Patent Publication Number: US-9420117-B2

Title: Systems and methods for matching call detail records for the same communication generated by different elements of an IP telephony system

Description:
This application is a continuation-in-part of U.S. application Ser. No. 13/837,603, filed Mar. 15, 2013, the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention is related to Internet Protocol (IP) telephony systems. More specifically, the invention is related to telephony devices and methods of routing telephony communications via an IP telephony system 
     When an IP telephony system receives an incoming communication, the communication can be routed through multiple elements of the IP telephony system before the call is either terminated to a customer telephony device, or passed off to another telephony system. In some instances, multiple ones of the elements which handle the incoming communication each generate a call detail record (CDR) containing various pieces of information about the communication. Each element that generates a CDR sends the CDR to a central CDR unit of the IP telephony system. 
     Also, a single element that is responsible for handing a communication can generate both a start CDR and a stop CDR for the communication. Thus, a single element may generate two CDRs for the communication, each of which include different items of information about the communication. 
     When multiple elements of an IP telephony system each generate a different CDR relating to the same communication, it is desirable for the CDR unit to match the different CDRs that are related to the same communication. Matching the various CDRs related to a single incoming communication is helpful in determining which elements of the IP telephony system were responsible for handling the communication, which can be helpful in troubleshooting when problems arise. Also, information collected from all of the CDRs can be useful in billing for the communication. Information contained in the various different CDRs also can be aggregated into a single final CDR for the communication, and the final CDR can be used for billing purposes, quality monitoring and assurance, and troubleshooting. For all these reasons, it is desirable to have systems and methods which can match multiple CDRs generated by different elements of the IP telephony system, but which all relate to the same communication. 
     In some instances, it is possible to link multiple different CDRs which have been created for the same telephony communication using call identification number information contained in the CDRs themselves. However, in some types of call flows, it is not possible to use the call identification number information in the CDRs to link all the CDRs that relate to a single communication. 
     In view of the foregoing, it is desirable to find an alternate method for linking a plurality of CDRs which have been generated by various elements of an IP telephony system, but which all relate to the same telephony communication. 
     Moreover, certain types of communication traffic will follow the same basic flow path through the elements of the IP telephony system. Although the actual physical devices that are used to carry each communication can vary from communication to communication, the basic flow paths are the same. It would be desirable to record the type of flow path that each communication follows in the final CDR that is created for the communication. However, determining the actual type of flow path that each communication follows can be difficult. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a communications environment including various elements which are associated with an Internet protocol (IP) telephony system operating in accordance with one embodiment of the invention; 
         FIG. 2  is a diagram of various elements of a processor that forms part of an IP telephony system in accordance with one embodiment of the invention; 
         FIG. 3  is a block diagram illustrating selected elements of an IP telephony system in accordance with one embodiment of the invention; 
         FIG. 4  is a diagram illustrating the call flow paths which can be traversed by a communication through elements of an IP telephony system in accordance with one embodiment of the invention; 
         FIG. 5  is a flow diagram illustrating steps of a method of matching call detail records that are for the same communication and which have been generated by different elements of an IP telephony system in accordance with one embodiment of the invention; and 
         FIG. 6  is a flow diagram illustrating steps of a method of identifying a seed CDR for a communication that follows a particular type of flow path, and for then identifying all related CDRs and creating a final CDR for the communication. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following detailed description of preferred embodiments refers to the accompanying drawings, which illustrate specific embodiments of the invention. Other embodiments having different structures and operations do not depart from the scope of the present invention. 
     In the following description, the terms VOIP system, VOIP telephony system, IP system and IP telephony system are all intended to refer to a system that connects callers and that delivers data, text or video communications using Internet protocol data communications. 
     As illustrated in  FIG. 1 , a communications environment  100  is provided to facilitate IP based communications. A first IP telephony system  120  enables connection of telephone calls between its own customers and other parties via data communications that pass over a data network. The data network is commonly the Internet  110 , however, private data networks may form all or a portion of the data communication path. The first IP telephony system  120  is connected to the Internet  110 . 
     In addition, the first IP telephony system  120  is connected to a first publicly switched telephone network (PSTN)  130 , a second PSTN  140 , and a second IP telephony system  170 . This allows the first IP telephony system  120  to receive telephony communications from and send telephony communications to each of these other communications systems. In some instances, the first IP telephony system  120  would receive an incoming communication directed to one of its own customers from one of these other communications system. The first IP telephony system  120  then terminates the call to the customer&#39;s telephony device. In other instances, the first IP telephony system may setup an outgoing call from one of its customers to a customer of one of these other communications systems. In still other instances, the first IP telephony system  120  may act as an intermediate party to connect a communication between two of these other communications systems. 
     In some instances, the first IP telephony system  120  accesses the Internet  110  via a gateway  122 . The gateway  122  allows users and devices that are connected to the first and second PSTNs  130 ,  140  and/or the second IP telephony system  170  to connect with users and devices that are reachable through the first IP telephony system  120 , and vice versa. In some instances, the gateway  122  would be a part of the first IP telephony system  120 . In other instances, the gateway  122  could be maintained by a third party. 
     Customers of the first IP telephony system  120  can place and receive telephone calls using an IP telephone  108  that is connected to the Internet  110 . Such an IP telephone  108  could be connected to an Internet service provider via a wired connection or via a wireless router. In some instances, the IP telephone  108  could utilize a cellular telephone system to access the Internet  110 . 
     Alternatively, a customer could utilize an analog telephone  102   a  which is connected to the Internet  110  via a terminal adapter  104 . The terminal adapter  104  converts analog signals from the telephone  102   a  into data signals that pass over the Internet  110 , and vice versa. Also, as illustrated in  FIG. 1 , multiple analog telephones  102   a  and  102   b  could all be coupled to the same terminal adaptor  104 . Analog telephone devices include, but are not limited to, standard telephones and document imaging devices such as facsimile machines. A configuration using a terminal adapter  104  is common where all of the analog telephones  102   a ,  102   b  are located in a residence or business, and all of the telephones are connected to the same terminal adapter. With this configuration, all of the analog telephones  102   a ,  102   b  share the same telephone number assigned to the terminal adaptor  104 . Other configurations are also possible where multiple communication lines (e.g., a second telephone number) are provisioned by the IP telephony system  120 . 
