Abstract:
A method and apparatus for obtaining call record information in a mobile telecommunication switching system. The information is obtained, not only from the base station serving a call at the time that of the call record information is requested, but also for obtaining such information from prior base stations serving the call and subsequent base stations serving the call. Whenever a call is handed off, the identity of the call record and the handing-off base station, as well as the identity of the handing-off base station and the mobile switching center, (MSC), serving the call in the previous base station are recorded in the handed to base station. When a request for call record information is received, the base station serving the call transmits such call record information, and also transmits a request to the immediately prior base station to transmit its call record information from the identified call record. The predecessor then requests a similar action from its predecessor, if any. The initial base station for serving the call is initialized to record that it has no predecessors. Advantageously, this arrangement allows call record information from all predecessor base stations to be obtained, and transmitted an MSC for subsequent processing in an operation support system.

Description:
TECHNICAL FIELD 
     This invention relates to arrangements for obtaining data for calls made by a selected mobile station. 
     PROBLEM 
     Base stations and mobile switching centers of a wireless telecommunication system are arranged to detect many kinds of errors. Sometimes, these errors are detected in the middle of a call, possibly after a mobile station has been handed off one or more times from earlier base stations. Under these circumstances, there is no good way in the prior art of capturing data for earlier stages of the call from earlier base stations. 
     SOLUTION 
     Applicant has solved the above problem, and made a contribution over the prior art in accordance with this invention, wherein a call record of a call, as maintained in a base station, includes an identity of the base station which passed the call, the call record identification for that call in that base station, and optionally, the identity of the mobile switching center that controls that base station; when an error condition is discovered, the base station that controls the call at the time of the discovery thereby has a link to its predecessor base station and call record, and that base station has a similar link to its predecessor; the original base station, of course, has no indication of a predecessor; data from the predecessor call records can then be transmitted to the mobile switching center as long as the call record, which, for any predecessor station could be inactive, if the mobile has been transferred to another base station, or active, if the station still serves the mobile in a soft hand-off situation, has not yet been cleared. Advantageously, this arrangement will, under normal circumstances, (i.e., sufficient memory space for retaining call records for most of the duration of a call), allow all call record data for a call being monitored to be retrieved, even if there was no indication at the time that a base station handed off a call, that the call was going to be monitored. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     FIG. 1 is a block diagram illustrating the operation of Applicant&#39;s invention; 
     FIG. 2 is a flow diagram illustrating the process of detecting a request for data about a call; 
     FIG. 3 is a flow diagram illustrating actions performed in the base station currently serving the mobile station whose call is being monitored; 
     FIG. 4 is a flow diagram illustrating actions performed in previous base stations; 
     FIG. 5 is a flow diagram illustrating actions performed when a base station hands off the call; and 
     FIG. 6 is a flow diagram illustrating actions required in a base station at the time the call originates or terminates over a base station. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a block diagram illustrating the operation of Applicant&#39;s invention. The diagram illustrates a mobile telecommunication system in which three different base stations, BS 1 , BS 2 , and BS 3 , have served, or are serving a call. The call, when originally established, had mobile station  20 , served by base station  1 ; subsequently, mobile station  20  went into an area served by base station  2 , and thereafter, mobile station  20  went into a cellular area served by base station  3 . The three base stations are in turn, controlled by, and have switching performed for them, by mobile switching center (MSC)  10 . Mobile switching center  10  is connected by a network  11 , comprising a common channel signaling network, (CCS  7 ), and a public switched telephone network, (PSTN), for interconnecting the MSC with another MSC  13 , for handling calls when a mobile strays outside the area served by MSC  10 , a land based switch  14 , for completing or originating calls, one of whose parties is land-based, and an operations support system, (OSS),  12  for providing operations, administration, and maintenance support to MSC  10 . Alternatively, an OSS  15  can be directly connected to MSC  10 . Base station  1  comprises control  30 , which includes a memory  31 , which in turn, includes a plurality of call records such as call record  32 , from when the call was originally established. The call record, in accordance with the principles of Applicant&#39;s invention, was initialized with the identity of a previous base station, a previous call record identification, and the identification of a previous system, (such as a system controlled by MSC  13 ). In this case, since the call was originally established in base station  1 , the call record contains a blank for all three of these previous indicators. Knowing when the mobile station moved to an area served by base station  2 , base station  1  sent a message, such as message  35 , identifying the call record, ( 37 ), within base station  1 , and the identity of the corresponding mobile station, ( 36 ). Accordingly, call record for this call in base station  2 , which in this example is call record  34 , is initialized with the identity of the previous base station ( 1 ), the identity of the previous call record ( 32 ), and the identity of the previous system, which in this case is  10 , since the call was served by MSC  10  while it was being served from base station  1 . (In this example, of course, the call continues to be served from MSC  10 ). The identity of the previous base station and previous system are supplied inherently as part of the hand-off process, and are used to initialize the call record appropriately in accordance with Applicant&#39;s invention. 
