METHOD FOR PREVENTING CONTINUOUS DIRECTION OF A CALL BETWEEN CENTRALS DUE TO ERROR PE DUCKS PE TRANSLATION Technical Field This invention relates to the field of telecommunications systems and more particularly to prevent the continuous routing of a call due to a translation data error in a central in such telecommunications systems. AMTECEPEMTES PE LA INVENCIÓN In the last decade, the demand for advanced telecommunications services has increased with the growth of population and technological innovation. A by-product of this demand is the frequent transfer of customer lines between exchanges. A common catalyst for the transfer of client lines between switches is the "end termination" of a PBX. End termination is a well-known process that starts when an existing switch approaches its service capability and it is anticipated that the switch will be unable to service the needs of its growing customer base. The increasing number of users that require additional telephone lines for equipment, such as fax machines and personal computers, has contributed to the end termination of many exchanges. During the termination process REF: 22761 end, the growth of a switch is terminated (ie the switch is "extremely terminated") and additional client lines are serviced by a new switch (often technologically more advanced) . Inevitably, some customers served by the switch finished in extreme, request service features that are only available to those served by the new switch. In this way, the transfer of lines from individual customers served by the plant that is terminated in an extreme (or "old") to a "new" plant is common. Changing the switching service of a particular customer line from one exchange to another requires manually retrieving customer line data from the old switch and supplying the same data to the new database on the new switch. If adding a new service feature is the impetus for the transfer, additional data concerning the newly added service feature must also supply in the client file data of the new switch. Since each PBX typically serves one or more "blocks" of directory numbers, where each block has a unique PBX code, the transfer of a client line from one switch to another usually involves a change of directory number . Most customers, however, want to retain their current directory numbers, subsequent to a central transfer. The directory numbers that these clients require are "transferred" directory numbers that are defined as telephone numbers that have a PBX code different from the switchboard PBX code by which the customer's line is currently serviced. To serve clients with transferred directory numbers, there are systems that allow receiving telephone calls to a customer line served by a switch, in a directory number that includes a PBX code assigned to another switch. An exemplary embodiment of this system can be found in U.S. Pat. No. 5,048,081 commonly assigned, granted to Gavaras and collaborators, with the title "Arrangement for Routing Packetized Messages" that was granted on September 10, 1991 (hereinafter the Gavaras et al. Patent). During the manual data transfer process where customer line data from the old switch is retrieved and supplied in memory of the new switch, a service technician must also provide translation data to the new switch, so that incoming calls intended for the client of the transferred directory number, can be directed properly. More particularly, translation data is provided in such a way that the new exchange can convert the transferred directory number identifying the preferred customer line into a specific customer line address in the new switch. A significant problem arises in the prior art, however, if incorrect translation data is provided in the new exchange or if the translation data has not been supplied in fact. Normally, calls directed to the dialed directory number corresponding to the transferred customer line are supplied to the new exchange according to one of the following scenarios for call flow: (1) the incoming call addressed to a customer line transferred is routed through the public switched telephone network directly to the new exchange by means of a point code converter, as described in the Gavaras et al. patent, or as a result of data-based interrogation; or (2) the incoming call is initially routed to the old exchange, which recognizes the call as directed to a transferred customer line and subsequently extends the call to the new switch over a trunk between switches, as is known in the art. Once the call is received at the new exchange, the switch attempts to complete the call to a customer line. The call termination implies that the new switch recognizes that the directory number corresponds to a switch client line address. If the new switch detects incorrect (or non-existent) translation data such that it is unable to complete the call to any of its client lines, however, the call is routed to the same switch over a trunk connection between switches, in accordance with the cantral code digits of the dialed directory number that identify the old switch. Upon receiving the call from the new switch, the old switch recognizes (for the second time, if the call was initially received on the old switch) that the directory number corresponds to a transferred customer line and extends the call back to the new switch, even on another trunk connection between switches. The round-trip addressing of the call between the old switch and the new switch continues until there are no more trunks between available switches. When no trunks are available between switches, other trunk connections in the network are accessed to direct the call between the switches. Eventually, a significant number of network trunks are occupied in the attempt to complete the call. In addition to failing to make the desired connection, unnecessarily occupying trunks results in call delays for the other calls in the network. Therefore, there is a need in the art to automatically identify translation data errors in a central office and prevent the continuous routing of a call between exchanges due to translation data errors.
