MXPA97006489A - Location of route in communication networks - Google Patents

Abstract

The present invention relates to a method for determining a restoration path (or an additional route) in a network of communications nodes arranged completely or partially in mesh, in which the step of sending a route locator signal from a node a neighboring node on a plurality of spare links from an interval to the neighbor node comprises the preceding sub-steps of: determining whether the node has a determination network node identity higher or lower in rank than that of the neighboring node; if it is in the highest range determination, send the route locator signal over the spare link corresponding to the lowest rank determination of the node ports associated with the interval, or if it is in the lowest range determination, send the route locator signal over the spare link corresponding to the highest range determination of the node ports associated with the interval. A contention protocol handles any contention that occurs because the two nodes connected to one interval make the interim assignment for one or more links simultaneously to different restoration paths in the contention protocol, the highest rank determination of the two nodes on which your interim allocation will be confirmed, and the lowest rank determination of the nodes knows that you must send an upward search signal for storage capacity that is not available

Description

LOCATION OF ROUTE IN COMMUNICATIONS NETWORKS BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to a method for finding, or determining, a route in a communications network; to a node arranged to carry out 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 designated as a restoration route, or a route may be required to complement an existing route that is being congested. As used herein, the term "additional route" includes both restoration routes and supplementary routes. 2. DESCRIPTION OF THE RELATED TECHNIQUE It is known, for example from the article "The Self-Healing Network: A Fast Distributed Restoration Technique for Networks Using Digital Cross-Connect Machines, "WD Grover, IEEE Globecom 87, and of United States Patent 4,956,835 (Wayne, D. Grover) to answer on two nodes (known as nodes of failure) connected to a faulty interval upon receipt of an interval failure alarm to initiate a real-time restoration process.The failure nodes are determined based on their unique network identities (IDs) whose node acts as a Issuer and whose node acts as a Selector (also known as Principal and Subordinate, respectively) For each of the links in the faulty range the Emitter repeatedly transmits (floods) respective route locator signals to its neighboring nodes (known as tandem nodes) that retransmit the signals to their neighboring nodes In a modality of the aforementioned US Patent a node only knows its own identity (ID) and turns on the ID of the node to which the connectivity has been lost by reading the last valid contents of a reception signal record on the affected port or ports that correspond to the damaged link or links, and in an alternative mode, a node stores and maintains an ID table of the neighbor node. The node that decides to act as the Selector now enters a waiting state and remains there until it receives a route locator signal. It then responds by transmitting a respective complementary reverse link signal (also known as a confirmation or return signal) to the Tandem node from which the route locator signal was received. The confirmation signal travels back through the tandem nodes establishing the required switch connections between the input and output ports of the node, and eventually arrives at the sending node, which then ceases to transmit the respective route locator signals, and proceeds to transmit on that newly established restoration route the traffic that would have been transmitted over the corresponding link of the faulty interval. The US Patent mentioned above also discloses that the restoration mechanism can be used to automatically provision the new circuit routes in a network by placing two nodes, between which it is desired to provide additional circuit routes (ie supplementary), directly in the states of the Issuer and the Selector with respect to an artificial fault between the selected nodes. The nodes would be supplied with artificial fault information including the number of circuit routes that are being searched.

