WO2002007348A1 - Anneau de protection partagee a optique hybride - Google Patents

Anneau de protection partagee a optique hybride Download PDF

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Publication number
WO2002007348A1
WO2002007348A1 PCT/US2001/022298 US0122298W WO0207348A1 WO 2002007348 A1 WO2002007348 A1 WO 2002007348A1 US 0122298 W US0122298 W US 0122298W WO 0207348 A1 WO0207348 A1 WO 0207348A1
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WO
WIPO (PCT)
Prior art keywords
incoming
otsn
protection
fiber
channel
Prior art date
Application number
PCT/US2001/022298
Other languages
English (en)
Inventor
Ming-Jun Li
Mark J Soulliere
Original Assignee
Corning Incorporated
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Corning Incorporated filed Critical Corning Incorporated
Priority to AU2001276929A priority Critical patent/AU2001276929A1/en
Publication of WO2002007348A1 publication Critical patent/WO2002007348A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0283—WDM ring architectures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0201—Add-and-drop multiplexing
    • H04J14/0202—Arrangements therefor
    • H04J14/021—Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
    • H04J14/0212—Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM] using optical switches or wavelength selective switches [WSS]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0287—Protection in WDM systems
    • H04J14/0293—Optical channel protection
    • H04J14/0295—Shared protection at the optical channel (1:1, n:m)

Definitions

  • the present invention generally relates to optical communication systems, and more particularly to a wavelength add drop multiplexer that enables a hybrid optical shared protection ring to operate outside of conventional SONET and SDH protection schemes.
  • Ring topologies have arisen to provide a number of networking elements with the ability to both listen and transmit on optical channels within the optical ring.
  • consecutive nodes are connected by point-to-point links which are arranged to form a single closed path or ring.
  • Information is transmitted from node to node around the ring, and the interface at each node is an active device that has the ability to create and accept messages.
  • the interface is part of a wavelength add drop multiplexer (WADM) that routes signals to and from the client network elements.
  • WADM wavelength add drop multiplexer
  • the WADM not only provides the client network elements a user attachment point, but also enables the node to function as an active repeater for re-transmitting messages that are addressed to other nodes.
  • rings must be physically arranged so that the nodes provide communication between the desired client network elements. If fact, certain client network elements may desire communication with one another while others may not. Optical signals therefore typically carry numerous channels to provide users with the desired communication links. Furthermore, the number of fibers being used to transfer the signals from node to node drastically effects the capacity of the ring and the structure of the WADM. For example, rings having a four-fiber architecture typically will transport working traffic on two of the fibers, and protection traffic on the other two fibers. The working traffic fibers will carry traffic in opposing directions, as will the protection traffic fibers. While this type of four-fiber architecture is acceptable for long distance networks, it is desirable to reduce the number of fibers required for "metro" networks. Such a reduction would ultimately provide more efficient bandwidth usage.
  • Synchronous Digital Hierarchy (SDH) network protection architectures These standards provide signaling protocols for various types of single channel optical networks but fail to address the WADM with any specificity. This is crucial since, as already discussed, the WADM is coupled to one or more single channel client network elements and provides access to the ring.
  • SDH Synchronous Digital Hierarchy
  • OTSn optical transmission section signal of n channels
  • multi-channel failures occur when either a fiber cut or a cable cut causes a loss in more than one optical channel of the OTSn.
  • Conventional SONET and SDH approaches have involved the construction of the ring such that protection capacity is switched in to restore working traffic. This is commonly termed "shared protection" because the same wavelengths are used for different client links.
  • a single channel failure typically occurs as a result of a WADM switching matrix failure or a client network element transmitter/receiver failure.
  • the present invention is a wavelength add drop multiplexer having a 4X4 switching matrix configuration, and is capable of supporting a 2-fiber ring architecture.
  • a first 4X4 switching matrix is optically coupled to a first incoming fiber carrying a first incoming optical transmission section signal of n channels (OTSn) and a second incoming fiber carrying a second incoming OTSn.
  • the first 4X4 switching matrix routes a working channel of the first incoming OTSn and a protection channel of the second incoming OTSn based on a desired switching configuration.