     In addition, a customer could utilize a soft-phone client running on a computer  106  to place and receive IP based telephone calls, and to access other IP telephony systems. In some instances, the soft-phone client could be assigned its own telephone number. In other instances, the soft-phone client could be associated with a telephone number that is also assigned to an IP telephone  108 , or to a terminal adaptor  104  that is connected to one or more analog telephones  102   a ,  102   b.    
     A third party using the first analog telephone  132  which is connected to the first PSTN  130  may call a customer of the IP telephony system  120 . In this instance, the call is initially connected from the first analog telephone  132  to the first PSTN  130 , and then from the first PSTN  130 , through the gateway  122  to the first IP telephony system  120 . The first IP telephony system  120  then routes the call to the customer&#39;s IP telephony device. A third party using the first cellular telephone  134  could also place a call to an IP telephony system customer, and the connection would be established in a similar manner, although the first link would involve communications between the first cellular telephone  134  and a cellular telephone network. For purposes of this explanation, the cellular telephone network is considered part of the first PSTN  130 . 
     In addition, mobile computing devices which include cellular telephony capabilities could also be used to place telephone calls to customers of the IP telephony system. A first mobile computing device  136 , as illustrated in  FIG. 1 , might connect to the first PSTN  130  using its cellular telephone capabilities. However, such devices might also have the ability to connect wirelessly via some other means. For example, the mobile computing device  136  might communicate with a wireless data router to connect the first mobile computing device  136  directly to a data network, such as the Internet  110 . In this instance, communications between the first mobile computing device  136  and other parties could be entirely carried by data communications which pass from the first mobile computing device  136  directly to a data network  110 . Of course, alternate embodiments could utilize any other form of wired or wireless communications path to enable communications. 
     Users of the first IP telephony system  120  are able to access the service from virtually any location where they can connect to the Internet  110 . Thus, a customer could register with an IP telephony system located in the U.S., and that customer could then use an IP telephone  108  located in a country outside the U.S. to access the services. Likewise, the customer could also utilize a computer outside the U.S. that is running a soft-phone client to access the first IP telephony system  120 . Further, in some instances a user could place a telephone call with the first analog telephone  132  or first cellular telephone  134  that is routed through the first PSTN  130  to the first IP telephony system  120  via the gateway  122 . This would typically be accomplished by the user calling a local telephone number that is routed to the first IP telephony system  120  via the gateway  122 . Once connected to the first IP telephony system  120 , the user may then place an outgoing long distance call to anywhere in the world using the first IP telephony system&#39;s network. Thus, the user is able to place a long distance call using lower cost IP telephony service provided by the first IP telephony system  120 , rather than a higher cost service provided by the first PSTN  130 . 
       FIG. 1  also illustrates that a second IP telephony system  170  may interact with the first IP telephony system  120  via the Internet  110 . For example, customers of the second IP telephony system  170  may place calls to customers of the first IP telephony system  120 . In that instance, assets of the second IP telephony system  170  interact with assets of the first IP telephony system  120  to setup and carry the telephone call. Conversely, customers of the first IP telephony system  120  can place calls to customers of the second IP telephony system  170 . The second IP telephony system could also interact with the other communications systems via a gateway  172 . 
     As illustrated in  FIG. 1 , the second PSTN  140  may be connected to a second analog telephone  174 , a second cellular telephone  176  and a second mobile computing device  178 . 
       FIG. 2  illustrates elements of a computer processor  250  that can be used as part of the first or second IP telephony systems  120 ,  170 , or as part of an IP telephony device, to accomplish various functions. Each of the IP telephony systems  120 ,  170 , or an IP telephony device, could include multiple processors  250 , along with their operating components and programming, each carrying out a specific or dedicated function. 
     The processor  250  shown in  FIG. 2  may be one of any form of a general purpose computer processor used in accessing an IP-based network, such as a corporate intranet, the Internet or the like. The processor  250  comprises a central processing unit (CPU)  252 , a memory  254 , and support circuits  256  for the CPU  252 . The processor  250  also includes provisions  258 / 260  for connecting the processor  250  to customer equipment, to service provider equipment, to IP network or gateways, as well as possibly one or more input/output devices (not shown) for accessing the processor and/or performing ancillary or administrative functions related thereto. The provisions  258 / 260  are shown as separate bus structures in  FIG. 2 ; however, they may alternately be a single bus structure without degrading or otherwise changing the intended operability of the processor  250 . 
     The memory  254  is coupled to the CPU  252 . The memory  254 , or computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, flash memory or any other form of digital storage, local or remote, and is preferably of non-volatile nature. The support circuits  256  are coupled to the CPU  252  for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. 
     A software routine  262 , when executed by the CPU  252 , causes the processor  250  to perform processes of the disclosed embodiments, and is generally stored in the memory  254 . The software routine  262  may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU  252 . Also, the software routines could also be stored remotely from the CPU. For example, the software could be resident on servers and memory devices that are located remotely from the CPU, but which are accessible to the CPU via a data network connection. 
     The software routine  262 , when executed by the CPU  252 , transforms the general purpose computer into a specific purpose computer that performs one or more functions of an IP telephony system  120 / 170  or an IP telephony device. Although the processes of the disclosed embodiments may be discussed as being implemented as a software routine, some of the method steps that are disclosed therein may be performed in hardware as well as by a processor running software. As such, the embodiments may be implemented in software as executed upon a computer system, in hardware as an application specific integrated circuit or other type of hardware implementation, or a combination of software and hardware. The software routine  262  of the disclosed embodiments is capable of being executed on any computer operating system, and is capable of being performed using any CPU architecture. 
     In the following description, references will be made to an “IP telephony device.” This term is used to refer to any type of device which is capable of interacting with an IP telephony system to complete a telephone call. An IP telephony device could be an IP telephone, a computer running IP telephony software, a terminal adapter which is connected to an analog telephone, or some other type of device capable of communicating via data packets. An IP telephony device could also be a cellular telephone or a portable or tablet computing device that runs a software client that enables the device to act as an IP telephone. Thus, a single device might be capable of operating as both a cellular telephone and an IP telephony device. 
     Moreover, certain devices that are not traditionally used as telephony devices may act as telephony devices once they are configured with appropriate client software. Thus, some devices that would not normally be considered telephony devices may become telephony devices or IP telephony devices once they are running appropriate software. One example would be a desktop or a laptop computer that is running software that can interact with an IP telephony system over a data network to conduct telephone calls. Another example would be a portable computing device, such as an Apple iPod Touch™, which includes a speaker and a microphone. A software application loaded onto an Apple iPod Touch™ can be run so that the Apple iPod Touch™ can interact with an IP telephony system to conduct a telephone call. 
