Patent Application
20080181605
The present invention relates generally to optical networks and, more particularly, to multi-degree optical node architectures.
Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of communicating the signals over long distances with very low loss of signal strength.
In recent years, the use of telecommunication services has increased dramatically. As the demand for telecommunication services continue to grow, various topologies of optical networks are emerging. For example, ring network topologies are evolving into mesh network topologies. Ring network topologies have several inefficiencies, such as information having to travel through each intermediate node before reaching the destination node and the fallibility of the entire ring network if there are multiple failures. Mesh network topologies provide several benefits over a ring network. While the network topology can be improved, existing optical node architectures are not efficient and effective in mesh network topologies. For example, conventional optical node architectures are not scalable to support the increased connectivity of optical nodes in mesh network topologies.
In accordance with the present invention, disadvantages and problems associated with conventional optical node architectures in mesh network topologies may be reduced or eliminated.
According to one embodiment of the present invention, an optical node includes a plurality of optical input components operable to receive a plurality of signals communicated in an optical mesh network. A plurality of optical drop components coupled to the plurality of optical input components, each optical drop component operable to select a signal to drop to one or more associated client devices from any one of the plurality of optical input components. A plurality of optical output components operable to transmit a plurality of signals to be communicated in the optical mesh network, and a plurality of optical add components coupled to the plurality of optical output components and operable to transmit copies of a plurality of optical add signals to the plurality of optical output components. Each optical output component is operable to select a signal to communicate in the optical mesh network received from any one of the plurality of optical add components and the plurality of optical input components.
Technical advantages of one or more embodiments of the present invention may include multi-degree optical node architectures that are scalable in mesh network topologies. The optical node architectures support multi-degree connectivity, dynamic light path provisioning, and mesh protection and restoration. Furthermore, the multi-degree optical node architectures are less cumbersome and less complex than conventional optical node architectures in a mesh network.
It will be understood that the various embodiments of the present invention may include some, all, or none of the enumerated technical advantages. In addition, other technical advantages of the present invention may be readily apparent to one skilled in the art from the figures, description and claims included herein.
For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
As mentioned above, mesh network 10 may be operable to communicate optical signals carrying information from one node 20 to one or more other nodes 20. In particular, mesh network 10 may allow client devices (not shown) coupled to a node 20 to communicate with one or more other client devices coupled to one or more of the other nodes 20.
Mesh network 10 communicates information or “traffic” over optical fibers 12. As used herein, “traffic” means information transmitted, stored, or sorted in mesh network 10. Such traffic may comprise optical signals having at least one characteristic modulated to encode audio, video, textual, and/or any other suitable data. The data may also be real-time or non-real-time. Modulation may be based on phase shift keying (PSK), intensity modulation (IM), or other suitable methodologies. Additionally, the traffic communicated in mesh network 10 may be structured in any appropriate manner including, but not limited to, being structured in frames, packets, or an unstructured bit stream.
Traffic may be carried in a single optical signal that comprises a number of optical channels or wavelengths. The process of communicating traffic at multiple channels of a single optical signal is referred to in optics as wavelength division multiplexing (WDM). Dense wavelength division multiplexing (DWDM) refers to multiplexing a larger (denser) number of wavelengths, usually greater than forty, into a fiber. The optical signal includes different channels combined as a single signal on optical fiber 12. WDM, DWDM, or other suitable multi-channel multiplexing techniques are employed in optical network 10 to increase the aggregate bandwidth per optical fiber 12. Without WDM or DWDM, the bandwidth in network would be limited to the bit rate of only one wavelength. With more bandwidth, optical networks are capable of transmitting greater amounts of information. For example, node 20 in mesh network 10 is operable to transmit and receive disparate channels using WDM, DWDM, or other suitable multi-channel multiplexing technique.
