Flexible node architecture with full protection

Optical node (1) comprising at least one input port (PA, PC, PE) and a plurality of output ports (PB, PD, PF), at least one add unit (3B, 3D, 3F) for adding at least one signal on an output port (PB, PD, PF), a broadcasting unit (8) for broadcasting on at least two output ports (PB, PD, PF) the express traffic received on an input port (PA, PC, PE), characterized in that the broadcasting unit (8) is configured for broadcasting at least one added signal on at least two output ports (PB, PD, PF).

The present invention is related to WDM networks and more particularly to node architecture within such networks.

A conventional node architecture is shown onFIG. 1. The node1has three input ports PA, PC and PE for receiving incoming traffic from nodes A, C and E, respectively, and three output ports PB, PD and PF for forwarding to nodes B, D and F, respectively, signals corresponding to the incoming traffic modified by dropping and/or adding signals. The node comprises drop units2A,2C and2E for dropping signals received from nodes A, C and E, respectively, and add units3B,3D and3F, for adding signals to be forwarded to nodes B, D and F, respectively. Incoming signals from nodes A, C and E are supplied to the drop units2A,2C and2D, respectively, and to wavelength blockers4. Each wavelength blocker4is adapted to stop the signals to be dropped but to let go through the other signals. This would apply to data signals. In case of e.g. video-on-demand signals, each wavelength blocker could be adapted to drop and let the signal go through (“drop and continue”). The node is configured so that each non-dropped signal received from nodes A, C and E is supplied—broadcast—through wavelength blockers4to each output PB, PD and PF. Thus in case, e.g. a fibre cut occurs between node1and node B, the signal forwarded to output PB may be received by node B through output PD or PF, provided that a further connection exists downstream of node1between node B and either node D or F. This provides protection for so-called express traffic (signals which not added in node1).

In this conventional node architecture, add units3B,3D and3F, for adding optical signals to be sent to nodes B, D and F, respectively, are inserted after the wavelength blockers4. Thus each signal input by each add unit3B,3D and3F is supplied through a single one output PB, PD or PF, respectively, to a single node B, D or F, respectively.

The node further comprises a control unit (not shown) for controlling the wavelength blockers and wavelength switches according to routing instructions received from the network manager.

FIG. 2is derived from another prior art node architecture based on wavelength switches (WS). A wavelength switch may be used as a N×1 multiplexer or a 1×N demultiplexer. Details on the functioning of a wavelength switch and the prior art node architecture may be found in e.g. “The MWS 1×4: a high performance wavelength switching building block”, T. Ducellier et al., presented at ECOC 2002.

As shown onFIG. 2, an incoming traffic from node A, C or E is forwarded to a drop unit2A,2C or2E, respectively, and to each one of wavelength switches5B,5D and5F, respectively. Each wavelength switch is used as a multiplexer and receives the traffic from each node A, C and E, as well as an add signal received from an add unit3B,3D and3F, respectively. Each wavelength switch is configured to block the signals to be dropped in drop units2A,2C and2E (or “drop and continue” as indicated with respect toFIG. 1). The signal outputs by each wavelength switch5A,5C and5E to nodes B, D and F, respectively, thus comprises the express traffic received from each node A, C and E, as well as the add signal received from the respective add unit3B,3D and3F.

A drawback of each one of the two arrangements shown onFIGS. 1 and 2is that when a fibre cut occurs between node1and node B (respectively D or F), the signal added by the add unit3B (respectively3D or3F) on output PB (respectively PD or PF) is not protected and is thus lost.

Iannone et al. J. of Lightwave Technology, IEEE Service Center, Vol. 14, pp 2184-2196 (XP000631516) disclose optical cross-connect architectures based on discrete components, such as demultiplexers, space switches and star couplers.

The purpose of the invention is to provide a better protection for added traffic.

This problem is solved by an optical node comprising at least one input port and a plurality of output ports, a drop unit for dropping at least one optical signal received on an input port, an add unit for adding at least an optical signal on an output port, a broadcasting unit for broadcasting on at least two output ports the express traffic received on an input port, characterised in that the broadcasting unit is configured for broadcasting at least one added signal on at least two output ports.

According to a preferred embodiment, the node further comprises at least one drop unit for dropping an incoming signal and a corresponding wavelength blocker for blocking the signal to be dropped and to let go through the express traffic.

According to a further preferred embodiment, the node comprises wavelength switches for receiving the express traffic from each input port and the added traffic from each add unit.

Preferably, the broadcasting unit is configured for combining each express traffic with its corresponding added traffic and to broadcast each combined traffic to each wavelength switch.

Alternatively, the broadcasting unit is configured for broadcasting each express traffic to each wavelength switch and for broadcasting each added traffic to each wavelength switch.

The broadcasting unit may also be located between the wavelength switches and the output ports and be configured for connecting at least the output port of one of the wavelength switches to at least an input port of at least two other wavelength switches.

The broadcasting unit advantageously comprises optical couplers.

The invention relates to a node which comprises at least one input port for receiving incoming traffic from at least one node and a plurality of output ports for forwarding traffic to a plurality of nodes.