     The following description will also refer to telephony communications and telephony activity. These terms are intended to encompass all types of telephony communications, regardless of whether all or a portion of the communications are carried in an analog or digital format. Telephony communications could include audio or video telephone calls, facsimile transmissions, text messages, SMS messages, MMS messages, video messages, and all other types of telephony and data communications sent by or received by a user. These terms are also intended to encompass data communications that are conveyed through a PSTN or VOIP telephony system. In other words, these terms are intended to encompass any communications whatsoever, in any format, which traverse all or a portion of a communications network or telephony network. 
       FIG. 3  illustrates selected elements of an IP telephony system  300  in accordance with one embodiment of the invention, although the IP telephony system  300  would include additional elements. The IP telephony system  300  includes a call set up unit  302 , a billing unit  304 , and CDR unit  310 . The CDR unit  310  includes a raw CDR database  312 , a CDR matching unit  314 , and a final CDR database  316 . The way in which these elements of the IP telephony system  300  operate to match CDRs relating to the same telephony communication are discussed in detail below. 
     As mentioned above, when an incoming telephony communication is received by the IP telephony system  300 , the incoming communication can be routed through multiple elements of the IP telephony system  300 . Several of those elements could generate one or more CDRs for the communication, and each of these CDRs would be forwarded to CDR unit  310  for storage in the raw CDR database  312 . Thus, the raw CDR database  312 , stores multiple CDRs which relate to the same telephony communication. 
     The CDR matching unit  314  is responsible for matching the multiple CDRs in the raw CDR database  312  that relate to the same telephony communication. In some embodiments, the CDR matching unit  314  then assigns a single global identification number for the communication, and the global identification number is recorded in each of the individual CDRs that have been generated for the communication. 
     In some instances, the global identification number may be an identification number that was originally assigned by one of the elements responsible for handling the communication. In other embodiments, the global identification number is generated by the CDR matching unit  314 , and then recorded in each of the individual CDRs for the communication. 
     Once multiple CDRs relating to the same communication have been identified, the CDR  310  unit may generate and store one or multiple final CDRs for the communication in the final CDR database  316 . If multiple final CDRs are generated, they may be linked by a common global call ID number appearing in all of the final CDRs relating to the same communication. The final CDRs could be used by the billing unit  304  to bill a customer or another communication system for handling the communication. Alternatively, information in the final CDR database  316  could be used for other purposes, such as determining the overall path that a communication took as it traversed the elements of an IP telephony system  300 . Such information could be useful in troubleshooting, quality monitoring, service assurance, and for other reasons. 
       FIG. 4  illustrates various call flow paths which can be traversed by different types of telephony communications.  FIG. 4  will be used to explain some typical call flow paths, and how the CDRs generated by elements of the IP telephony system which handle those call flows can be matched to one another.  FIG. 4  is also used to show how at least one call flow will result in the generation of CDRs which are difficult to match to one another. 
     In a simple inbound termination call flow, a call originates at a first analog telephone  402 , and the call is directed to the IP telephony device  452 . A customer of the IP telephony system  410  would use the IP telephony device  452 . As reflected in  FIG. 4 , because the first analog telephone  402  receives its telephony service from a publically switched telephone network (PSTN)  404 , the call is initially routed to the PSTN  404 , and the PSTN  404  forwards the call to an inbound gateway  412  of the IP telephony system  410 . At this point, the call would have a first call ID number. The inbound gateway  412  forwards the call on to an inbound routing gateway  414 . Before doing so, however, the inbound gateway  412  assigns a second call ID number to the call, and this second call ID number is reflected in the messaging received by the inbound routing gateway  414 . From the perspective of the inbound gateway  412 , the first call ID number is an ingress call ID number, and the second call ID number is an egress call ID number. The CDR that is generated by the inbound gateway  412  will include the first and second call ID numbers in data fields labeled the ingress call ID and egress call ID, respectively. 
     The inbound routing gateway  414  then assigns a third call ID number to the call, and forwards the call to an inbound proxy server  430 . The inbound proxy server  430  determines the identity of an outbound proxy server  432  capable of communicating with the customer&#39;s IP telephony device  452 , and forwards the communication to the outbound proxy server  432 . The outbound proxy server  432  then terminates the call to the customer&#39;s IP telephony device  452  via the Internet  450 . 
     When the IP telephony system  410  operates as described above, the inbound gateway  412  and the inbound routing gateway  414  each generate a CDR for the communication, and the CDRs are forwarded to the CDR unit  420 . This CDR unit  420  could be as illustrated in  FIG. 3 , and include a raw CDR database which stores each of the CDRs generated for the communication. 
     Both of the CDRs would include an ingress call ID number and an egress call ID number. For example, the CDR generated by the inbound gateway  412  would list the first call ID number originally assigned by the PSTN  404  as the ingress call ID number, and the second call ID number assigned by the inbound gateway  412  would be listed as the egress call ID number. Likewise, the CDR generated by the inbound routing gateway  414  would list the second call ID number as the ingress call ID number, and the third call ID number assigned by the inbound routing gateway  414  would be listed as the egress call ID. 
     The second call ID number would appear as both the egress call ID number of the first CDR and the ingress call ID number of the second CDR. Thus, a CDR matching unit of the CDR unit  420  can match the first CDR to the second CDR using the call ID number information recorded in the first and second CDRs. 
       FIG. 4  also illustrates that a considerably more complex call flow can result in the generation of additional CDRs by other elements. For example, assume that the user of the first IP telephony device  452  has instructed the IP telephony system  410  to forward any incoming calls directed to the IP telephony device  452  to an alternate cellular telephone  462 , which receives its service from a mobile telephony system  460 . As a result, a call originating from the analog telephone  402  that is initially intended for the IP telephony device  452  is ultimately forwarded to the mobile telephony system  460  for termination to the cellular telephone  462 . 
     In this call flow, the first analog telephone  402  generates an outgoing communication which is directed to the IP telephony device  452 . Because the first analog telephone  402  receives its telephony service from the PSTN  404 , the call is initially routed to the PSTN  404 , and the PSTN  404  forwards the call to the inbound gateway  412  of the IP telephony system  410 . At this point, the call has a first call ID number. The inbound gateway  412  forwards the call on to the inbound routing gateway  414 . Before doing so, the inbound gateway  412  assigns a second call ID number to the call, and this second call ID number is reflected in the messaging received by the inbound routing gateway  414 . The inbound routing gateway  414  then assigns a third call ID number to the call, and forwards the call to the inbound proxy server  430 . 