  • the multiplexer further includes a second 4X4 switching matrix optically coupled to the first incoming fiber and the second incoming fiber.
  • the second 4X4 switching matrix routes a protection channel of the first incoming OTSn and a working channel of the second incoming OTSn based on the desired switching configuration.
  • the wavelength add drop multiplexer supports multiple pairs of 4Xx4 switching matrices to provide protection for multiple optical channels.
  • the wavelength add drop multiplexer also has a control system for establishing the switching configuration of the switching matrices. Routing working traffic and protection traffic from a single fiber to a pair of 4X4 switching matrices ultimately allows for simultaneous protection from multi-channel failures and single channel failures.
  • an optical shared protection ring for interconnecting client network elements.
  • the ring includes a plurality of wavelength add drop multiplexers optically coupled to the client network elements, and a two-fiber architecture optically coupled to the wavelength add drop multiplexers.
  • the two-fiber architecture transports a set of working channels and protection channels of a first OTSn between the wavelength add drop multiplexers in a first direction.
  • the two-fiber architecture further transports a set of working channels and protection channels of a second OTSn between the wavelength add drop multiplexers in a second direction.
  • the result is a hybrid optical shared protection ring that provides simultaneous protection from. multi-channel failures and single channel failures regardless of whether or not the transported signals are SONET/SDH based.
  • FIG. 1 is a schematic illustration of an optical shared protection ring implementing the presently preferred wavelength add drop multiplexer in accordance with the principles of the present invention
  • FIG. 2 is a diagram of a wavelength add drop multiplexer in accordance with the principles of the present invention
  • FIG. 3 is a diagram of a wavelength add drop multiplexer configured for one hundred percent add drop connectivity in accordance with the principles of the present invention.
  • FIG. 4 is a diagram of a wavelength add drop multiplexer configured as a through node in accordance with the principles of the present invention
  • FIG. 5 is a diagram of a wavelength add drop multiplexer showing n channels in accordance with the principles of the present invention
  • FIG. 6 is a block diagram showing the 4X4 nature of the wavelength add drop multiplexer switch matrices in accordance with the principles of the present invention
  • FIG. 7 is a schematic illustration of an optical shared protection ring with a single fiber failure switching in accordance with the principles of the present invention
  • FIG. 8 is a diagram of Node B shown in FIG. 7;
  • FIG. 9 is a block diagram of a switch matrix controller in accordance with the principles of the present invention.
  • FIG. 10 is an illustration of a node signaling system for the failure and repair of a single fiber failure as shown in FIG. 7 in accordance with the principles of the present invention;
  • FIG. 11 is a schematic illustration of an optical shared protection ring with a cable failure undergoing adjacent node (or end-node) switching in accordance with the principles of the present invention
  • FIG. 12 is a diagram of Node B shown in FIG. 11;
  • FIG. 13 is a diagram of Node D shown in FIG. 11;
  • FIG. 14 is a schematic illustration of an optical shared protection ring with a cable failure undergoing non-adjacent node (or end-node) switching in accordance with the principles of the present invention
  • FIG. 15 is a diagram of Node B shown in FIG. 14;
  • FIG. 16 is a diagram of Node D shown in FIG. 14;
  • FIG. 17 is a diagram of a wavelength add drop multiplexer with a switch matrix failure wherein the multiplexer is configured for one hundred percent add drop capability
  • FIG. 18 is a diagram of a wavelength add drop multiplexer with a switch matrix failure wherein the multiplexer is configured as a through node in accordance with the principles of the present invention
  • FIG. 19 is a diagram of a wavelength add drop multiplexer with a client network element transmitter failure wherein the multiplexer is configured in accordance with the principles of the present invention
  • FIG. 20 is a diagram of a wavelength add drop multiplexer with a client network element receiver failure wherein the multiplexer is configured in accordance with the principles of the present invention
  • FIG. 21 is a diagram of a wavelength add drop multiplexer connected to provide three distinct levels of protection
  • FIG. 22 is a diagram of a wavelength add drop multiplexer connected to a SONET bidirectional line switched ring client network element
  • FIG. 23 is a schematic illustration of a first alternative optical shared protection ring with a fiber cut wherein the multiplexer is configured in accordance with the principles of the present invention
  • FIG. 24 is a diagram of Node B shown in FIG. 23;
  • FIG. 25 is a schematic illustration of a second alternative optical shared protection ring with a cable cut wherein the multiplexer is configured in accordance ⁇ with the principles of the present invention
  • FIG. 26 is a diagram of Node B shown in FIG. 25;
  • FIG. 27 is a diagram of a pair of wavelength add drop multiplexers configured to interconnect two rings in accordance with the principles of the present invention.