A first embodiment of a node architecture according to the invention is shown onFIG. 3. In this embodiment, as a matter of example, the node1comprises three input ports PA, PC and PE for receiving an incoming traffic from nodes A, C and E, respectively, and three output ports PB, PD and PF for forwarding traffic to nodes B, D and F. It further comprises drop units2A,2C and2E for dropping signals received on input ports PA, PC and PE, respectively, and add units3B,3D and3F for adding signals on output ports PB, PD and PF, respectively.

The node1further comprises wavelength blockers4A,4C and4E for blocking (or “drop and continue”) the signals to be dropped to drop units2A,2C and2E, respectively. Downstream of each wavelength blocker the signals supplied by add units3B,3D and3F are coupled to the express traffic going through wavelength blockers4A,4C and4E, respectively. Upstream of the output ports PB, PD and PF are also located wavelength switches5B,5D and5F (in this case 3×1 switches). The wavelength blockers4A,4C and4E and the wavelength switches5B,5D and5F are controlled by a control unit7according to routing instructions received from the network manager. As in the prior art, a broadcasting unit8broadcasts each express traffic received on input ports PA, PC and PE to each wavelength switch5B,5D and5F. This broadcasting unit may be comprised of a plurality of optical couplers9.

According to the invention, each signal supplied by the add units3B,3D and3F is also broadcast to each output port PB, PD and PF. This is achieved in the embodiment ofFIG. 3by combining the express traffic with the added traffic upstream of the broadcasting unit8. Thus, the broadcasting unit8does not only broadcast the express traffic, as in the prior art, but also the added traffic.

Therefore in case of a fibre cut between node1and e.g. node B, the traffic added by the add unit3B can still be received by node B, provided that a connection exists between node B and either node D or F.

A second embodiment of the invention is shown onFIG. 4. This embodiment has the same general structure as the one of the prior art embodiment shown onFIG. 2. The difference is that the traffic added by each add unit3B,3D or3F is broadcast directly to each one of the wavelength switches5B,5D and5F. This is achieved by modifying the broadcasting unit8: a first set of couplers10broadcasts each express traffic to all wavelength switches5B,5D and5F and a second set of couplers11broadcasts each added traffic to all wavelength switches5B,5D and5F.

The second embodiment of the invention is simpler than the first embodiment of the invention in that it does not require the wavelength blockers4A,4C and4E, the blocking of the dropped signals being carried out by the wavelength switches5B,5D and5F.

Although this is at present not considered to be of any advantage, it is possible when needed to combine in a node1an architecture with a wavelength blocker and an add unit as shown onFIG. 3, between one input port and one output port, and an architecture with no wavelength blocker as shown onFIG. 4, between another one input port and another one output port.

A third embodiment of the invention is shown onFIG. 5. This embodiment is similar to the one of the second embodiment except in the arrangement of the broadcasting unit8. In this embodiment, the added traffic supplied by each add unit3B,3D and3F is forwarded directly to the respective wavelength switch5B,5D and5F. The broadcasting unit8is located between the wavelength switches5B,5D and5F and the output ports PB, PD and PF and is arranged to broadcast each signal supplied by a wavelength switch, e.g.5B, to one input of each of the two other wavelength switches5D and5F.

It will be apparent to the man skilled in the art that other arrangements of wavelength blockers and/or wavelength switches, combined with an appropriately configured broadcasting unit, may be used to achieve the result of broadcasting the added traffic.

In the embodiments described with reference toFIGS. 3 to 5, the wavelength switches are of the N×1-type. Other types of wavelength switches may also be used, such as 2×N-type switches. A M×N switch may be obtained by combining M×1 and 1×N switches, as shown for example, in the case N=M=4, on FIG. 1 of the article “The MWS 1×4: A high performance wavelength switching building block”, already cited.

An embodiment of the invention with 2×3 switches is shown onFIG. 6. In this embodiment, the drop units2A,2C and2E are connected as in the previous embodiments of the invention. The express traffic received on input ports PA, PC and PE is supplied to an input port of a respective 2×3 wavelength switch12A,12C and12E. The second input port of each 2×3 wavelength switch receives the respective added traffic provided by the respective add unit3B,3D and3F. The three output ports of 2×3 wavelength switch12A are then each connected to an input port of 3×1 wavelength switches5B,5D and5F. Similarly, the output ports of 2×3 wavelength switches12C and12E are each connected to an input port of 3×1 wavelength switches5B,5D and5F.

This configuration provides the required protection of the express traffic and of the added traffic.

On all the embodiments of the invention shown onFIGS. 3 to 5, optical amplifiers are provided at the input ports and the output ports of node1. It is to be understood that these amplifiers are optional and may be omitted if there is no need to amplify the signals received or sent by the node1. On the other hand, amplifiers may be needed on add/drop splitters to recover any signal power loss.

The invention was described with a node1comprising three input ports and three output ports. The invention is of course not limited to this arrangement, but encompasses any node comprising at least one input port and a plurality of output ports. The number of input ports may be different—larger or smaller—than the number of output ports. Also, drop units need not to be present after each input port of the node1. A node with no drop unit falls within the scope of the invention. In the case a drop unit is not needed, then the corresponding wavelength blocker in the embodiment shown onFIG. 3is not necessary. Similarly, add units need not to be present for each output port of the node. A node with at least one add unit falls within the scope of the invention. Also, although it is preferable that each added traffic be broadcast to all output ports of the node, the invention encompasses a node were at least one added traffic is provided on a plurality but not all of the output ports.