MXPA98000754A - Search for route in communication networks - Google Patents

Abstract

The present invention relates to a method for determining a recovery path (or an additional path) in a complete or partially polygonal communications network of nodes, comprising fixing, in a node that initially determines to be a slave end node for an existing route , a waiting time to receive a number of identifications from the advance route buscador from which it will select the identification that represents the potential recovery route that has the shortest length and returns an identification of the route confirmation, commute, the have not been received route finder identifications at the end of the waiting time, to act as a master end node for the existing route and send inverse route finder identifications to their nearby nodes, switching, upon receipt of a route finder identification inverse in a node that is initially determined to be the master end node for an ex route isnt, to act as a slave end node and to send a corresponding return identification. When a slave end node receives the return identification indicating that the potential recovery path no longer has sufficient capacity, the node will switch to act as a master end node. When an advance route finder identification is received after a node has sent a reverse route finder identification, a priority route confirmation identification is issued. the route finder identifications have a count field to indicate the direction of travel and the number of times the sending node has changed to act as a master end node, the forward identifications have counts 1.3, etc. and the reverse identifications have counts 2.4, etc. When a node has sent an identification of the forward route finder, it received an identification of the reverse route finder, sends a confirmation identification and subsequently receives a priority confirmation identification, unless a return identification is received two recovery routes will be established and the nodes will select the best

Description

SEARCH FOR ROUTE IN COMMUNICATIONS NETWORKS DESCRIPTION OF THE INVENTION 1. Field of the Invention This invention relates to a method of searching, or determining, a route in a communication network; to a node placed to execute the method; and to a network comprising such nodes. A route may be necessary to replace an existing route that has failed and the route is referred to as a recovery route, or a route may be required to complement an existing route that is being congested. As used herein, the term "additional route" encompasses both recovery routes and complementary routes. 2. Description of the Related Art It is known, for example, from the article "The Self-Healing Network: a Fast Distributed Restoration Technique for Networks Using Digital Cross -Connect Machines", .D. Grover, IEEE Globecom 87, and from the North American patent 4,956,835 (Wayne D. Grover) that respond to two nodes (known as fault nodes) connected to a direct double link with failure for the reception of a direct double-link fault alarm to start a real time recovery process. Fault nodes determine on the basis of their unique network identities (IDs) whose node acts as Emitter and whose node acts as Selector (also known as Master and Slave respectively). For each one of the links of the direct double link with the Emitter failure, it repeatedly transmits (floods) the respective route search symbols to the nearby nodes (known as tandem nodes) which emit the flooding of the identifications of their nearby nodes. . In one embodiment of the aforementioned North American patent, a node only knows its identification (ID) and teaches the ID of the node to which the connectivity has been lost by reading the last valid contents of a reception identification record on the ports affected that correspond to the link or links with failure and in an alternative modality a node stores and maintains a table near node ID. The node that decides to act as Selector now enters a waiting state and remains there until it receives an identification from the route finder. It then responds by transmitting a respective complementary reverse link identification (also known as confirmation or return identification) to the Tamden node from which the route finder identification was received. The confirmation identification moves backward through the tandem nodes establishing the required switch connections between the node's input and output ports, and eventually arrives at the transmitter node, which then stops transmitting the route finder identifications. respective and proceeds to transmit on that recently established recovery route the traffic that would have been transmitted on the corresponding link of the direct free link with failure. The aforementioned North American patent also discloses that the recovery mechanism can be used for the automatic provisioning of new circuit routes in a network by placing two nodes, between which it is desired to provide additional (ie complementary) circuit routes, directly within the networks. Emitter and Selector states with respect to an artificial fault between the selected nodes. The nodes would be complemented with an artificial fault information that includes the number of circuit routes that are being searched. Also, U.S. Patent No. 5,065,399 (Hasegawa et al.) Discloses a recovery technique, in response to a failure of a link between two nodes, the emitting failure node transmits a help message (equivalent to the identification of the Grover route finder) to its nearby nodes by requesting the use of an uncommitted bandwidth of the respective links to those nodes (or the use of both unencumbered bandwidth as necessary for the recovery of the fault path between nodes with failure) and start the waiting time. Upon receipt of a request, each node records in a table the reflections, the identity of the transmitter of the message and the «bandwidth required, providing provided that such bandwidth is not smaller, nor the greater reflex count for the same bandwidth than any previously requested. Each node container constructs its own request message in which it is identified as the transmitter, requests the maximum bandwidth necessary or available, or increments the mirror count by one. These messages are then transmitted to all nearby nodes. The failed node Selector records all received messages within a waiting time, selects the best recovery route and returns to its nearby transmitter an acknowledgment message ifying the bandwidth available in that restoration path. If the indicated bandwidth remains available, that nearby node confirms the acknowledgment message and transmits its own acknowledgment message to its nearby node requesting the highest bandwidth. However, if the indicated bandwidth is not available, the node does not take any action and eventually the node with the sending failure will enter the timeout and send another batch of help messages.

If the full bandwidth of the fault link is not recovered in an individual wave of help messages (request), the emitting fault node simply initiates a second wave requesting the balance of the bandwidth loss on the available links. The prior art methods for determining an additional route require that a sending node triggers a timeout when it floods the route finder identifications to its nearby nodes, and sends a repeated flood of route finder identifications in the event that there is no confirmation identification that has been received from the node closest to the termination of that waiting time. The waiting time value of the sending node is determined by the expected transit times of the route finder identifications through the network, which themselves determine the time operated in the Selector node so that an optimal route is selected. from various identifications of the route finder received, and the maximum possible transit time of the conformation identification through the network through the selected optimal route.

BRIEF DESCRIPTION OF THE INVENTION According to a first aspect of the invention, there is provided a method for determining an additional path in a total or partially polygonal communication network of nodes, the method comprising the steps of: determining according to a respective predetermined master / slave relationship , in each of the pairs of nodes, between whose pair there exists an existing route, the node of the pair that is to act as a master end node with respect to the existing route and the other node that is to act as a master end node with with respect to the existing route and the other node that is to act as a slave end node, the determination stage starting in response to the reception, in each of the pairs of nodes, of a signal indicating an additional route that is required with respect to the existing route; send from a node to its nearby nodes an identifier of the forward route finder for the existing route; receive in a node an identification of the forward route finder, determining if the receiving node is the slave end node for the route exists and in the case that it is not, emit the identification of the received forward route finder towards its nodes close; determine on the other node at the end of a predetermined waiting time triggered * by receiving said signal, a potential additional route and send, 'from the other node on the potential additional route a route confirmation identification identifying the route additional potential; and storing the details of the potential recovery path in a node to the receipt therein of the route confirmation identification; and the method that is characterized by the steps of: responding on the other node, in the case that the waiting time of a potential additional route has not been determined, and in the case that the other node has sent an identification route confirmation even if it has received a return identification indicative of the insufficient capacity for the potential additional route in an intermediate node on the potential additional route, switching to act as a master end node with respect to the existing route; send an identification of the reverse route finder for the existing route from the other node to its nearby nodes; and responding to the node upon receipt therein of the reverse route finder identification to switch to act as a slave end node with respect to the existing route, to determine a respective potential additional route and to send a corresponding route confirmation identification . The present invention allows faster recovery since the Selector node transmits the identifiers of the route finder before the sending node can know that retransmission is required.

Preferably, a node determines the respective potential additional path to the reception of the reverse route finder identification. Alternatively, the other node determines the respective potential additional path at the termination of a predetermined wait time triggered by receipt of the reverse route finder identification. Preferably, the signal indicating that an additional route is required with respect to the existing route is received from an intermediate node of the existing route. Preferably, the step of responding to the node is included, when acting as a slave end node and has sent the corresponding route confirmation identification, upon receipt of a corresponding return identification indicative of the insufficient capacity for the respective potential additional route in a node intermediate thereof, to switch to act as a master end node for the existing route and to send an identification of the respective forward route finder.

Preferably, the identifiers of the route finder comprise a count field and the step of sending an advance route finder identification from the node comprises a sub-step of setting the respective count field to a first predetermined number of a parity on the first occasion that the node sends an "identification of the forward path finder and set the respective count field for the respective next successive number of the parity on each successive occasion that the node switches to act as the master end node and the step of sending the identification of the reverse route finder from the other node comprises a sub-step of setting the respective count field to a first predetermined number of opposite parity on the first occasion that the other node sends an identification of the reverse route finder and fix the count field respective for the next successive number of the other parity on each or successive casión that the other node commutes to act as master end node. According to a second aspect of the present invention, a node is provided for use in a complete or partially polygonal communications network of nodes, the node being positioned: to respond, in use upon receipt of a signal indicative of a requirement for an additional route with respect to an existing route for which there is an extreme route to determine whether it will act as a master end node or slave end node choritus; to send, in use, to its nearby nodes, in response to a determination that the master route node will act as an advance route finder identification for the existing route; to receive, in use, a route finder identification and to determine whether or not it is an end node for an existing route identified by the route finder identification and, in response to a determination that it is not an end node, issue the identification of the received route finder to its nearby nodes and, in response to the determination that it is an end node and subsequent to a preceding determination that the node is the slave end node for the existing route identified by the identification of the search engine of route, determine, at the end of a predetermined waiting time triggered by the reception of the signal, a potential additional route for the existing route identified by the identification of the route finder, and to send on the potential additional route an identification of Route confirmation for the route exists identified by the identification of the route finder; and to store, in use, the details of a potential additional route upon receipt thereof of a route confirmation identification for an existing route for which it is acting as a master end node; and characterized because it is placed: to respond, when acting as slave end node, at the end of the predetermined waiting time in the absence of a determination of a potential additional route, and the reception of a weight signal indicative of insufficient capacity for the potential additional route at an intermediate node on the potential additional route, to switch to act as a master end node with respect to the route. existing identified by the identification of the route finder and to send an identification of the reverse route finder for the existing route to its nearby nodes; and to respond, when acting as a master end node with respect to the existing route, to the reception therein of an identification of the reverse route finder for that existing route to switch to act as a slave end node with respect to the existing route , to determine a potential additional route and to send a corresponding route confirmation identification on the additional potential route. Preferably, the node is placed e-to determine the respective potential additional path to the reception of the reverse route finder identification. Alternatively, the node is positioned to determine the respective potential additional route at the termination of a predetermined wait time triggered by the receipt of the reverse route finder identification. Preferably, the node is positioned to incorporate, in use, a count field in the route finder identifications, and placed (a) to set, when initially acting as the master end node, (i) the count field of a identification of the forward route finder for a first predetermined number of a parity on the first occasion that the node sends an identification of the forward route finder for the existing route and (ii) the respective contour field for the successive number of an parity on each subsequent successive occasion that the node switches to act as the master end node for the existing route and also (b) to set, when initially acting as a slave end node, (i) the count field of an identification of the route finder Inverse for a first predetermined number of opposite parity on the first occasion that the node sends a reverse route finder identification for the existing route , and (ii) the respective count field for the next successive number of the other parity on each subsequent successive occasion that the node switches to act as the master end node for the existing route. According to a third aspect of the present invention, a complete or partially polygonal communication network of nodes is provided, wherein the nodes are identical and in accordance with the second aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS A specific embodiment of the present invention will now be described by way of example with reference to the drawing in which: Figure 1 is a diagram of a network of interconnected nodes.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE MODALITIES The specific modality of this "invention refers to a process of recovery in real time to establish a recovery route in a network of comunicacion.es and the following description will be limited to this although it can be seen that such process does not need to be the only process of restoration in a network although it can be combined with a previously planned recovery process Consider a route through the network 10 between the end nodes A and E passing through the intermediate nodes B, C and D and comprising a sequence of bidirectional links within double direct links AB, BC, CD and DE, and allows this route to have the unique route ID "X." The direct double links between the nodes include working links and free links, and each work link is part of a route only one, consider also that in an excavator the direct double CD link has been separated and that the nodes C and D, the nodes with failure to detect the CD double direct link failure, have decided to look for a recovery path between nodes A and E. This decision may be based on one or more criteria, for example the use of a potential link recovery solution (deviation) between nodes with failure would result in length full path (total number of direct double links), which exceeds a predetermined limit. Such criteria are not part of the present invention and will not be described further. The failing nodes will act, correspondingly, to find a respective recovery path for each of the other routes that use CD double direct link. The order in which the recovery paths are established can be determined by classifying the routes in order of priority, although such classification is not part of the present invention and will not be described. Failed nodes as a result of the aforementioned decision will generate a respective help identification (referred to herein as a help message) for an X route and for any other route affected by the DC direct link failure, and send those help messages to the respective extreme nodes of the route. In variants, if more than one route is affected, a single help message is used containing the IDs of all affected routes. Each of the different identifications used in the recovery process have a header and an end, the header that includes a four-bit identification type field. The different types, as will be described in more detail below, are normal route finders (also known as forward route finder), reverse route finder (also known as back route finder), route finder, alarm, help, return, returns (also known as confirmation) and priority return. The information section of an identification comprises a four-bit flood count field, an accumulated route length field of * eight bits *, a four-bit reflection count field1, uxt '.-- field of count of Four-bit route ID, one or more sixteen-bit route ID fields and a corresponding number of eight-bit circuit number fields. As the help messages pass through their respective intermediate nodes, they separate the connections in the route with corresponding failure. Each node will issue a help message received over the link corresponding to the route ID contained in the help message.

Therefore, node C, which has determined that it is experiencing a failure of route X, sends a help message from node D, since it knows that the direct double bond CB contains the output link for route X, and in a similar manner, the node D sends a help message to the node E. These help messages contain in the respective route ID fields the unique ID of the fault route and any other route having a circuit in the double direct link with CD failure. Each node knows its own network ID and contains a box that stores the route IDs for which an end node is, and the network IDs of the other end nodes. When node B receives the help message, it checks its stored table to find if it is an end node for the identified route and where, as in this case, it is not an end node, it will transmit the help message on the outbound link associated with that route (a direct double-link link BA) and separates the connection from that route by removing the route and the link data from its connection box. When node A receives the help message, it determines that it is an end node 'for route X and will proceed to determine if it is a higher classification route or a lower classification in relation to the stored ID of the other end node (E) for that route, based on the network IDs (ordinal numbers) of the nodes. If the latter will act as a master node (also known as a sending node, and if the latter will act as a slave node (also known as a selector node) and in this example node A has a higher ranking network ID that the node E and therefore the reception of the help message, will establish a recovery route for the X route, and assumes the role of master.In a similar way, when the node E receives the respective help message, it will determine that it is an end node for the X route and will proceed to determine if it is a higher classification or a lower classification in relation to the stored ID of the other end node (A) for that route In this example, the node E has an ID of classification network lower than node A and therefore upon receipt of the help message, to establish a recovery route for route X, will assume the role of slave.

The node A now transmits for the route with failure X a pathway detector that floods through the network. The identification contains the ID of route X, the capacity required for the route and has its flood count field set to one. As the determination floods through the network, the advance or delay nodes increase the reflex count field and update the cumulative path length field by the length of the direct double link over which the identification was received. In the variants, this last field is updated by the length of the direct double link on which the identification is being issued. The delay nodes advance identification over only those direct double links that can provide the required capacity (that is, they have a sufficient number of free circuits), although they do not mark that capacity as reserved. They also check the reflex count of a received signal and do not take action if the count is greater than a predetermined maximum. This sets a limit to the geographical extent of flooding. In the variants, the additional flood control or alternatively comprises the verification of a time of the origin field in the identification and does not take action if the identification is older than a predetermined limit, or it verifies the cumulative route length field and does not Take action if the accumulated route length is greater than a predetermined limit or any combination of those control mechanisms. The master node A, when it has transmitted the identification of the route finder, will enter an inactive state to wait for the receipt of a signal of a return identification. At the termination of node E, which is to act as a slave for the route with failure X, it initiates (triggers) a waiting time to wait for the receipt of the corresponding route finder identifications containing the same route ID as in the help message. Each of such identifications received within the waiting period is stored. In the waiting time of the slave node E, it selects from all the identifiers of the route finder for the route with failure X, the optimal recovery route, for example the one with the lowest jump count or the lowest route length, and sends a return signal of return (also referred to as a route confirmation identification) back through the node from which the route finder identification was received. This return identification is identical to the identification of the route finder except for the content of the identification type field that is loaded to identify the identification as a return identification that moves to the master node A, although in the variants the node E further eliminates any route ID and the associated required capacity other than that for route X. As the return identification passes through the nodes of the selected recovery path, each of those nodes verifies that the requested capacity is still available, to the connection between the corresponding switch ports, creates an eight-bit node ID field and writes its ID within this field so that the master node field A can know all the nodes of the route.

The reception of the return identification, the master node A knows that the recovery path now exists, as identified by the intermediate node IDs or identification delay and now sends a route marker identification to the node E, by means of the recovery route, to inform the intermediate nodes of the recovery route and then proceed with the transmission of traffic. When the invention is used to find a complementary route, the route plotter identifier can be sent to the existing route. This use of a route tracer identification is known in the art and does not form part of the present invention. Can beTHE. although a delay node has sufficient capacity and was able to issue the route finder identification, that capacity has been taken by the establishment of another recovery route before the receipt of the corresponding return identification. In this case the delay node sends to the slave node E a return identification which separates any connections already made at the intermediate nodes on that route and indicates to the slave node E that the selected recovery route is no longer available. Upon reception of such return identification, the slave node E changes to act as a master node for that route, generates an identification of the route finder with its flood count field set to two and sends it to its nearby nodes. This identification is also referred to as an identification of the reverse route finder. It will be appreciated that identifications with odd flood counts can be identified as successive attempts made by the original master to find a recovery path and that identifications with even flood counts can be correspondingly identified as successive attempts made by the original Slave. The first reception on the master node A of a reverse route finder identification for route X causes node A to change from acting as a master node to act as a slave node for that route. The node A, now acting as a slave node, responds by immedia issuing a return identification on the link on which the identification of the reverse route finder was received. This identification has the appropriate code for a return identification in its identification type field and also has its flood count field set to two. In the variants, node A, when acting as a slave, initiates a waiting time in response to receiving an identification of the reverse route finder, stores all identifications of the reverse route finder received within the waiting period and selects the optimal recovery path at the end of the waiting period. The slave node E is set to switch to act as a master node if no identifications of the route finder have been received at the end of the wait time. If a route finder identification is subsequently received after node E has switched to act as a master, node E will still act as a slave for that route finder identification and send a priority return signal that has a count. of one flood. As this identification moves back along the corresponding recovery path, it is recognized by the intermediate nodes as it requires priority handling and is placed in front of any established queue with minimal delay and it is likely that such return identification Priority will reach the identification of the reverse route finder. In this case the master node A will respond normally, although it will know by means of the identification type that the node E has changed its roles from slave to master and has sent an identification of the reverse route finder to its nearby nodes. The node A will therefore wait to receive the identifications of the reverse route finder, although these are redundant and can be ignored. The node E, which acts as a master and has sent the identifiers of the reverse route finder and possibly also acts as a slave and has sent a priority return identification, will now be in a wait state. If there is insufficient capacity on the recovery path for the priority return identification so that the entire distance is moved to the end node A, a return message will be sent from the appropriate blocking node and received at the node E (which acts now as a master, will be ignored since the node E has already sent the reverse route identifications and the node E will continue to wait for a reverse return identification from the other end node A. In the case where a return identification of priority does not reach the reverse route finder identifications, node A will act as a slave node at the first reception of a reverse route finder identification of flood count two, returning an inverse return identification (also of flood count two) and then subsectorly receives the priority return identification and simultaneously acts as a master node for this identification. If the reverse return identification does not go through and the return message is returned to node A, then no further action is necessary since an established recovery path is in existence. If, on the other hand, the reverse return identification is received in the slave node E (which acts as a master node) then the corresponding recovery path is therefore established. Subsequently, both extreme nodes A and E -will notice, by means of additional messages that identify the nodes of the routes that there are two recovery paths and one of the end nodes A and E (the original master node A, say) will decide that route will separate and which will take the appropriate action. If the master node A does not receive the waiting time a return identification or an identification of the reverse route finder, it will send another identification of the forward route finder, this time with the flood count field increased by two. Similarly, the slave node E, if it does not receive within a respective timeout from switching to act as a master a return signal or an identification of the forward route finder, will send another identification of the reverse route finder with its flood count field increased by two. This process can be terminated for a predetermined time in which it is considered unlikely that a recovery or additional route can be found. The above-described method of searching a recovery path in a network can be used to find a complementary route by sending instructions from a network control center to two end nodes of a congested route so that they treat the congested route as a fault and initiate the method of the invention for finding an additional route (also known as an alternative route) between the two end nodes.

Claims (11)

1. A method for determining an additional path in a complete or partially polygonal network of communications of nodes, the method comprises the steps of: determining according to a respective predetermined master / exclave relationship, in each pair of nodes, between which pair there is a existing route, a node of the pair that acts as a master end node with respect to the existing route and the other node that acts as a slave end node, the determination step starting in response to 1-a? eception, - »in each pair of nodes, of a signal indicating that an additional route is required with respect to the existing route; send an identification of the forward route finder for the existing route from a node to its nearby nodes; receive in a node an identification of the forward route finder, determining if the receiving node is the slave end node for the existing route and, in the case that it is not, issuing the identification of the received forward route finder to its nearby nodes; determine on the other node, at the end of a predefined waiting time triggered for signal reception, a potential additional route and send from the other node on the potential additional route a route confirmation identification identifying the additional route potential; and storing the details of the potential restoration path in the node to the receipt therein of the route confirmation identification; and the method being characterized by the steps of: responding on the other node, in the event that the waiting time of a potential additional route has not been determined, and in the event that the other node has sent a confirmation identification of route even though it has received a return identification indicative of the insufficient capacity for the potential additional route in an intermediate node on the potential additional route, switching to act as a master end node with respect to the existing route; send an identification of the reverse route finder for the existing route from the other node to its nearby nodes; and responding to the node upon receipt therein of the reverse route finder identification to switch to act as a slave end node with respect to the existing route, to determine a respective potential additional route and to send a corresponding route confirmation identification .

2. A method of claim 1, wherein a node determines the respective potential additional path upon receipt of the inverse route finder identification.

3. A method of claim 1, wherein a node determines the respective potential additional path at the termination of a predetermined wait time triggered by the receipt of the reverse route finder identification.

4. A method as claimed in any of claims 1 to 3, wherein the signal indicating that an additional route with respect to the existing route is required is received from an intermediate node of the existing route.

5. A method as claimed in any one of claims 1 to 4, which includes the step of responding to the node, when acting as a slave end node and has sent the corresponding route confirmation identification, upon receipt of a corresponding indicative return identification of insufficient capacity for the respective potential additional route in an intermediate node thereof, to switch to act as a master end node for the existing route and to send an identification of the respective route finder.

6. A method as claimed in any one of claims 1 to 5, wherein the identifiers of the route finder comprise a count field and, wherein the step of sending an advance route finder identification from a node comprises a sub-step. setting the respective count field to a first predetermined number of a parity on the first occasion that a node sends an identification of the forward route finder and setting the respective count field for the respective next successive number of the parity on each successive occasion that the other node switches to act as master end node, and the step of sending the reverse route finder identification from the other node comprises a sub-step of setting the respective count field for a predetermined number of opposite parity on the first occasion that the other node sends a reverse route identification and fix the respective count field for the respective next successive number of the other parity on each successive occasion that the other node switches to act as the master end node.

7. A node for use in a complete or partially polygonal communications network of nodes, the node that is placed: to respond, in use, to the reception of a signal indicative of a requirement for an additional route with respect to an existing route for which is an extreme route to determine if it will act as a master end node or as a slave end node; to send, in use, to its nearby nodes, in response to a determination that it will act as a master end node, an identification of the forward route finder for an existing route; receive, in use, an identification of the route finder and to determine whether or not it is an end node for an existing route identified by the route finder identification and, in response to a determination that it is not such an extreme node, to emit the identification of the received route finder to its nearby nodes, and, in response to a determination that it is such an extreme node and subsequent to a preceding determination that the node is the slave end node for the existing route identified by the identification of the search engine of route, determine, at the end of a predetermined waiting time triggered by the signal, an additional potential route for the existing route identified by the identification of the route finder, and to send on the potential additional route a confirmation identification of route for the existing route identified by the identification of the route finder; and to store, in use, the details of the potential additional route upon receipt thereof of a route confirmation identification for an existing route for which it is acting as a master end node; and characterized in that it is positioned: to respond, when acting as a slave end node, to the termination of a predetermined waiting time in the absence of a determination of a potential additional route, and for the reception of a return identification indicative of insufficient capacity for the potential additional route in an intermediate node on the potential additional route, to switch to act as a master end node with respect to the existing route identified by the route finder identification and to send a reverse route finder identification for that route existing towards its nearby nodes; and to respond, when acting as a master end node with respect to the existing route, to receive in it the identification of the reverse route finder for that existing route to switch to act as a slave end node with respect to the existing route, to determine a respective potential additional route, and to send a corresponding route confirmation identification on the respective potential additional route.

8. A node of claim 7, and positioned to determine the respective potential additional path to the reception of the inverse route finder identification.

9. A node of claim 7, and positioned to determine the respective potential additional path to the termination of a predetermined wait time triggered by the receipt of the inverse route finder identification.

10. A node as claimed in any of claims 7 to 9, positioned to incorporate, in use, a count field in the route finder identifications, and placed (a) to set, when initially acting as a node master end, (i) the count field of a - identification of the forward route finder for a first predetermined number of a parity on the first occasion that the node sends an identification of the forward route finder for the existing route and (ii) the respective control field for the next number successive parity on each subsequent successive occasion that the, node switches to act as a master end node for that existing route and also (b) to set, when initially acting as a slave end node, (i) the count field of an inverse route finder identification for a first predetermined number of opposite parity on the first occasion that the node sends a reverse route finder identification. for the existing route, and (ii) a respective count field for the next successive number of the other parity on each subsequent successive occasion that the node switches to act as a master end node for that existing route.

11. A complete or partially polygonal communications network of nodes, wherein the nodes are identical and as claimed in any of claims 7 to 10. SUMMARY OF THE INVENTION A method for determining a recovery path (or an additional route) in a complete or partially polygonal network of communications of nodes, comprises setting, in a node that initially determines to be a slave end node for an existing route, a waiting time for receive a number of identifications from the forward route finder from which it will select the identification representing the potential recovery route having the shortest length and return a route confirmation identification; switch, if no identifications of the route finder have been received at the end of the waiting time, to act as a master end node for the existing route and send inverse route finder identifications to their nearby nodes; switching, upon receipt of a reverse route finder identification in a node that is initially determined to be the master end node for an existing route, to act as a slave end node and to send a corresponding return identification. When a slave end node receives the return identification indicating that the potential recovery path no longer has sufficient capacity, the node will switch to act as a master end node. When an identification of the forward route finder is received after a node has sent an identifier of the reverse route finder, a priority route confirmation identification is issued. The route finder identifications have a count field to indicate the direction of travel and the number of times the sending node has switched to act as the master end node, the forward identifications have counts 1.3, etc ..., and the reverse identifications have counts 2.4, etc .... When a node has sent an identification of the forward route finder, it received a reverse route finder identification, sends a confirmation identification and subsequently receives a confirmation identification Priority, unless a return identification is received, two recovery paths will be established and the nodes will select the best one.