BRIEF DESCRIPTION OF THE INVENTION According to a first aspect of the present invention, there is provided a method for determining an additional route in a communications network arranged completely or partially in mesh of nodes, the method comprising the step of sending a route locator signal from a node to a neighboring node on a spare link from an interval to the neighbor node, and is characterized by the previous steps of: determining the range of the links in the interval; and determining based on the respective unique network node identities of the node and the neighboring node if the node is in a first or second rank determination relationship with respect to the neighboring node; and the method is characterized in that the sending step comprises: if the node is in the first relationship, sending the route locator signal to the neighboring node over the lowest range determination of the currently available spare links in the range; or if the node is in the second relationship, send the route locator signal to the neighboring node on the highest range determination of the currently available spare links in the range. An advantage of the present invention is that the two nodes at the opposite ends of a range can independently assign links from the set of spare links in the interval to restore faulty routes, starting from the spare parts of rar-gc Higher and lower range determination, respectively, and thus avoid the spare parts contest, or, in the worst case, the limit concentration to the situation in which both nodes simultaneously have provisionally assigned the same Spare or spare parts for two different restorations. A contention protocol handles containment in which, for example, the highest rank determination of the two nodes knows that their provisional assignment will be confirmed, and that the lower range determination of the two nodes knows that they must send a signal Upward search for storage capacity that is not available. Preferably, when the route locator signal is a return route locator signal, the steps of: detecting when one or more spare links of the interval that have already been assigned per node for ur route are included. restoration identified in a first return route locator signal sent to the neighbor node are required for a restoration route identified in a second return route locator signal subsequently received from the neighboring node; and, in response, if the node is in a predetermined relationship of one of the first and second relationships, maintain the assignment of one or more rep links = e; or if the node is in another of the first or second relationships, change the assignment of one or more spare links from the restoration path identified in the first route locator signal back to the restoration path identified in. the second return route locator signal, sending to the subordinate end node which originated the first return route locator signal a corresponding upward search signal to cancel the assignments for the replacement links corresponding to one or more replacement links, modifying the first return route locator signal by reducing the content of a required storage capacity field with the restoration path of the first return route locator signal by the storage capacity of one or more intervals, and sending the first modified return route locator signal to the neighbor node. Alternatively, when the route locator signal is a return route locator signal, the steps of: detecting one or more spare links of the interval that has been assigned by the node for a restoration path identified in a first one are included. return route locator signal sent to the neighbor node, are required for a restoration route identified in a second return route locator signal subsequently received from the neighboring node; and, if the node is in one of the first and second predetermined relations, and not an end node for the restoration path identified in the second return path locator signal subsequently received from the neighboring node; and, in response, maintain the assignment of one or more spare links; modifying the second return route locator signal received by reducing the content of a required storage capacity field associated with the restoration path of the second return route locator signal by the storage capacity of one or more intervals; and sending the second modified return route locator signal to the corresponding neighbor node. Preferably, the sending step comprises sending the return route locator signal over each of the lowest range determination of not the highest range determination as the case may be, of the currently available replacement links in the range, where n is the content of a required storage capacity field associated with the restoration path of the return route locator signal.

According to a second aspect of the present invention, there is provided a node for use in a network of communications nodes completely or partially in mesh, the node being arranged to send, during use, a route locator signal to a neighbor node on a spare link from an interval to the neighbor node, and is characterized by being arranged to determine, during use, based on the respective unique network node identities of the node and the neighboring node if the node is in a first or a second rank determining relationship with respect to the neighboring node; and if in the first relation, send the route locator signal over the spare link corresponding to the lowest range determination of the node ports associated with the interval; or if in the second relation, send the route locator signal over the spare link corresponding to the highest range determination of the node ports associated with the interval. Preferably, the node is further arranged to detect when, during use, one or more spare links in the range that have already been allocated by the node for a restoration route identified in a first return route locator signal sent to the Neighbor node are required for a restoration path identified in a second return route locator signal subsequently received from the neighbor node; and, in response, if the node is in one of the first or second predetermined relations, to maintain the assignment of one or more spare links; or if the node is in another of the first and second relations, to change the assignment of one or more spare links from the restoration path identified in the first route locator signal back to the restoration path identified in the second return path locator signal, send to the subordinate end node that originated the second signal of the return path locator a corresponding upward search signal to cancel the assignments for the spare links corresponding to one or more spare links, and send to the neighboring node a second modified return route locator signal in which the content of a required storage capacity field associated with the restoration path of the second return route locator signal is reduced by the storage capacity of one or more intervals. Alternatively, the node is further arranged to determine when, during use, one or more spare links of the interval that has been allocated by the node for a restoration path identified in a first return route locator signal sent to the neighbor node are required for a restoration path identified in a second return path locator signal subsequently received from the neighboring node; and, in response, if the node is in one of the first and second predetermined relations, maintain the assignment of one or more spare links; and if the node is at an end node for the restoration path identified in the second return route locator signal subsequently received from the neighbor node, send to the corresponding neighbor node a second modified return route locator signal in which the content of a required storage capacity field associated with the restoration path of the second return path locator signal is reduced by the storage capacity of one or more intervals. Preferably, the node is arranged to send, during use, the return path locator signal over each of the lowest determination of range n, or the highest range determination as the case may be, of the linkages of Spare currently available from the interval, where n is the content of a required storage capacity field associated with the restoration path of the return route locator signal. According to a third aspect of the present invention, there is provided a network of communications nodes arranged completely or partially in mesh, wherein the nodes are substantially 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 drawings in which: Figure 1 is a diagram of a network of interconnected nodes; Figure 2 is an enlarged portion of the network of Figure 1; and Figure 3 is a diagram showing the connection of the spare links between two nodes of the network.

