Abstract:
Methods for locating a missing called mobile unit in a telecommunications network are disclosed. With various equipment manufacturers present in the telecommunications industry, methods for use with a variety of equipment made by those manufacturers are necessary. The equipment in the network would include mobile units, home location registers and mobile switching centers. Through alterations in the operation of the home location registers and/or the mobile switching centers, the responses to page requests and/or routing requests are varied from the typical responses. Through those variations, missing called mobile units may be located in an efficient manner, regardless of the equipment provider.

Description:
FIELD OF THE INVENTION 
     The present invention broadly relates to the field of mobile telecommunications, and specifically to “flood paging” where multiple mobile switching centers (MSCs) are paged to locate a mobile unit that is not where it was last known to be, i.e. not where its last seen pointer (LSP) indicates. 
     BACKGROUND OF THE INVENTION 
     Telephones have become a staple of modem life. Originally telephones were located in peoples&#39; homes, businesses and in external phone booths. Thanks to changes in the field of telecommunications, people are now able to take advantage of cellular technology, such that mobile units can now be carried along with the users, wherever they may go. 
     Cellular service providers generally maintain certain information regarding the mobile units to facilitate the proper routing of incoming phone calls to the desired recipients. Further information that needs to be transmitted to the mobile units may include the feature sets, which would dictate the features that are available on the subscribed mobile units. A home location register is able to determine which mobile switching center a subscribed mobile unit last registered with or visited, by referring to a last seen pointer. The home location register is then able to provide the feature set to the mobile unit, transfer incoming calls, for the mobile unit, and transfer outgoing calls from the mobile unit. 
     As mobile units are by definition mobile, it is very important for the cellular service providers to keep track of their locations. If a mobile unit cannot be located by the cellular service provider, i.e. it is not in the location indicated by the last seen pointer, then the mobile telephone will be non-functional as related to its intended purpose of receiving telephone calls, regardless of its location. 
     Within a large metropolitan area, several mobile companies will be competing for cellular customers. Consider an area where there are three such companies, A, B, and C. Each such provider will have its own mobile switching centers (MSCs). Further, each company maintains at least one home location register (HLR) for its cellular subscribers. When a call is placed, it may or may not be directed to a customer of the same service provider. The call may originate in many ways. For example, the call may come from outside the area from a distant company, or the caller may be using a non-cellular phone, or it may be from one customer of service provider A to another such customer of service provider A. Or, it may be from a customer of service provider A to a customer of service provider B. Whatever the circumstances, the service provider of the caller must attempt to complete the call to the called mobile unit, regardless of whether the service provider of that called party is service provider A, B, or C. 
     To facilitate the completion of calls to cellular customers, each provider maintains its own HLRs. When a call is made by a customer of A to a customer of A, then service provider A consults its own HLR to see where the called mobile unit was last located and attempts to complete the call there. But if the call is made by a customer of A to a customer of B, then provider A will request call delivery information from B, and B consults its own HLR to see where the called mobile unit is located and returns information to A regarding how to complete the call. Thus, multiple HLRs may be consulted, depending on the circumstances. 
     Sometimes the called party (the mobile unit) is not, in fact, located in the same region served by the pointer on the corresponding HLR. Alternatively, the mobile unit may be switched off and not able to receive an incoming call. Whatever the circumstance, the customer&#39;s service provider occasionally will not find the mobile unit at its last known location and will need to find the called unit by a process called flood paging. 
     Locating a missing mobile unit is therefore an extremely important task in the realm of cellular telecommunications. Sometimes messages will be lost within a telecommunications system and must be delivered to a missing mobile unit. Also, a situation might arise where a mobile unit is moving along a border representing the extreme points where service is provided by a MSC. Depending on where the mobile unit is located as related to the border, multiple MSCs might provide service to a mobile unit, where the mobile unit will be bouncing back and forth between those MSCs. One way of locating a missing mobile unit is through a method called flood paging. Flood paging involves sending location request signals to all of the MSCs under the control of a home location register. The MSC which has control of the mobile unit responds to the location request. When there is only one vendor in the market, such a proprietary method is acceptable. 