  • FIG. 28 is a diagram of the wavelength add drop multiplexers shown in FIG. 27 wherein the multiplexers are configured for one hundred percent interconnection capability;
  • FIG. 29 is a diagram of the wavelength add drop multiplexers shown in FIG. 27 wherein the multiplexers are configured to separate traffic traveling on the two rings; and
  • FIG. 30 is a diagram of the wavelength add drop multiplexers shown in FIG. 28 wherein a working link cable cut has occurred.
  • a hybrid optical shared protection ring in accordance with the present invention is shown generally at 40. It can be seen that the ring 40 interconnects client network elements 50, 52, 54, 56, and provides protection from all single points of failure.
  • Node A includes client network element (NE) 50, client NE 56 and wavelength add drop multiplexer (WADM) 60.
  • Node B includes client NE 52, client NE 54 and WADM 62.
  • the ring 40 is configured to provide a first communication link between client NE 54 and client NE 56.
  • a second communication link exists between client NE 50 and client NE 52.
  • the ring 40 has a plurality of WADMs 60, 62, 64, 66 optically coupled to the client network elements.
  • the ring 40 also has a two-fiber architecture 42 optically coupled to the WADMs 60, 62, 64, 66.
  • the two-fiber architecture 42 transports a working channel and a protection channel of a first optical transmission section signal of n channels (OTSn) between the WADMs in a first direction (shown as counter- clockwise).
  • OTSn optical transmission section signal of n channels
  • the traffic traveling in the first direction is carried on fiber 1.
  • the two- fiber architecture 42 further transports a working channel and a protection channel of a second OTSn between the WADMs in a second direction (shown as clockwise).
  • the traffic traveling in the second direction is carried on fiber 2.
  • the OTSn signals traveling on either fiber can transport up to n optical channels on n different wavelengths. Half of these wavelengths (n/2, presuming that n is even) are reserved for working traffic, and the other half are reserved for protection traffic. While many wavelength assignment schemes are available, the preferred scheme is selected such that the wavelengths of working traffic traveling clockwise around the ring 40 must be disjoint from the wavelengths of the working traffic traveling counterclockwise around the ring 40. Thus, any working wavelength ⁇ j traveling counterclockwise on fiber 1 has,
  • Any protection wavelength ⁇ k also traveling counterclockwise on fiber 1 has,
  • protection traffic is simultaneously on wavelength ⁇ k between client NE 50 and client NE 52. As already discussed, both the working and protection traffic travel from Node A to Node B on the same fiber. Similarly, the return traffic from client NE 52 to client NE 50 has a working optical channel on wavelength ⁇ k and a protection optical channel on wavelength ⁇ j .
  • An optical channel arriving from port 72 may either travel through towards port 74, or drop, have its optical channel overhead terminated, and have its constituent client signal travel towards a client NE.
  • a two-fiber WADM with one hundred percent add drop capability one could have up to 2n separate pairs of client signals.
  • the WADM 70 further includes a control system 90 for establishing the switching configuration of the matrices 71, 73.
  • the switch matrices 71, 73 are in fact 4X4.
  • FIG. 3 a WADM 62 configured for one hundred percent add drop capability is shown under normal (i.e. failure free) conditions. It is important to note that for a multichannel OTSn signal carrying n optical channels, there can be as many as n/24X4 matrices 71 and also n/2 more 4X4 matrices 73. For simplicity, only two are shown in FIG. 3. The illustrated multiplexer corresponds to Node B from FIG. 1.
  • the control system 90 has configured the WADM 62 to function as part of an add drop node.
