MXPA97005344A - Switching techniques without errors in ani network - Google Patents

Abstract

The present invention relates to a method for performing error-free switching in a ring network comprising one or more rings and comprising a data transmission means exhibiting a transmission delay, the network defining a plurality of transmission paths. transmission of data along the transmission medium that includes a first route and a second route, the method is characterized in that it comprises in combination the steps of: comparing the transmission delays of at least predetermined sections of the first and second routes; a first predetermined delay to at least one of the first and second routes, of the value of the first delay that depends at least in part on the results of the comparison, adding a second predetermined delay to at least one of the first and second routes to allow the alignment of the signals transmitted in the first and the second routes and the commutation without errors between the first and the second r utas, switching between the first and second routes, and adjusting at least one of the first and second delays to reduce cumulative delays in at least one of the first and second routines

Description

SWITCHING TECHNIQUES WITHOUT ERRORS IN RING NETWORK Technical field This invention relates to error-free switching in ring networks, and more particularly refers to this switching through the use of delays.

BACKGROUND OF THE INVENTION The capacity of the optical fiber medium that has traffic has increased exponentially for at least two decades. The ability to restore traffic from a failure in a network within a very short time has become of paramount importance to service providers and their customers. Highly reliable services are already being offered in an advanced fiber network, SONET by a restoration method that reroutes the affected signals to their destinations in the case of one or multiple failures in the network when deriving or diverting the locations within a period of relatively short time. Depending on the type of restoration method used, the restoration time varies from 50 milliseconds (msec) to several minutes.

REF: 25210 In addition to the accidental failures, there are activities planned in a network that interrupt the active services temporarily. These activities include: civil works on the fiber route, updating the node equipment on the signal path, and returning a signal from a temporary restoration route to its original route and vice versa. While, it is prohibitively expensive to implement error-free switching capability in the case of an accidental network failure, which would require at least three independent and dedicated routes for each signal path, switching methods have already been proposed and implemented without error of signals in the SONET / SDH and ATM networks in the case of a planned intrusion. Assuming that 50% of all intrusions are planned and 50% are accidental, it is possible within the current network architecture to eliminate 75% of all intrusions by re-routing the signals in an error-free manner because each intrusion , planned or accidental, is associated with another to return the signals to their original routes. Error-free switching to prevent any planned intrusion, which comprises most all intrusions, is particularly important for large business customers who use the network for large data transfer. For these customers, the high quality and minimally intrusive services offered by error-free switching are important. In a network based on the Bidirectional Line Switched Ring (BLSR), SONET, the efficient use of the capacity of the ring depends on the traffic design within the rings. Since the design will change as the traffic within the ring grows, traffic rearrangement activities within a BLSR will increase significantly. Therefore, the ability to switch without errors is important in the BLSR environment. Although error-free protection switching has been provided in a mesh network based on interconnections, there is no known method for providing error-free protection switching in a ring network, such as BLSR. In the error-free switching methods above, a signal in a working channel is duplicated at the originating node and both copies of the signal are received at the destination node, one from the working channel and the other from an alternate channel on a physically alternate route. Figure 1 illustrates the two alternate routes, the original AC route and the ABC alternate route, for a circuit between two A and C nodes. The associated nodes are equipped with light wave LT terminals and DSC 3/3 interconnection systems. As well as the route termination equipment (PTE, for its acronym in English). Central A receives data from a DS3, E4 circuit of 140 million bits per second (Mb / s). In the origin node A, the signal joins with the alternate route ABC (Figure 2). At the receiving node C, the interconnection system that receives both signals is equipped with an elastic storage of size 2d for each signal. The value of d is equal to the maximum differential delay between the original route (AC) and any other alternate route, possible. A delay equal to d is equal to the elastic storage in the original signal at the route termination node c, when the signal is stable for the first time. The signals transmitted simultaneously on the AC and ABC routes are then aligned in frame by adjusting the delay in the elastic storage in the ACB alternate route. The payload within the alternating payload box is then aligned with that in the working channel to take care of the indicator values, different from the two synchronous payload envelopes, identical (SPE, for its acronym in English) within the two different boxes of SONEN / SDH. Then, error-free switching can be performed to switch the signal from the AC route to the ABC without an individual bit error. Further examples of error-free switching, known are found in U.S. Patent Nos. 5,051,979 and 5,285,441. Although the method described above works sufficiently well for networks based on interconnections, it is inapplicable to ring networks. The present invention solves the problem of providing error-free switching in ring networks.

