IL148391A - Switching assembly for protected optical path - Google Patents

Description

148391/2 |Am «υοικ ^o 1? Am«n raD-in Switching assembly for protected optical path ECl Telecom Ltd.

ECIP/F039/IL Switching Assembly for Protected Optical Path Field of the invention The present invention relates to switching devices, such as digital switches, optical cross-connecting switches with add-drop ability, and the like.

Background of the invention In modern telecommunications networks, where digital information is transferred along great distances and passes a huge number of network elements, it is highly subjected to errors and faiilts. Moreover, data streams transmitted via modern transport communication lines are usually high rate data streams which incorporate^ therein a number of component, lower rate data streams. A ready example of a system where high rate data streams are transmitted via transport networks is a so-called SDH/SONET system of optical signals hierarchy. In SDH, high rate virtual containers STM-4, STM-16, STM-64 and STM-256 are composed, according to the modular principle, from a number of basic containers STM-1 (having a speed of 155.5 Mbps), wherein STM-1 in turn, is built from lower rate data streams or so-called low order granularity data streams E-l, T-l, TU-11,TU-12, etc. Such combined data streams are usually formed at one point of the network for the purpose of long distance transmission, and are to be disassembled at another network point for transmitting to various customers. Errors or faults, in case they occur in transmission lines of such high order data streams, would affect a great number of customers.

In order to ensure reliable protected service, telecommunication networks may provide transmission of data over two separate paths, one of which is called a main path and the other - an alternate or protective path. The arrangement is such that if the main path fails, the alternate path continues transmitting the data, thereby protecting it. The combination of the main path and the alternate path is usually termed a "protected path".

Optical switching devices, intended for the above-described networks, have a trend to grow into more and more complex systems where thousands of low order granularity incoming data streams are processed to form thousands of low order granularity outgoing data streams. Depending on a particular switching device, the internal processing may include disassembling of one or more high rate incoming data streams in order to output particular portions thereof. For example, some portions of incoming signals (say, information transmitted over particular WDM optical channels) may be dropped to customers. Likewise, the optical switching device may perform internal reassembling of the data to form one or more newly combined outgoing data streams. For example, a modern digital cross-connect DXC, for switching an incoming data stream STM-4, processes inside 4x81 of component low granularity streams TU-11 or 4x63 of low granularity streams TU-12.

To perform the complex processing inside such a switching device, a great number of internal connections are to be configured in advance for any particular data stream incoming the device. The configuration of internal connections is usually bound to particular input contact(s) assigned to the paths via which the mentioned data stream enters the switching device. A number of output contacts are also to be reserved for one or more outgoing portions of the stream. If the incoming data stream is a high rate data stream, and the switching device decomposes the incoming data stream into low granularity streams for internal processing, the number of internal connections is much higher.

To secure the uninterrupted service, the high rate data stream transmitted via its main path is fed to one input contact (or group of contacts), while the data stream transmitted via the alternate path is fed to another (alternative) input contact or contacts group of the same switching device.

As has been mentioned above, the alternate path starts playing its part when there is a fault on the main path, so the information can be found only on the alternate one. It means that, when the fault is detected, the switching device is supposed to start working with the data stream obtained at the alternative input contact(s), and to output the processed data stream via a different (alternative) plurality of output contact(s). Usually it also means that if at least a portion of the data stream is to be forwarded to the next network element in the line (i.e., passes the device "through"), it must be transmitted further via the protective path determined for it in the network, and not via the main path which is now faulty.

Moreover, it means that the internal connections established in the switching device for processing the "main" data stream, will not suit any more and should be reconfigured. The reconfiguring is extremely complex in cross-connects, it is usually performed by changing information in software tables defining internal connections in the switch at any range of granularity. In other words, the tables should provide for that the "main" stream components be replaced by the "alternative" components and the connections be restructured for these "alternative" stream components.

In any case, the reconfiguring requires additional software development and reduces efficiency of the equipment.