Nodes 20 in mesh network 10 may comprise any suitable nodes operable to transmit and receive traffic in a plurality of channels. In the illustrated embodiment, each node 20 may be operable to transmit traffic directly to four other nodes 20 and receive traffic directly from the four other nodes 20. For example, as illustrated in
Nodes 20 in mesh network 10 may use any suitable route to transmit traffic to a destination node 20. As discussed above, fibers 12 may each be a single uni-directional fiber, a single bi-directional fiber, or a plurality of uni- or bi-directional fibers. For example, node 20a transmitting traffic to node 20d may transmit the traffic over fibers 12a, 12b, and 12c or, alternatively, over fibers 12a, 12d, and 12e. Many other paths are possible. Therefore, if fiber 12b fails, node 20a may continue to transmit traffic to node 20d over an alternate path. Fibers 12 may fail or break for any number of reasons, such as being cut, being tampered with, or other occurrences. Furthermore, one or more nodes or other equipment in a path may fail. Mesh network 10 addresses the possibility of failing fibers and/or equipment by allowing flexibility in transmitting traffic between nodes 20.
One challenge faced by those attempting to implement a mesh network topology rather than a ring network topology is existing optical node architectures for a mesh network topology. Particular current node architectures include photonic cross-connect architectures and multi-degree reconfigurable optical add/drop multiplexer (ROADM) architectures based on Wavelength Selective Switches (WSS). A limitation of the ROADM nodes is that these nodes can only support up to eight degrees (or eight connections with other nodes). Additionally, the ROADM nodes have only local add/drop capability for each degree. A limitation of the photonic cross-connect architecture is scalability. For example, for a photonic cross-connect node to support eight degrees, a large 640×640 switch is needed to handle the multiple degrees. For these reasons, a conventional ROADM node and a conventional photonic cross-connect node cannot fully support dynamic provisioning (directing traffic to any suitable fiber), mesh protection, and mesh restoration.
Modifications, additions, or omissions may be made to mesh network 10 without departing from the scope of the disclosure. The components and elements of mesh network 10 described may be integrated or separated according to particular needs. Moreover, the operations of mesh network 10 may be performed by more, fewer, or other components.
In the illustrated embodiment, node 20 includes splitters 22 and 26, WSSs 24 and 28, multiplexers 30, demultiplexers 32, and transponders 34 coupled to form a flexible, multi-degree node architecture. Splitters 22 and 26 represent optical couplers or any other suitable optical component operable to split an optical signal into multiple copies of the optical signal and transmit the copies to other components within node 20. In the illustrated embodiment, each splitter 22 may receive an input signal from mesh network 10 and each splitter 26 may receive an optical signal added at node 20. Splitters 22 and 26 may be configured to receive traffic over a particular fiber and split the received traffic into multiple copies. For example, splitters 22 are configured to receive traffic over input fibers 21 and to split the traffic into P copies. Splitters 26 are configured to receive traffic from associated multiplexers 30 and split the traffic into n copies. Multiplexers 30 represent any suitable optical component operable to receive and combine add traffic in disparate optical channels, transmitted by associated transponders 34 from one or more client devices, into a WDM or other optical signal for communication to splitter 26.
Splitters 26 are included on the add side of node 20 to support full connectivity for traffic being added by node 20. Having splitters 26 on the add side of node 20 supports the flexibility of transmission desired in mesh network 10. Each splitter 26 receives traffic from a multiplexer 30 and may be configured to pass a copy of the traffic to each WSS 24 over a fiber, port, or other connection. During operation, splitters 26 may pass traffic to WSSs 24 to be transmitted over another fiber 21. Therefore, traffic may continue to be added from transponders 34 even if a fiber 21 fails. For example, if traffic is previously transmitted over fiber 21a but fiber 21a fails, splitter 26a may forward traffic to be transmitted over another operable fiber, such as fiber 21c.
WSSs 24 and 28 may comprise any suitable optical components operable to receive multiple optical signals and output a portion or all of one or more of the received signals. In the illustrated embodiment, WSSs 24 receive copies of one or more add signals from splitters 26 and WSSs 28 receive copies of one or more input signals from splitters 22.