BRIEF DESCRIPTION OF THE INVENTION A network suitable for use in conjunction with the present invention may have one or more rings and include two or more data transmission routes. In this ring network, error-free switching can be achieved by comparing the transmission delays inherent in at least some sections of the two or more routes. One way to make the comparison is by comparing the lengths of the sections. A first delay is added to at least one of the two routes. The value depends at least in part on the results of the comparison of the transmission delays. A second delay is added to at least one of the two routes to allow the alignment of the signals transmitted on the routes and the error-free switching between the two routes. Then the switching between the two routes occurs, and at least one of the first and second delays is adjusted to reduce the cumulative delays in at least one of the routes. According to another aspect of the invention, error-free protection switching can be achieved for a link configured with rings connecting switching nodes, by measuring the length of the ring and the length of a section of the ring defining a first path between the access and exit nodes. A first delay is introduced only when the length of the section of the ring is less than half the length of the ring. Before the signals are switched from the first route to an alternate route, the signals on the route are aligned in phase. By using the above techniques, error-free switching in a ring network can be achieved with a degree of accuracy, reliability and speed previously not obtainable.

BRIEF DESCRIPTION OF THE FIGURES In the figures: Figure 1 is a block diagram of a prior art method of error-free switching not suitable for a ring network; Figure 2 (a) is a block diagram illustrating a prior art method for adding the delay to a DCS-based network; Figure 2 (b) is a block diagram illustrating a prior art method of in-frame alignment of two signals transmitted over a DCS-based network; Figure 3 is a block diagram illustrating a bidirectional line switched ring network suitable for use with the present invention; Figure 4 is a block diagram illustrating a network protection switching method illustrated in Figure 3 which is suitable for use with the present invention; Figure 5 (a) is a block diagram illustrating pre-planned rerouting in an individual ring network according to a preferred form of the invention; Figure 5 (b) is a block diagram illustrating error-free switching for pre-planned pre-routing in an individual ring network according to a preferred form of the invention; Figure 6 (a) is a block diagram illustrating the switching from a first route to a second route after the failure of a section of the first route according to a preferred form of the invention; Figure 6 (b) is a block diagram illustrating a return to the first route shown in Figure 6 (a) after the fault has been corrected according to a preferred form of the invention; Figure 7 is a block diagram illustrating a route through a network having two rings; Figure 8 is a schematic illustration of a preferred form of error-free alignment and switching in the network shown in Figure 7 according to a preferred form of the invention; Figure 9 (a) is a schematic distraction of a preferred form of certain preliminary steps by which the delay can be changed to an end node of the second ring of the network shown in Figure 7; Figure 9 (b) is a schematic illustration of a preferred form of additional steps by which the delay change initiated in Figure 9 (a) can be terminated; Figure 10 is a flow diagram illustrating a preferred form of error-free switching in an individual ring network according to a preferred form of the present invention; and Figure 11 is a flow chart illustrating a preferred form of error-free switching in a two-ring network according to a preferred form of the invention.

DETAILED DESCRIPTION Principles of Operation of Bidirectional Line Switched Rings (BLSR) In a network based on point-to-point light wave links and / or connected by interconnection systems, the switching point is always the end point where the signal is received from both the working and alternating channels. This is also true in the case of a dedicated protection ring (sub-network connection or SNC protection according to the ITU-T terminology and the route switched ring in the ANSI terminology) in which there is a dedicated alternate channel for each work channel. However, the high bandwidth BLSR SONET / SDH (shared MS protection ring or MS-SPR ring in ITU-T terminology) are used extensively to form high capacity structure networks. The switching points in these rings are not in the receiving nodes. The basic principles of operation of the BLSR (MS-SP ring) are as follows: (1) Half the capacity in each section of the ring, is used for the work traffic and the remaining half is available in case of a failure in any section of the ring and these slots of protection are shared by the fault in any location of the ring. (2) When a section fails, a working section is replaced by the concatenated protection section around the other side of the ring. (3) Because a section is replaced by another section, the switching on the adjacent nodes of the fault location is performed despite the final destinations of the signals within the ring. The typical operation of a BLSR (or MS-SP ring) is shown in Figure 3. For illustration purposes, the BLSR includes an OC-48 / STM-16 two-fiber ring 20 with error-free switching at the STS- level. 3c. However, it should be noted that, the principles discussed here apply equally to STS-1 signals and also to 4-fiber rings.