EP 1 037 492 A2 discloses an approach for performing fault recovery in an optical communications network. An optical switch is connected to working optical fibers and protection optical fibers, which carry WDM (wave division multiplexing) optical signals. The optical switches possess functionality to switch over the optical signals among the working optical fibers and the protection optical fibers. The optical switch includes dual unit optical switches that have a common driving mechanism. The common driving mechanism is configured to perform simultaneously a switching operation of the unit optical switches to alter a switching state of the optical switch. Monitoring devices are distributed throughout the node to monitor the transmitted optical signals over the optical fibers, and to output monitoring signals that indicate one or more faults in these optical fibers. In response to the monitoring signals, a control device outputs control signals to the optical switches to effect an optical protection scheme.

The solution is focussed on the fault recovery and on determining healthy transmission lines in rings when the fault is detected. No attention is paid to the problem of reconfiguring internal connections in a complex switching device in the presence of a fault.

To the best of the Applicant's knowledge, the problem of reconfiguring the switching devices handling high rate data streams by handling their "low granularity" components has not been resolved in a simple way in the prior art.

Object of the invention It is therefore an object of the invention to provide an optical switching device for a protected optical line, capable of effectively handling high rate data streams in cases of a fault on the line.

Another object of the invention is to provide a method of controlling an optical switching device in a protected optical line.

Summary of the invention The above object can be achieved by providing a method of controlling a switching device inserted in a protected line formed, in an optical communication network, from a main path and an alternative path for transmitting a high rate data stream, the method comprising: - handling, in the switching device, lower rate data streams being components of said high rate data stream fed into the switching device from the main path via one or more input contacts associated with the main path, by using internal connections configured in the switching device, - in case of a fault in the main path, feeding to the switching device the high rate data stream from the alternative path via the one or more input contacts associated with the main path, thereby preserving said internal connections without reconfiguring thereof.

More particularly, the method comprises - providing the switching device having pre-configured internal connections for processing there-inside m high rate data streams by handling lower rate data streams being components of said high rate data streams, - assigning k (k Both the step of selecting, and the switching of the alternative path can be provided under control of the Network Manager. However, at least part of the operations may be performed by a local control unit associated with the switching device.

In one particular version, when k In another case, when k=m, the alternative path can sometimes be selected from other paths incoming a network node comprising the switching device, and caused to be switched to the switching device via the IM of the faulty main path. This option is explained in more detail in the portions of the description related to the switching assembly.

It should be noted, however, that "k" may also contain among them paths carrying such data streams which does not need to be protected.

In any case, the pre-configured internal connections in the "low granularity" switching device are preserved intact, like the device continues working with the data stream transmitted over the main path of the protected line.

The protected line is typically an optical protected line comprising two optical fiber paths, one of them being the main and the other being intended for serving as an alternative path, when required.

In the most preferred version of the method, in case of detecting a fault on the incoming portion of a main path, it also comprises switching the outgoing portion of the main path to the outgoing portion of the selected alternative path.

For the case when k Such a procedure enables the switching device to function successfully in networks which operate according to the widely known MSPring protocol, where, if a fault occurs in a section of the main path, all the network starts using the alternative path.

It is understood that the switching device may be inserted in more than one protected lines, and the method steps will be performed with respect to each of the protected lines "mutatis mutandis", whenever detecting a fault on the incoming portion of the main stream of a particular protected line.

It should be noted, however, that in a case of fault on a main path, the protected optical line can be formed based on one of the following approaches: - one main path has a corresponding one alternative path ("1 to 1"); - one alternative path serves a number "k" of main paths ("k to 1"), and - a number "k" of main paths are served by a number "n" of alternative paths, where each of "n" may serve each of the "k" ("k to n").

The last two approaches are usually implemented in complex telecommunication networks such as mesh networks. For such networks, the proposed method of control is the unique and universal solution which, in case of a fiber cut or another fault on the main path, enables urgent switching to any alternative path selected by the Network Manager, without reconfiguring the switching device to input contacts of this particular alternative path which was even unknown in advance.

The main path is to be understood as the one currently in use among the two paths forming the protected line.