     The inbound proxy server  430 , however, knows that the call should be forwarded to the cellular telephone  462 . As a result, the inbound proxy server  430  sends the call to an outbound routing gateway  440  with instructions to route the call the cellular telephone  462 . The signaling sent from the inbound proxy server  430  to the outbound routing gateway  440  includes the third call ID number that was originally assigned by the inbound routing gateway  414 . The outbound routing gateway  440  then assigns a fourth call ID number to the communication and forwards the call on to the outbound gateway  442 . The outbound gateway  442  assigns a fifth call ID number to the call, and forwards the communication on to the mobile telephony system  460  for termination to the cellular telephone  462 . 
     When the IP telephony system  410  operates as described above, the inbound gateway  412 , the inbound routing gateway  414 , the outbound routing gateway  440  and the outbound gateway  442  each generate a CDR for the communication, and the CDRs are forwarded to the CDR unit  420 . Each of the CDRs would include an ingress call ID number and an egress call ID number. For example, the CDR generated by the inbound gateway  412  would list the first call ID number originally assigned by the PSTN  404  as the ingress call ID number, and the second call ID number assigned by the inbound gateway  412  would be listed as the egress call ID number. Likewise, the CDR generated by the inbound routing gateway  414  would list the second call ID number as the ingress call ID number, and the third call ID number assigned by the inbound routing gateway  414  would be listed as the egress call ID. 
     The second call ID number would appear as both the egress call ID number of the first CDR and the ingress call ID number of the second CDR. Thus, a CDR matching unit of the CDR unit  420  can match the first CDR to the second CDR using the call ID number information recorded in the first and second CDRs. In a similar manner, the second CDR generated by the inbound routing gateway  414  can be linked to the third CDR generated by the outbound routing gateway  440  by the third call ID number. Further, the third CDR can then be matched to the fourth CDR generated by the outbound gateway  442  by the fourth call ID number. This process makes it possible to identify all of the CDRs which were issued by various elements for the same communication. 
     Another type of call flow is an outbound termination call flow. In this type of call flow, a call originates from a customer of the IP telephony system, and the call is sent to a telephony device that is served by some other telephony system. For example, a customer of the IP telephony system using IP telephony device  452  could place an outgoing call to cellular telephone  462 . During this call flow, the call setup signaling would first pass from the IP telephony device  452  to a proxy server  432 . The proxy server  432  sends the call on to an outbound routing gateway  440 . The outbound routing gateway  440  sends the call on to an outbound gateway  442 . The outbound gateway  442  then passes the call off to the mobile telephony system  460 , which completes the call to the cellular telephone  462 . 
     In an outbound termination call flow, the CDR generated by the outbound routing gateway  440  will not correspond to any CDRs generated by an inbound routing gateway  414 , as occurs for forwarding call flows discussed above. In other words, in the case of a forwarding call flow, the inbound routing gateway  414  will have passed the call to the outbound routing gateway  440 , likely via an inbound proxy server  430 . The inbound routing gateway  414  will generate a CDR for the forwarding call flow which includes an egress call ID. The outbound routing gateway  440  will then pass the call along to the outbound gateway  442 , and it will generate a CDR that has an ingress call ID identical to the egress call ID in the CDR generated by the inbound routing gateway  414 . On the other hand, if the call flow is an outbound termination, the outbound routing gateway  440  will generate a CDR that has an ingress call ID which has been assigned by the IP telephony device  452  which initiated the call. As a result of all these factors, one can identify CDRs generated by the outbound routing gateway  440  which relate to outbound termination call flows by looking for CDRs generated by the outbound routing gateway  440  that have an ingress call ID that does not match the egress call ID of any CDRs generated by the inbound routing gateways  414 . In other words, one reviews all CDRs generated by the outbound routing gateways  440  for a particular time window, looking for CDRs with ingress call IDs that do not match the egress call IDs of any CDRs generated by inbound routing gateways  414  in the same general time window. Any such CDRs must have been generated as part of an outbound termination call flow. 
     Another call flow type occurs when the IP telephony system receives call traffic from a first telephony service provider, and passes the call traffic along to a second telephony service provider. This call flow type is referred to as a transit flow. For example, in a transit call flow, the PSTN  404  may deliver a call to the inbound gateway  412  of the IP telephony system  410 , and ask that the IP telephony system  410  deliver the call to the cellular telephone  462 . The inbound gateway  412  sends the call to an outbound gateway  442 , and the outbound gateway passes the call off to the mobile telephony system  460 , which completes the call to the cellular telephone  462 . In some instances, the inbound gateway  412  may consult a routing server to determine the best outbound gateway to select. The selection of the proper outbound gateway may be based on cost considerations, quality considerations, and/or other factors. Also, in some embodiments, the inbound gateway  412  may pass the call off to a separate server which determines that the call is intended to a telephony device which is not directly served by the IP telephony system, and which selects an appropriate outbound gateway to use to send the call on to a telephony service provided capable of terminating the call to the called party. The separate server then forwards the call on to that outbound gateway. 
     In a transit call flow, both the inbound gateway  412  and the outbound gateway  442  will generate CDRs. However, the call ID appearing in the egress call ID field of the CDR generated by the inbound gateway  412  will match the call ID appearing in the ingress call ID field of the CDR generated by the outbound gateway  442 . Thus, it is relatively easy to match the CDRs generated by the inbound gateway  412  and the outbound gateway  442  for the same call. 
     In an inbound termination call flow, a call received from another telephony service provider is terminated to a customer of the IP telephony system. For example, if the user of the first analog telephone  402  called the IP telephony device  452 , it would be an inbound termination call flow. The call would initially pass from the analog telephone  402  to the PSTN  404 , and then from the PSTN  404  to the inbound gateway  412 . The inbound gateway  412  would pass the call to the inbound routing gateway  414 . The inbound routing gateway  414  would pass the call to an inbound proxy server  430 , and the inbound proxy server  430  passes the call to an outbound proxy server  432 . The outbound proxy server would then terminate the call to the IP telephony device  452  via an Internet server provider via the Internet  450 . In an inbound termination, the only devices which generate a CDR are the inbound gateway  412  and the inbound routing gateway  414 . 
     In some embodiments, an inbound termination call flow may be received by the inbound gateway  412 , and then passed directly to the inbound proxy server  430 . In other words, in some embodiments, the inbound routing gateway  414  may not be present. In that instance, the only CDR generated for the inbound termination call flow would be the CDR generated by the inbound gateway  412 . 