There are two fibers 20 and 22 between each pair of adjacent nodes A-F in the ring 24 of two fibers. Each fiber, half of the tax time slot 1-8 (8 STS-3s) (illustrated by solid line 1) is used for normal traffic and the remaining time slots 9-16 (illustrated by dashed line 9) ) remain normally empty. The slots 9-16 are used in a shared base for any fault within the ring 24. An AD signal between the nodes A and D in an ABCD path is established in a time slot 1 of the outer fiber 20 (in the opposite direction). to the hands of the clock). Its counterpart D-A signal is set to a DCBA path in slot 1 of the inner fiber 22 (clockwise). When there is a fault in an extension in the ABCD path as shown in Figure 4 (ie, section BC), the signal AD is switched at the node B (adjacent to the fault) to the slot 9 of the inner fiber 22 . The signal A-D up at node C in slot 9 of the inner fiber 22. Then, the signal A-D is switched from the slot 9 of the inner fiber 22 to the slot 1 of the outer fiber 24. The ABCD path of the original signal is thus restored by relocating the BC fault section (channels 1-8) along the concatenated BAFEDC route (channels 9-16).

It should be noted that the ring nodes perform the functions of both light wave terminals and 3/3 interconnection systems. However, there are two key differences. First, the bridge and switch nodes in a BLSR are not the source and receive nodes as in a DCS-based network. Second, bridging and switching takes place in a BLSR automatically without an order from the external control system. The communication between the nodes in a BLSR for the connection with bridge and switching takes place via the two bytes Kl and K2 of the SONET header that use the APS (Automatic Protection Switching) protocol.

Faultless Switching in a DCS Network is Unsuitable for a Ring Network In a ring network, switching is not performed at the receiving node. In contrast, the switching takes place in the nodes adjacent to a fault section. Therefore, the locations of the switching points for any failed signal are not predetermined. For example, if section BC fails (Figure 4), then bridging and switching occurs at nodes B and C, respectively. According to the error-free switching method in a DCS-based network, a delay is to be provided at the receiving end. However, since the end nodes are not the switching nodes in a BLSR, the delay in the end node can not be used to align the two signals in an intermediate switching node. Therefore, the error-free switching method used in the DCS-based network is unsuitable for a BLSR-based network. In addition, an error-free switching method suitable for an individual ring needs to be modified to extend to a multi-ring situation because the addition of a delay in each ring can lead to an unacceptable amount of accumulated delay in the signal path .

The Error-free Switching in an Individual Ring There are two typical situations in which error-free switching in a ring network can be applied: 1) when a signal between two nodes originally established at a ring site needs to be rerouted across the other side of the ring (eg, to the growth of ring traffic); and 2) After a failed section is repaired, and a signal needs to be returned to its original route through its repaired section.

