Abstract:
A telecommunications network includes at least an active and a standby call server, the standby call server becoming active upon failure of the active call server. To facilitate rapid switch-over from the active to the standby call server and to prevent the loss of call processing data for calls in the call setup stage, the active call server sends call information to the standby call server during intervals in which the active call server is awaiting subsequent signaling messages from elements of the telecommunications network. In this way, the standby call server has the call information needed to commence call processing upon failure of the active call server, and the active call server makes efficient use of time while awaiting a reply signaling message.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to redundant call processing. In particular, the invention relates to a method and apparatus for copying call information expeditiously and in a way that allows in-progress call processing to continue if an active call processor fails. 
     2. Description of Related Art 
     To assure reliability, redundancy is often built into telecommunications networks. Most network equipment, including call processors and databases, are duplicated to provide greater reliability in the event of equipment failure. For example, active call processors are backed-up by duplicate equipment, referred to as a standby call processor. Call processors are used during the call set-up stage (i.e., the time from call initiation to establishing the call connection) to process information, transmit instructions regarding routing, allocate network resources, approve the call and the billing, and gather further information where needed. If the active call processor fails, the standby call processor can take over to process new incoming calls. 
     To perform properly, the standby call processor must have the same information that is available to the active call processor. Thus, the standby call processor is periodically updated and the data synchronized with that of the active call processor. Generally, wherever network data is duplicated, it is periodically updated and synchronized. However, periodic updating is a problem when failure occurs between the updates. Thus, new technology is needed to reduce the effects of the failures between the updates. 
     SUMMARY OF THE INVENTION 
     This invention provides a redundant call processing system that ensures call processing in the event of a failure of an active call server by maintaining in a standby call server the same information regarding the call as the active call server. In a telecommunications network, an active call server is backed up by a standby call server. The active call server receives an initial signaling message from an interface server to initiate a call. The active call server processes the initial signaling message and generates call information for the call. This information includes, but is not limited to, the content of the signaling message received; registers containing transient data about the call, such as counter and timer values; customer identification; and customer data and logic, for example. The active call server may then send a request back to the interface server requesting more information regarding the call. When the request is sent, the active call server copies the call information and sends the copy to the standby call server. 
     The interface server periodically determines if the active call server has failed. If the active call server has not failed, the interface server sends subsequent signaling messages to the active call server. However, if the active call server has failed, the interface server sends the subsequent signaling messages to the standby call server. In this way, the telecommunications network can insure, in the event of a failure of the active call server, that calls that have been initiated, but not established, will be established. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail with reference to the following drawings, wherein like numerals refer to like elements, and wherein: 
     FIG. 1 illustrates a telecommunications network; 
     FIG. 2 illustrates a switching network; 
     FIG. 3 illustrates a distributed database architecture; 
     FIG. 4 is a block diagram of a call server; 
     FIG. 5 shows the operation of the call servers in the event of a failure; 
     FIG. 6 illustrates an alternate embodiment of the telecommunications network; and 
     FIG. 7 is a flowchart illustrating the operation of the distributed database architecture of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Modern call processing relies heavily on database queries. Currently, many calls rely on database queries during the call setup stage. These include calls such as automated collect calls, 800 number calls, 900 number calls, and prepaid calling card calls, among others. Even many routine calls now rely on information contained in network databases for call processing. For example, determining whether a customer has a valid account is typically done via a database query and fraud control methods commonly involve database queries during call setup. 
     FIG. 1 shows a telecommunications network  10  according to the invention. Calls are placed from communications devices, such as telephones  11  to other communications devices, such as telephones  12 . The calls are routed through switching networks  100 , that are used to complete call connections. 