It should be appreciated that the same method can be used for returning to the main path from the alternative one when the faulty path is recovered. In this case, as well as in the general definition, the term "main path" will be understood as the path currently in use.

According to another aspect of the invention, there is also provided a switching assembly for serving high rate data streams in an optical communication network, the switching assembly comprising a switching device and a controllable bridging unit, wherein the controllable bridging unit having M input contacts or groups of contacts respectively assigned to M communication paths, each of said paths being suitable for transmitting a high rate data stream in the optical communication network; the switching device having pre-configured internal connections for processing there-inside m high rate data streams from those obtained by the controllable bridging unit via said M telecommunication paths, wherein M>m, and wherein the processing is performed by handling lower rate data streams being components of said high rate data streams; the controllable bridging unit, upon being informed that a particular path of said M paths is faulty while another one of said M paths is selected to serve an alternative path to the faulty one, is capable of controllably and respectively bridging between the input contact or group of contacts assigned to the faulty path and the input contact or group of contacts assigned to the selected alternative path; thereby connecting the switching device to the selected alternative path, while preserving the internal connections in the switching device without reconfiguring thereof.

Usually, functions of detecting faults in the optical network paths and selecting alternative paths for protecting the traffic are functions of the Network Manager, therefore the controllable bridging unit is preferably controlled by the Network Manager. However, the assembly may comprise an internal local control unit responsible for such operations.

Whenever the alternative path is selected, it forms with the basic path (which will be called " a main path") a so-called protected line, regardless the fact whether the alternative path is selected before or after detecting the fault on the main path.

In a case M>m, the switching assembly is capable of serving m main paths, with protecting them by means of M-m alternative paths: if M-m >m, one alternative path may be assigned per each main path; in all remaining occurrences, one or more alternative paths are ready for serving m main paths if fault occurs in one or more main paths.

In a case M=m, the switching assembly is capable of serving m high rate data streams transmitted via m main paths without protecting thereof; however, it may serve k The switching assembly is suitable for serving at least one protected line for transmitting a high rate data stream, formed in an optical communication network from one main path and one alternative path. Preferably, it is intended for serving more than one protected lines.

In the most preferred embodiment of the switching assembly, the assembly is integrated.

Further, the controllable bridging unit can be provided with one or more input contacts IM assigned to an incoming portion of the main path, one or more input contacts IA assigned to an incoming portion of the alternative path; the bridging unit being capable of bridging between the contact(s) IM and the respective contact(s) IA upon receiving a command that a fault is detected on the incoming portion of said main path and that said alternative path is selected for said main path. thereby connecting the switching device to the alternative path of said protected line, while preserving the internal connections in the switching device without reconfiguring thereof.

It is quite understood that the controllable bridging unit is also provided with M output contacts or groups of contacts respectively assigned to M telecommunication paths, each of said paths being suitable for transmitting a high rate data stream in the optical communication network; In one particular embodiment, the bridging unit is provided with one or more output contacts OM assigned to an outgoing portion of a particular main path, and with one or more output contacts OA assigned to an outgoing portion of the alternative path assigned to the particular main path.

For serving in the networks acting according to the MSPRing protocol, the bridging unit may also be capable of bridging the contact(s) OM and the corresponding contact(s) OA associated with the outgoing portion of the alternative path, in case of detecting the fault on the main path.

The switching device may physically be provided with all the mentioned contacts IM, IA, OM and OA. However, owing to the fact that according to the invention, the switching device never handles data streams fed directly from the alternative path, it may physically comprise just the IM and OM contacts, while the contacts IA and OA be provided in the switching assembly.

The incoming high rate data stream may be inputted to the switching assembly via a serial port, therefore we speak here about a possibility of having more than one input contacts; the same applies to the outgoing data stream (for example, STM-16 can be inputted via four input contacts, each carrying one STM-4 stream).

Of course, the assembly should be capable of disconnecting the bridged contacts when the faulty path is recovered, thereby returning from the alternative path to the main one.