     As the mobile telephone industry is growing very quickly, new parties are entering the cellular telecommunications market. In the future, cellular service providers will invariably have equipment produced by more than one vendor in their telecommunications networks. There is therefore a need for a method in which flood paging can take place across a telecommunications network, regardless of the particular vendor whose equipment is being used. 
     The current standard for cellular radiotelecommunications intersystem operations provides for one-to-one transactions. For example, when a vendor receives a routing request, it must respond. Further, the standard does not discuss sending out more than one route request per transaction. The current interpretation of the standard does not explicitly state that transactions must be one-to-one. By implementing methods which permissibly deviate from the one-to-one transaction standard, the vendors will be able to allow functions which are currently not available across a multiple vendor system, such as flood paging. 
     SUMMARY OF THE INVENTION 
     In the preferred embodiment of the present invention, a method for flood paging in a mobile telecommunications system is disclosed, wherein the method comprises the steps of sending a request from a home location register to each of a plurality of mobile switching centers, wherein the request indicates an identifier for a called mobile unit, sending a plurality of pages from the plurality of mobile switching centers, wherein the plurality of pages includes the identifier for the called mobile unit, providing a page response from the called mobile unit to at least one of the plurality of mobile switching centers and providing an acknowledgment of location by at least one of the plurality of mobile switching centers to the home location register. 
     In another embodiment of the present invention, one or more of the plurality of mobile switching centers does not provide an acknowledgment of location to the home location register. 
     In an embodiment of the present invention, the home location register forwards a location request signal to a mobile switching center that is attempting to complete the incoming call to the called mobile unit. In a variation of this embodiment, the call is delivered to the first MSC responding with a tldn received by the home location register. 
     In another embodiment, the home location register maintains an index of the requests sent to each of the plurality of mobile switching centers. 
     In another embodiment, the home location register makes a determination as to which acknowledgment of location to act upon. 
     The embodiments further describe in a telecommunications system of the type having a plurality of mobile units, a plurality of mobile switching centers, a called mobile unit and a home location register, the improvement wherein the home location register provides a location request. wherein the plurality of mobile switching centers provide at least one paging signal to the called mobile unit, wherein at least one of the plurality of mobile switching centers is a serving mobile switching center, and wherein only the serving mobile switching center provides a message to the home location register in response to a response to the paging signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may better be understood with reference to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like elements, and in which: 
     FIG. 1 shows a basic, multi-vendor telecommunications system; 
     FIG. 2 is a flowchart of the steps used in attempting to connect a mobile to an incoming call: 
     FIG. 3 is a flowchart of the preferred method of flood paging according to aspects of the present invention; 
     FIG. 4 is a flowchart of a first alternative method of flood paging according to aspects of the present invention; and 
     FIG. 5 is a flowchart of a second alternative method of flood paging according to the aspects of present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a plurality of mobile units  10   a ,  10   b , . . . ,  10   y ,  10   z . Further, a called mobile unit  12 , which represents the mobile unit which is to receive a particular incoming call, is shown Associated with the plurality of mobile units  10   a ,  10   b , . . . ,  10   y ,  10   z , and called mobile unit  12  is a plurality of mobile switching centers (MSCs)  16 ,  17 ,  18 , and  19 . For example, in a major metropolitan area, competing service providers may include Ameritech, Primeco, Sprint PCS. etc. Each competitor maintains its own home location registers and mobile switching centers. Mobile switching centers define the services that are offered to mobile units in a telecommunications network. These services may include call waiting, call hold, caller identification, data services, and call forwarding. Also associated with the plurality of mobile units  10   a - 10   z  and called mobile unit  12  is visited MSC  20 , which is the MSC with which called mobile unit  12  last registered or visited, and originating MSC  21 , which is the MSC that is attempting to connect a call. Not all of the plurality of mobile units  10   a - 10   z  and called mobile unit  12  are in contact with each MSC. Finally, a home location register (HLR)  14  is shown. A home location register is a device which assists a cellular service provider in the routing of telephone calls in a mobile telecommunications system HLR  14  is associated with MSCs  16 - 21 . A single HLR  14  is shown in FIG. 1, however it is possible for a cellular service provider to have more than one HLR in an area. In such a case where there are multiple HLRs for a particular cellular service provider, the HLRs do not interact with each other. Instead, the MSCs interact with the HLRs and with other MSCs. Within the United States. cellular service providers use their own home location registers, and not the home location registers of other cellular service providers. In some countries outside the United States, calls are delivered through the closest mobile switching center (MSC), regardless of ownership. 