DETAILED DESCRIPTION OF THE EXEMPLARY MODALITIES The specific embodiment of the present invention relates to a real-time restoration process for establishing a restoration path in a communication network and the following description will be limited to these, although it will be appreciated that such a process need not be the only restoration process. in a network, but can be combined with a pre-planned restoration process. In Figure 1 a network 10 is shown consisting of a number of nodes 12, each having a unique network identity, linked by the intervals 14. For the purposes of this description, the node network identities are the letters of reference of the superior case, although in practice they are not numerical, and reference will only be made to nodes A to K. To avoid possible confusion, the reference letter "I" is not used. The individual intervals 14 will be designated by the two node identities of the respective pair of nodes between which a range is connected, for example the interval AB (or interval BA, depending on, for example, the direction of a signal). Of the many routes in the network 10 between the respective pairs of extreme nodes, this description will only consider three existing routes having the IDs "X", "Y" and "Z" of unique routes. Route X is between the extreme nodes A and E, which pass through the intermediate nodes B, C and D (also known as tandem), and which comprise a sequence of bidirectional links within the intervals AB, BC, CD and of; the route Y is between the extreme nodes A and G, passing through intermediate nodes B, C and F and comprising a sequence of bidirectional links within the intervals AB, BC, CF and FG; and the Z route is between the D and J end nodes, which pass through intermediate C and H nodes and which comprise a sequence of bidirectional links within the DC, CH and HJ ranges. These nodes and intervals are shown in Figure 2 in which, for clarity, other nodes and intervals are omitted. The intervals between the nodes comprise work links and spare links, and each work link is part of a respective unique route. The path capacity is expressed in terms of circuit numbers, but the capacity is added or subtracted, in link units. Within a range in the links are determined and identified sequentially by, in this example, the reference letters of the lower case. Specifically, with reference to Figure 3, the interval FK has ten work links from a to j, (not shown) and six spare links k to p. For convenience, you have the lower rank determination in this description (but there is no reason why you should not have the highest rank determination). The links in a range are connected to the node ports in a connection numbering convention in which the lower rank determination link is connected to the lower range determination link of the corresponding ports in both associated nodes. In this example, the node F has eight intervals with respect to its neighboring nodes (only two are shown in Figure 3), and the aap links of the FK interval are respectively connected to ports F101 to F116 of the node F. The node K has four neighboring nodes and aap links are connected correspondingly to ports K45 to K60 of node K. Consider that an excavator has separated a conduit near node C and that it contains both the CD interval and the CF interval at that point. In this case, the nodes C and D, ie the fault nodes for the X route, after detecting the failure of the CD interval, decide that a restoration path will be found between the nodes A and E, and similarly the nodes C and F decide that a restoration path will be found between nodes A and G, and nodes D and C decide that a restoration path will be found between nodes D And J- For ease of explanation, it will be assumed that no other route has failed, although it will be understood that, in practice, the fault nodes will act, correspondingly, to find a respective restoration route for each of the other routes they have experienced. a failure link. The order in which these restoration routes are established may be predetermined by determining the rank of the routes in the order of priority, but such determination of rank is not part of the present invention and will not be described. Each failure node will now generate, as a result of the aforementioned decision, a common help signal (designated here as a help message) for its associated failure paths, and will send the common help message to the respective end nodes of the routes. In this way, node C will send its common help message for routes X, Y and Z to nodes B and H, because those are the neighboring nodes for these routes, node F will send its common help message for route Y to node G, and node D will send its common help message for route X to node E. It will be appreciated that although node D is a failure node for route Z it is also an end node for that route. Each of the various signals used in the restoration process has a header and a record, the header includes a four-bit signal type field.