  • Node B has one hundred percent add drop capability at an optical channel using wavelength ⁇ j eastbound and ⁇ k westbound, hi other words, the first 4X4 switching matrix 71 drops the working channel of the first incoming OTSn to a working output and drops the protection channel of the second incoming OTSn to a protection output.
  • the first 4X4 switching matrix 71 is optically coupled to a first outgoing fiber 77 and a second outgoing fiber 78.
  • the first 4X4 switching matrix 71 adds a protection input to the first outgoing fiber 77 and adds a working input to the second outgoing fiber 78.
  • the first outgoing fiber 77 carries a protection channel of a first outgoing OTSn
  • the second outgoing fiber 78 carries a working channel of a second outgoing OTSn.
  • the second 4X4 switching matrix 73 drops the protection channel of the first incoming OTSn to a protection output and drops the working channel of the second incoming OTSn to a working output. It will be appreciated that the second 4X4 switching matrix 73 is further optically coupled to the first outgoing fiber 77 and the second outgoing fiber 78. Under normal conditions, the second 4X4 switching matrix 73 adds a working input to the first outgoing fiber 77 and adds a protection input to the second outgoing fiber 78. The result is that the first outgoing fiber 77 carries a working channel of a first outgoing OTSn and the second outgoing fiber 78 carries a protection channel of a second outgoing OTSn.
  • Node B may have just one add drop (fifty percent), or no add drops (a through node). In other words, the add drop configuration of any WADM node may differ from wavelength to wavelength.
  • FIG. 3 the signals chosen by the client network elements are circled.
  • the protection add drop traffic from client NEs 52 and 54 are placed onto the protection capacity of the WADM 62.
  • the client NE 52 and client NE 54 protection traffic is "extra traffic" ⁇ namely, traffic that gets transported, but is discontinued when the optical shared protection ring performs self- healing. This implies a ranking of failures for those times when simultaneous failures exist.
  • a multi-channel failure requiring a ring switch will take precedence over a single channel failure requiring the use of the extra traffic connection. This makes sense, because protecting a multi-channel failure heals more traffic than protecting one (or even several) single channel failures.
  • WADM 62 places the working add signal from client NE 52 onto protection capacity traveling away from the failure, namely through Nodes C and D to Node A. WADM 60 performs a similar action, such that the interrupted traffic is restored. This rearrangement occurs for each set of optical channels at other wavelengths that were interrupted by the fiber failure.
  • Working traffic not affected by the fiber failure e.g. client NE 56 to client NE 54 is not interrupted). The protection copies of the traffic that existed as extra traffic, however, have been disconnected.
  • Node B detects a failure of the incoming multichannel signal (termed an Optical Multiplex Section signal within ITU-T Recommendation G.872).
  • Node B disconnects its extra traffic, and sends a "signal fail - ring switching" request to Node A on both the long and short paths around the ring.
  • Node C receives a switch request message from Node B. Since neither the source nor destination addresses in the message match Node C, it knows that it is an "intermediate node.”
  • Node C (1) disconnects its extra traffic, (2) configures its protection wavelengths to be through channels, and (3) bidirectionally passes through all received switch request messages.
  • Node B's request then continues to Node D, which takes the same intermediate node actions.
  • Node A is not aware that there is a problem. After receiving a switch request message from Node B, it disconnects its extra traffic, performs a headend switch, and sends a switch request back to Node B. When Node B receives this request, it connects its affected add signals to outgoing protection capacity (head end switch), and connects its affected drop signals to incoming protection capacity (tail end switch). The state of Node B at that point is shown in Figure 8. After receiving the head and tail end switched indication from Node B, Node A performs a tail-end switch. The signal between client NEs 50 and 52 is thus restored.
  • head end switch outgoing protection capacity
  • tail end switch tail end switch
  • the ring does not immediately revert back to its normal state, but waits for a preset "wait-to-restore" time. This prevents the ring from reconfiguring during a repair period where valid-looking signals may briefly appear at the nodes adjacent to the failure.
  • the wait-to-restore time expires, and the ring switches are taken down in an order that prevents misconnected traffic.
  • the extra traffic needs to be restored as well.
  • an explicit message allowing extra traffic to return may be necessary. Such a message is presumed at time T4.