     There are at least two ways in which a call for called mobile unit  12  will originate. First, a call can be land-based, meaning it does not originate from a mobile unit. Land-based calls are within what is referred to as a public switch telephone network. Within the public switch telephone network are associated mobile switching centers which are used in transmitting calls to mobile units. The associated mobile switching centers act as originating MSC  21  in the above description. Second, a call can be cellular-based, meaning it is call from a mobile unit to called mobile unit  12 . Within the cellular-based calls, the calls can be inter-provider or intra-provider. For intra-provider calls, the originating MSC  21  contacts HLR  14 , which then attempts to connect the call to called mobile unit  12 . For inter-provider calls, the originating MSC  21  within a first cellular service provider&#39;s network will contact a second MSC which is from the called unit&#39;s cellular service provider&#39;s network. The second MSC will contact the HLR for the called unit&#39;s cellular service provider and obtain information about the called mobile unit, so as to allow the call to be completed. 
     FIG. 2 shows a flowchart of the steps used in attempting to connect a mobile to an incoming call. One of the functions of home location register  14  is maintaining a pointer indicating where a mobile telephone was last seen. Such a pointer provides HLR  14  with an initial starting point when a call is to be received by called mobile unit  12 . When HLR  14  receives a location request from originating MSC  21  indicating that there is a telephone call for called mobile unit  12 , the location of called mobile unit  12  must be determined. Such a location request is generally done in a cellular manner. Block  22  represents originating MSC  21  sending a location request to HLR  14 . 
     HLR  14  references the last seen pointer to determine the last known location of called mobile unit  12 . More specifically, the last seen pointer indicates which MSC in the cellular service network was last used by the called mobile unit  12 . For discussion, this may be MSC  20 , which can be referred to as the “last registered MSC”  20 . It is called last registered MSC  20  because it is the last MSC with which the called mobile unit  12  registered. This is represented by block  23 . 
     As shown in block  24 , HLR  14 , in response to the location request (see block  22 ), transmits a routing request to the MSC indicated by the last seen pointer, last registered MSC  20 . The routing request contains a transaction identifier which allows HLR  14  to keep track of outstanding transactions, such as routing requests. Then, as shown in block  26 , last registered MSC  20  receives the routing request from HLR  14  (see block  24 ) and then sends out a paging request to the called mobile unit  12 , which is identified based upon a unique mobile identifier number. 
     As represented by block  28 , the determination of whether called mobile unit  12  is within the range of the last registered MSC  20  must be made. Either the called mobile unit  12  will receive the paging request from last registered MSC  20 , or it will not receive the paging request. In the case where called mobile unit  12  successfully receives the paging request (see block  30 ), the called mobile unit  12  will send a page response to the last registered MSC  20 , which, in this case is also the serving MSC. The serving/last registered MSC  20  will provide HLR  14  with a temporary local directory number (tldn) (see block  32 ) which is then used to allow the called mobile unit  12  to receive the incoming call. This is effectuated by having HLR  14  forward the temporary local directory number (tldn) to originating MSC  21 . 
     Upon receipt of the temporary local directory number of the called mobile telephone  12 , originating MSC  21  processes the incoming call in the following manner. By performing digit analysis, originating MSC  21  is able to determine how to route the call to called mobile unit  12 . More specifically, originating MSC  21  determines which trunk group is best to transfer the call towards the serving MSC. The serving MSC, through the use of the mobile identifier number is able to complete the call to called mobile unit  12 . Upon receipt of the call, called mobile unit  12  may provide an indication that there is an incoming call. 
     In the case where the last registered MSC  20  does not receive a page response from called mobile unit  12  during a predetermined time interval (see block  36 ), last registered MSC  20  will provide HLR  14  with a route request denied signal, as a result of no response to the paging request (see block  37 ). 