The different types are normal common path locator (also designated as common forward path locator), common reverse path locator (also known as common backward path locator), route tracker, alarm, common help, range determination, and return (also known as confirmation) . The information section of a common route locator signal comprises a four-bit flood count zone, a four-bit hop count zone, a four-bit route ID count zone, one or more zones of Sixteen-bit path ID, and a corresponding number of eight-bit circuit number zones. The information section of a common help signal comprises a four-bit route ID count zone, one or more sixteen-bit route ID zones, and a corresponding number of eight-bit circuit number zones, such that in the case of the signal sent from node C to nodes B and H, its counting area and ID contains the three numbers, the three zones ID contain, respectively, X, Y and Z, and the three zones The associated circuit number contains the respective storage capacities of these routes. As the common help messages pass through their respective intermediate nodes they break the connections on the corresponding faulty route. Each node will transmit a common help message received over the link or links that correspond to the route IDs contained in the common help message.

Each node knows its own network ID and contains a table that stores the route IDs by which it is an end node, and the network IDs of the other end nodes. When node B receives the common help message, it will check its stored table to find if it is an end node for any of the routes identified, and where, as in this case, it is not an end node for route X or for the route And, it will transmit the common help message about the outgoing links associated with those routes (BA interval links), and it will break the connections for those routes by removing the route and the link information from its connection table. The node H similarly transmits the common help message to the node J. When the node A receives the common help message, it will determine that it is at the end node for the X and Y routes, and will continue to determine if it is of further determination high rank, or lower range determination with respect to the stored IDs of other extreme nodes, that is, E for route X and G for route Y, based on the unique network IDs (ordinal numbers) of the nodes. If it is the first, then it will act as a main node (also known as a sending node), and if it is the last node then it will act as a subordinate node (also known as a selector node). In this example node A has a higher range determination network ID than both node E and node G, and therefore upon receipt of the common help message will assume, to establish a restoration path for routes X And Y, the role of the principal. Similarly, when the nodes E and G receive the respective common help message, each will determine that it is an end node for a route identified in the help message, and will continue to determine whether it is in the upper range determination or in the lower determination of rank with respect to the stored ID of the other end node for its associated route (X or Y). In this example, both nodes E and G have a lower range determination network ID than node A, and therefore upon receipt of the common help message, each will assume, to establish a restoration path for X routes and Y, the role of the subordinate. Node A, as the principal, now transmits a common forward route locator signal for the failed X and Y routes, ie send the signal over the spare links to its neighboring nodes. These in turn transmit the received signal, which thus floods through the network. This signal contains the IDs of the X and Y routes, the respective required storage capacities for the routes, number two in its route ID count zone, and has its flood count zone set to one. As the signal floods through the network, the transmitting and relaying nodes (ie those nodes that are not extreme nodes for any route IDs in the signal) increase the hop count zone. The relay nodes transmit the common signal over all the intervals. No verification is done to see if the spare storage capacity over an interval is sufficient for the total storage capacity of a faulty route, and the nodes do not mark that storage capacity as reserved. The relay nodes verify the hop count of a received signal and do not act without the count being greater than a predetermined value. This sets a limit to the geographical degree of flooding. In the variants, the additional flood control or alternatively comprises verifying a time zone of origin in the signal and does not act if the signal is older than a predetermined limit. The main node A, when it has transmitted the common route locator signal, will enter a passive state to await the reception of the respective return signals. After the determination of the node E that will act as a subordinate for the faulty X route, an intermediate starts to (trigger) to wait for the reception of a corresponding route locator signal containing the route identification X and thus indicates a route of Potential restoration of unknown storage capacity. If no forward route locator signal has been received for route X for the end of the temporary suspension period, node E will change to act as principal for route X and send a reverse route locator signal to its neighboring nodes , but this aspect of restoration is not part of the present invention and will not be described further. After the first reception of such forward route locator signal within the intermediate, the subordinate node E generates a return signal (also called a route confirmation signal) and sends it back through the node from which received the forward route locator signal. This return signal is similar to the route locator signal, but differs in that the content of the signal type zone is changed to identify the signal as a reverse signal that travels to the main A node, the route ID count zone is omitted, the individual route ID area containing the route ID X is used, and a single zone is used for the required storage capacity. The subordinate node E ignores any route locator signals received subsequently for route X. In this example, it has been assumed that non-separation restoration paths are allowed, and that the first forward path locator signal for route X received by node E has traversed a route through nodes B, C, K and F; the first forward path locator signal for route Y received by node G has similarly traversed a route through nodes B, C, K and F, and that the first forward path locator signal for the route Z received by node J has traversed a route through nodes F, K and H. It has also been assumed that the storage capacity required