile device answers an attempted call may be factor in the sequence of the call flow.

However, to illustrate the embodiments of the present invention, call flow130ofFIG. 6is provided. With reference thereto, a hard hand-off request is transmitted from the cell site114to the mobile switching center112(at line132). The mobile switching center112then transmits a facility directive (FACDIR2) invoke message to the mobile switching center116(at line134). As noted above, it should be appreciated that this invoke message will typically include the data to indicate to the target (or border) mobile switching center116to take over ring back responsibility for the terminating call. Implementation of ring back may be realized in any number of known manners.

It will be understood that the present invention is particularly useful where the mobile device120is answered after FACDIR2 invoke but during the hand-off procedures while still within an area associated with the serving (anchor or intermediate) mobile switching center112. In this case, as shown in the call flow130, the mobile device120is answered and sends a message to the cell site114(at line136). Consequently, the cell site114sends an answer message to the serving (anchor or intermediate) mobile switching center112(at line138). The mobile switching center112then sends an ISANSWER invoke message to the target (or border) mobile switching center116(at line140). It should be appreciated that the target (or border) mobile switching center116then ends the ring back so that the party calling the mobile device120does not continue to hear ring back and the call is connected or switched on the target (or border) MSC after the mobile device120has actually been answered. Ending of the ring back to the calling party may be accomplished using a variety of known techniques. The mobile switching center116then sends an ISANSWER return result to the serving (anchor or intermediate) mobile switching center112(at142).

At some point, a return result is sent from the target (or border) mobile switching center to the serving (anchor or intermediate) mobile switching center with respect to the facility directive, or invoke message (at line144). It will be understood that the procedures of the present invention, i.e., transmission of the ISANSWER invoke message from the serving (anchor or intermediate) mobile switching center112to the target (or border) mobile switching center116, may be implemented or may be induced to happen at any point after the facility directive invoke message is sent from the mobile switching center112to the mobile switching center116. So, although the portions of the call flow relating to this feature (e.g., lines136,138,140and142) are shown as occurring between the lines134and lines144, these functions may also be performed, e.g., after the (FACDIR2) return result, such as that shown at line144, is transmitted.

Normal procedures for hand-off are then conducted and may take a variety of forms. In the example shown, a “retuning” message is sent from the serving mobile switching center112to the cell site114(at line146). Ultimately, the cell site118confirms the hand-off procedures (at line148). Last, the mobile-on-channel message is sent from the target (or border) mobile switching center116to the serving mobile switching center112(at line150).

It should be appreciated that the invention has been described in terms that generally apply to forward hand-off procedures. However, it will be understood that the invention may also be applied to other hand-off procedures, such as, but not limited to, hand-back situations and “hand-off to third” scenarios. Those of skill in the art will recognize any changes to, for example, the messaging scheme to implement the invention in such environments.

The above description merely provides a disclosure of particular embodiments of the invention and is not intended for the purposes of limiting the same thereto. As such, the invention is not limited to only the above-described embodiments. Rather, it is recognized that one skilled in the art could conceive alternative embodiments that fall within the scope of the invention.