BRIEF DESCRIPTION OF THE INVENTION This need is solved and a technological advance in the telecommunications technique is achieved by the method and system of the present invention that allow a central in a telecommunications system to detect the existence of a translation data error and prevents continuous routing of a call between exchanges. In the preferred embodiment of the method and system of the present invention, a call addressed to a transferred directory number (i.e. a transferred client line) is received in a new exchange. Upon receiving the call, the new exchange determines whether translation data is required to connect the call to the customer line. In response to a decision that translation data is required, the new switch determines if a translation data indicator (TDE) is placed on this particular transferred directory number, indicating that a previous attempt to connect the call to a client failed. . If they are not found in a TDE indicator, the new switch connects the call to a customer line, or if the call can not connect to a customer line, the call returns to the switch corresponding to the number code digits of the number of marked directory, and places a TDE indicator. If a TDE indicator has already been placed, the call is connected to a circuit for announcement in the new exchange, and the routing of the call to the switch corresponding to the central code digits of the dialed directory number (i.e. the old switch). The TDE indicator is placed by the new switch as a result of an unsuccessful attempt by the switch to connect an incoming call to a client line on the switch and thus avoids unsuccessful redirection of the call between the old switch and the switch. new switch Subsequent to placing the TDE indicator, the new control panel also transmits an error message to a central control and maintenance center, so that service personnel can be alerted to the existence of translation data error. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified block diagram of a telecommunications system in which the present invention can be practiced; and Figure 2 is a flow chart of the steps that are performed in the telecommunications system of Figure 1, in accordance with a preferred embodiment of the method of the present invention. DESCRIPTION DFTATTAnA Figure 1 shows the telecommunications system
100 comprising the first exchange 104 (the "old" switch) and the second exchange 130 (the "new" switch). Also illustrated is the point code converter 108, which is used to direct calls from the public switched telephone network (PSTN) 10, to a telecommunications system 100, as described in the Gavaras et al. Patent. Alternate modes of the present invention may not employ a point code converter. The first exchange 104 is identified by the code numbers of exchange "555" and includes: the main processor 106 for managing the global control and maintenance functions; the main switch memory 107 for storing amplitude data of the system; the interface 110 for receiving messages from the point code converter 108 via the signaling link 109; and the switching module (SM) 112 to serve as an interface to client lines and PSTN lo (via trunk 122). SM 112 comprises controller 114, memory 116, network unit 118 and trunk installation 119. All internal switch components are interconnected by data links 103. In this embodiment, a single switch module serving a single client, through customer line 121, it is illustrated for reasons of clarity. An operational exchange includes multiple switching modules and serves many more customers. In a preferred embodiment of the present invention, the second hub 130 is the 5ESS digital switch manufactured and sold by AT &; T. The new switch 130 is identified by the code numbers of exchange "777" and includes three main components: administrative module AM 132; communication module (CM) 134 and switching modules (SM) 136 and 150. The AM 132 is responsible for managing the overall control and maintenance functions, and interconnects with the interface unit 133 via the data link 135. The interface unit 133 receives messages from the code converter 108 on signaling link 111. CM 134 serves as a communication conduit between AM 132 and the switching modules. The communication between the various components within the second exchange 130 (except for the connection between AM 132 and the interface unit 133) is achieved by network control and synchronization (NCT) links 135. As the convention dictates, the links Dual NCTs are illustrated between the switching modules (SM 136 and SM 150) and CM 134. The SM 136 comprises the controller 138 for module control, the memory 140 for storing information including translation data 141 and the data error indicator Translation (TDE) 143, network element 144 for interconnecting with client lines and trunk installation 145 to coordinate trunk connections with other switches. Signaling links 146A and 146B are also illustrated between the controller 138 of SM 136 and the controller 114 of the SM 112. As is known in the art, messages between the SM 136 and SM 112 are issued over a signaling link to establish trunk connections. between switches. In this mode, the first control connection 149 and the second trunk connection 151 have been established between trunk facilities 119 and 145 according to well-established procedures. There is a predetermined amount of trunk connections available between the old switching module 112 and the new switching module 136. In this way, if all the trunks between the old switch 104 and the new switch 130 are taken at any given time, calls earrings that require a connection between the switches, can not be completed until a trunk is available. The continuous redirection of a call due to translation data error in a switch (which occurs in the prior art as described above) potentially results in use of all trunks between switches, such as the old switch 104 and the new switch 130 , such that other calls that require addressing between the switches can not be completed in a timely manner. The SM 136 serving the customer line 123 identified by the directory number "(708) 555-1234" and previously served by SM 112 of the switch 104, is connected to PSTN 10 via trunk 124. SM 150 comprises the controller 152, memory 154 and network element 156 that includes the trunk installation 157. SM 150 communicates with SM 136 via CM 134 but is also illustrated in Figure 1 having a bidirectional trunk connection established 158, between its trunk installation 157 and the installation of trunk 145 of SM 136. In this mode, SM 150 serves a single customer through a customer line 159. The center for control and maintenance of power plant (MCC) 160 verifies all the exchanges in the telecommunications system 100 MCC 160 is interconnected with the main processor 106 of the old switch 104 and AM 132 of the new switch 130 by data links 161 and 163, respectively. In alternate modes, MCC 160 can also be interconnected to each switch module in telecommunication system 100. Figure 2 is a flowchart of the steps performed by the new switch 130, to identify translation data errors and to prevent translation error. continuous routing of a call according to a preferred embodiment of the method of the present invention. As an example, consider that a subscriber called by a central office in another telecommunications system (not shown) sends a call to a called party served by a customer line transferred 123 in the new exchange 130, by dialing the directory number transferred from the calling party "708-555-1234". Also consider that previous calls to the transferred customer line have not been received on the new switch. In a preferred embodiment, the process begins at step 200, when the call is received at the old switch of the called party (ie the first exchange 104) of the PSTN 10 via the trunk 122. At the decision stage 202, the old switch 104 determines whether the call goes to a transferred customer line. If the result of decision stage 202 is a "NO" determination, the call is completed to a customer line on the old switch. If, as in this example, the result of the decision stage 202 is a "YES" determination, the process continues to step 204 where the old switch 104 sends a message to the new switch 130 on the signaling link 146A, for Take a trunk connection to the new switch that now serves the transferred client line. In step 206, the old switch 104 extends the call over the taken trunk connection 149, which is established as a result of the signaling in the previous stage. In step 208, the new switch 130 receives the call. In an alternate mode, the incoming call is not supplied to the switch corresponding to the code numbers of exchange "555", the dialed directory number (ie the old switch 104) but on the contrary extends over PSTN 10, by means of the code converter 108, directly to the new switch 130 (in any mode, the call arrives at the new switch in step 208).