According to the most preferred embodiment of the switching assembly, the switching device is in the form of a matrix (switching fabric, or switching network) comprising a number of lower order component optical switches, while the incoming said data stream, whenever being fed to the switching device, is decomposed into a plurality of component lower order data streams respectively handled by said component optical switches, and the bridging unit being adapted for switching the incoming data stream before being decomposed, by coupling the IM contacts with the I A contacts.

In other words, the bridging unit should effect the switching operation before decomposing the incoming stream ( and as close as possible to forming the outgoing stream), so as to perform a minimal number of switching actions, each of them outside the optical switching device but still within the integrated assembly.

Typically, the switching device is a complex cross-connect device for optical systems (which is often called a time-space switch). In the case of a cross-connect (time-space switch), high rate data streams are usually disassembled into component "lower granularity" data streams which are processed in space and time by the component switching elements of the cross-connect to create one or more resulting data stream(s).

The incoming data stream may, but must not be always transferred into a through passing outgoing data stream. If the switching device is OADM (Optical Add Drop Multiplexer), portions of the incoming data stream may be deflected in the switching device, to be further dropped. Also, some data streams may arrive to the switching device not via the main or alternative paths - for example, may be added to the switching device and, upon the processing inside, be combined with the outgoing data stream.

In the case of OADM, the switching device comprises additional output contacts intended for dropping at least some component data streams of the incoming data stream, and additional input contacts for adding one or more component data streams instead of the dropped ones.

So, any outgoing data stream is composed from a plurality of the component data streams, including the component data streams of the incoming data stream and those added to the switching device.

The inventive solution becomes extremely advantageous when the switching device is designed to perform time-switch operations for a number of high rate data streams, since reconfiguring of internal connections in the switch (in case of one or more failures in the paths which carry the high rate incoming data streams) requires time and resources and sometimes is just impossible.

To realize advantages of such an assembly, it should be noted that the switching device is arranged without any spare capability for reconfiguring the internal connections and may therefore be cheaper due to having a lower complexity, mostly from the point of embedded software. Due to that, the switching device usually comprises only contacts assigned to main path(s) of the protected line(s).

The higher the rate of the incoming data streams, and the lower the granularity of the switching device, the greater the efficiency of the proposed invention. Moreover, the greater the number of paths which can be used as alternative to the main paths handled by the switching device, the more advantageous the invention is.

The most important advantage of the switching assembly is that it can be flexibly used in complex optical networks, such as mesh networks. In such networks, node receives data streams from many adjacent nodes and therefore takes care of a great number of paths, of which some are considered main paths and some may serve alternative paths to the mentioned main paths. Due to the complex topology of the network, multiple faults may occur in the paths, and the Network Manager ( or the local control unit) may arbitrary select which paths are considered main and which are alternative at a time. For example, one alternative path may protect a number of main paths, or any particular path may serve an alternative path for each and any of other paths incoming the switching assembly.

It is therefore very important that the switching device in the assembly is independent and invariant to the selections made outside, while the controllable bridging unit performs any required combinations with its input contacts or groups of contacts assigned to M paths.

Since there is no need in reconfiguring internal connections of the switching device, the assembly easily fulfils the requirement of urgently switching to any incoming alternate path which is pointed out by the Network Manager or the responsible control unit.

Further aspects and details of the invention will become apparent as the description proceeds.

Brief description of the preferred embodiments The invention will be further described and illustrated with reference to the following non-limiting drawings, in which: Fig. 1 is a simplified illustration of a mesh network with a node comprising a switching device.

Fig. 2 schematically illustrates a switching assembly according to the invention.

Fig. 3 - is a schematic illustration of the function of the proposed optical switching assembly in case of a failure on the main path of a protected optical line.

Fig. 4 - is a schematic illustration of the optical switching device performing functions of OADM Fig. 5 - shows an embodiment where one common alternate path is used for a n optical umber of main paths, and where the switching device performs recomposing of the data streams.