     FIG. 2 shows an exemplary switching network  100  for processing telephone calls, including executing database queries. A telephone switch  101  connects calling parties to called parties. The switch  101  also transmits call information to a database  103  via the signaling network  102 , which may be preferably implemented using an AT&amp;T SS7 signaling network, capable of transferring information between databases. For example, a telephone call from a calling party is received at the switch  101 . The switch  101  relays call information, such as the telephone number, to the database  103  via the signaling network  102 . As will be discussed later, the database  103  is a complex processor that manages and analyzes call information. The switching network  100  may include a plurality of databases such as databases  103  and  104 , and one or more switches such as switch  101  and switch  105 . The database  103  evaluates the call information and returns instructions via the signaling network  102  to the switch  101 , to complete the call connection. The database  103  my also in turn execute triangular signaling by interrogating the database  104  for the necessary call information, and return that information to switch  101 . 
     FIG. 3 shows the database  103  in more detail. The database  104  is identical to the database  103 , and the following description of the database  103  applies equally to the database  104 . The database  103  includes a plurality of interface servers  120 , an active call server  140  and a backup call server  141 . The interface servers  120  and the active and backup call servers  140  and  141 , respectively, are coupled together by a high speed interface  130 . Also as shown in FIG. 3, the database  103  includes administrative servers  150  and  151 . The administrative servers  150  and  151  will be described later in more detail. 
     Incoming call information, or signaling messages, from the signaling network  102  are received by one of the plurality of interface servers  120 . The interface servers  120  perform initial processing of the caller information, such as ensuring that all expected bits are received and that the call information is properly formatted. The interface server  120  then forwards the signaling message to the active call server  140  via the high speed interface  130 . The high speed interface  130  may be a local area network (LAN), for example. The call server  140  processes the signaling message and returns a response with directions to the interface server  120 , based on the processing results. The interface server  120  in turn returns the response to the switch  101  through the signaling network  102 . 
     As shown in FIG. 3, the database  103  may include the standby call server  141 . In one embodiment, the standby call server  141  is used to backup the active call server  140  in the event of a failure of the active call server  140 . Thus, the standby call server  141  does not process signaling messages from any of the plurality of interface servers  120  until a failure of the active call server  140  occurs. 
     In an alternative embodiment, each of the call servers  140  and  141  can process signaling messages and formulate call information, thus sharing the call processing load. In this case, the call servers  140  and  141  act as the standby call server for each other. That is, the call server  140  backs up the call server  141  and also acts as an active call server and the call server  141  backs up the call server  140  and also acts as an active call server. 
     FIG. 4 shows the active call server  140  in more detail. An interface  160  receives signaling messages from the high speed interface  130 . The interface  160  then sends the signaling message to a query processor  170  via a two-way signal bus  161 . The query processor  170  reviews the context of the signaling message, and compares the context to data stored in a persistent memory  180 . For example, an initial signaling message may include a telephone number of the called party, such as an 800 number. Associated with the 800 number may be specific routing instructions. For example, the routing instructions could direct the call to be routed to Tulsa on weekends and Chicago on weekdays. The query processor  170  determines how the signaling message is to be processed based on the context of the call information in the persistent memory  180 . In the example above, the query processor  170  determines the day of the week. If the day of the call was a Saturday, for example, the query processor  170  issues routing instructions to route the call to Tulsa. 
     In another example, the signaling message could include an 800 number to connect the caller to an 800 service. The 800 service could include a menu of options for the caller to choose from such as “press 1 for orders, press 2 for billing inquiries, press three to talk to a representative.” On receipt of the signaling message containing the 800 number, the query processor  170  searches the persistent memory  180  for data related to the 800 number and retrieves the selected option menu. Then, the query processor  170  may direct the switch  101  to provide the option menu in an audio format to the caller, for example. 
     After receiving the initial signaling message, the query processor  170  creates call information for the call. The call information may include a transaction register, received initial and subsequent signaling messages and response messages, for example. The transaction register may include specific routing information for the call and a transaction identification, for example. The query processor  170  then stores the call information in a short-term memory register  190 . Because the call information contains information needed to complete the call connection, if it is copied to the backup call processor  141 , the call connection may be completed, even in the event of a failure of the active call processor  141 . This is most important when the call is a complex call requiring multiple transactions between the switch and the database. 