  • timers are set after receiving "No Request" messages from adjacent nodes, and extra traffic is reconnected after the timers expire.
  • the switch matrix control system 90 uses its internal ring algorithm to send out switch commands to the various matrices.
  • FIG. 11 demonstrates the adjacent node switching scenario. It can be seen that the cable cut causes failures of both fibers 1 and 2 at a location not adjacent to either of the add drop nodes. This example also presumes that WADM 66 and WADM 64 (i.e. the nodes adjacent to the cable cut) perform a loop back switch, similar to what is done in SONET and SDH based shared protection rings.
  • the cable cut affects the working optical channel traveling between client NE 54 and client NE 56.
  • the self-healing occurs by looping the affected working optical channels away from the failure onto the protection capacity, and eventually placing those optical channels back onto working capacity.
  • the optical channel from client NE 54 to client NE 56 takes a routing of Node B to Node C, back to Node B, then Node A, Node D, then back to Node A.
  • Nodes not adjacent to the failure, such as Nodes A and B must therefore through- connect their protection capacity. All connections designated as extra traffic are therefore disconnected.
  • FIG. 12 demonstrates that the protection copy of traffic between client NE 50 and client NE 52 is disconnected (though the working traffic remains).
  • the adjacent nodes take all the optical channels originally destined for the working OTSn towards the failure and place them on the protection OTSn away from the failure.
  • the switching action for Node D in FIG. 11 is shown in FIG. 13.
  • FIG. 14 Another response to a cable cut can be non-adjacent node (or end-node) switching as shown in FIG. 14.
  • the cable cut between Nodes C and D has interrupted both the working and protection versions of the traffic between client NE 54 and client NE 56.
  • adjacent node switching FIG. 11
  • a "head-end” and "tail-end” switch with WADM 60 and WADM 62 simplifies the routing, as shown in FIG. 14.
  • the switch matrix configuration for WADM 62 is shown in FIG. 15. It will be appreciated that non- adjacent node switching disconnects extra traffic.
  • FIG. 16 demonstrates that through nodes (even those adjacent to the failure), are not obliged to do any loop back switching.
  • a switch matrix failure in Node B causes electrical protection switching within client NEs 50 and 56.
  • a switch matrix failure occurring in a through node causes electrical protection switching within client NE 56, but no optical switching (for an optical multiplex section shared protection ring).
  • a multichannel failure could simultaneously invoke optical shared protection along with client level electrical protection switching. To prevent this competition, the electrical protection switching could delay its response to allow time for optical protection switching to occur.
  • FIG. 19 shows WADM 62 for a transmitter failure in client NE 52. It will be appreciated that this also causes a single channel failure that a conventional optical shared protection ring would not heal.
  • a second level of protection can be provided by transporting signals as work traffic with only optical shared protection.
  • This type of connection is provided to client NE 120 and protects against multi-channel failures such as fiber cuts, cable cuts, and optical multiplexer/de-multiplexer failures.
  • a third level of protection can be provided by transporting signals as extra traffic with no protection.
  • Such a connection is provided to client NE 130. Such a connection may be desirable for SONET or SDH based clients.
  • FIG. 22 a fourth level of protection is shown for client NE 140, such as a SONET 2-fiber bi-directional line switched ring node.
  • client NE 140 such as a SONET 2-fiber bi-directional line switched ring node.
  • the client NE 140 will therefore provide its own protection.
  • the WADM 100 would need to suspend any reconfigurations of the working traffic connections during a failure.
  • This capability is analogous to the non-pre- emptable unprotected traffic (NUT) feature of SONET BLSRs.
  • NUT non-pre- emptable unprotected traffic
  • a disadvantage of this configuration is that a failure of an optical switch matrix leads to isolation of the client NE 140.
  • FIG. 23 shows a first alternative approach to healing a fiber cut. It can be seen that the hybrid optical shared protection ring 40' retains the working optical channel on the other fiber that was not affected (i.e., the traffic from client NE 50 to client NE 52). This traffic is restored the long way around the ring, but the working traffic from client NE 52 back to client NE 50 is retained. A close up of WADM 62 is shown in FIG. 24.