Detailed description of the preferred embodiments Fig. 1 illustrates a fragment of a mesh network formed by nodes (Network Elements) NEl, NE2,...NE6. The nodes are interconnected by bi-directional links. For example, node NEl receives three incoming paths, among which the paths from NE2 and NE5 are considered main paths carrying data streams necessary for processing in the node NEl. The third incoming path is considered alternative to the main path from node NE5 to node NEl : it can be used for transmitting information from the node NE5 via the node NE6 to node NEl if the main path is faulty. The whole alternative trail is marked by a wavy line. Owing to the ring structure existing in the illustrated mesh configuration, other combinations can be found. Even more options for selecting main and alternative paths can be found with respect to the node NE2.

The drawing explains the fact that in the mesh networks, there is a great variety of selecting trails for forwarding data from one node to another, so the main paths and alternating paths incoming the node may be selected quite arbitrary. Actually, any path may be selected to be main, and any one - to be an alternative to the main. In such networks, in case of a fault on a main path, the alternative path is selected dynamically by a Network Manager. If the main path transmits a high order data stream which is to be switched at the node, and the main path fails, the switching device in the node should immediately get ready for receiving the data stream from another path.

If there is relatively a small number of incoming paths, as illustrated in Fig. 1, the node may be configured for any of them. But if the number of paths reaches hundreds and thousands, both configuring and reconfiguring in the switching device becomes impossible.

Fig. 2 illustrates one embodiment of a proposed switching assembly 1 for high rate data streams, including a switching device 2 and a controllable bridging unit comprising two sub-units 3 and 4. The bridging sub-unit 3 is connected to M incoming paths. The switching device 2 is designed for switching m high rate data streams incoming via m paths. In this embodiment, m For example, one of M paths incoming the bridging sub-unit 3, is marked 5 and is considered a main path. It is normally fed to the switching device 2 where it is processed. If a fault occurs on the path 5, and a path 6 is selected by the Network Manager NM (not shown) as the alternative path to path 5, the bridging sub-unit 3 switches the path 6 (the dotted line 7) so that it arrives to the switching device via the input contact assigned to the path 5. The switching device 2 therefore does not need any reconfiguring and does not feel any difference in its operation.

Optionally, if the Network Manager requires that, in case a main path is faulty the system should continue working on the alternative path (like in the MSPRing protocol), the bridging sub-unit 4 will activate a coupling 9. The coupling 9 will bridge the processed data stream 8' which is usually outputted via the main path 5', to the alternative path 6'.

Fig. 3 schematically shows an assembly 10 comprising a switching device 11 intended for switching a number of data streams which arrive to the device (at its right side). In this embodiment, M=m and each main path (Ml,... Mn) is protected by a particular alternative path (Al, ...An). Fig. 3 is a simplified illustration of the assembly proposed in the present application, comprising a complex cross-connecting device inserted in a number of protected optical lines. For example, a data stream No.l can be transmitted both over a main path 12 and an alternative path 14 which together form a protected path; the incoming portion of the protected path is marked 16. For the sake of simplicity, let the incoming portion of the main path 12 is connected to the device 11 via an input connector 18, which is also marked as IM1 (Input Main 1). In this example, the alternative path 14 directly enters the device 10 via an input alternative contact (IA) 20. Another exemplary data stream ( the n-th data stream) is fed to the switching device via a protected path 22. The switching device 11 comprises pre-configured internal connections (shown very schematically as 24), which perform the switching operation inside the device to produce outgoing portions of the data streams. The device is pre-configured to provide the switching operation between the input contacts (IM1, IMn) of the main paths and the output contacts (OM1, OMn) of the main paths. Actually, the alternative paths which may have their input contacts on the switching device, do not require internal configuring. However, some configuring may be provided and when the alternative paths are not used for replacing the main paths, they may serve for transmitting via the switching device some extra information which can be dropped whenever the path is required for its major purpose.

The figure shows an outgoing portion 16' of the protected path of the data stream No.l . The outgoing portions of the main and the alternate paths are respectively marked 12' and 14', and are associated with output contacts OM1 and OA1.