     When faced with a situation where the last registered MSC  20  cannot serve called mobile unit  12 , action must be taken to locate the missing mobile. Flood paging, which refers to paging numerous MSCs in search of the called mobile unit  12 , is then necessary. 
     Preferred (First) Embodiment 
     The preferred embodiment of the method of the present invention for flood paging in a telecommunications system is illustrated in FIG.  3 . Upon receiving a route request denied signal from last registered MSC  20 (see block  38 ). HLR  14  must then attempt to locate the called mobile unit  12  within the cellular telecommunications system. Earlier, HLR  14  had sent a routing request to last registered MSC  20  with which called mobile unit  12  had last registered. In the preferred embodiment, flood paging would take place in the following manner. HLR  14  will send a routing request including the same transaction identifier to the plurality of MSCs  16 ,  17 ,  18 ,  19 ,  20  and  21  within the cellular telecommunications network (see block  40 ). This allows HLR  14  to send out multiple routing requests, but expect a single response, as HLR  14  would have a single outstanding request related to the above. An identifier indicating that the system is in flood paging mode would also be included within the routing request. Each of the plurality of MSCs  16 ,  17 ,  18 ,  19 ,  20  and  21 , will then send a page to called mobile unit  12  (see block  42 ). As described with reference to FIG. 1, it must be determined whether called mobile unit  12  is within the range of a particular MSC x  (see block  44 ), where MSC x  is one of the plurality of MSCs  16 ,  17 ,  18 ,  19 ,  20  and  21 . If called mobile unit  12  is within the range of a particular MSC x , it will respond with a page response to that MSC (see block  50 ). MSC x , is therefore the serving MSC. If called mobile unit  12  is not within the range of a particular MSC x , the paging request will time out after MSC x  does not receive a response within a predetermined time interval (see block  46 ). Unlike the prior art, MSC x  does not send a route request denied signal to HLR  14  when the paging request times out. This is because one of the other MSCs within the plurality of MSCs  16 ,  17 ,  18 .  19 ,  20  and  21 , will be the serving MSC. The serving MSC will receive a page response from the called mobile unit  12  and will provide HLR  14  with a temporary local directory number. 
     Another instance in which flood paging is useful is when the last seen pointer within HLR  14  for called mobile unit  12  is blank or empty (see block  39 ). If called mobile unit  12  has not registered, the last seen pointer will not provide any information which can be used to locate the mobile. Flood paging allows HLR  14  a way of locating a mobile that has not registered. 
     In essence, the preferred embodiment allows HLR  14  to locate a missing called mobile unit  12  in a telecommunications system which contains equipment of more than one vendor. In the prior art, the MSCs would necessarily provide responses to the home location register for each location request. This would imply that the HLR would receive numerous responses in a flood paging situation., with the HLR subsequently transferring numerous signals to the originating MSC indicating that the location of called mobile unit  12  is not under the control of some MSCs, along with a signal indicating that called mobile unit  12  is under the control of a serving MSC. By adjusting the manner in which the MSCs operate, flood paging as described in this preferred embodiment may take place in a telecommunications system containing MSCs made by different manufacturers without having to replace HLR  14 . This is true because the HLR would only receive an indication that the location of called mobile unit  12  was identified and is under the control of the serving MSC , and would not receive additional responses from MSCs which do not have control of called mobile unit  12 . 
     Second Embodiment 
     An alternative method of flood paging is shown in FIG.  4 . This is a case where, unlike in the preferred method described with reference to FIG. 3, the manner in which HLR  14  operates is adjusted, as opposed to adjusting the manner in which the MSCs operate. As in the preferred method, it is assumed that flood paging is necessary because either the last registered MSC  20  sends a route request denied signal or the last seen pointer within HLR  14  for called mobile unit  12  is blank or empty (see blocks  60  and  62 ). Upon the recognition that either the last seen pointer is blank or the receipt of a route request denied signal from last registered MSC  20  (see block  64 ), HLR  14  must then attempt to locate the called mobile unit  12  within the cellular telecommunications system. 