     When the mobile station  20  moves to the area served by base station  3 , and is handed off to base station  3 , the call record  36  in base station  3 , is initialized with the previous base station ( 2 ), the previous call record identifier ( 34 ), and the previous system ( 10 ), through another use of message type  35 , as well as the other hand-off messages. Recording the previous system makes it possible to obtain call record data from another MSC, if the mobile station was handed-off across MSC boundaries. 
     Suppose that at some point, such as during the time when the call is being served by base station  3 , a request is made to get data for the call, or an abnormal condition is detected in MSC  10 , or a serving base station. If the request is made from an operation support system such as OSS  12 , either automatically or through a request from the craft attending OSS  12 , a message  40  containing the mobile station identifier  41 , and an indication that this is a data request  42 , is sent over the CCS  7  network  11 , to MSC  10 . MSC  10  would then forward a message  45 , to base station  3 . Message  45  would include an identifier of the mobile station  46 , and an indication that this is a request for data about the call  47 . 
     In response to receipt of this data, base station  3  transmits the call record data for the call involving the identified mobile station  20 . The message, type  55 , contains the mobile station identification  56 , and the call record data  57 . 
     In addition, base station  3  transmits a message  50  to base station  2 . The message  50  contains the call record identifier  51 , (in this case,  34 ), and a request that data about the call be sent to the MSC, ( 52 ). In response to receipt of message  50 , base station  2  transmits a message  55 , containing the identity of the mobile station  56 , and the call record data for the call  57 , as it existed in base station  2 . In addition, base station  2  transmits a message  50 , containing the call record identifier  51 , (in this case  32 ), and a request that data be transmitted to the MSC, ( 52 ) to the previous base station, base station  1 . In response to receipt of this message  50 , base station  1  transmits the contents of its call record for that call, i.e., the contents of call record  32  in another message  55 , including the identifier of the mobile station  56 . Base station  1  does not transmit a message  50  to a previous base station, because it recognizes that there is no previous base station, since the record in its call record of previous base station, previous call record, and previous system are all zero, or blank. 
     Using this arrangement, the three base stations transmit to the MSC the data in their call records for the call that is presently being made from, or to, mobile station  20 . 
     Additionally, if the mobile station moves from base station  3  to another base station, (including one of base stations  1  and  2 ), base station  3  sends a message  50  to the handed off base station to continue the link. At the time of the hand-off, base station  3  also transmits another call record data message  55 , to MSC  10 . 
     When the call disconnects, the base station serving the call at the time of the disconnect, sends a message  55  to MSC  10  to complete the record for the call. 
     FIGS. 2-6 are flow charts illustrating the method of Applicant&#39;s invention. The flow charts are implemented using control processors under program control in the MSC  10 , and the base stations  1 ,  2 , or  3 . 
     FIG. 2 is a flow diagram illustrating the operation of the process of detecting a request for data about a call. Action Box  201  shows that the MSC, itself, detects a call condition that requires the call to be monitored. For example, an MSC may receive a message containing an invalid base station number. Action Block  203 , the MSC receives a request for monitoring the call. The request is likely to come from an operation support system, which may automatically detect the condition requiring call monitoring, or which may transmit the request on the basis of a request initiated by the craft at the operation support system. In either case, the MSC sends a call monitoring request to the base station serving the mobile station to be monitored, (Action Block  205 ). 
