Optical add drop multiplex (oadm)

OPTICAL INPUT-DRIVE MULTIPLEXER

Engineering

The present invention relates to a method or system for implementing a self-recovering node architecture in a fiber ring network, and more specifically to an optical feed-drop multiplexer.

Prior art

A fiber ring network is a collection of nodes forming a closed loop to which each node is connected via a duplex communication means. The SDH / SONET ring architecture uses Add Drop Multiplexers (ADM) to feed and drop local channels and to conduct forward through channels. A self-reversing ring is a ring network with extra bandwidth so that interrupted service can be automatically restored after a network failure.

Current technology, disclosed in U.S. Patent No. 5,185,736 to Tyrrel et al., Can only protect against fiber defects, but not node failure. U.S. Patent 4,704,713 to Haller et al. a method is provided for solving a knot failure but not a fiber failure. In addition, this solution is not unknown in terms of service, bit rate and code granularity due to the electro-optical conversion performed at every other node.

Wavelength division multiplexing has hitherto focused on packet switched networks as disclosed in U.S. Patent No. 4,979,879 to Habbab et al. , 4,797,879 Eda 5,208,692,

Mr McMahon. All of these solutions are for local area networks (LANs) and do not compete with SDH / SONET systems.

Upgrading the SDH / SONET is expensive. If any sub-node is modified, eg by increasing the bit rate, all other sub-nodes in the ring must also be changed. However, the introduction of a multi-wavelength network layer can increase flexibility. New transmission formats can be adopted at different wavelengths within the same fiber network, e.g., a physical ring.

When the entire traffic flow is concentrated on the same fiber, the protection requirements for the tire increase. One desirable feature of protection is simple, fast and efficient handling whenever a fault occurs.

Summary of the Invention

A first aspect of the present invention is directed to a method of configuring down nodes or a down node system against both optical node and fiber defects comprising a working ring and a spare ring, each node having monitoring points, selective optical filtering means, 2x2 optical switching means, and the method further comprising monitoring the inputs and outputs of each sub-node of the stepped and spare ring for the functional and standby ring by means of monitoring means monitoring the monitoring points, generating an alarm signal by means of monitoring means detecting loss of the signal in the lower node, positioning the down node that caused the alarm signal from the first state to one of the possible states depending on the alarm signal generated, and selecting the down node switch configuration according to the new state.

Other objects and steps of the method and system of the present invention are set forth in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its other objects and advantages will be best understood from the following detailed description and accompanying drawings, in which:

Fig. 1 is a simple block diagram of an optical self-reversing ring according to the invention; is marked Node 1 and Node 2, when folded, Figure 5 similarly shows a line change diagram for the three nodes designated Node 2, Node 3 and Node 4, Figure 6 is a flowchart showing folding a WDM self-returning ring, and Figure 7 is a flowchart showing a linebacking WDM self-returning ring.

Explanation of an illustrative embodiment

Figure 1 illustrates a self-reversing ring having two optical fiber groups 10 and 11 which connect a plurality of down nodes 21-27 into a ring structure coupled to a master node 20 (OXC) and a DXC / HUB 16, respectively. In Figure 1, each subnode is shown as an optical input drop multiplexer number n (OADMn). The input drop multiplexer OADM includes at least two monitoring points 31 and 32, two selective optical filters 33 and 34, a 2x2 optical switch 35, and two optical amplifiers 37 and 38, as shown in Figure 2. To achieve both fibers, if only one transceiver can be used with only one transmitter and receiver, eg Line TeRMinal. In addition, according to the prior art, each subnode contains its own processing unit (not shown) which manages the transmission of signals to and from the network.

Each node 21-27 can generate alarm signals Ιχ and I2, which serve as the basis for switching decisions to be made after a fiber or node fails. A portion of the signal is separated at two monitoring points 31, 32 near each node. Both the working ring 10 and the spare ring 11 are monitored by at least one such monitoring point as shown in Figure 2.

The alarm signals Ιχ and I2 are derived from the monitoring means Μχ and M2, which are simple detectors that determine whether or not a signal is present in the fiber, i.e. whether a particular part of the fiber is intact or not. When M ^ _ detects the loss of signal in the working ring 10, it generates and transmits an alarm signal I] _. Similarly, M2 generates an alarm signal I2 when the signal disappears from the spare ring 11.

The nodes may be in different states, characterized by the manner in which the optical switch is configured and the way in which the optical filter is activated, for example which inputs and and outputs are connected to each other. The four basic states of the nodes are:

SI The entire system is flawless and the traffic runs on a functioning tire.

S2 Line change and traffic have been transferred to a spare tire.

Folding after node. The fiber is broken somewhere after the node (the fiber length between this and the next node). The outgoing signals must be sent backwards, i.e. to the spare ring.

Folding before knot. The fiber is broken somewhere between the node and the previous node. The outgoing signals are transmitted in the active ring.

Under normal circumstances (there are no defects in the fibers and the nodes are working properly), the nodes send to a working ring 10. However, the fiber must have a signal for the monitoring system to know if the fiber is defective or not. Therefore, for example, a split signal or spontaneous emission amplified by optical amplifiers 38 may be used as an additional means of transmitting a signal to the spare ring 11 for monitoring purposes.