Regardless of whether the incoming call is received by the old switch 104 or PSTN 10, in the decision step 210, the new switch 130 determines whether the translation data is required to complete the call to a customer line. A call is completed when a switch detects the appearance of a client line associated with the dialed directory number of the call. The equipment in the customer premises does not necessarily have to be associated with the customer line. Also, once the call is completed to a customer line, other features, such as call forwarding, may additionally direct the call. If the result of decision step 210 is a "NO" decision, the call is connected to a client line in step 211. However, if the result of decision stage 210 is a "YES" decision, the process continues to decision stage 212 where it is determined whether there is a TDE indicator associated with a dialed directory number. If the result of the decision step is a "YES" decision, the process continues to step 234 described below. If, as in this case, the result of the decision step 212 is a "NO" decision, the process continues to step 213 where an attempt is made to retrieve the translation data from the SM 140 memory of a new switch 130
At the decision stage 214, a determination is made as to whether the translation data was in fact recovered from SM 140. If the result of the decision stage 214 is a "NO" decision, the process continues to step 220 at wherein the new switch 130 sends a signaling message to the old switch 104 (the switch is identified by the central code digits of the dialed directory number) on the signaling link 146B to configure a trunk connection in such a way that the call can be returned to the old switch 104, in the event that the call accidentally extended to the new switch. If the result of the decision step 214 is a "YES" decision, however, the process continues to step 216 where an attempt is made to complete the call to a client line of the switch 130, when searching for a projection of a client line address specified in the translation data. At the decision stage 218, a determination is made if the call was in fact completed to a customer line in the previous stage. If the result of decision step 218 is a "YES" decision, the process ends in step 219. However, if the result of decision step 218 is a "NO" decision, the process returns to step 220. In step 222, the new switch 130 sends an indicator on the signaling link 146B to the old switch 104, noting that translation data error was found and that the taken trunk will remain connected until the release by the new switch 130. Simultaneously, in step 224, the new switch 130 sets a TOE indicator in the switching memory 140, meaning that there is translation data error associated with the dialed directory number, and that future calls received over any trunk connection for that The particular directory number will be terminated to an advertisement circuit 137 which informs the calling party that the call can not be completed. In step 224, the new switch 130 sends an error message to MCC 160 on the data link 163, indicating that a TDE flag has been placed for that particular dialed directory number. Eventually, when the error has been corrected, MCC 160 sends a message "clear TDE indicator" to the new switch 130 via data link 163 so that future calls are not directed to the announcement circuit. The process continues to step 226 wherein the bidirectional trunk connection 151 is established between the trunk facilities 119 and 145 of the old switch 104 and the new switch 130, respectively, and the call extends back to the old switch 104 over the connection. Even when translation data error was found on the new switch 130, the call is extended back to the old switch 104, in case the call was initially accidentally delivered to the new switch. In step 228, the old switch 104 receives the call via the trunk connection 151. In step 230, the old switch 104 determines that the call is routed to a transferred client line, and the new call returns to the switch 130 over the bi-directional trunk connection 151. In step 232, the new switch receives an extended call by the old switch 104 on the same trunk, i.e. the trunk connection 151. The process continues to step 234 wherein the new switch 130 terminates the call to an advertisement circuit 137 and releases the trunk connection 151 over which the call was extended. In this way, erroneous translation data maintained in a central office does not result in the continuous routing of a call between "old" and "new" exchanges in a telecommunications system. The routing continues the call is prevented because the new switch terminates the call to an announcement circuit before identification of translation data errors. In addition, a central switch control and maintenance center is automatically alerted by the new exchange, when translation data errors are detected in such a way that optimistically the error is corrected before a complaint is filed by client. It will be understood that the embodiments described above are for illustrative purposes only. Numerous other assemblies of the invention can be designed by those skilled in the art, without departing from the scope of the invention. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following: