MXPA98001620A - Determinista solution of an optima restoration route in a telecommunication network - Google Patents

Abstract

After the detection of a fault, the sending node (8) transmits a restoration message including a weighted identifier for the tandem nodes (2, 4, 6, 12). After detection of an input restore message, a tandem node (2, 4, 6, 12) retrieves the weighted identifier of the restoration message and modifies it with a weight associated with the available link (100, 200) to from which the message of restoration was received. The modified weighted identifier is reinserted into the restore message and the message is transmitted downstream. The selector node (10) compares the weighted identifiers of the received restoration messages and selects an alternate route with the best ponderator identifier

Description

DETERMINISTIC SOLUTION OF AN OPTIMAL RESTORATION ROUTE IN A TELECOMMUNICATIONS NETWORK RELATED APPLICATIONS This invention relates to the following inventions set forth in: a request by W. Russ entitled "System and Method for Solving Substantially Simultaneous Bidirectional Demands of Available Capacity" (RIC-95-009) filed on June 7, 1995, which has serial No. 08 / 483,578; a request from Russ et al., entitled "Automated Trajectory Verification for Restoration Based on SHN" (File No. RIC-95-010), filed on June 7, 1995, which has serial No. 08 / 483,525; an application by W. Russ entitled "Automated Restoration of Unrenovated Link and Nodal Faults" (File No. .RIC-95-059) filed on June 7, 1995, which has serial No. 08 / 483,579; a request from Russ et al., entitled "Method and System for Resolving the Containment of Available Capacity Circuits of a Telecommunications Network" (File No. RIC-95-005) filed on June 6, 1995, which has the No. of series 08 / 469,302; an application by J. Shah entitled "Method and System for Identifying Fault Locations in a Communications Network" (File No. RIC-95-022) filed on June 7, 1995, which has serial No. 08 / 481,984; a request from Russ et al., entitled "System and Method for Same Estimation of Optimal Available Capacity for a Distributed Restoration Scheme" (File No. RIC-95-008) filed on June 22, 1995, which has the No series 08 / 493,477; a request from Sees et al. entitled "System and Method to Reconfigure a Telecommunication Network to its Normal State After the Repair of the Failure" (File No. RIC-95-013) filed on June 22, 1995, which has Serial No. 08 / 493,741; and a request from Shah et al. entitled "Information Based on the Established Trajectory and the Allocation of Available Capacity for the Restoration of the Distributed Network" (File No. RIC-95-021) filed on June 22, 1995. has serial No. 08 / 493,747. The related applications noted above, the exposures of which are incorporated for reference to this application, are all to be assigned to the same assignee of the present invention. FIELD OF THE INVENTION The present invention relates to a telecommunications network having a plurality of intelligent nodes or switches interconnected by a plurality of intervals for effecting a plurality of communication circuits, and more particularly to a method for optimally selecting an alternate route for the restoration of interrupted traffic between two adjacent nodes. The present invention also relates to a system for performing the optimal alternate route selection method and the specific overflow protocols and reverse link identifications used to carry out the inventive method. BACKGROUND OF THE INVENTION The survival capacity of the network is of utmost importance in a telecommunications network, since the loss of services in the network during only a very short period of time can tremendously affect the capacity of the network and cause a significant loss of income. The distributed restoration (DRA) algorithm of the self-healing network (SHN) set forth in U.S. Patent 4,956,835 teaches the selection of a shorter path K to restore interrupted traffic between the adjacent nodes. However, the? 835 method is based on a non-deterministic approach that is subject to the various dynamic delay characteristics present in a network at the particular time at which an interruption occurs. As a consequence, the method? 835 does not guarantee that a restoration path, or alternate route, is chosen that is optimal for a given malfunction in the network. To be elaborated, method 835 theoretically restores traffic in a mesh network by operating in parallel in a distributed manner to select from the available available capacity the restoration connections or available links. Although in theory the distributed method '835 will always select the shortest path K to restore affected traffic, in fact, this method is affected by the delays found by overflow restoration identifications through all the nodes of the network. This is basically due to the non-uniform nodal processing delays of the various nodes in the network. In other words, the propagation (or transmission and retransmission) of the restoration identifications (or messages) for both overflow and reverse link sequences on different alternate routes is limited by the speed at which the various nodes along the Different alternate routes detect and process messages. Putting it differently, the available capacity provided to a network is based on the assumption that restoring interrupted traffic will behave according to a shorter path rule. If this shorter path rule is not followed, then restoration may not be possible due to the lack of available capacity for certain portions of the network. Therefore, the assumption is that all the network equipment behaves in the same uniform way throughout the network. Even the fact that some devices may take longer than others to process the messages passing through them means that the theoretically shorter path rule, as set forth in the 835 patent, will not always yield a truly restoration path. optimal to restore interrupted traffic. SUMMARY OF THE INVENTION The present invention makes a deterministic approach to restoring the interrupted traffic in a distributed network by means of the proportion, in each one of the nodes of the network, of a memory table for storing a plurality of weights, each one identifying itself with an input connection to the node. The weights do not depend on time and for the modality to be treated below are distance measurements such as, for example, the respective lengths of the available links connecting the node to its adjacent nodes. Each available link that connects a node to one of its adjacent nodes is assigned a weight, that is, a mileage that is fixed and therefore deterministic. The detectors can be constructed in the respective ports to which the links are connected in order to detect the signals or input messages.

When a failure occurs in an in-service link that connects two adjacent nodes, after detection of the failure, by agreement, one of the nodes is designated as the sending node while the other is a selector node. The sending node initiates a restoration process by constructing an overflow identification (or restoration message) to begin the SHN process. For the present invention, the restore message is constructed to have an additional field in order to store a weighted identifier that is updated by each node that reaches the restore message. The weighted identifier can be a distance value that is set, for example, to 0 at the sending node. As the restore message is directed towards a tandem node, the weighted identifier is retrieved by the processor in the tandem node. The weight stored in the table in the tandem node that corresponds to the available link from which the restoration message reaches the tandem node is retrieved and adds to the weighted identifier already recovered. In the case that the weighted identifier is a distance value, the value of the length of the available link is added to the existing distance value. The incremented distance value is inserted again in the weighted identifier field of the restore message. The newly weighted restoration message then propagates to nodes downstream in its search for an alternate route to the selector node. This process is repeated every time the restore message arrives in a tandem node. In this way, assuming that an untimely restoration has not occurred and that the restoration message has a sufficiently large hop count, the restoration message, when it finally reaches the selector node, will contain in its weighted identifier field an identifier weighted whose value is a sum of all the sections of the alternate route that the restoration message has passed through. For the case where the weighted identifier is a distance value, such a distance value represents the total distance of the alternate route from the sending node to the selector node. Therefore, since distance does not depend on time, a deterministic approach is taken to find an alternate route. The restoration message containing the optimal weighted identifier is chosen by the selector node so that the route alternates that that restoration message route has traversed, is used to restore the interrupted traffic. In the event that the weighted identifier is a distance value, the restore message containing the shortest distance value is chosen from among the restore messages arriving at the selector node within the predetermined restore timeout period. To confirm that the alternate route chosen is indeed the optimal alternate route, a reverse restoration message, or a reverse link identification, it is constructed by the selector node and transmitted over the chosen alternate route. This reverse restoration message has an inverse weighted identifier field, which may be, for example, an inverse distance field having a value set at the selector node by being added to the distance value of the alternate route chosen. When the reverse restore message arrives at a tandem node, the inverse process takes place in which the tandem node retrieves from its table the weight associated with the available link from which the reverse message is received. The stored weight is decreased from the weighted identifier value so that, as the successive tandem nodes are traversed by the reverse restore message, their weighted reverse identifier inverse value is successively decreased. By the time the reverse restore message reaches the sending node, the weighted identifier must have the same value as the value of the weighted identifier field of the restoration message that was sent by the sending node. In the case that the weighted identifier field is a distance field, the distance value for the reverse restore message, after its arrival at the sending node, must be the same as the value of the distance field of the message of restoration sent by the emitting node, for example 0. According to the above, the present invention provides a deterministic approach that is not affected by the various time delays or nodal processing of the different nodes in a network distributed through the which cross the restoration messages in an attempt to find alternate routes for the restoration of traffic interrupted in the network. BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages noted above and others of the present invention, will become more apparent from the following description in which reference is made to an embodiment of the invention taken in conjunction with the accompanying drawings in where: Figure 1 shows an exemplary portion of a telecommunications network and the interconnections of the various nodes; Figure 2A is an illustration of the structure of a restoration message; Figure 2B is an illustration of the structure of a reverse restore message; Figure 3A is the exemplary network shown in Figure 1 with alternate routes that have been found in response to a fault between two adjacent nodes; Figures 3B-3E each show one of the alternate routes shown in Figure 3A; and Figures 4A-4D, in combination, provide a flow diagram illustrating the operation of the present invention. DESCRIPTION OF THE PREFERRED MODALITY An exemplary portion of a telecommunications network for explaining the present invention is illustrated in Figure 1. As shown, a plurality of intelligent nodes 2, 4, 6, 8, 10 and 12 are interconnected with each other through intervals, and more specifically by links. Each of the links could be a connection of either an asynchronous digital service level 3 (DS-3) or a synchronous transport signal level (STS-n) or an optical carrier signal level (OC-n) . For the embodiment of Figure 1, each of the nodes 2-12 is a digital crossover connection switch (DCS) made, for example, by Alcatel Network Systems that has manufactured the Model No. 1633-SX. Of course, similar cross-connection equivalents or switches may also be used. For ease of explanation, within each of the nodes 2-12 there is shown a processor P and a memory M, which comprises in addition to other stores, a storage table specific to the present invention. Within each of the nodes a number of ports are also provided, identified as or S, which designate respectively operational and available ports. These ports provide input / output connections between each of the nodes and their adjacent nodes. For example, it is shown that node 2 has three links, that is, 2 1, 2W2 and 2S, which are connected to its adjacent node 8. The links 2W1 and 2W2 are links in operation that are each connected to ports in operation corresponding to nodes 2 and 8. The link 2S is an available link connecting node 2 to node 8 through corresponding available ports. In addition, node 2 is connected to node 4 by means of two available links 4S1 and 4S2. Similarly, node 4 is shown connected to node 6 by two available links 6S1 and 6S2. The available links 12S1 and 12S2 connect node 6 to node 12, while the available links 10S2 and 10S3 connect node 12 to node 10. An available link 8S is also shown connecting node 8 to node 4 and an available link 10S1 connecting the node 10 to node 4. Finally, a link in operation 8 is shown to connect node 8 to node 10. For the modality of figure 1, suppose that in addition to the available links, there are a number of links in operation that interconnect the various nodes. However, for reasons of simplicity, only one link in operation 8 is shown connecting node 8 to node 10 and two links in operation 2W1 and 2W2 connecting node 2 to node 8. As stated above, each of the nodes has a memory M comprising a storage table. The table has various weights stored therein, each corresponding to an available link that connects to a particular one of the available ports of the node. Taking node 2 for example. As shown, there are three available links, namely, 2S, 4S1, and 4S2, each connected to a corresponding available port of node 2. According to the above, the storage table has three weights corresponding to each of the available links. These weights may reflect a particular deterministic characteristic associated with the available links. An example of such a weighted feature is a distance value, for example, a mileage value as represented by the length of the available link that separates node 2 from its adjacent nodes. In this way, assuming node 2 separates from node 8 for 100 miles, then a distance value of 100 for the available link 2S is stored in the table of node 2. Similarly, in the node 2 table, distance values are also stored for the available links 4S1 and 4S2 which incidentally have the same value with respect to both available links connecting node 2 to node 4. For the mode of Figure 1, suppose that node 2 is separated from node 4 by 100 miles. According to the above, the table in node 2, for the modality of figure 1, has three values, each of 100, respectively, associated with the corresponding available links. The respective distances of the other links available for the modality of Figure 1 are shown in brackets in Figure 1. Figure 1 also shows an operational support system (OSS) 14 that connects and monitors the total operation of the various nodes For reasons of simplicity, only the nodes 8, 10 and 12 are shown by being connected to the OSS 14. For the present invention, note that the OSS 14 can provide the storage tables in each of the nodes with updated values, in the case that the interconnections change between the various nodes. Other functions of the OSS 14 and its interconnections with the various nodes of the network can be gathered from the co-pending requests referred to above. In each of the intelligent nodes of the embodiment of Figure 1, but shown only specifically in the node 10, there also resides a synchronizer T. This synchronized provides a predetermined restoration time period during which a selector node may receive different overflow identifications, or restoration messages, from a sending node. At the end of the predetermined time period, there is a timeout to prevent the selector node from receiving additional restore messages. A more detailed discussion of the synchronizer is provided in the above-referenced application RIC-95-005. When there is a fault in a link in operation connecting two adjacent nodes, for example a malfunction or a cut of the 8W fiber optic link shown in Figure 3A, according to the SHR DRA approach, one of the adjacent nodes which interpolate or frame the fault is designated a sending node while the other is designated a selector mode. An overflow identification or restoration message such as that shown in Figure 2A is constructed by the sending node and sent to its adjacent nodes. Each of these intermediate nodes, also known as tandem nodes, after the reception of the restoration message, will also send it if it determines that this is not the selector node to which the message was destined. Such retransmission of the restoration message may be referred to as propagation. Given the appropriate propagation and whenever there is no restoration wait time, the restore message will eventually reach the selector node. The specific construction of the restoration message, as shown in Figure 2A, comprises a number of fields. An identification type field 16 provides an identifier for the message, ie, this is a restore message. A field of I.D. of emitting node 18 identifies the sending node. A field of I.D. selector node 20 identifies the selector node to which the restore message is intended. An Index field 22 for the embodiment of the present invention is a unique integer that identifies the port and therefore the available link from which the sending node sends the restoration message. The index, together with the identifiers of the sending node and the selector node, provides an identification of the restoration message to the tandem nodes and to the selector node. Next, in the restoration message there is a hop count field 24 containing a value designating the number of nodes to which the downstream restore message can be sent. For example, a hop count 10 means that the restore message may be broadcasting to 10 downstream nodes, decreasing the hop count value of 10 each time it is received by a downstream node. The last important field for the restoration message of the present invention is a weighted identifier field, shown as if it were the distance field 26 in Figure 2A. This is where a deterministic weighted value is stored, such as, for example, a distance field value. When constructed by the sending node, if a distance field value is actually used as the weighted identifier, it is set to 0 by the sending node. Each of the fields of the restoration message of Figure 2A actually has a number of bits. For example, the identification type field 16 may have 4 bits, the emitter node identifier field and the selector node identifier field may each have 8 bits, and the index and hop count field may have each one 15 bits. As far as the distance field 26 is concerned, a sufficiently large number of bits, for example of 15, is provided for the same in the restoration message so that the value of the longest possible alternate route in the network could be stored in it. With reference to Figure 3A, it can be seen that when a failure is detected, for example in the link in operation 8, the adjacent nodes 8 and 10 will determine from each other who the sending node will be and who is about to become the selector node. By conventional SHN practice, the lower number node is designated the emitter while the higher number node is designated the selector. For the embodiment of Figure 3A, the emitter is therefore the node 8 while the selector is the node 10. As shown, a restoration message such as that shown in Figure 2A is sent from the emitter 8 to its adjacent node 2 through the available link 2S. In addition, since the node 8 is also connected to the node 4 via an available express link 8S, a duplicate restore message likewise overflows to the node 4 from node 8. The restoration messages from the sender 8 are propagated through the various nodes of the network until they reach the selector node 10. In fact, as shown in Figure 3A, there are four different alternate routes found by the restoration messages from the sending node 8 to the selector node 10. It is assumed that for the embodiment of Figure 3, the synchronizer T in the node 10 has been set for a predetermined period of time such that a number of restoration messages will be received by the selector node 10 before there is a time. Standby. Each of the restoration messages received in node 10 represents an alternate route. To determine which of these alternate routes received is to be designated as the optimal route to restore interrupted traffic on the link 8, the selector node 10 retrieves, from each of the received restoration messages, the values of its distance field. 26. As will be discussed below, the selector node 10 chooses the restoration message with the lower distance value since the alternate route traversed by that restoration message is the shortest. This establishes an alternate restoration route based on the data ported by the chosen restoration message, which represents the available links crossed by the restoration message. Figures 3B-3E each show an alternate path traversed by one of the restoration messages. As shown in Figure 3B, a restore message is sent by node 8 to node 2 through the available link 2S. Since node 2 has an available link that connects to node 4, recognizing that it is not the selector node, node 2 transmits the restoration message through the available link 4S1 to node 4. The restoration message is transmitted also by node 4 to node 10 through the available link 10S1. The selector node 10, which recognizes that the restoration message is intended for it, determines that a first alternate path has been found. The information related to the first alternate trajectory is carried by the restoration message. It is returned to node 2 for a further discussion of the present invention. After detection of the arrival of the restoration message by the detector in the available port 2SP1, the processor P in the node 2 retrieves the value stored in the distance field 26 of the restoration message. In addition, the processor P relates its storage table to the distance value associated with the available 2S link, which is connected to the available port 2SP1. Since the distance value stored in your table is 100 (for the available 2S link), the processor P adds that distance value to the existing value of the distance field 26, that is, 0. The distance field value now updated, that is, 100, is inserted into the distance field 26 and the restoration message is then directed from the available port 2SP1 to the 2SP2 and sent on its way to the available link 4S1. Similarly, when the restoration signal from node 2 arrives at node 4, specifically at the available port 4SP1 for example, it is detected by the detector in it and reported to processor P of node 4. The value of the field of distance 26 of the restoration message is retrieved again and summed with the distance value stored in the table of node 4 associated with the available link 4S1. The updated distance value 200 (100 + 100) is inserted into the distance field 26; and the updated restore message is then routed to the available port 4SP2 and transmitted over the available link 10S1 in order to go to node 10. In node 10, a distance value of 200 (for the available link 10S1) is retrieved from the storage table of node 10 and added to the existing value of distance field 26. According to the above, the alternate route represented by 8-2-4-10 has a distance value of 400. This value it can indicate, for example, that the first alternate route is 400 miles.

The second alternate route found is shown in Figure 3C. There, the restore message is sent by sender 8 over the available link 8S so that it is received by port 4SPS3 of node 4. After updating the distance value from 0 to 200 in node 4, the message of updated restoration is transmitted by node 4, through its available port 4SP4 over the available link 10S1 to the selector node 10. In node 10, recognizing that this is the selector node identified by the restoration message, the value of distance 200 associated with the available IOS link is added to the existing distance value. According to the above, the alternate route shown in Figure 3C, similar to the alternate route shown in Figure 3B, also has a distance value of 400. The alternate route of Figure 3C can be represented as 8-4-10 . In figure 3D a third alternate route received by the selector node 10 is shown to restore traffic interrupted by the failure in the link in operation 8. For this alternate route, the restoration message ran from node 8 to node 2 to node 4 to node 6 to node 12 and finally to node 10. According to the above, this alternate route can be represented as 8-2-4- 6-12-10. In terms of the distance value, by adding the distances separating the respective pairs from the adjacent nodes (or the respective links of the corresponding available links connecting the adjacent nodes), it is found that the alternate route of the 3D figure has a value distance of 600. Figure 3E shows the last alternate route found to restore traffic interrupted by the link failure in 8W operation. This last alternate route is represented by the restoration message that has to travel from node 8 to node 4 to node 6 to node 12 and node 10. The combined distance value of this route alternates 8-4-6-12-10 is 600. Of the four alternate paths found, as represented by the four restoration messages arriving at the selector node 10, obviously two would not be considered (8-2-4-6-12-10 of 3D and 8). -4-6-12-10 of Figure 3E) since each has a distance value of 600. Of the remaining two, that is, 8-2-4-10 of Figure 3D and 8-4-10 of Figure 3C, each of which has a distance value of 400, it is clear that each of these two alternate trajectories is acceptable. In the case that only one alternate path having the shortest distance is found, that path will be chosen, of course, by the selector node 10 to be the alternate route over which the traffic can be restored. However, when it is found that there is more than one alternate route that has the same best optimum identifier value or distance value, an additional step needs to be taken to determine which of these alternate routes is the optimum route. For the present invention, a different attribute of the restore message may be used. One such exemplary attribute of the restoration messages is the hop count, as indicated in field 24. For the alternate routes of FIGS. 3B and 3C it can be seen that the alternate route 8-2-4-10 has a use of hop count of 4 while alternate route 8-4-10 of figure 3 has a use of hop count of 3. According to the above, the optimal alternate route, provided that the value of the distance field is the same for the respective restoration messages could be determined by examining the number of hops used for each restoration message through its hop count field. Accordingly, for the embodiment shown in Figures 3A-3E, the optimum alternate route chosen by the selector node 10 is the alternate route 8-4-10. The optimal alternate route thus chosen not only has the lowest mileage, but also requires the least number of jumps between the nodes. To confirm that the alternative route chosen 8-4-10 is actually the optimal route, once the decision has been made, the selector node 10 constructs a reverse restoration message, or a reverse link identification, as shown in Figure 2B. The reverse restore message is similar to the restore message shown in Figure 2A except for one exception, i.e., the replacement of the distance field 26 with an inverse distance field 28. In contrast to the value placed by the sending node 8 in the distance field 26 of the restoration message of figure 2A, the transmitting node 10 inserts in the inverse distance field 28 of the reverse restoration message of figure 2B, the value of summed distances that had been previously calculated for the message of restoration of entrance. The reverse restore message is transmitted to the port 10SP1 from which it had previously received the restore message, and then transmits it over the available IOS link to the node 4. The node 4, after the detection of the reverse restoration message of input, which is coincidentally identified in the identification type field 16 as a reverse restore message, retrieves from its storage table the distance value associated with the available link 10S1. This associated available link value is decreased or subtracted from the value retrieved from the inverse distance field 28. The remaining inverse distance value, ie 200 (400-200) is inserted in the inverse distance field 28; and the updated reverse restore message is then transmitted through the available port 4SP3 over the available link 8S to the sending node 8. The sending node 8, after the detection of the incoming restoration message by the detector in the available port 8SP2 , retrieves the inverse distance value from the reverse restore message. The distance value associated with the available link 8S is then retrieved from its storage table and subtracted from the recovered inverse distance value. If a value of distance 0 results, the sending node 8 confirms that the alternate route 8-4-10 is in fact the optimal alternate route towards which interrupted traffic between node 8 and node 10 can be restored by the fault occurring in the link in operation 8. As noted previously, the number of restore messages received by the selector node may be limited by the predetermined restore time established by the synchronizer T according to the contention problems noted in the above-referenced RIC-95-005 application. The operation of the present invention is illustrated with reference to the flow chart incorporated in Figures 4A-4D.

As represented by block 30, each node of the network is first provided with a weight table, for example a distance table with indicators for the various available links connected to the node. Each node of the network is also provided with detectors in its ports in operation to detect any malfunction or failure that may occur in the links in operation connected to them. In other words, when there is a failure in a link in operation, the adjacent nodes to which the faulty link is connected detect each failure at their respective operating link ports. This is shown in decision block 32. Each of the nodes remains alert to the detection of any malfunction. If a malfunction is detected, by block 34, the adjacent nodes that enclose the fault determine among themselves what is to be the emitting node and which is the selector node. After such designation, the sending node constructs a restore message of Figure 2A by block 36. The value of the weighted identifier field or distance of the restoration message is then set to 0, or any value given in the block 38. After this, the sending node overflows the restore message to its adjacent nodes for propagation in block 40. After receipt of a restore message, each tandem node reads the distance field of the restore message by block 42. Based on the port from which the restore message is received, the tandem node searches for the distance value associated with the available input link from its storage table in block 44. Once the distance value is recovered from both the restore message and its storage table, the tandem node updates the value of the distance field with its table value of b Search, by block 46. In the next step 48, the newly updated distance value is inserted in the distance field of the restoration message. After this, the updated restore message is distributed in multiple to nodes downstream of that node in tandem, by block 50. The selector node, having detected a failure and having been designated as the selector node, waits for any restoration message from input through block 52. When a restore message is received, the determination is made whether synchronizer T is in standby in block 54. Otherwise, the selector node will wait for other restore messages through block 56. If the synchronizer is in standby, the selector node, by block 58, reads the respective distance fields of the restore messages. The read distance field value of the last received restore message is compared to the distance field values of all, if any, of the restore messages received by block 60. After this, the selector node selects the restoration message representative of the shortest alternate route, for example, based on the lowest value in this distance field, by block 62. If there is an alternate route valued further below, then the alternate route becomes the route optimal alternate for restoration. This is represented by decision block 64 and block 68. However, if there is more than one restore message having the lowest distance field value, at least one additional common parameter (or characteristic) of those restoration messages valued from the lowest distance field. This is represented in block 66. For the present embodiment, as stated above, one such additional parameter may be the jump count. The selector node then constructs a reverse restoration message with a reverse distance field value for the block 70. This reverse restoration message is sent together with the selected alternate route to the sending node. When a reverse restoration message reaches the sending node, the sending node will confirm that the alternate route selected by the selector is actually the optimal alternate route if the field value of the inverse distance is 0. This is represented by block 72. Although a preferred embodiment of the present invention is disclosed herein. The present invention, for purposes of explanation, numerous changes, modifications, variations, substitutions and equivalents, all or in parts, should now be apparent to those skilled in the art to which the invention pertains. In accordance with the foregoing, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims (29)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. 1. In a telecommunications network having a plurality of nodes interconnected by a plurality of links in operation and available links, a method for determining an optimal alternate route between adjacent first and second nodes, to restore interrupted traffic between them, comprising the steps of: (a) providing a table in each of the nodes of said network to store respective weights each corresponding to an available link connecting each of said nodes and another adjacent node; (b) sending restoration messages from said first node to said second node through various available links connecting the various nodes of said network to find alternate routes to restore traffic between said first and second nodes, including each restoration message a field for storing a weighted identifier representative of the various available links connecting the various nodes through which said restoration message traverses; (c) using the appropriate weight provided in the table in each of the various nodes through which each said restore message traverses to re-weight the identifier stored in said field of each said restoration message as each said restoration message passes from said first node to said second node through the various available links and the various nodes; and (d) choosing from the restoration messages received in said second node the restoration message with the best weighted identifier to establish said optimal alternate route in order to restore interrupted traffic between said first and second nodes. The method according to claim 1, characterized in that said step (a) further comprises the step of equalizing the weight of a corresponding available link with the distance separating each said node and the other adjacent node connected to each said node by said link available corresponding; and wherein the identifier stored in said field of each said restoration message is re-weighted by adding the distance separating each said node and said other adjacent node to any distance already stored in said field; said method further comprises the step of: transmitting each said restoration message with said recalled distance to the nodes downstream thereof to find alternate routes to said second node. 3. The method according to claim 1, characterized in that it further comprises the steps of: establishing a predetermined period of time during which the restoration messages from said first node are to be received by said second node; and proceeding with said step (d) at the end of said predetermined time period. The method according to claim 1, characterized in that it further comprises the step of: adding another field to each said restoration message to store a weighted attribute to be used by said second node to decide whether the alternate route traversed by each said restoration message it is the optimal alternate route if said second node receives more than one restoration message having the same best weighted identifier. The method according to claim 1, characterized in that it further comprises the step of: sending a reverse restoration message from said second node to said first node through said optimal alternate route, said reverse restoration message including another field that has a reverse identifier representative of the various links available connecting the various nodes of said first node to said second node to establish said optimal alternate route, said inverse identifier changing by an amount associated with each available link of said alternate optimal route said message The reverse restoration path traverses so that the successive amounts of said inverse identifier are changed in said other field as said reverse restoration message is directed through successive available links and nodes., respectively, of said second node to said first node. The method according to claim 5, characterized in that it further comprises the step of: confirming said optimal alternate route as the route to redirect interrupted traffic between said first and second nodes, when the inverse identifier of said reverse restoration message, then to reach said first node, be the same as the identifier of the restoration message, before being sent by said first node, chosen by said second node to establish said optimal alternate route. The method according to claim 2, characterized in that it further comprises the step of: setting the size of said field in order to have enough bits to store the identifier representative of the optimum alternate route distance. 8. In a telecommunications network having a plurality of nodes interconnected by a plurality of links in operation and available links, having occurred a failure between two adjacent nodes to interrupt the traffic traversing between them, a method to find an alternate route optimal for redirecting interrupted traffic between said adjacent nodes, comprising the steps of: (a) designating one of said adjacent nodes as an emitter and the other of said adjacent nodes a selector; (b) storing in a memory in each of the nodes of said network, the respective distances separating each said node from the other nodes connected thereto by corresponding available links; (c) sending restoration messages from said sender to said selector through various available links connecting various nodes of said network to find at least one alternate route to restore interrupted traffic between said sender and said selector, including each of said restore messages a distance field that has a given value in said emitter; (d) updating the value of the distance field for each said restoration message with the stored distance corresponding to the available link from which each said restoration message arrives in each of said crossed nodes as each said restoration message traverses from node to node through the various links available to said selector; and (e) choosing from among the restoration messages received in said selector, the restoration message with the lowest updated distance value in its distance field to establish said optimum alternate route between said emitter and said selector. The method according to claim 8, characterized in that it further comprises the steps of: establishing a predetermined period of time during which the restoration messages coming from said emitter are to be received by said selector; and proceeding with said step (e) at the end of said predetermined time period. The method according to claim 8, characterized in that it compares the step of: adding another field to each said restore message to store an attribute to be used by said selector to choose the restore message in order to establish said optimal alternate route if said selector receives more than one restore message that has the same lowest updated distance. The method according to claim 10, characterized in that said attribute is a hop count, said method further comprising the step of: choosing the restore message having the lowest hop count among the restore messages received by said selector to establish the optimal alternate route. The method according to claim 8, characterized in that it further comprises the step of: sending a reverse restoration message of said selector to said emitter through said optimal alternate route, said reverse restoration message including another field having a value of representative inverse distance of the combined distances of the various available links connecting the various nodes of said emitter to said selector to establish said optimum alternate route, said inverse distance value being subtracted in an amount corresponding to the distance of the available link of said alternate route optimal traversed by said reverse restore message as said reverse restore message traverses said optimal alternate path so that the successive available link distances are subtracted from said inverse distance value as said reverse restore message is directed to through links and nodes d successive isponibles, respectively, of said optimal alternate route. The method according to claim 12, characterized in that it further comprises the step of: confirming said optimal alternate route as the route to redirect interrupted traffic between said emitter and said selector if the inverse distance value of said reverse restoration message, when said reverse restoration message reaches said emitter, it is the same as the value given in the distance field of the restoration message, before it is sent by said emitter, chosen by said selector to establish said optimal alternate route. 14. A telecommunications network comprising: a plurality of nodes interconnected by a plurality of links in operation and links available; a table provided in each of the nodes of said network for storing respective weights each corresponding to an available link connecting each said node to another adjacent node; a first node provided for sending restoration messages to a second node through various available links connecting various nodes of said network in order to find alternate routes to restore the traffic flowing between said nodes, first and second, through a link in operation when a failure occurs in said link in operation, each restoration message including a field to store a weighted identifier representative of the various links available that connect the various nodes through which each restoration message passes through, providing the appropriate weight in the table in each of the various nodes through which each said restoration message is passing which is being used to re-weight said weighted identifier as said restoration message passes from said first node to said second node; and providing said second node to choose from among the restoration messages received therein, the restoration message with the best weighted identifier establishing an optimal alternate route to redirect interrupted traffic between said first and second nodes, due to said failure. The network according to claim 14, characterized in that the weight of a corresponding available link is equal to the distance separating each said node and the other adjacent node connected to each said node by said corresponding available link; wherein the identifier stored in said field of each said restoration message is re-weighted by adding the distance separating said said node and said other adjacent node to any distance already stored in said field of each said restoration message; and wherein each said restoration message with said distance added to the nodes is transmitted downstream to find alternate routes to said second node. The network according to claim 14, characterized in that it further comprises: synchronizing means for establishing a predetermined period of time during which the restoration messages from said first node are received by said second node, said second node proceeding with the selection of between the restoration messages received therein, the restoration message with the best weighted identifier establishing said optimal alternate route at the end of said predetermined time period. The network according to claim 14, characterized in that each said restoration message further comprises another field for storing a weighted attribute to be used by said second node in order to decide whether the alternating route traversed by each said restoration message is the alternate route. optimal if said second node receives more than one restoration message having the same best weighted identifier. The network according to claim 14, characterized in that said second node is provided for sending a reverse restoration message to said first node through said optimal alternate route, said reverse restoration message including another field having an inverse identifier representative of the various available links connecting the various nodes of said first node to said second node to establish said optimal alternate route, said inverse identifier changing in an amount associated with each available link of said optimal alternate route in order to change the successive amounts said inverse identifier in said other field as said reverse restoration message is directed through successive available links and nodes, respectively, of said second node to said first node, said optimal alternate route being confirmed as the route to redirect traffic interrupted between said nodes, first and second, if the inverse identifier of said reverse restoration message, when said reverse restoration message reaches said first node, is the same as the identifier of the restoration message, before it is sent by said first node, chosen by said second node to establish said optimal alternate route. The network according to claim 15, characterized in that the size of said field comprises enough bits to store the identifier representative of the optimal alternate path distance. The network according to claim 14, characterized in that said identifiers in said table of each of the nodes of the network are provided respectively with corresponding distances separating said node from all the adjacent nodes to which each said connection is connected. node through at least one or more available links. 21. In a telecommunications network having a plurality of nodes interconnected by a plurality of links in operation and available links, having occurred a failure between two adjacent nodes to interrupt the traffic that passes between them, a system to find an alternate route optimal for redirecting interrupted traffic between said adjacent nodes, comprising: processing means provided in each of said nodes of said network, one of said adjacent nodes being designated one emitter and the other of said adjacent nodes a selector; a memory provided in each of the nodes of said network for storing the respective distance values separating each said node and other nodes connected thereto by corresponding available links; and restoration messages that are sent from said sender to said selector through various available links connecting various nodes of said network to find at least one alternate route to restore the interrupted traffic between said emitter and said selector, including each of said restoration messages a distance field having a given value in said transmitter, the value of the distance field being updated for each said restoration message with the stored distance corresponding to the available link from which said restoration message arrives in each of said nodes traversed as each said restoration message traverses from node to node through the various links available; choosing said selector from among the restoration messages received therein, the restoration message with the lowest updated distance value in its distance field to establish said optimal alternate route between said emitter and said selector. The system according to claim 21, characterized in that it further comprises: synchronizing means for establishing a predetermined period of time during which the restoration messages coming from said emitter are received by said selector, said selector proceeding at the election, from among the restoration messages received therein, of the restore message with the lowest updated distance in its distance field at the end of said predetermined time period. The system according to claim 21, characterized in that each said restoration message further comprises another field for storing an attribute to be used by said sender to choose the restoration message in order to establish said optimal alternate route if said sender receives more than one restore message that has the same lowest updated distance value. The system according to claim 23, characterized in that said attribute is a hop count, and wherein said selector chooses the restore message having the lowest hop count among the messages having the same updated distance value plus low to establish the optimal alternate route. The system according to claim 21, characterized in that it further comprises: a reverse restoration message that is sent from said selector to said emitter through said optimal alternate route, said reverse restoration message including another field having a value representative inverse distance of the combined distances of the various available links connecting the various nodes of said transmitter to said selector to establish said optimal alternate route, said inverse distance value being subtracted in an amount corresponding to the distance of the available link of said route optimal alternate traversed by said reverse restore message as said reverse restoration traverses said optimal alternate path so that the successive available link distance amounts are subtracted from said inverse distance value as said reverse restoration message is directed through links and successive available nodes, respectively, of said optimal alternate route, said optimum alternate route being confirmed as the route for redirecting interrupted traffic between said emitter and said selector if the inverse distance value of said reverse restore message, when said reverse restore message reaches said emitter, is the same as the given distance of the restoration message, before being sent by said emitter, chosen by said selector to establish said optimal alternate route. 26. In a telecommunications network having a plurality of nodes interconnected by a plurality of links in operation and links available, having occurred a fault in the link in operation connecting two adjacent nodes in order to interrupt the traffic passing between them, one of said adjacent nodes being designated one emitter and the other of said adjacent nodes a selector, a memory provided in each of the nodes of said network to store respective distance values separating each said node and the other nodes connected to it by means of available links, a restoration message sent by said emitter to its adjacent nodes and then, if necessary , propagated by said adjacent nodes to various nodes of said network for the subsequent propagation until it reaches said selector to find an optimal alternate route in order to redirect the interrupted traffic between said emitter and said selector, said restoration message comprising: an identifier of issuer to identify said issuer; a selector identifier to identify said selector; an index to identify the link in defective operation; and a restoration message distance value preset to a given value in said emitter, said distance value being updated as said restoration message traverses from node to node through the various links available as each of the nodes , after receipt of said restoration message, retrieve from its memory the stored distance value corresponding to the available link from which the restoration message arrives and add said recovered stored distance value to the distance value of the existing restoration message , said distance value of the restoration message continues to be updated until said restoration message reaches said selector. The restoration message according to claim 26, characterized in that the nodes of said network, which are neither sender nor selector, are designated tandem nodes, said restoring message further comprising: a hop count whose value is decreased by one each time said restoration message traverses towards a tandem node as it traverses said selector. The restoration message according to claim 27, characterized in that each of said emitter identifier, selector identifier, index, distance value of the restoration message and hop count, reside in a corresponding field each comprising a plurality of bits, the respective sizes of each corresponding field being different, the field containing said restoration message distance value being large enough to accommodate the maximum distance value of any alternate route. 29. In a telecommunications network having a plurality of nodes interconnected by a plurality of links in operation and available links, having occurred a failure in the link in operation connecting two adjacent nodes in order to interrupt the traffic passing between the same, a memory provided in each of the nodes of said network to store respective distance values separating each said node and the other nodes connected thereto through corresponding available links, one of said adjacent nodes being designated one emitter and the other of said adjacent nodes a selector, a reverse restoration message sent by said selector to its adjacent nodes and then, if necessary, propagated by said adjacent nodes to various nodes of said network for further propagation until it reaches said emitter to confirm a alternate route found by a restoration message from said issuer in order to redirecting interrupted traffic between said sender and said selector which is the optimal alternate route, said reverse restoration message comprising: an emitter identifier to identify said sender; a selector identifier to identify said selector; an index to identify the link in defective operation; and an inverse distance value having the combined distance values of all the available links connecting the nodes along said alternating route traversed by said restoration message of said emitter to said selector, said inverse distance value being reduced as that said reverse restoration message traverses from node to node through the various links available from said alternate route, as each of the nodes, after receiving said reverse restoration message, retrieves from its memory the value of stored distance, corresponding to the available link from which the reverse restoration message arrives and decreases said stored distance value, recovered, from the existing inverse distance value, said inverse distance value continues to decrease until said restoration message reaches said distance. transmitter; said reverse restoration message confirming the alternate route that it traverses to be said optimal alternate route if its inverse distance value is 0 when it reaches said emitter.