Pre-Planned Re-routing in an Individual Ring Pre-planned rerouting is typically used when an established signal that originates and terminates within an individual ring needs to be rerouted through the other direction of the ring. The efficient utilization of the capacity of a BLSR depends on the routing of traffic on the ring which in turn depends on the given traffic design. As traffic grows in the ring, the traffic design changes. Therefore, it is necessary to reroute signals established within a BLSR. As shown in Figure 5 (a), an AD signal is established between nodes A and D on the ABCD path on channel 1. As the pattern or traffic pattern changes over the years, it may be necessary to change the AD signal to the AFED route. The error-free switching to reroute these signals from one ring direction to the other will thus improve the quality of service in a significant way in a ring-based network. Since this re-routing is pre-planned, bridging and switching can be achieved at the originating and terminating nodes, respectively, provided that elastic storage at node D has been provided with an appropriate delay when it was established. the AD signal. Signal A-D is bridged to node A in an empty channel (eg channel 5 on the AFED route of fiber 22). Error-free switching is performed from route ABCD to AFED on node D. Figure 5 (b) illustrates the switching configuration in this situation. The delay d? provided in the ESI elastic storage at node D on channel 1 of the ABCD route ensures that the alternate route on channel 5 of the AFED route is shorter than the original ABCD route. The delay d? must be provided when you first establish the A-D signal. The size of the elastic storage can be calculated from the following two equations: (1) ta + lw = lR (2) íw + d? = ¿A + da Where t w, ta and IR are the lengths of the optical path for a signal in the work path ABCD, in the alternate path AFED, and the complete ring 24, respectively. A delay d "is added to the working path when the signal A-D is established and a delay is added to the alternate path to align the identical signals transmitted from the node A in both directions around the ring. This is, the identical signals are transmitted simultaneously on the ABCD and AFED routes so that they can be aligned in phase on the node D. If the work route is shorter than the alternate route. { U = a or ¿w = lR / 2), then a delay d "= (íR - 2 t") is added when the signal A-D is established. When the AD signal needs to be routed on the other side of the ring through the AFED route, two identical signals can be aligned from both sides of the ring at node D with a small delay setting (da = 0) on the alternate route of the signal (that is, the AFED route) in storage ES2. Since the minimum value of can be as little as zero, the size of the elastic storage ESI must equal iR. If, on the other hand, the work path ABCD is larger than the alternate route AFED (w = ía or ew = lR / 2), then the elastic storage in the work path should not be provided with any delay in its totality (da = 0). When the AD signal needs to be switched to the alternate route on the other side of the AFED ring, it is necessary to add a delay da = (2 ew - eR) on the alternate route AFED to align two identical signals simultaneously on the ABCD routes and AFED. Since the maximum value of tw can be equal to lR, the size of fR for elastic storage ES2 is sufficient. Depending on whether the working channel is shorter or larger than the alternate channel, a delay must be provided during the establishment of the signal. Therefore, it is necessary to determine the lengths of the work route, the alternate route, and the complete ring. These measurements can be made by routing a pair of signals between a pair of nodes in both directions around the ring and comparing the arrival time of the signals at the receiving node. From these measured delay differences for each pair of nodes, the lengths of each section can be easily calculated and stored in a database of the ring terminals. In this way, either the delay times or route lengths may be used to determine the delay value added to the elastic stores of the various routes described in this specification and claims. The reference to the transmission delay is proposed to cover the route length and vice versa. The design of the elastic storage size of a ring terminal will depend on the ring as large as possible. For example, if the maximum ring length is 1000 km, the propagation delay around the ring is approximately 5 msec. Therefore, the size of the elastic storage needed for each STS-3c route in a ring terminal is 97.5 Kbytes. The required aggregate RAM in an OC-48 ring terminal is 3.12 Mbytes with the elastic stores in the receiving path from both sides of the ring as shown in Figure 5 (a). It is assumed that the delay is added to the elastic storage at the node receiving a signal. However, as discussed in the next section, when a signal is returned to the original route after a failure, the delay is added to the switching node which is not necessarily the receiving node. The accumulated delay in the intermediate node guarantees that the route around the other direction of the ring is shorter and therefore the commutation can be made without errors in this situation as well.