     Earlier, HLR  14  had sent a routing request to the last registered MSC  20  with which called mobile unit  12  had last registered. In this second embodiment, flood paging would take place in the following manner. HLR  14  will send a routing request including the same transaction identifier to all of the MSCs (MSC 0  MSC 1 , . . . , MSC V , . . . , MSC S  . . . , MSC x ) within the cellular telecommunications network (see block  66 ). MSCV represents the last registered MSC  20 . MSC 5  represents the serving MSC, and MSC, represents a MSC within the network which is being discussed. An identifier indicating that the system is in flood paging mode would be included within the routing request. Each MSC will then send a page to called mobile unit  12  (see block  68 ). As described with reference to FIG. 1, it must be determined whether called mobile unit  12  is within the range of a particular MSC x , (see block  70 ). If called mobile unit  12  is within the range of a particular MSC x , it will respond with a page response to MSC x , (see block  76 ). MSC x , is therefore the serving MSC. If called mobile unit  12  is not within the range of a particular MSC x , the paging request will time out after MSC x , does not receive a response within a predetermined time interval (see block  72 ). The timed out MSC x , will then send a route request denied signal to the HLR  14  (see block  74 ). 
     The second embodiment has placed the adjustments in HLR  14 , in that HLR  14  is able to keep track of the outstanding routing requests (see block  82 ). By determining which MSCs have responded with route request denied signals, and which MSC has responded with a temporary local directory number, HLR  14  is able to determine which MSCs is serving the called mobile unit  12  as that MSC provided the temporary local directory number (see block  84 ). HLR  14  then forwards the temporary local directory number to the originating MSC  21 , so that the call can be completed (see block  86 ). 
     It is possible that more than one MSC will receive a page response from the called mobile unit  12 . Because the adjustments are within HLR  14 , HLR  14  is able to respond to the first successfully received temporary local directory number and to disregard subsequently received temporary local directory numbers. Those subsequent signals are not acted upon, as a serving MSC S  has been located which can contact the called mobile unit  12 . 
     Third Embodiment 
     A third embodiment is represented by FIG.  5 . As in the preferred (first) embodiment it is assumed that flood paging is necessary because either the visited MSC sends a route request denied signal or the last seen pointer is blank or empty (see blocks  90  and  92 ). Upon the recognition that either the last seen pointer is blank or the receipt of a route request denied signal from last registered MSC  20  (see block  94 ), HLR  14  must then attempt to locate the called mobile unit  12  within the cellular telecommunications system. In this embodiment, flood paging would take place in the following manner. HLR  14  will send a routing request including the same transaction identifier to a plurality of MSCs within the cellular telecommunications network (see block  96 ). An identifier indicating that the system is in flood paging mode would be included within the routing request. Each MSC will then send a page to called mobile unit  12  (see block  98 ). As described with reference to FIG. 1, it must be determined whether called mobile unit  12  is within the range of a particular MSC x . (see block  100 ). If called mobile unit  12  is within the range of a particular MSC x  it will respond with a page response to MSC x  (see block  106 ). MSC x  is the serving MSC. The serving MSC will then send a temporary local directory number to HLR  14  (see block  108 ). If called mobile unit  12  is not within the range of a particular MSC x , the paging request will time out after MSC x , does not receive a response within a predetermined time interval (see block  102 ). The timed out MSC x  will then send a route request denied signal to HLR  14  (see block  104 ). 
     As in the second embodiment, the adjustments have been placed in HLR  14 , in that HLR  14  is able to keep track of the outstanding routing requests (see block  112 ). HLR  14  waits for all outstanding response before taking action. HLR  14 , upon receiving all of the responses from the MSCs, determines which response from the plurality of MSCs it should act upon (see block  114 ). The temporary local directory number is then forwarded from HLR  14  to the originating MSC  21  (see block  116 ). 
     It is possible that more than one MSC will receive a page response from the called mobile unit  12 . If more than one MSC receives a page response from the called mobile unit  12 , the HLR  14  will resultantly receive more than one temporary local directory number. Because the adjustments have been placed in HLR  14 , HLR  14  is able to make determinations based upon, for example, signal quality. This determination may be based upon the possible degradation of the page response signal due to distance from the MSC S . Upon determining which temporary local directory number is best to act upon, or on selecting a temporary local directory number, HLR  14  then transmits that information to the originating MSC.  21 . In this way, overlapping MSCs will not cause a problem in a flood paging situation. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.