for routes X, Y and Z are three, two and four, respectively. As a return signal passes through the nodes of the potential restoration path, each of these verifies what storage capacity is available, makes the appropriate connections between the corresponding switch ports, and creates an ID zone of eight-bit node, in which you write your node ID. The node compares the required storage capacity with the available storage capacity, and if the storage capacity required is not greater than the available storage capacity it will make the connections for the required storage capacity and send the signal back to the next storage node. the potential restoration route. However, if the storage capacity required is greater than the available storage capacity, the node will make connections for the available storage capacity and transmit the signal with the number of the required storage capacity area replaced by the storage capacity available, and will also send to the subordinate end node a range determination signal containing the route ID and the value of the difference between the storage capacity required and the storage capacity to dismantle the connections that have already been made for the storage capacity that can not be established on the particular restoration path. After the reception of the return signal, the main node A knows that there is now a restoration route, identified by the IDs of the intermediate node or relay in the signal, and knows the capacity of that particular restoration route, and now sends A route tracer signal to node E, via the restoration path, to inform it of the intermediate nodes of the restoration path. When the invention is used to find a supplementary route, the route tracer signal can be sent over the existing route. This use of a route tracer signal is known in the art and does not form part of the present invention. In this specific example (Figure 3), it is assumed that the return signal from node E (for route X) arrives at node F substantially at the same time as the return signal (for route Z) arrives at node K from the transmitting node H, and that E is of higher rank determination that F and H is of higher range determination than K. The node E will have sent the return signal on the replacement link of determination of the lowest range of the EF interval , and this will have been received by node F over, say, port F15. The node F now performs a number of things, namely: it determines the storage capacity required for route X from the return signal (three) and assigns ports F15, F16 and F17 (three spare links of the FE interval) for the restoration path, node E will already have determined that the EF interval had sufficient spare storage capacity; determines that the node to which it has to send the return signal for the X route and finds that this is the K node; verifies the FK interval for the required storage capacity and, after finding that the required storage capacity (three) is not greater than the spare storage capacity (six), now proceeds to determine the relative determination of range of identities F and K of the node, and assumes that F is of higher rank determination than K, assigns the three lowest rank determination links, k, ky, for the restoration path for route X, making connections between the three ports F15, F16 and F17 and the three ports FUI, F112 and F113 corresponding to the links k, k and m, over the FK interval; transmits the signal back to the node K on the spare link k, and subsequently receives from the node K a return signal for the route Z. Similarly, the node K does a number of things, namely: determines the capacity storage required (four) for the Z route from the return signal transmitted by the H node and assigning four ports, K7, K8, K9 and K10 over the KH interval, for the restoration route, the H node will have determined that the HK interval had enough spare storage capacity; determines the node to which it has to send the return signal for the Z route and finds that this is the F node; verify the KF interval for the required capacity in the return signal for the Z route and, after finding the required storage capacity (four) is not greater than the spare storage capacity (six), now proceeds to determine the determination of the relative range of the identities K and F of the node and, given that K is of inner determination of rank that F, assigns the four links of higher rank determination, p, o, n and ÍT ?, for-- the restoration route for route Z, making the respective connections between the four ports K7, K8, K9 and K10 over the interval KH, and fourth ports K60, K59, K58 and K57, respectively corresponding to the links p, o, n and m, over the KF interval; transmits the signal back to the node F on the link p, and subsequently receives from the node F a return signal for the route X. The node K will receive on the spare link k connected to its port K55 the return signal for the route X requiring a storage capacity of three links, and enter the contention mode, since it has assigned and connected the links p, o, n .and rn, and similarly, the F node will receive on the spare p link connected to its port F116 the return signal for the route Z requiring a storage capacity of four links, and will enter the contention mode, since it has already assigned the links k, 1 and m. In this case, the contest will be with respect to whose route it will have priority over the assignment of the spare link m. Based on the highest determination of the range the node has priority, the node K: will assign the link to the return signal for the X route; will transmit the return signal for route X with its unnamed storage capacity zone - node C; change the assignment of the link for the restoration route for route Z to the links p, o and n; will break the connection between the K57 port and the port K10 and will make a new connection between the K57 port and a port over the interval Will regenerate an upward search signal for the Z route with the value one in the storage capacity zone to indicate the deficit of storage capacity, and send the signal search up to node H via port K10. Because the two nodes connected to an interval know the port numbers of the spare links, it is sufficient that the return signal is sent over the lowest rank determination replacement link (or the highest range determination, as the case may be) because the receiving node can determine, for a required storage capacity of n, the n-rank replacement links of lower rank determination. However, in the variants, the transmitted signal may be updated by the transmitting node to contain the identities of the assigned links, or a node may send the return signal on all the spare links allocated for a route.