WSSs 28 are included on the drop side of node 20 to support full connectivity for traffic being dropped at node 20. Each WSS 28 may be configured to pass traffic received over a particular fiber 21 to an associated demultiplexer 32. During operation, WSSs 28 may be reconfigured to pass traffic from another fiber to the associated demultiplexers 32 (and then to associated transponders 34). Therefore, any transponder 34 may receive traffic from any input fiber, which supports the flexibility desired in mesh network 10. Demultiplexers 32 represent any demultiplexers or other optical component operable to separate the disparate channels of WDM, DWDM, or other suitable multi-channel optical signals. Demultiplexers 32 are operable to receive an optical signal carrying a plurality of multiplexed channels from WSS 28, demultiplex the disparate channels in the optical signal, and pass the disparate channels to associated transponders 34 (for communication to one or more client devices). Transponders 34 represent any suitable optical components operable to transmit and/or receive traffic on a channel. Transponders 34 communicate traffic to and from client devices.
In operation, each splitter 22 in node 20 may receive a WDM or other multi-channel input optical signal from mesh network 10. Splitter 22 splits the received input signal into several copies. A copy of the input signal is transmitted to each WSS 24 (where some or all of the channels may be passed through node 20 to mesh network 10) and transmitted to each WSS 28 (where some or all of the channels may be dropped at node 20). WSS 24 does signal (wavelength) blocking and/or filtering. For example, each WSS 24 is configured to select one or more of the signals (wavelengths) received from splitters 22 (pass-through) and/or one or more of the signals (wavelengths) received from splitters 26 (add) for communication to network 10. Each WSS 28 is configured to drop traffic received from a particular input fiber 21 to an associated demultiplexer 32. Each demultiplexer 32 receives the traffic, separates the traffic into the constituent channels, and drops each channel to its associated transponder 34. For example, splitter 22a receives traffic over input fiber 21a. Splitter 22a copies the traffic and transmits a copy to each WSS 24 and each WSS 28. In the illustrated embodiment, WSS 28a may be configured to transmit traffic received over input fiber 21a to demultiplexer 32a. In such a case, WSS 28a receives copies of each input signal, but selects the signal received over fiber 21a for transmission to demultiplexer 32a. Demultiplexer 32a transmits the traffic to transponders 34 for communication to one or more client devices.
If a fiber or equipment failure prevents the receipt of traffic over input fiber 21, the architecture of node 20 provides for mesh protection and restoration. In mesh network 10, traffic may be re-routed to node 20 of
As mentioned above, node 20 may also add traffic to mesh network 10. Transponders 34 may transmit such traffic to an associated multiplexer 30, which combines traffic in multiple channels into a WDM signal and transmits the WDM signal to the associated splitter 26 over a fiber 21. Splitter 26 creates copies of the signal and transmits a copy to each WSS 24. As mentioned above, each WSS 24 may be configured to transmit a particular received signal over a particular output fiber 21. WSS 24 forwards the selected signal to mesh network 10 over the particular fiber 21.
The architecture of node 20 may also improve the flexibility of adding signals to node 20 from client devices. If a fiber or equipment failure occurs, the architecture of node 20 allows add traffic that was previously being output via one output fiber 21 to be output from another output fiber 21, which provides for mesh protection and restoration. For example, multiplexer 30a transmits an added signal to be transmitted on fiber 21a to splitter 26a. Splitter 26a copies the added signal and provides a copy to each WSS 24. Referring to the above example, if fiber 21a fails, the traffic transmitted on fiber 21a may be rerouted to fiber 21c. Because splitter 26a provides copies of the traffic to each WSS 24, WSS 24c may be configured to output the particular add signal from splitter 26a onto fiber 21c.
Modifications, additions, or omissions may be made to node 20 illustrated in
WSSs 52, 54, 56, and 58, multiplexers 60, demultiplexers 62, and transponders 64 may function in a similar manner to splitters 22, WSSs 24, splitters 26, WSSs 28, multiplexers 30, demultiplexers 32, and transponders 34, respectively, described above in conjunction with
Optical Cross-Connect switch (OXC) 66 may be operable to forward traffic from any input fiber 21 to any output fiber 21. OXC 66 is any suitable optical device that provides for switching in the optical domain. OXC 66 in node 50 provides for dynamic reconfigurability in case of partial mesh connectivity within the node. For example, OXC 66 may remotely configure the pattern of connectivity between WSSs 52, 54, 56, and 58. In pre-existing nodes, using an OXC in high-degree nodes is difficult because the OXC would be a large size. For node 50, a smaller size OXC may be used in high-degree nodes. In the illustrated embodiment, to achieve full mesh connectivity between input and output fibers 21 and 100% add/drop, P=2n. The size of OXC 66 would be 2 nP×2 nP. To achieve partial mesh connectivity between input and output fibers 21 and 50% add/drop, P<2n, and the size of OXC 66 would be 1.5 nP×1.5 nP.
Node 50 may operate in a similar manner to node 20, described above in conjunction with
Modifications, additions, or omissions may be made to node 50. For example, node 50 may include any suitable number of WSSs 52, 54, 56, and 58 to handle the addition of degrees to node 50. As another example, WSSs 52 and 56 may be replaced with splitters. As yet another example, node 50 may include more than one OXC 66 to enable redundancy. If node 50 includes a pair of OXC 66 cards, node 50 may include a splitter or a switch coupled to each WSS that communicates traffic to/from the splitter or switch and both OXC 66 cards. For example, each output of a WSS 52 may be coupled to a splitter to forward the traffic on the fiber to each OXC 66 card. Each input of a WSS 58 may be coupled to a switch that receives traffic from each OXC 66 card, and transmits the traffic from one of the OXCs 66 to WSS 58. The components of node 50 may be integrated or separated according to particular needs. Moreover, the operations of node 50 described may be performed by more, fewer, or other components without departing from the scope of the present disclosure.
WSSs 102, 104, 106, and 108, multiplexers 110, demultiplexers 112, and transponders 114 may function in a similar manner to splitters 22, WSSs 24, splitters 26, WSSs 28, multiplexers 30, demultiplexers 32, and transponders 34, respectively, described above in conjunction with
WSSs 118 and 120 operate in a similar manner as discussed with respect to WSSs 22 and 24 as described above in conjunction with
An optical loop back between WSSs 102 and 104 provides for the above-mentioned advantages. Additionally, optical impairments, such as dispersion and polarization mode dispersion, may be reduced, which improves optical reach and performance. Another advantage of the optical loop back includes improving blocking performance of network 10, which reduces wavelength contention.
In an exemplary embodiment of operation, traffic on fiber 21n is transmitted from WSS 104n to WSS 118. WSS 118 provides the constituent channels of the traffic to regenerator 122. Regenerator 122 improves the quality of and/or modifies the traffic using any suitable technique and transmits each channel to WSS 120, which combines the constituent channels into a WDM signal. The signal travels on fiber 21n to WSS 102n. Although described with respect to input fiber 21n, traffic needing regeneration from any input fiber 21 may be sent to output fiber 21n for regeneration. After regeneration, the traffic is then sent to the appropriate output fiber 21 using WSS 102n. Furthermore, any output fiber 21 and associated WSS 102 may be involved in the regeneration. The operation as described in conjunction with
Modifications, additions, and omissions may be made to node 100. For example, any suitable optical components may replace WSSs 102 and 106, such as splitters. As another example, node 100 may operate without an OXC 116 and have a similar structure as node 20 with the addition of an optical loop back. As yet another example, WSSs 118 and 120 may be a demultiplexer and a multiplexer, respectively. The components of node 50 may be integrated or separated according to particular needs. Moreover, the operations of node 50 described may be performed by more, fewer, or other components without departing from the scope of the present disclosure.
Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.