     If the call is a simple call (i.e., one in which the call connection can be completed using only one signaling message and one response), the query processor  170  will delete the call information from the register  190  upon determining that the response message has been successfully sent. 
     If a fault occurs in the active call server  140  between the time that the initial signaling message is received and a response is returned to the switch  101 , the call connection may fail. However, in the case of the simple call, the waiting time between receipt of the initial signaling message and sending the response is very short, and thus a failure is not likely. 
     In the event of a complex call (ie., one in which several signaling messages and responses may be required to complete the call connection), the query processor  170  must process additional signaling messages and formulate additional responses. As the additional signaling messages are received at the active call server  140 , the query processor  170  updates the call information by adding additional data to current call information, modifying the current call information and replacing the current call information with a new set of call information, for example. The updated call information is then stored in the register  190 . 
     An information copier  200 , under control of the query processor  170 , copies the call information that is stored in the register  190  and forwards the thus-copied call information to the interface  160 . Thus, when call information is created or updated, the query processor  170  directs the information copier  200  to make a copy of the call information and forward it to the interface  160 . The interface  160  then transmits the copy of the call information to the standby call server  141 . 
     The standby call server  141  is identical to the active call server  140 . Thus, the copied call information from the active call server  140  is stored in the register  190  of the standby call server  141 . 
     The query processor  170  determines that the connection is established by means of its internal logic or by means of a message received by the active call server from the switch  101 . The query processor  170  then deletes the call information from the register  190  and sends a message to the standby call server  141  to also delete the call information for that call. In the example of a simple call, the query processor  170  deletes the call information from the register  190  when the call connection is completed. Because the call information was not copied to the backup call server  141 , the query processor  170  does not send a delete message to the backup call server  141 . 
     The copying and transfer of the call information is possible in the case of complex transactions because the active call server  140  “waits” for a significant portion of the time interval between signaling messages. For example, the total interval in which the active call server  140  is actively processing a signaling message may be on the order of 100 milliseconds. The waiting period (i.e., approximately the time from sending the response to receipt of the next signaling message) may be on the order of seconds, tens of seconds or minutes. Because the active call server  140  is waiting, and the call information is unchanging during the waiting period, sufficient time is available to copy the call information and forward it to the standby call server  141 . 
     As long as the active call server  140  is functioning normally, signaling messages will be processed in the active call server  140  and the call information copied to the standby call server  141 . However, in the event of a failure of the active call server  140 , the database  103  must be reconfigured in order to continue processing any calls that are still in the setup stage. 
     FIG. 5 shows the operation of the database  103  in the event of a failure of the active call server  140 . In the illustrated example, a failure of the active call server  140  occurs after receipt of the initial signaling message and return of the response and before receipt of the next signaling message. In FIG. 5, the interface server  120  sends an initial signaling message  121  to the active call server  140 . The active call server  140  processes the initial signaling message  121 , and determines that further input is needed from the switch  101  or from another database in the switching network  100 . The active call server  140  sends a response  122  to the interface server  120  and creates the call information for the call. The call information is then copied and a copy  123  is forwarded to the standby call server  141 . 
     At some time subsequent to the receipt of the response, the interface server  120  determines that the active call server  140  has failed. The interface server then designates the standby call server  141  as the new active call server. The interface server  120  then sends a subsequent signaling message  124  associated with the call to the call server  141 . Because the call information was copied to the call server  141 , the call server  141  is able to correctly process subsequently received signaling messages and to return call handling instructions to the switch  101  to complete establishing the call. When the call connection is established at the switch  101 , the call server  141  will then delete the call information associated with that call from the register  190 . 
     In the above discussion, the copy  123  is presumed to be transmitted to the standby call server  141  before the active call server  140  fails. However, if the copy  123  is not transmitted before the failure, the call connection cannot be completed. 