Assume that node F now receives the return signal for route Y from node G, it will send an upward search signal containing the deficit storage capacity that was not able to connect, in this case, two, and the node G will respond by transmitting a reverse route locator signal for route Y. As mentioned above, node A will know from the contents of the circuit number area in the received return signal for route X that the storage capacity of the restoration path is the same as the required value, and then it will send a route tracer signal on the restoration path A, B, C, K, F, E to inform the node E of the identities of the nodes in tandem. On the other hand, in the case of the Z route, the node D will know from the content of the circuit number zone in the return signal received for the Z route that the capacity of the restoration route (D, F, K, H, J) is less than the storage capacity required, and will change to act as a subordinate node for the Z route for the deficiency and wait for the reception from the J node of a reverse route locator signal for the Z route After reception by node J of the upward search signal sent by node K, the subordinate node J changes to act as the main node for route X, generates a route locator signal with its flood count zone set for two, and with the storage capacity required in this signal set to the value in the upward search signal (ie, the circuit deficit), and sends it to the neighboring nodes. This signal is also designated as a reverse path locator signal. It will be appreciated that signals with odd flood counts can be identified as successive attempts made by the original principal to find a restoration path, and those signals with flood counts can be correspondingly identified as successive attempts made by the original subordinate. Node A responds to the first reception of a reverse route locator signal sent by node G by changing paca to act as a subordinate node and immediately sending a return signal on the link on which the reverse route locator signal is He received. This signal has the appropriate code for a return signal in its signal type field, has its flood count zone set for two, and also has its circuit number area set to the value in the reverse path locator signal received. Node E, which acts as the principal and which has sent the reverse path locator signals, will now be in the wait state.

The method described above for finding a restoration path in a network can be used to find a supplementary route by sending instructions from a network control center to the two extreme nodes' of a congested route so that they can treat the congested route as faulty and starting the method of the invention to find an additional route (also known as an alternate route) between the two end nodes. It will be appreciated that although the modality has been described with reference to a small network and that for convenience the number of links in an interval has been correspondingly small (sixteen), in a large network a range will comprise hundreds of work links and hundreds of links spare. An advantage of the aforementioned modality is that two of the nodes at the opposite ends of a range can independently allocate links from a set of spare links in the range to restore the faulty routes, starting from the lowest range determination spare parts. and higher rank, respectively, which avoids the contention for the spare parts until the situation of the limit in which both nodes simultaneously have provisionally assigned the same spare or spare parts for two different restorations. It will be appreciated that such a boundary contention event does not always occur, because the remaining spare or spare parts can be provisionally assigned by one node and confirmed by the other node after receipt of the return signal before another node is ready to verify the availability of spare parts and make their provisional location for a restoration route. Any contention that occurs has to do with a contention protocol in which the upper range determination of the two nodes knows that their provisional assignment will be confirmed, and the lowest rank determination of the two nodes knows that they must send a signal Upward search for storage capacity that is not available.

Claims (11)

1. A method for determining an additional route in a network of communications nodes completely or partially in mesh, the method comprises the step of sending a route locator signal from a node to a neighboring node on a spare link of an interval to neighboring node, and is characterized by the previous steps of: determining the range of the links in the interval; and determining based on the respective unique network node identities of the node and the neighboring node if the node is in a first or second rank determination relationship with respect to the neighboring node; and the method is characterized in that the sending step comprises: if the node is in the first relationship, sending the route locator signal to the neighboring node over the lowest range determination of the currently available spare links in the range; or if the node is in the second relationship, send the route locator signal to the neighboring node on the highest range determination of the currently available spare links in the range.

2. The method according to claim 1, characterized in that the route locator signal is a return route locator signal, and includes the steps of: detecting when one or more spare links of the interval have already been assigned by the node for a restoration route identified in a first return route locator signal sent to the neighbor node are required for a restoration route identified in a second return route locator signal subsequently received from the neighboring node; and, in response, if the node is in a predetermined relationship of one of the first and second relations, maintain the assignment of one or more spare links; or if the node is in another of the first or second relationships, change the assignment of one or more spare links from the restoration path identified in the first route locator signal back to the restoration path identified in the second signal return path locator, send to the subordinate end node that originated the first return path locator signal a corresponding upward search signal to cancel the assignments for the spare links corresponding to one or more spare links, modify the first return path locator signal reducing the content of a required storage capacity field with the restoration path of the first return path locator signal by the storage capacity of one or more intervals, and sending the first signal of modified return route locator to the neighbor node.

3. The method according to claim 1, characterized in that the route locator signal is a return route locator signal, and includes the steps of: detecting one or more spare links of the interval that has been assigned by the node for a restoration path identified in a first return route locator signal sent to the neighbor node, are required for a restoration path identified in a second return route locator signal subsequently received from the neighboring node; and, if the node is in one of the first and second predetermined relations, and is not an end node for the restoration path identified in the second return route locator signal subsequently received from the neighboring node; and, in response, maintain the assignment of one or more spare links; modifying the second return route locator signal received by reducing the content of a required storage capacity field associated with the restoration path of the second return route locator signal by the storage capacity of one or more intervals; and sending the second modified return route locator signal to the corresponding neighbor node.