According to the invention, if a fault is detected on the incoming portion 12 of the main path (schematically indicated with an asterisk), the input contacts IM1 and IA1 are to be bridged by a bridging sub-block 26 (see a coupling 25 there-inside, activated by a control unit 27). As a result, the switching device 11 does not have to be re-configured.

In the drawing, the output contacts OM1 and OA1 are also bridged and it is performed in a bridging sub-unit 28, by a coupling 29. This option is designed for networks using the MSPRing protocol. Thus, the transmitting of the outgoing data stream to further elements in the communication network is provided via the alternate path 14'. The fact that the alternate path, and not the main path, is temporarily in use is important for the following NE in the path according to the MSPRing protocol.

The alternate path will be considered the working path for that particular data stream as long as the fault on the main path is not fixed. Control of the bridging is performed by the control unit 27, which reacts to faults on the incoming paths and activates couplings of the respective input and output contacts. The control unit may be either a part of the assembly 10, or be substituted by function of the Network Manager (not shown). The drawing shows only one exemplary circuit formed by the controlled bridging sub-blocks for handling a fault (such as a fiber cut) in the path 12. Faults on other incoming paths are handled similarly, by creating other couplings in the bridging block 26 (and preferably, also in the bridging block 28).

Fig. 4 illustrates an assembly 30 comprising a switching device 31 which is capable of switching component data streams of the incoming one or more protected data streams, and also performs add-drop operations. The switching device 31 is therefore an example of OADM (Optical Add-Drop Multiplexer). This drawing shows, inter alia, that a number of data streams incoming the switch may be obtained by demultiplexing an optical signal transmitted via any particular main path M (see function of DEMUX 32) For example, an SDH STM-16 optical data stream Mo can be decomposed by a DEMUX 32 into 16 x 84 component TU-11 data streams transmitted via 16 x 84 separate paths Moo, Mol ...Mon.

For switching between a faulty main path and a suitable alternative path, there is provided a bridging sub-unit 40. In this embodiment, M>m, i.e., the number of paths incoming the assembly 30 is greater than the number of paths processed by the switching device 31.

It should be noted that one alternative path can be used for serving a number of main paths. Though such an arrangement is critical from the point of fixing multiple faults, but is practical and economic. To provide a more reliable system, a number of alternative paths (Ao ... Ai) can be used all the main paths (Mo,...Mn).

In the proposed assembly 31, signals transmitted via the alternative paths such as Ao and others could also be demultiplexed. However, there is actually no need in that and it will be seen below.

Some of the component data streams, obtained from the DEMUX 32, can be dropped by DROP channels of the OADM (one channel is shown, dropping the stream Mio). The place of the dropped streams can be fulfilled by adding stream(s) via one or more ADD channels (one of them is shown and is marked as Mio').

Internal connections 33 in the switching device 30 are configured only for the main component data streams; none internal connections are prepared for alternative component data streams.

The component data streams outgoing the switch OADM from its right side are rearranged within the switching device 31 and further multiplexed by MUX 34 into outgoing data streams Mo', Mi' ...Mn'. If alternative paths are required for outgoing data streams (Ao\ An' are shown), they can be formed by switching the information from the obtained main streams by the bridging sub-unit 34. The units 40 and 42 are controlled by a control unit 36 which, like that in Fig. 3, may be part of the Network Manager system.

In a specifc example, a fault (schematically marked with the asterisk 38) is determined in the incoming main path Mo, the control unit 36 commands to bridge the incoming main path Mo and the selected for it alternative path (say, Mo and Ao by a simple input bridging sub-block 40. ) Owing to that, the switching device 31 will receive, via the input contacts assigned to the main path Mo, demultiplexed components of the data stream which was transmitted via the alternative path Ao. How the required data stream was provided on the path Ao, is not described in the frame of the present application. Simultaneously, the paths Mo' and Ao' are bridged at the output of the MUX 34, by a symmetrical simple sub-block 42. The bridging sub-blocks 40 and 42, as well as the MUX and DEMUX 32 and 34 are considered to be part of the integrated switching assembly.