Return to the Original Route After the Restoration of the Ring When a signal is restored using the ring switching protocol defined in the ANSI and ITU-T (G.841) standards in the case of an accidental failure, the restoration is not error-free (which occurs within 50 msec). However, when the faulty section is repaired and the restored signal is returned to its original path, the signal switching may be without errors. As shown in Figure 6 (a), when there is a fault in section BC, the signal originally on the ABCD route (ie, A-D) takes the ABAFEDCD route. The shared protection channel 9 of the fiber 22 is used by the BAFEDC part of the protection route. When the failed section is repaired, the signal is received from node C also from channel 1 on the original ABCD route of fiber 20. As shown in Figure 6 (b), the elastic storage ES4 on channel 1 of the ABCD route on fiber 20 on node C is then adjusted with the delay dc to align the two copies of the signals on node C with the condition that the protection channel route delay of the ABAFEDC route is more than route delay on channel 1 on the ABC route of the fiber 20. As shown in the previous section, an elastic storage size equal to the length of the ring path is insufficient to align the identical signals routed on both sides of the channel. ring. The size of the elastic storage needed for error-free restoration of a signal after failure will now be described. The length of the route, íprot? of a protection channel when a section with fault i is given by (3) ipro t = tw - l 'i = ew + íR - 2 1' and (4) ÍÍ + e 'i =? R where, £ w is the length of the signal path in the original path (ABCD in Figure 6 (a)), t ± is the path length of the failed section i (BC), and l 'i is the path length of the ABAFEC route of the protection section. If there is a restriction that the length of the route of the largest section in a ring is less than half the length of the ring. { e ± = IR / 2 for all i), then it is evident from equation (3) that (5) ew < ef r:. < ew + tR Therefore, an elastic storage size of d = lR in the original signal path is sufficient to ensure that two identical signals can be aligned in node C with the appropriate delay added to the elastic storage ES4 in the original path (channel 1, fiber 20) on node C. Yes, on the other, no restriction is imposed on the length of the possible section yi? < tR / 2, the protection route is shorter than the work route. Since no delay can be added to the active signal, it is necessary to add a delay equal to (2 ti - tR) in the protection path when a signal is switched to that route and in the failure of the ith section. To provide error-free switching in this situation as well, the two ring ones must have the link length information (manifold section) available, so that the network can add an appropriate amount of delay in the protection path when there is a fault in an adjacent section. The case of a node failure is equivalent to two adjacent link faults. Therefore, in the case of a node failure, the added delay in the protection path is equal to (2 tL + 2l .: -tP) when i and i-1 are the links adjacent to the node with failure. Therefore, the far end switching node needs to have the information in the failed section or sections for error-free switching without any restriction on the section lengths. This information is available to the switching nodes through the K2 byte in the section headers used in the ring protection switching protocol. That is, the data necessary to determine the transmission delay or the physical length of each section of a route are stored and transmitted with the signals that are routed. Alternatively, this data can be stored in the nodes in the ring network. With the information in which the section or sections fail and the corresponding section lengths (or transmission delay), the transmission node needs to add an appropriate delay before switching and after a signal path failure occurs. . If the delay provided at the end node (for example, node D) is not removed and a delay equal to tR is added at an intermediate node (for example, the delay added to storage ES4 at node C) for switching without errors again, then the total delay in the work route (for example, route ABCDE of fiber 20) will exceed the tP. To avoid buildup of the delay, if there is a failure in any section of a signal path, the delays of all elastic stores in the signal path including one in the end node must be removed. Both types of intrusions due to traffic routing and return to the original route subsequent to the repair of a fault in a single ring can be without errors, provided that the ring terminals are equipped with elastic storage of size RR in the route of each tributary on the receiving side as shown in Figure 5 (a) and each node has a data base for the link length information (or transmission delay).