     There are, however, some call flows which result in the generation of multiple CDRs which cannot be matched using the call ID numbers in the ingress call ID and egress call ID fields of the CDRs. One example is a transfer call flow. As will be explained below a transfer call flow involves first and second legs. It is possible to use the ingress call IDs and egress call IDs of the CDRs for the first leg to match up the CDRs that relate to the first leg of the transfer call flow. In the same fashion, one can use the ingress and egress call IDs to match up the CDRs generated for the second leg of a transfer call flow. However, it can be difficult to match the first leg to the second leg. 
     In a transfer call flow, the first analog telephone  402  generates an outgoing communication which is directed to the IP telephony device  452 . The call is initially routed to the PSTN  404 , and the PSTN  404  forwards the call to the inbound gateway  412  of the IP telephony system  410 . At this point, the call has a first call ID number. The inbound gateway  412  forwards the call on to the inbound routing gateway  414 . Before doing so, the inbound gateway  412  assigns a second call ID number to the call, and this second call ID number is reflected in the messaging received by the inbound routing gateway  414 . The inbound routing gateway  414  then assigns a third call ID number to the call, and forwards the call to the inbound proxy server  430 . The inbound proxy server  430  then forwards the call to the outbound proxy server  432  for termination to the IP telephony device  452 . 
     In some instances, the outbound proxy server terminates the call to the IP telephony device  452  via the Internet, and the call begins. However, the user of the IP telephony device  452  then decides to transfer the call to another telephony device, such as the cellular telephone  462 . In other instances, the outbound proxy server  432  may know that the call should be immediately transferred to the cellular telephone  462 , and the IP telephony device  452  may not even be involved in the call flow. 
     Regardless, the outbound proxy server  432  then sends a “refer” message to the inbound gateway  412  that originally received the incoming call. The refer message indicates that the call is to be transferred to the cellular telephone  462 . The refer message received by the inbound gateway  412  will include a calling party identifier, a called party identifier, and an identifier for the telephony device to which the call is to be transferred. These identifiers are typically telephone numbers. Thus, the refer message will include the telephone number of the analog telephone  402  as the calling party identifier, the telephone number of the IP telephony device  452  as the called party identifier and the telephone number of the cellular telephone  462  as the “transfer to” identifier. 
     When the inbound gateway  412  receives the refer message from the outbound proxy server  432 , the inbound gateway  412  generates two CDRs. It generates a “stop” CDR for the original inbound call leg that extended to the IP telephony device  452 . This basically completes the first leg of the transfer call flow. The inbound gateway  412  also generates a “start” CDR for a new outbound call leg that will extend to the cellular telephone  462 . This is the beginning of the second leg of the transfer call flow. Details of those CDRs will be discussed below. 
     The inbound gateway  412  assigns a seventh call ID number to the call and sends the call flow to a new inbound proxy server  416 . The new inbound proxy server  416  sends the call on to the outbound routing gateway  440  without changing the seventh call ID. The outbound routing gateway  440  assigns an eighth call ID number to the call and passes it on to the outbound gateway  442 . The outbound gateway  442  assigns a ninth call ID number and passes the call on to the mobile telephony system  460  for termination to the cellular telephone  462 . 
     Although the call processing described above makes it possible for the call to be transferred from the IP telephony device  452  to the cellular telephone  462 , it is difficult to match up all the CDRs from the first and second legs of the transfer call flow. The refer message that is sent from the outbound proxy server  432  to the inbound gateway  412  does not include a call ID number. As a result, when the inbound gateway generates a CDR that initiates the second outbound leg that extends to the cellular telephone  462 , the CDR lacks a call ID number in the ingress call ID field. This basically breaks the chain of call ID numbers that is otherwise used to match up all the CDRs that relate to the same communication. 
     More specifically, it is possible to match up the first CDR generated by the inbound gateway  412  and the second CDR generated by the inbound routing gateway  414  because the second call ID number appears in the egress call ID field of the first CDR and the ingress call ID field of the second CDR. 
     It is also possible to match up a CDR generated by the inbound gateway  412  when it transfers the call to the inbound proxy server  416  and the CDR generated by the outbound routing gateway  440  because the seventh call ID number appears in both CDRs. These two CDRs can also be matched to the CDR generated by the outbound gateway  442  because the eighth call ID number appears in both the CDR generated by the outbound routing gateway  440  and the CDR generated by the outbound gateway  442 . 
     However, there is no clear link between the first and second legs of the transfer call flow, because the refer message sent from the outbound proxy server  432  to the inbound gateway  412  lacks a call ID number. It is, however, possible to match up the CDRs using different pieces of information in the CDRs. 
     As mentioned above, when the inbound gateway  412  receives the refer message from the outbound proxy server  432 , it generates a first “stop” CDR for the first leg of the transfer call flow, and it generates a second “start” CDR for the second leg of the transfer call flow that extends to the cellular telephone  462 . Those two CDRs will both include the same calling party identifier and called party identifier. In addition, because the CDRs are generated at essentially the same time by the same element of the IP telephony system—the inbound gateway  412 —certain timing information in the CDRs will also be identical, or very nearly identical. 
     In some embodiments, the timing information could be a “time-to-transfer” value, which is indicative of the time that elapsed between the point in time when the first call leg began and the point in time when the first call leg ended and the “stop” CDR was generated. This time-to-transfer value will appear in both the “stop” CDR and the new “start” CDR generated by the inbound gateway  412 . More specifically, the time-to-transfer value may be an integer number which basically represents the current state of a counter that is maintained by the gateway. The “stop” CDR generated by the inbound gateway  412  will have exactly the same or very nearly the same counter number as the “start” CDR generated by the inbound gateway  412  for the second outbound leg of the transfer call flow that extends to the cellular telephone  462 . 
     The timing number (which could be the time-to-transfer value or some other timing value) can be used, possibly in conjunction with the calling party identifier and the called party identifier, to match up the two CDRs. And when those two CDRs are matched, they provide a link between the first and second legs of the transfer call flow, and all CDRs generated for the communication can be linked together. 
     In still other embodiments, a call group ID number which is assigned by gateway, and which is also stored in a field of the CDRs may also be used to create unique transfer ID numbers which can link the two legs of a transfer call flow. 