Fig. 5 illustrates an example of yet another embodiment 40 of the invention - (an integrated assembly), comprising a switching assembly 41. The switching assembly 41 incorporates a bridging unit and a switching device with a demultiplexer and a multiplexer therein. Three incoming data streams A, B and C arrive to the assembly 41 via respective main paths. Eaclrof these data streams comprises component data streams, for example A comprises (al, a2, a3...). In this example, only one alternative (protecting ) path exists for protecting the incoming main paths, and is shown as P (pi, p2,...). The component data streams belonging to those received via the main paths are separated and rearranged by the switching device 41 and are outputted in the form of combined outgoing data streams (shown at the left side of the assembly 41). The combined outgoing data streams are marked A', B' and C. In other words, the function of the switching device was to rearrange, say, the incoming stream B so that stream B' is obtained. The stream of the protecting path P is outputted from the switching device as P'.

The re-arrangement in the assembly 41 can be performed due to the fact that it comprises a system (say, a switching fabric or switching network reminding a matrix) of component optical switching devices, which are not shown. The switching fabric is capable of providing demultiplexing and switching of high rate data streams being multiplexed from low rate component data streams, and also capable of further combining high rate data stream from the switched component low rate data streams.

The assembly 41 actually constitutes a complex, low order granularity switching device (fabric) capable of handling low rate data streams.

A number of internal connections in the matrix usually achieve huge values and therefore, reconfiguring of the internal connections would be a difficult task. Would the reconfiguring be required, it would have involve introducing changes in numerous software tables of connections of each and every component switching element.

As proposed according to the invention, in case of a fault such as a fiber cut shown as an asterisk on the path B, a control unit 42 of the assembly ensures switching the information transmitted via the main path to the protecting path. In this example, it is shown as switching the information transmitted via the path B before location of the fiber cut, onto the protecting path P. Simultaneously, the unit 42 initiates the bridging in the switching device 41 to switch the information, entering the device from the incoming path P, onto the input contacts assigned to the path B. In this particular example, such input contacts are illustrated as a single point where the main path B enters the device 41. The circuitry active in the described case of fault is illustrated by dotted lines.

In the presence of a fiber cut in any of the main paths A, B, C, all the outgoing data streams will be formed in the previously configured switching device 41 which will neither perceive nor undergo any changes. The outgoing data streams A', B', C will comprise there-inside appropriate components which were just transmitted via a loop formed by the protecting path P.

Preferably, the CU block 42 also initiates switching the outgoing data stream, obtained at the path B', onto the outgoing protecting path P', until the path B is fixed.

When the path P is not in use for replacing any of the main paths A,B or C, it may transmit via the device 41 an extra information ( if the device enables to do so). The extra information may be intended for a following node in the network, and is transmitted to it via the path P'. In case the path P is required for protecting one of the main paths A, B C, the extra information may be dropped, as agreed by the protocol.

However, there may be a regime where one or more of the paths A,B,C do not require any protection at all. A similar situation may be applied to any of the above Figures 2 to 4. In such a case no bridging operation is performed even if a fault occurs on the path, since the control unit or the network manager will not select a protection path for the faulty path.

While the present invention has been described with reference to the attached embodiments, it should be appreciated that other versions of the method and other implementations of the assembly can be proposed within the scope of the invention defined below.

Claims (19)

CLAIMS:

1. A method of controlling a switching device inserted in a protected line formed, in an optical communication network, from a main path and an alternative path for transmitting a high rate data stream, the method comprising: - handling, in the switching device, lower rate data streams being components of said high rate data stream fed into the switching device from the main path via one or more input contacts associated with the main path, by using internal connections configured in the switching device, - in case of a fault in the main path, feeding to the switching device the high rate data stream from the alternative path via the one or more input contacts associated with the main path, thereby preserving said internal connections without reconfiguring thereof.

2. The method according to Claim 1, further comprising steps of: - providing the switching device having pre-configured internal connections for processing there-inside m high rate data streams by handling lower rate data streams being components of said high rate data streams, - assigning k (k

3. The method according to Claim 2, wherein k

4. The method according to Claim 2, further comprising, in case of detecting a fault on the incoming portion of a main path, switching the outgoing portion of the main path to the outgoing portion of the selected alternative path.

5. The method according to any one of the preceding claims, to be used in a mesh network where one or more of the alternative paths serve a number of the main paths, and wherein one of said alternative paths forming the protected line with a presently faulty main path.

6. The method according to any one of the preceding claims, where the main path is the one currently in use among the two paths forming the protected line.

7. A switching assembly for serving high rate data streams in an optical communication network, the switching assembly comprising a switching device and a controllable bridging unit, wherein the controllable bridging unit having M input contacts or groups of contacts respectively assigned to M communication paths, each of said paths being suitable for transmitting a high rate data stream in the optical communication network; the switching device having pre-configured internal connections for processing there-inside m high rate data streams from those obtained by the controllable bridging unit via said M telecommunication paths, wherein M>m, and wherein the processing is performed by handling lower rate data streams being components of said high rate data streams; the controllable bridging unit, upon being informed that a particular path of said M paths is faulty while another one of said M paths is selected to serve an alternative path to the faulty one, is capable of controllably and respectively bridging between the input contact or group of contacts assigned to the faulty path and the input contact or group of contacts assigned to the selected alternative path; thereby connecting the switching device to the selected alternative path, while preserving the internal connections in the switching device without reconfiguring thereof.

8. The assembly according to Claim 7, wherein the bridging unit is controlled by an internal control unit.

9. The assembly according to Claims 7 or 8, designed for serving one or more of said protected lines.

10. The assembly according to any one of Claims 7 to 9, being integrated.

11. The assembly according to any one of Claims 7 to 10, wherein the controllable bridging unit is provided with one or more input contacts IM assigned to an incoming portion of the main path, one or more input contacts IA assigned to an incoming portion of the alternative path; the bridging unit being capable of bridging between the contact(s) IM and the respective contact(s) IA upon receiving a command that a fault is detected on the incoming portion of said main path and that said alternative path is selected for said main path, thereby connecting the switching device to the alternative path of said protected line, while preserving the internal connections in the switching device without reconfiguring thereof.

12. The assembly according to any one of Claims 7 to 11, wherein the controllable bridging unit is also provided with M output contacts or groups of contacts respectively assigned to M telecommunication paths, each of said paths being suitable for transmitting a high rate data stream in the optical communication network;

13. The assembly according to Claim 12, wherein said bridging unit is provided with one or more output contacts OM assigned to an outgoing portion of a particular main path, and with one or more output contacts OA assigned to an outgoing portion of the alternative path assigned to the particular main path, and wherein the bridging unit is capable of bridging the contact(s) OM and the corresponding contact(s) OA associated with the outgoing portion of the alternative path, in case of detecting the fault on the main path.

14. The assembly according to any one of Claims 7 to 13, being capable of disconnecting the bridged contacts when the faulty path is recovered, thereby returning from the alternative path to the main one.

15. The assembly according to any one of Claims 7 to 14, wherein the switching device is arranged from a number of lower order component optical switches, while the incoming said data stream, whenever being fed to the switching device, is decomposed into a plurality of component lower order data streams respectively handled by said component optical switches, and the bridging unit being adapted for switching the incoming data stream before being decomposed, by coupling the IM contacts with the I A contacts.

16. The assembly according to Claim 15, wherein the switching device is a low order granularity switching fabric capable of handling low rate data streams.

17. The assembly according to any one of Claims 7 to 16, wherein the switching device is a complex time-space switch.

18. The assembly according to any one of Claims 7 to 17, wherein the switching device is OADM (Optical Add-Drop Multiplexer).

19. The assembly according to any one of Claims 7 to 18, designed for operating in a mesh network where one or more of the alternative paths serve a number of the main paths, and wherein one of said alternative paths forms the protected line with a presently faulty main path. ECIP/F039/IL