Multiple Ring Network If an end-to-end signal is established in multiple rings and an error-free switching function is incorporated in each ring, the total delay in the signal path is equal to the sum of the path lengths of all the rings. The total delay in the signal path in this situation can be large. For example, a signal in 5 rings each of a length of 2000 km would have an effective delay equal to 10,000 km or 50 msec. According to ITU-T Recommendation G.114, the maximum, permissible, unidirectional delay for telephone connections is 400 msec. Although the added delay is still much less than 400 msec, the quality of the connections with this large delay and without the echo cancellation is perceived as a disturbance. A general guide for good quality voice connections is to use an echo canceller in the signal path if the unidirectional delay is more than 25 msec. In this way, with echo cancellation, the added delay does not significantly affect the quality of the signal. In high quality networks, echo cancellation is used in each circuit. In addition, it is not necessary to add delay in each ring of the signal path. When a signal fails, the delays in elastic storage in the affected route of the signal are removed to avoid the accumulation of delays. If the signal path is confined within an individual ring, the removal of the delays can be achieved without any intervention from an external control system due to the APS communication channel between the nodes within the ring. However, when a multiple ring signal is established, there is no channel available to communicate between the multiple rings to perform the delay removal within the ring switching time, 50 msec. The use of a data communication channel (DCC, for its acronym in English) for this purpose is not enough. The accumulation of the delay can be avoided by changing the delay from any intermediate node in the signal path to the terminal node and vice versa without affecting the signal. As shown in Figure 7, an A-Q signal is established between node A and node Q on rings 1 and 2 along route ABCDPQ. Ring 1 includes the nodes AF and ring 2 includes nodes PS and D. Ring 2 has the same arrangement of the figures as shown in Figure 3, and the fibers of ring 2 corresponding to similar fibers of ring 1 they are shown by a similar numbering and the letter A. In this way, the fiber 20A of the ring 2 corresponds to the fiber 20 of the ring 1. The rerouting without errors of the signal in any of the rings in this route from one side of the ring the other would require that the length of the work route in each ring be greater than tR / 2. Therefore, a delay in the egress node of a ring is added if tw = a tF / 2. No delay is added if the length of the work route is greater than tR / 2. For example, delays can be added to ESI storage on channel 1 of fiber 20 of ring 1 and storage ES5 on channel 1 of fiber 20A of ring 2. Alternatively, ESI storage could be provided without delay and storage ES5 could be provided with an individual delay having a value corresponding to the largest of the individual delays that would otherwise be added to both ESI and ES5 storage. In the case of a failure on channel 1 in ring 1, the storage delay ES5 can be changed to ESI storage in order to switch a signal from the ABCD route to the AFED route. The delay switching can be carried out in the manner described in conjunction with Figures 9A and 9B. In this way, rerouting without errors is independently provided and handled for each ring individually. As shown in Figure 6B, after an error-free switching for the restoration to its original route the elastic storage ES4 at the switching node (node C) maintains a delay d. The additional or maximum delay may be equal to tR in the worst case scenario. This delay is cumulative. For example, after the error-free restoration from a failure in section BC in ring 1 of the type described in conjunction with Figure 6B, a dw case is added to storage ES4 in node C (Figure 8). If .and another failure in the DP section in the ring 2, then the restoration without errors may require the additional delay added in the node P. If during the second failure of the ring 2, the delay of the node C is not removed, the delay Total will accumulate. In this delay it can not be removed within 50 msec because it will require isolation between them and control. However, it can be changed from the switching node (node C) of the ring 1 to the elastic storage ES5 in the egress node (node Q) of the ring 2 without error. When a delay is changed from any intermediate node to an end node, a failure will be detected anywhere in the signal path at the end node, and the changed delay can be removed in detecting the failure. If there is a fault in the BC section, the delays, if any, in the D and Q nodes in the route serving the signal AQ are removed and the signal AQ is rerouted to the fiber 22 and then restored to the fiber 20 as described in conjunction with Figures 6A and 6B. During the restoration to fiber 20, the ESI and ES5 storages are again provided with their original delays, if any. As shown in Figure 8, there is a delay "added to the elastic storage ES4 at node C when it becomes stored from a failure in section BC. This delay needs to be changed to storage ES5 at the Q node end of ring 2 with error-free switching. With reference to Figure 9A, to change the delay at node C to node Q, the signal A-Q is bridged at the source node A on the protection channel 9 of the fibers 20 and 20A. If a protection access feature is available within the add / drop multiplexers (DAM) serving the network (not shown), then the AQ signal bridged on channel 9 can be transmitted through ring 2 as it is shown in Figure 9 (a). If it is not available for protection access, then any other empty service channel can be used. The bridge-coupled A-Q signal is then received at the end Q node. At the same time, signal A-Q is being transmitted on channel 9, another electrical signal is transmitted from node A to node Q on channel 1 of fibers 20 and 20A. Then, the two signals are aligned at the end node Q with the appropriate delays added to the elastic storage ES6 in the bridged signal on channel 9. Then the error-free switching is performed to move the signal from the source route in channel 1 to the dotted route on channel 9. Subsequently, the delay "at node C in the work path on channel 1 (in storage ES4) is removed, and the delays at the egress nodes (ie , nodes D and Q) of each ring are left unchanged. Then, the two identical signals that were transmitted on channels 1 and 9 are again aligned in the node Q with the appropriate delay added in the elastic storage ES5 in the node Q in the working channel 1 and are switched without error from the route dotted on channel 9 to the original route on channel 1 as shown in Figure 9B. The delay at the intermediate node C is thus changed from node C to the end Q node with error-free switching. This delay in storage ES5 can be removed during the next failure in any of the rings in the signal path. The change of the delay to the end node thus eliminates the accumulation of delays.