     In some instances, other information could also be used to facilitate the matching of CDRs. For example, a timestamp value in the CDRs could also be used. The timestamp values, in conjunction with the timing value, could be used to uniquely identity the CDRs with respect to all other CDRs that are generated by the elements of the IP telephony system. Thus, adding the timestamp information to the other information may provide a powerful tool to match CDRs for the same communication. 
     In one embodiment, a first transfer identification number is generated using information contained in the first “stop” CDR that is generated by the inbound gateway  412  for the first leg of the transfer call flow. The first transfer identification number can be based on the calling party identifier, the called party identifier and the counter number in the first “stop” CDR. The first transfer identification number could be created by simply chaining the digits of those three values together in a particular order. Alternatively, the calling party identifier, the called party identifier and the counter number could be combined according to any mathematical formula or transformation to generate a transfer identification number. 
     Next a second transfer identification number is created using the calling party identifier, the called party identifier and the counter number in the second CDR generated for the second, outbound leg of the transfer call flow. The calling party identifier and the called party identifier will be identical, and the counter number will be identical, or very nearly identical. As a result, the second transfer identification number will be identical to the first transfer identification number, or nearly identical. For these reasons, if a first transfer identification number generated from a first CDR is the same, or nearly the same, as a second transfer identification number generated from a second CDR, we know that the two CDRs relate to the same transfer call flow, and the two CDRs can be used to link the two legs of the transfer call flow. 
     In reality, the CDRs generated by the elements of the IP telephony systems are constantly flooding in as each of the elements of the IP telephony system act to handle various call flows. Those CDRs are initially held in the raw CDR database  312 . The CDR matching unit  314  must then try to match up the CDRs belonging to the same communication. Because of the way the system operates, and because of the volume of CDRs involved, it is no simple matter to match up CDRs relating to the same communication, even using the transfer ID number method outlined above. 
     The inventors envision a process where the CDR matching unit  314  first uses the call ID number matching methods described above to match CDRs relating to the same inbound termination call flows, outbound termination call flows, forwarding call flows, transit call flows and other call flows which generate CDRs capable of being matched from only the information contained in the ingress call ID and egress call ID fields. Once those CDRs have been matched, there will still be a group of unmatched CDRs relating to transfer call flows and other call flows that result in the generation of CDRs that cannot be matched using only the information in the ingress call ID and egress call ID fields. The transfer call ID technique described above would then be used to match up those remaining CDRs. 
       FIG. 5  illustrates a method that could be performed by a CDR matching unit  314  of a CDR unit  310  of an IP telephony system  300  to match CDRs using the transfer call ID technique. The method  500  begins and proceeds to step S 502 , where a first transfer ID number is calculated or generated using information in a first unmatched CDR. The method then proceeds to step S 504  where another unmatched CDR is selected from a group of unmatched CDRs. In step S 506 , a transfer ID is calculated or generated for the selected CDR using information in the second CDR. 
     In step S 508  a check is performed to determine if the first transfer ID number is the same, or nearly the same, as the second transfer ID number. If not, the method proceeds to step S 510  to determine if the selected CDR was the last available CDR that was available for matching to the first CDR. If so, the method ends. If not, the method returns to step S 504  and another CDR is selected from a group of unmatched CDRs. The calculation step S 506  and comparison step  508  are then repeated for the newly selected CDR. Steps S 504 , S 506 , S 508  and S 510  repeat in a looping fashion until all unmatched CDRs have been selected and compared, or until one of the comparisons performed in step S 508  indicates that the transfer ID numbers are the same or nearly the same. If this occurs, the method proceeds to step S 512 , and it is determined that the first and selected CDRs are from the same communication. The method then ends. 
     A method as described above would be repeated until all the unmatched CDRs are matched to another CDR, or until no more matching is possible. 
     In some embodiments, the transfer ID number is calculated based on the calling party identifier, the called party identifier and a counter number in the CDRs. However, other information could also be used to calculate or generate the transfer ID number. For example, a timestamp value and/or an hour of the day that the CDR was generated could also be used to calculate or generate the transfer call ID number. Also, in alternate embodiments, only the called party identifier or only the calling party identifier could be used. In still other embodiments, it might be possible to use an identifier associated with the “transfer to” party. Virtually any combination of information that is present in both the CDRs could be used to calculate the transfer ID number. 
     The counter number that is used to calculate the transfer ID number could be representative of an internal time clock of the gateway generating the CDRs, or it could be representative of the duration of the communication that gives rise to the CDRs. In alternate embodiments, the counter number could be representative of other timing information. The important point, however, is that the counter number is likely to be the same, or very nearly the same, in the two CDRs generated by the inbound gateway  412  during a call transfer call flow. 
     The foregoing descriptions showed how a transfer ID calculated for first and second CDRs can be used to link two legs of a transfer call flow. However, the same basic procedures could be used to link one or more legs of other types of call flows that result in the generation of CDRs that are otherwise difficult to connect. 
     When one is attempting to match a first CDR to a second CDR which relates to the same communication, one would compare the first CDR to a group of candidate CDRs which are likely to have been generated for the same telephony communication. One can utilize a time window to select a group of candidate CDRs which are to be compared to a first CDR for a telephony communication. The time window would be for a period of time that begins when the first CDR was generated and for a short period of time thereafter. 
     Although many of the above examples were given with respect to a call which originated from a first telephone, and which was directed to a second telephone, the matching methods described above are not limited to matching CDRs generated for telephone calls. CDRs which are generated in connection with other types of communications handled by an IP telephony system can also be matched to one another in similar ways. 
     As mentioned above, once all the CDRs that have been generated for a communication have been identified, the information contained in the individual CDRs can be used by the CDR unit  310  to create a final CDR for the communication that is stored in the final CDR database  316 . In some embodiments, information about the call flow type of the communication may be recorded as part of the final CDR. In addition, an identity of the call flow originator and call flow terminator may also be recorded. This information could be used for various purposes, such as assessing the volume of traffic that conforms to each call flow type. Likewise, it can be helpful to know where the call traffic for a certain types of call flow typically originates and terminates. 
     Although the above described procedures allow one to determine which CDRs relate to the same communication, this information alone is not always indicative of the call flow type of the communication. However, it is often possible to review CDRs to look for information in a CDR that indicates that the CDR must have been generated as part of a particular call flow type. Once one determines that a CDR must have been generated for a communication conforming to a particular call flow type, one can then use the above-described methods to identify all the other CDRs that relate to that same communication. And once all the CDRs for a particular communication have been identified, one can generate a final CDR for the communication that includes the call flow type, as well as the flow originator and flow terminator. 