  • This approach means that WADM 60 would not have to perform a tail-end switch. In fact, it is simpler for both nodes to perform head-end and tail-end switches, as in the preferred embodiment, regardless of whether the failure is unidirectional or bi-directional. There may also be operational benefits to having both the "go" and "retum” services travel over matching facilities regardless of whether conditions are normal or failed.
  • FIG. 25 shows a second alternative embodiment of the present invention as ring 40". Comparing this approach with the embodiment shown in FIG. 7, it can be seen that the working "go" and “return” channels are on the same wavelength ( ⁇ j ), instead of on different wavelengths. Similarly, the protection go and return channels are both on a wavelength ( ⁇ j ) different from the working wavelength.
  • a close up of WADM 62 is shown in FIG. 26. Specifically, a fiber cut on port 1 of Node B results in the protection add drops of client NE 52 being connected onto the protection capacity of port 2. This is to be contrasted with the preferred embodiment wherein the same fiber cut results in the working add drops of client NE 52 to be connected on to the protection capacity of port 2.
  • the WADM in FIG. 26 would sometimes drop protection add drop connections (e.g. to client NE 54) while keeping other protection add drop connections (e.g. to client NE 52).
  • the WADM 62, and hence the optical shared ring 40 would not operate as a conventional optical shared protection ring whereby extra traffic is disconnected during failures. This can be viewed as a disadvantage as compared to the preferred embodiment.
  • a second distinction with respect to the second alternative embodiment is that client NE 52 must also throw its electrical switch. This could potentially add to the service restoration time.
  • the WADM 62 would have to convert the add drop wavelength ⁇ j to ⁇ k in order to use the ring protection capacity.
  • FIG. 27 shows the interconnection of two fiber rings.
  • the interconnecting WADMs use 4X4 switch matrices.
  • the client NEs are replaced by the interconnecting node of ring 2, and vice versa.
  • the working and protection link cables are preferably deployed through different routes to avoid being cut at the same time.
  • FIG. 28 shows the connections inside the switch matrices 152, 154, 162, 164 for the case where traffic traveling on the two rings is interconnected.
  • FIG. 29 shows the connections inside the switch matrices 152, 154, 162, 164 for the case where the traffic traveling on the two rings is separated.
  • FIG. 28 shows the connections inside the switch matrices 152, 154, 162, 164 for the case where the traffic traveling on the two rings is separated.

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Small-Scale Networks (AREA)
  • Optical Communication System (AREA)

Abstract

L'invention concerne un multiplexeur WADM (wavelength add drop multiplexer) qui possède une configuration de matrice de commutation 4X4 unique et capable de supporter une architecture en anneau à 2 fibres. Une première matrice de commutation 4X4 est couplée optiquement à une première fibre entrante portant un premier signal de transport optique entrant de n canaux (OTSn) et une seconde fibre entrante portant un second signal de n canaux (OTSn). La première matrice de commutation 4X4 achemine un canal de fonctionnement des premiers OTSn entrants et un canal de protection des seconds OTSn, à partir de la configuration de commutation désirée. Le WADM comprend également une seconde matrice de commutation 4X4 couplée optiquement à la première fibre entrante et à la seconde fibre entrante. La seconde matrice de commutation 4X4 achemine un canal de protection des premiers OTSn entrants et un canal de fonctionnement des seconds OTSn entrants à partir de la configuration de commutation désirée. Le WADM possède également un système de commande permettant d'établir la configuration de commutation des matrices. Le trafic de fonctionnement d'acheminement et le trafic de protection à partir d'une fibre unique vers une paire de matrices de commutation 4X4 permet d'obtenir finalement une protection simultanée provenant de défaillances multi-canaux et aussi de défaillances de canal unique.
PCT/US2001/022298 2000-07-17 2001-07-16 Anneau de protection partagee a optique hybride WO2002007348A1 (fr)

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Publication number Priority date Publication date Assignee Title
DE10308306A1 (de) * 2003-02-26 2004-10-28 Siemens Ag Verfahren und Anordnung zur Übertragung von Working-Signalen und Protection-Signalen über optische Datennetze
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US10996983B1 (en) 2006-05-01 2021-05-04 Open Invention Network Llc Job scheduler for remote maintenance of servers and workstations

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