     FIG. 6 shows another embodiment of the switching network  100  according to the invention. In FIG. 6, the switch  101  receives signaling messages and forwards the signaling messages to the signaling network  102  via the transmission line  106 . The signaling network  102  forwards the signaling messages to an active database  303 . The switching network  100  also includes a standby database  304 . The database  303  contains one or more call servers that receive signaling messages from the switch  101  and send back response messages when more data is required from the switch  101  or from another database in the switching network  100 . The call server in the database  303  creates the call information for the call, copies the call information and forwards the call information to the standby database  304  over a transmission line  307 . The transmission line  307  could be a dedicated wide area network, the signaling network  102  or a standard T 1  or T 3  line, for example, as long as the data transmission speed is sufficient to transmit the call information during the waiting period between sending a response and receiving the subsequent signaling message. If the active database  303  fails, the call can continue to be processed by the switching network  100  because the standby database  304  maintains up-to-date call information for the call. 
     Returning to FIG. 3, administrative servers  150  and  151  perform functions such as updating static information contained in the persistent memory  180  of the active call server  140 . For example, if a user of the telecommunications network desires to change call routing for an 800 number on the weekends from Tulsa to Topeka, the administrative server  150 , for example, would receive the request and would send a message to the active call server  140 . The active call server  140  would then copy this information and forward it to the persistent memory  180  in the standby call server  141 . In this way, the static data contained in the persistent memories  180  of the active call server  140  and the standby call server  141  are maintained current. Alternately, the administrative server  150  could send the same message to both the active call server  140  and the standby call server  141 . 
     FIG. 7 is a flowchart illustrating the operation of the database  103  of FIGS. 3 and 4. The process begins in step S 100 . In step S 101 , the interface server  120  receives a message. The message may be an initial signaling message or a subsequent message. The process then moves to step S 102 . In step S 102 , the interface server  120  selects an active call server  140 . The process then moves to step S 103 . In step S 103 , the interface server  120  sends the message to the active call server  140 . The process then moves to step S 104 . 
     In step S 104 , the query processor  170  determines if the message is an initial signaling message or a subsequent message. If the message is the initial signaling message, the process moves to step S 105 . If the message is a subsequent message, the process moves to step S 106 . In step S 105 , the query processor formulates call information. The process then moves to step S 108 . 
     In step S 106  the query processor determines if call information is present. If call information is present, the process moves to step S 108 . Otherwise, the process moves to step S 107 . In step S 107 , the active call server  140  aborts the call. The process then returns to step S 100 . 
     In step S 108 , the query processor  170  determines if more data is needed. If more data is needed, the process moves to step S 110 . Otherwise the process moves to step S 109 . In step S 109 , the query processor  170  sends a final instruction message to the interface server  120 . The process then moves to step S 113 . In step S 113 , the query processor  170  determines if the call information was copied. If the call information was not copied, the process moves to step S 100  and waits for messages. Otherwise, the process then moves to step S 114 . In step S 114 , the query processor  170  of the active call server  140  sends a message to the standby call server  141  to discard the copy of the call information. The process then moves to step S 100  and waits for messages. 
     In step S 110 , the query processor  170  of the active call server  140  determines if a standby call server is available. If a standby call server is not available, the process moves to step S 112 . Otherwise, the process moves to step S 111 . 
     In step S 111 , the query processor  170  of the active call server  140  sends a current copy of the call information to the standby call server  141 . The process then moves to step S 112 . In step S 112 , the interface server  120  sends a request to the switch  101  or other network element for additional information. The process then moves to step S 100  and waits for messages. 
     As shown in FIG. 4, the query processor  170  is preferably implemented on a programmed general purpose computer. However, the query processor  170  can also be implemented on a special purpose computer, a programmed microprocessor or micro controller and peripheral integrated circuit elements and ASIC or other integrated circuit, additional signal processor, a hard wire electronic or logic circuit such as a discrete element circuit, a programmable logic device such as APLD, PLA, FPGA or PAL or the like. In general, any device capable of implementing a finite state machine for implementing a flowchart shown in FIG. 7 can be used to implement the query processor  170 . 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments and the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.