     Alternatively, information about the call flow type, the call flow originator, the call flow terminator, and possibly a global call ID number may be recorded in each of the individual CDRs that are generated for a particular communication. Information in the individual CDRs could then be accessed and used for various purposes. 
     The basic process for generating a final CDR is illustrated in  FIG. 6 . The method  600  begins and proceeds to step S 602  where the information contained in CDRs generated from a certain element of the IP telephony system is reviewed to identify a “seed” CDR that must have been generated for a communication conforming to a particular call flow type. Once a seed CDR has been identified, in step S 604  the information in the seed CDR is used to identify all the other CDRs that relate the same communication. In step S 606  information in all the CDRs for that communication is used to generate a final CDR for the communication. The final CDR is then stored in the final CDR database  316  of the CDR unit  310 . Alternatively, information about the call flow type, call flow originator, call flow terminator and a global call ID could be copied into each individual CDR that was generated for the communication. 
     A method as illustrated in  FIG. 6  would be repeated many times to match all the CDRs generated for multiple communications, and to generate final CDRs for each communication. The review performed in step S 602  would look for different types of information in the CDRs depending on the call flow type, as will be explained in more detail below. Also, depending on the call flow type, one would review CDRs generated by different types of elements of the IP telephony system, as will be explained below. 
     For example, and with reference to  FIG. 4 , in a transit call flow, the call is first received at an inbound gateway  412  from a first partner carrier. The inbound gateway then sends the call to an outbound gateway  442 , which passes the call on to a second partner carrier that terminates the call to the called telephony device. The inbound gateway  412  is typically connected to multiple inbound trunk groups, each of which is connected to a different carrier. As a result, when the call is received on a particular trunk group, the inbound gateway  412  knows the identity of the carrier delivering the call to the IP telephony system  410 . 
     To help identify the call as a transit call flow, and to help identify the partner carrier that delivered the call to the IP telephony system  410 , when the inbound gateway  412  creates a start CDR for the communication, the inbound gateway adds a code number onto the beginning of the called number appearing in the called number field of the CDR. A different code is used for calls received over each incoming trunk group. Because each trunk group delivers calls from a different carrier, the code that is added to the called number field is indicative of the identity of the carrier that delivered the call to the IP telephony system. 
     The code that is added to the called number in the called number field of the CDR can also be indicative of the call flow type. For example, if the inbound gateway  412  receives a call that is not for one of the customers of the IP telephony system  410 , this means the call will be a transit call flow. And a certain range of code numbers can correspond to transit call flows, with each code in the range being reserved for a different carrier that delivers transit calls to the IP telephony system  410 . 
     When the CDR unit  310  is reviewing CDRs to identify CDRs that were generated for transit flow communications, as part of a process of generating final mediated CDRs for transit flow communications, the CDR unit  310  can look for CDRs generated by inbound gateways that have a code inserted into the called number field of the CDR indicative of a transit call flow. In some embodiments, the presence of the code in the called number field can be detected by comparing the value in the called number field of the CDR to the value in the dialed number field of the CDR. Normally, the value in the called number field of a CDR will be identical to the value in the dialed number field of the CDR. For transit call flows, however, the inbound gateway  412  will have added a special code to the value appearing in the called number field, which means the value in the called number field will not match the value in the dialed number field. If one looks for the difference between the two values, one can extract the code that was added. And the code that was added will indicate that the CDR is for a transit call flow. The extracted code may also indicate the identity of the flow originator, which is the carrier that delivered the call to the IP telephony system. 
     As explained above, one can then match the egress call ID in the CDR generated by the inbound gateway  412  to the ingress call ID in the CDR generated by the outbound gateway  442  to match the CDRs generated by the inbound gateway  412  and the outbound gateway  442  for that communication. The CDR generated by the outbound gateway  442  will include information that identifies the carrier to which the call was sent for termination. Thus, the information in the CDRs can be used to generate a final CDR for the communication that includes the call flow type—transit—as well as the flow originator and the flow terminator. 
     In the case of transit call flows, one looks at CDRs generated by inbound gateways that have a called number that does not match the dialed number. One then extracts the code that was added to the called number field, and this code is used to determine that the CDR is from a transit call flow, and possibly also to determine the identity of the flow originator. Once the seed CDR for a transit call flow is identified, information in the seed CDR is used to identify the other CDRs that relate to the same communication, and information from all the CDRs is used to generate the final CDR for the communication. In alternate embodiments, one could simply look for a special code that has been inserted into a particular field of a CDR to identify CDRs that conform to a particular call flow type. In other words, it may not be necessary to compare the values present in two fields of a CDR to determine that a code has been inserted into one of the fields. Instead, it may be possible to simply search a single field for a particular code that has been inserted into the field by one of the elements of the IP telephony system in order to mark the CDR as being one generated for a communication following a particular type of flow path. This would be the case for both transit flows, as well as other call flow types. 
     Moreover, the code that is inserted into a field of a CDR to mark the CDR as having been generated for a communication following a particular flow path need not be inserted into a field that is used for other purposes. Instead, an element of the IP telephony system could insert such a code into a field of a CDR that would normally be blank, or which is not being used for other purposes. 
     Further, the code that is inserted into a field of a CDR could be indicative of not just the flow type of the communication, but other information as well. In the example given above, the code inserted into the called number field is also used to indicate the trunk group from which the communication was received by an inbound gateway. Thus, the code is also indicative of the identity of the telephony service provider that sent the communication to the inbound gateway. In other instances, the code could be indicative of other information, in addition to the flow type of the communication. Still further, a code inserted into a CDR might not be indicative of the flow type of the communication, but rather some other aspect of the communication. 
     In the case of other call flow types, one can identify the seed CDR in other ways. For example, in the case of an outbound termination call flow, the call will be initiated by a customer of the IP telephony system  410 , and the call will be placed to a telephony device served by some other telephony service provider. With reference to  FIG. 4 , a customer of the IP telephony system  410  using IP telephony device  452  would initiate the call, and call setup signaling would be delivered to a proxy server  432  of the IP telephony system  410  via an Internet service provider. The proxy server  432  would pass the setup request on to an outbound routing gateway  440 . Thus, the first element of the IP telephony system  410  that generates a CDR for such a communication would be the outbound routing gateway  440 . The outbound routing gateway  440  passes the call to the outbound gateway  442 , and the outbound gateway  442  passes the call off to a different telephony service provider for termination to the called party. 