The change of the delay from an intermediate node in the source route to the end node comprises several steps and requires coordination between the ADM terminals within the rings. The coordination function between the ADMs in different rings requires a synchronized network management system that controls all the rings in the signal path or there must be a communication and control link between the network management systems, separated for different rings . Otherwise, manual coordination between the various rings would be extremely complicated and prone to error. The provision of this network management system is within the skill of the technique in SONET networks. In addition, since the size of the elastic storage for each ring is equal to the length of the ring, the ADMs must be designed such that the size of the elastic storage equals the length of the largest possible ring that can be deployed in the complete network . Figure 10 illustrates a preferred method for providing error-free switching in an individual ring network of the type shown in Figure 3. In step SI, a route is established from node A to node D. In step S2, Transmission delays or the lengths of several sections of the routes in the ring are compared. Whether or not delay is added to node D depends on this comparison. In step S3, no delay is added in the node D. This is an important feature that reduces the cumulative delays that decrease the quality of the data transmission. If the delay is required, it is added in step S12. In step S4, a decision is made to switch from the ABCD route to the AFED route. In step S5, a delay (eg, storage ES2 (Figure 5B)) is added by phase alignment. In step S6, error-free switching is achieved (for example, when switching from the ABCD route to AFED (Figure 5B)). This is an important feature that provides error-free switching for pre-planned rerouting such as when traffic on an initial route requires switching to an alternate route. At the end of step S6, any additional delay at node D is removed from the original route (eg, route ABCD). Step S7 describes a type of route section failure in which only some of the channels of a fiber are interrupted. With reference to Figure 3, a fault could occur if channel 1 of the ABCD route is interrupted, while channel 9 of that route remains operational. An example of the switching described by step S8 is the switching from channel 1 to channel 9 on route ABCD on fiber 20. After switching, the delay of channel 1, which includes the delay, if any, is removed. in node D. in steps SIO and Sil, after the fault has been cleared in channel 1, assuming the failure was in section BC, a small delay can be added to storage ES4 in channel 1 to align the signal on channel 1 with the signal on channel 9. In step S14 server, the transmission delays of the appropriate sections of a route are compared to determine the delay, if any, to be added. In step S9, the delay is added (for example, to storage ES3 (Figure 6A)) to achieve error-free switching. The delay previously added to the route with failure (for example, route ABCD), such as the delay, if any, added to node D, is removed. In step S15, no delay is added, and the delay is removed from the faulty route, including node D. In steps S16 and S17, after the fault is corrected, switching is achieved without error after the step alignment delay is added. An example of step S17 is the added storage delay E4 described in conjunction with Figure 6B. With reference to Figure 11, in step S40, a route is established from node A and ring 1 to node Q of ring 2 (Figure 8). In step S41, the transmission delays or the lengths of several sections of the routes in rings 1 and 2 are compared. Whether or not delay is added to node D or node Q depends on this comparison. This is an important feature that reduces the cumulative delays that can decrease the quality of data transmission. If delay is required, it is added in step S43 either node Q alone or to nodes D and Q. Steps 344-S46 can be understood from the description of steps S4-S6 of Figure 10. After the step S46, any of the delays added aücionalmente in the nodes of exit of a work route are deleted. Step S47 describes the same type of fault as step S7 of Figure 10. An example of step S48 is the switching of a route from channel 1 to channel 9 as shown in Figure 9A due to a failure in the section BC of channel 1. In steps S50 and S51, after the failure in channel 1 is corrected, the work path is switched back to channel 1 after a phase alignment delay is added to storage ES4 in channel 1 (Figure 8). In step S52, the delay added to storage ES4 is changed to node D in a manner similar to the delay change to node Q described in conjunction with Figures 9A and 9B. Step S53 refers to a failure of the type shown in Figure 4 in section BC. In step S54, the transmission delays of the appropriate sections of a route are compared to determine the delay, if any, to be added. In step S49, the delay in the protection path (for example, storage ES3, FIG. 8) is added in the term of step S49, any delay added in a faulty route during the previous error-free switching is removed, which includes any step added to node D. In step S55, no delay is added to the protection path in order to minimize cumulative delays. At the end of step S55, any delay in a faulty route is removed, including the delay in the node D. In steps S56 and S57, after the failure of the work route is corrected, commutation is achieved without errors when adding a phase alignment delay (for example, the delay added to storage ES4, Figure 6B). In step S52, the delay added in step S57 is changed to node Q as described in conjunction with Figures 9A and 9B. Those skilled in the art will recognize that preferred embodiments may be altered without departing from the spirit and scope of the invention as defined in the claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the present invention is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property: *