Figure 2 is a more detailed block diagram of a down node having optical filters 33, 34, a monitoring block and a 2x2 optical switch block 35 having two inputs and two outputs. The available node states control the optical switch block. The table in Fig. 3 shows a list of possible states of the node SI-S4 and corresponding optical switch configurations and monitoring signals.

According to the present invention, in the case of fiber breakage, either of the two procedures can be selected, namely

(a) folding the tire; or

(b) line change.

a) Folding

Figure 1 is a block diagram of a self-recovering ring.

Fiber Tear in Working Ring 10 for Subnode 21 (OADM] _) and Subnode 22 (OADM)₂) sometimes causes the following events:

The M 1 at node 22 (OADM 2) detects a signal loss (no signal on the working ring 10) and transmits an alarm signal I 1 to the switch which folds in front of the ring, i.e. switches the node to state S4. When node 22 is in state S4, no signal is transmitted in the spare ring at node 21, see the table in Figure 3. As a result, M2 at node 21 detects signal loss and sends an alarm to I2 at processor card 21. As a result, node 21 folds backwards, i.e. enters state S3. The other nodes do not detect any change. Figure 4 symbolically illustrates the course of events.

Conversely, if the fiber had been broken in the spare ring 11, the same events would occur in the reverse order. Furthermore, it should be noted that when there are m nodes in an optical network ring, the down node OADM_m is the same as OADMq.

In the case of a knot failure, the ring is folded in exactly the same way as in the case of fiber breakage. In both cases, M 1 or M 2 simply detects the loss of the signal, the cause of disappearance does not change the action.

(b) Line change

If line switching is selected, fiber interruption between the lower nodes 21 and 22 of the active ring 10 in FIG. In state S2, node 22 gives signal I1 to the next node 23 which also enters state S2. Similarly, in node S2, this node gives a signal Ιχ to the next node, finally moving this node to state S2, etc. A schematic representation is shown in Figure 5.

Breaking the fiber somewhere else in the tire causes the same events to occur in the same order. Fiber breakage in the spare ring 11 is detected at the node and subsequently reported to the management system. In this case, no further action is taken.

One state of a node that has not been processed is bypass operation. This becomes quite important when a node fails, when several nodes use the same wavelength. If one of them fails, the others can still transfer data. The optical signal is then simply transmitted through the node. This can be easily accomplished in the OADM optical input-drop multiplexer by setting the optical filters to steady state, see Figure 2. The dormant value (when no voltage is applied) should be a direct current for filters 33, 34 and a node status SI for the switch, see table in Figure 3.

Aside from the advantages in the event of failure, the optical feed-drop multiplexer of the present invention can also simplify adding and removing nodes in an existing optical network.

Of course, the optical input-drop multiplexer node of an optical network can be designed in many ways using components other than those shown in this illustrative embodiment without departing from the spirit, object, and circuitry of the present method and system as defined in the appended claims.

Flowcharts

Fig. 6 is a flowchart illustrating the folding of a self-recovering WDM ring. Initially, all nodes are set to state SI and remain in that state until the fault occurs. If a fault occurs at node n, the monitoring unit detects a signal loss (there is no signal in the running ring 10) and sends an alarm signal to the switch 35 of the node n.

When node n is in state S4, no signal is transmitted to the spare ring 11 at node n-1. This causes the signal loss signaling signal I2 to be activated at node n-1, which alarm signal I2 is transmitted to the n-1 processor card. As a result, node n-1 folds back, i.e. enters state S3. This is shown in the right-hand section of Figure 6. The other nodes do not detect the change.

Instead, if the fiber had been broken in the spare ring 11, it would have followed the same events, but in the reverse order shown in the left part of Figure 6. When a node fails, the ring folding is performed in exactly the same way as in the case of fiber breakage. In either case, M 1 or M 2 simply detects the loss of the signal, the reason why the signal is lost does not change the action.

If the ring has two faults in the same fiber represented by the control signals marked with an asterisk (*), then at least the node affected will be disconnected, but the rest of the network will continue to operate. Each event is preferably reported to the management system.

Finally, Fig. 7 is a flowchart illustrating a line reversal of a self-recovering WDM ring. Initially, all nodes are set to state SI and remain there until a fault occurs.

If there is a break in the working ring 10, this will result in a signal Ιχ at node n. Node n responds by activating the filter in spare ring 11, i.e., by placing the node in state S2. Node n in state S2 forwards signal I1 to the next node n + 1, which also enters state S2. This node, in state S2, also forwards the signal I] _ to the next node and so on. As a result, all nodes in the network then use the spare ring 11 instead of the working ring 10, whereby the necessary folding is to use the working ring 10 instead of the spare ring 11. If the control unit 2 detects a defect in both fibers of the tire (control unit 1 and 2), indicated by an asterisk (*), the tire will break.

The detecting node informs the management system of fiber breakage of the spare ring 11. In this case, no further action is taken.