     As explained above, one can locate seed CDRs for outbound termination call flows by reviewing all CDRs generated by the outbound routing gateways  440  looking for CDRs that have an ingress call ID that does not match the egress call ID of a CDR generated by an inbound routing gateway  414 . Any such CDRs are necessarily a part of an outbound termination call flow. 
     And once a seed CDR for an outbound termination call flow is identified, the corresponding CDR generated by the outbound gateway  442  for the same communication can be identified by matching the egress call ID of the CDR generated by the outbound routing gateway  440  to the ingress call ID of the CDR generated by the outbound gateway  442 . Information from both CDRs can be used to generate a final CDR for the communication that identifies the communication as being an outbound termination call flow. In this instance, the flow originator may be identified as the Internet service provider that delivered the original call setup request from the customer&#39;s IP telephony device  452 . The flow terminator could be identified as the egress trunk group to which the outbound gateway  442  delivers the call for termination, or possibly the identity of the telephony service provider that is connected to that egress trunk group. 
     In the case of a call forwarding call flow, the call will initially be directed to a customer of the IP telephony system. However, once the call is received, an element of the IP telephony system will determine that the call should be forwarded to some other telephony device which is not served by the IP telephony system. In a typical call forwarding scenario, an incoming call directed to a customer of the IP telephony system  410  is received at an inbound gateway  412 . The inbound gateway  412  passes the call to an inbound routing gateway  414 . The inbound routing gateway  414  passes the call to an inbound proxy server  430 . In some instances, the inbound proxy server may determine that the call should be forwarded to a different telephone number, such as the number for the cellular telephone  462 . In other instances, the call might get passed on to an outbound proxy server  432 , and the outbound proxy server determines that the call should be forwarded to a different telephone number. Regardless, the inbound proxy server  430  or the outbound proxy server  432  passes the call on to an outbound routing gateway  440 . The outbound routing gateway  440  passes the call on to an outbound gateway  442 , and the outbound gateway  442  passes the call to some other telephony service provider capable of terminating the call to the “forwarded to” number. 
     Under this type of a call flow, the inbound routing gateway  414  or the inbound gateway  412  will generate a stop CDR for the communication that includes a “forwarded to” telephone number. And the forwarded to number will be different from the called or dialed number. Thus, to identify a seed CDR for forwarded call flows, one can review the stop CDRs generated by the inbound gateways and the inbound routing gateways looking for stop CDRs that have a called number or dialed number that is different from the forwarded to number. And once a seed CDR for a forwarding call flow is identified, information in that CDR can be used to identify all the other CDRs for the communication, as described above. All the CDRs can then be used to generate a final CDR for the communication that indicates the communication was a forwarded call flow, and that identifies the flow originator and the flow terminator. In this instance, the flow originator could be the ingress trunk group from which the inbound gateway received the call. The flow terminator could be the egress trunk group to which the outbound gateway  442  delivered the call for termination to the forwarded to number. 
     As explained above, it can be difficult to correctly identify all the CDRs that relate to a transfer call flow. Basically, there are two separate legs to the transfer call flow, and it can be difficult to match the first leg to the second leg. However, identifying seed CDRs for each leg is relatively easy. 
     In the description provided above, we explained that at the end of the first leg of a transfer call flow, the outbound proxy server  432  sends a refer message back to the inbound gateway  412  that initially received the call, asking that the call be transferred to a different number. When the inbound gateway  412  receives the refer message, it generates a stop CDR which includes the “transfer to” telephone number. This basically ends the first leg of the transfer call flow. The inbound gateway  412  also generates a start CDR for the second leg of the transfer call flow, and the start CDR also includes a transfer to telephone number. However, because the inbound gateway  412  received the refer request from an outbound proxy server  432 , the start CDR for the second leg of the transfer call flow will lack an ingress call ID. 
     To identify a seed CDR for the first leg, one can review stop CDRs generated by inbound gateways looking for stop CDRs that include a transfer to telephone number. One does not want to use the start CDRs generated for the second leg of transfer call flows. So one can filter out and ignore any CDRs that do not include an ingress call ID. Any CDRs generated by an inbound gateway that includes both a transfer to telephone number and an ingress call ID are necessarily CDRs from the first leg of a transfer call flow. And once such a seed CDR is identified, one can use the seed CDR to identify all the other CDRs for the first leg of the same communication. 
     To identify a seed CDR for the second leg of a transfer call flow, one can again look for CDRs generated by an inbound gateways that include a transfer to telephone number, but this time one will only look for such CDRs that lack an ingress call ID. Alternatively, one could look for CDRs generated by the inbound gateways which have an ingress trunk which is identical to the egress trunk. The ingress trunk group will only match the egress trunk group in the case of CDRs generated in response to a refer message. Any such CDRs having a transfer to telephone number but which lack an ingress call ID, or where the ingress trunk group matches the egress trunk group are necessarily from the second leg of a transfer call flow. And once such a seed CDR is identified for the second leg of a transfer call flow, information in the seed CDR can be used to identify all the other CDRs for the second leg. 
     Once the CDRs from the first legs and the CDRs from the second legs of transfer call flows have been grouped together, the methods explained above can be used to match up the first and second legs. And once the CDRs from the first and second legs of a transfer call flow have all been identified, the CDRs can be used to generate a final CDR for the transfer call flow. 
     In some embodiments, each leg of the transfer call flow could be tracked separately, and a separate final CDR could be created for each of the first and second legs. In other embodiments, only a single final CDR may be created for the entire transfer call flow. Depending on which method is used, the flow originator and flow terminator could change. 
     In the case of an inbound termination call flow, one can locate a seed CDR by looking for CDRs generated by the inbound gateways  412  and/or inbound routing gateways  414  which include an egress call ID that does not match the ingress call ID of any CDRs generated by the outbound routing gateways  440  or outbound gateways  442 . Any such CDRs would necessarily be for an inbound termination call flow. Assuming the inbound termination call flow passes through both an inbound gateway  412  and an inbound routing gateway  414 , the CDRs generated by both of those elements can be matched to one another because the egress call ID in the CDR generated by the inbound gateway  412  will match the ingress call ID of the CDR generated by the inbound routing gateway. And once all CDRs have been located for an inbound termination call flow, a final CDR for the communication can be generated using information from both CDRs. The call flow type will be recorded at an inbound termination call flow, the call flow originator can be recorded as the trunk group from which the inbound gateway received the communication (or the identity of the telephony service provider that is connected to that inbound trunk group), and the flow terminator can be recorded as the Internet service provider that connected the call to the IP telephony device  452 . 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.