4. The method according to any of claim 2 or claim 3, characterized in that the sending step comprises sending the return path locator signal over each of the lowest range determination of n, or the highest determination of range, as the case may be, of the currently available replacement links in the interval, where n is the content of a zone of required storage capacity associated with the restoration path of the return route locator signal.

5. A node for use in a network of communications nodes completely or partially in mesh, the node being arranged to send, during use, a route locator signal to a neighboring node on a spare link from an interval to the neighboring node , and characterized by being arranged to determine, during use, based on the respective unique network node identities of the node and the neighboring node if the node is in a first or a second relationship with respect to the neighboring node; and if in the first relation, send the route locator signal over the spare link corresponding to the lowest range determination of the node ports associated with the interval; or if in the second relation, send the route locator signal over the spare link corresponding to the highest range determination of the node ports associated with the interval.

6. The node according to claim 5, characterized in that it is further arranged to detect when in use, one or more spare links of such interval that have already been assigned by the node for a restoration path identified in a first pager signal return path sent the neighboring node are required for a restoration path identified in a second return path locator signal subsequently received from the neighboring node; and, in response, if the node is in one of the first or second predetermined relations, to maintain the assignment of one or more spare links; or if the node is in another of the first and second relations, to change the assignment of one or more spare links from the restoration path identified in the first route locator signal back to the restoration path identified in the second return path locator signal, send to the subordinate end node that originated the second signal of the return path locator a corresponding upward search signal to cancel the assignments for the spare links corresponding to one or more spare links, and send to the neighboring node a second modified return route locator signal in which the content of a required storage capacity field associated with the restoration path of the second return route locator signal is reduced by the storage capacity of one or more intervals.

7. The node according to claim 5, further characterized in that it is arranged to determine when, during use, one or more spare links of the interval that has been allocated by the node for a restoration path identified in a first locator signal of return route sent to the neighbor node are required for a restoration path identified in a second return route locator signal subsequently received from the neighboring node; and, in response, if the node is in one of the first and second predetermined relations, maintain the assignment of one or more spare links; and if the node is at an end node for the restoration path identified in the second return route locator signal subsequently received from the neighbor node, send to the corresponding neighbor node a second modified return route locator signal in which the content of a required storage capacity field associated with the restoration path of the second return path locator signal is reduced by the storage capacity of one or more intervals.

8. The node according to any claim 6 or claim 7, characterized in that it is arranged to send, during use, the return path locator signal over each of the lowest range determination of n, or the highest determination of rank as the case may be, of the currently available replacement links in the interval, where n is the content of a zone of required storage capacity associated with the restoration path of the return route locator signal.

9. A node for use in a network of communications nodes completely or partially in mesh, the node being substantially as described herein with reference to the drawings.

10. A network of communications nodes arranged completely or partially in mesh, characterized in that the nodes are substantially identical and in accordance with any of claims 5 to 9.

11. A method for determining an additional path in a network of communications nodes completely or partially in mesh, the method being substantially as described herein with reference to the drawings. SUMMARY A method for determining a restoration path (or an additional route) in a network of communications nodes completely or partially in mesh, wherein the step of sending a route locator signal from a node to a neighboring node on a plurality of spare links from an interval to the neighbor node comprises the preceding sub-steps of: determining whether the node has a determination network node identity higher or lower in rank than that of the neighboring node; and if it is at the highest rank determination, send the route locator signal over the spare link corresponding to the lowest rank determination of the node ports associated with the interval; or if it is in the lowest range determination, send the route locator signal over the spare link corresponding to the highest range determination of the node ports associated with the interval. A contention protocol handles any contention that occurs because the two nodes connected to one interval make the interim assignment for one or more links simultaneously to different restoration paths in the contention protocol, the highest rank determination of the two nodes know that their interim allocation will be confirmed, and the lowest rank determination of the two nodes knows that they must send an upward search signal for the storage capacity that is not available.