     FIG. 3 illustrates actions performed in the base station currently serving the mobile station whose call is being monitored. Action Block  301  indicates a situation programmed into the base station, wherein the base station detects a condition that requires the call to be monitored. Action Block  303  indicates that a message sent in Action Block  305 , (FIG.  2 ), from the serving MSC requires that a call be monitored. In either case, transmits the state of the call record for the mobile station being monitored to the MSC, (Action Block  305 ). In addition, the base station currently serving the call, transmits a call record monitoring request to the previous base station, (Action Block  307 ). This request, sent in a message type  50 , includes the identity of the call record in the previous base station. Subsequently, the call may be handed-off to another base station, (Action Block  311 ). The base station transmits its call record state to the MSC, (Act ion Block  312 ). Then, in accordance with one feature of this invention, the call monitoring request is transmitted to that next base station, (Action Block  313 ); the call monitoring request if a message type  50 , and includes the call record identifier of the base station sending the request. While the primary purpose of this invention is to track sources of errors by examining the previous records, for some cases, the subsequent call messages may also contain useful information. Further, the identity, (including the identity of the serving MSC), is transported in the hand-off messages so that the call record can be initialized with the identity of the handing-off base station and MSC, as well as the identity of the call record in that base station. 
     If the call is not handed off to another base station, then when the call is terminated, (Action Block  315 ), the base station transmits its call record state at the time of termination to the MSC, (Action Block  317 ). 
     FIG. 4 illustrates actions performed in previous base stations. A previous base station receives a call monitor request from its next base station, (Action Block  401 ). This call monitor request includes this request in a message type  50 , which includes the identification of the call record in the receiving base station. The base station transmits the call record state of the identified call record to the MSC, (Action Block  403 ), and it transmits a call record request (of message type  50 ), to its previous base station, if any, (Action Block  405 ). The “if any” situation is identified by the absence of a previous call record identifier, previous base station, and previous system in the call record for the call. 
     FIG. 5 illustrates actions performed when a base station hands off a call. The base station hands off the call, (Action Block  501 ), and transmits the identity of the call record for this call in the transmitting base station to the next base station, (Action Block  503 ). The message of Action Block  503  is a type  50  message. The next base station then initializes its call record for the call with the identity of the previous call record, (received in message  50 ), and the identity of the previous base station and previous system received in other hand-off control messages, (not shown). 
     FIG. 6 illustrates actions required in a base station at the time of origination, or at the time the call originates or terminates on a base station, in order to implement Applicant&#39;s invention. The call originates or terminates on a base station, (Action Block  601 ). The base station then initializes its call record with a blank previous call record, blank previous base station, and blank previous system, (Action Block  603 ). This is to prepare for Action Block  405 , (FIG.  4 ), to allow a base station to avoid transmitting a call record request to a previous base station if there is no such previous base station. 
     In this embodiment, an inter-system call hand-off is assumed to be possible. This is the reason for having and maintaining a previous system segment in the call record. For cases in which inter-system call hand-offs are not allowed, it is not necessary to maintain this segment. 
     The call record is further enhanced to include the identity of the predecessor base station, the identity of the call record for that call in that predecessor base station, and the identity of a predecessor mobile switching center. If base station  2  discovers that there is an error condition in a particular call, and that data for that call should be reported to the mobile switching center, it sends a message  50 , to the predecessor base station  1 , including the call record identifier  51 , and an indication that monitoring data has been requested for dependent indication station  52 , that monitoring data has been requested for that call. Base station  1  will then transmit a message  55 , including the identity of the mobile station of that call  56 , and the call record data for that call  57 . If base station  1  had a predecessor base station, it would make a similar request of that predecessor base station as base station  2 , made of base station  1 . If base station  1  has no predecessor, then the predecessor base station identity and a predecessor call record identity would be blank. 
     The above is a description of one preferred embodiment of Applicant&#39;s invention. Many other arrangement will be apparent to those of ordinary skill in the art, without departing from the scope of Applicant&#39;s invention. Applicant&#39;s invention is, therefore, only limited by the attached Claims.