Claims (16)

PETVINDTCATIONS

1. A method for performing error-free switching in a ring network comprising one or more rings and comprising a data transmission medium exhibiting a transmission delay, the network defining a plurality of data transmission routes to 1 ^ length of the transmission medium including a pri:; route and a second ru * - ^, the method is characterized in that it comprises in the steps of: comparing the transmission delays of at least predetermined sections of the first and second routes; adding a first predetermined delay to at least one of the first and second routes, of the value of the first delay that depends at least in part on the results of the comparison; adding a second predetermined delay to at least one of the first and second routes to allow the alignment of the signals transmitted in the first and second routes and the error-free switching between the first and the second routes; switch between the first and second routes; and adjusting at least one of the first and second delays to reduce cumulative delays on at least one of the first and second routes.

2. A method according to claim 1, characterized in that the value of the first delay is substantially zero in the case that the transmission delay along one of the first and second routes to which it is added to the first delay is greater than the transmission delay along the other of the first and second routes.

3. A method according to claim 1, characterized in that the second delay is substantially zero in the event that the transmission delay along one of the first and second routes to which the second delay is added is greater than the delay of the second delay. transmission along the other and the first and second routes.

4. A method according to claim 1, characterized in that the value of the pr.rier delay is substantially equal to twice the delay along the section minus the delay along the ring network as a whole.

5. A method according to claim 1, characterized in that the step of comparing comprises the steps of: storing data from which the lengths of the sections of the first and second routes can be derived; and compare the lengths.

6. A method according to claim 5, characterized in that the step of storing data comprises the step of transmitting data with the signals.

7. A method according to claim 1, characterized in that adjusting at least one of the first and second delays comprises the step of erasing one of the first and second delays.

8. A method according to claim 1, characterized in that the step of adjusting at least one of the first and second delays comprises the step of changing at least one of the first and second delays.

9. A method according to claim 1, characterized in that the network comprises a first and a second ring, wherein the step of adding the first delay occurs in the first ring and wherein the step of adjusting at least one of the first and second Delays include the step of changing at least one of the first and second and delays to the second ring.

10. A method according to claim 1, characterized in that the network comprises a first ring and a second ring wherein the step of adding the first delay occurs in the second ring, wherein the step of adding a second predetermined delay comprises the step of adding a second predetermined step to the first ring and wherein the step of adjusting at least one of the first and second delays comprises the step of erasing at least the second delay of the first ring.

11. A method according to claim 1, characterized in that the step of adjusting at least one of the first and second delays further comprises the step of adding a third delay to the second route in the second ring.

12. A method for performing error-free protection switching for a ring-configured high-speed link connecting a plurality of switching nodes comprised of an access node and an egress node, the method is characterized in that it comprises the steps of: measuring the ring length and the length of a ring section defining a first route for the propagation of traffic signals between the access and egress nodes; introducing a first delay in the propagation of the traffic signals only when the length of the section of the ring is less than half the length of the ring; and in response to a need for an alternate route to connect the access and egress nodes, introduce a second delay in the transmission of the traffic signals crossing the alternate route such that the traffic signals on the first route and on the route alternate in phase.

13. The method according to claim 12, characterized in that the first delay is introduced in the egress node.

14. The method according to claim 12, characterized in that it also comprises the step of: in response to a failure of the first route in the propagation of the traffic signals, establishing the second delay for the alternate route that is equal to twice the length of the first route minus the length of the ring.

15. The method according to claims 13 and 14, characterized in that it also comprises the step of: removing the first delay in the egress node before establishing the second delay.

16. A method according to claim 12, characterized in that the second delay is set close to zero when the length of the section of the ring is greater than half the length of the ring.