Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q3/00—Selecting arrangements
  • H04Q3/0016—Arrangements providing connection between exchanges
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
  • H04L69/40—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q3/00—Selecting arrangements
  • H04Q3/0016—Arrangements providing connection between exchanges
  • H04Q3/0062—Provisions for network management
  • H04Q3/0075—Fault management techniques
  • H04Q3/0079—Fault management techniques involving restoration of networks, e.g. disaster recovery, self-healing networks

Definitions

• This invention relates to telecommunications networks. More particularly, this invention relates to apparatus and methods for improving the reliability of mesh telecommunications networks. Improved reliability is achieved by providing high restorative capacity for restoring network integrity should portions of the network become inoperative.
• Networks are ubiquitous; they are the backbone of many services and conveniences.
• automated teller machines are part of banking networks that conveniently increase access to banking services.
• Many modern retail cash registers are part of a network used by retailers to track sales, set prices, and maintain inventory.
• Telephone, computer, and cable TV systems are all further examples of services made possible by telecommunication networks.
• Traffic enters a network usually at a node is transported through the network via links and other nodes until a destination is reached, and then exits the network usually at another node.
• Nodes provide the routing necessary to either input (or “add”) new traffic to the network, output (or “drop”) traffic from the network, or direct traffic from one portion of the network to another.
• Links provide traffic paths between nodes. Overseeing the operation of a network is some kind of control. Control may be centralized, where all traffic management decisions are made by a central controller, or decentralized, where individual nodes have limited traffic management capabilities. Networks vary in size and complexity. For example, a network could consist of a handful of computers connected together in a single office, or could consist of millions of telephone customers connected together across a continent.
• Network configurations also vary.
• a "mesh" network is one in which most nodes are connected to three or more other nodes.
• a symmetrical mesh network results when each node is connected to an equal number of other nodes (except at the periphery of the network) .
• An asymmetrical mesh network results when nodes are connected to a variable number of other nodes.
• a ring network is an interconnection of "rings," in which nodes and links are connected in a circular fashion.
• Links can be of various transmission media, but more commonly, are either fiber-optic cable or coaxial cable. Individual links can vary in length from a few feet to hundreds of miles. Links that are part of a larger network, such as a telephone system, are usually carried on overhead utility poles, in underground conduits, or in combinations of both.
• Nodes can range in complexity from simple switching or relay devices, as may be found in smaller networks, to entire buildings containing thousands of devices and controls, as may be found in larger networks. Nodes can be implemented electronically, mechanically, optically, or in any combination thereof.
• Nodes generally known as cross-connects, perform a variety of functions. They perform basic traffic routing such as adding traffic to, dropping traffic from, and directing traffic through the network. Nodes also provide status to a network control system. In those networks where control is centralized, nodes simply transmit status to, and execute instructions from, the control system. In those networks with decentralized control, nodes are more complex enabling them to communicate with other nodes and make traffic routing decisions. Thus, nodes serve a variety of purposes based on the type of network control and the particular needs of a given network location.
• the amount of data transported by a network can be very large. Typical data transfer rates for a fiber-optic link can range from 2.5 gigabits per second to 10 gigabits per second.
• a "bit” is a binary digit, which is the basic unit of computer data.
• a “gigabit” is a billion bits. Accordingly, any disruption in network traffic flow can be devastating. Of particular concern are telephone networks, where hundreds of thousands of individual communications could be transporting through the network simultaneously.
• network reliability that is, the continuous availability and operation of a network, is commonly a top priority of network operators.
• Network control and link integrity are two areas that can have the greatest impact on network reliability. For example, a control system malfunction is likely to affect some, if not all, of a network's performance.
• Link failures cause tremendous traffic losses (2.5 to 10 gigabits per second).
• backup control systems must be provided to maintain control should the main control system fail, and spare links should be installed to permit rerouting of traffic disrupted by link failures.
• One known mesh network that includes such reliability features is a long distance telephone network.
• a central controller monitors and controls the entire network, and several back-up systems ensure continuous operation.
• Each node communicates with the controller, sending status and receiving instructions for properly routing traffic.
• Working links connect the nodes and provide dedicated pathways for transporting traffic.
• a number of spare links which do not regularly transport traffic, are installed in particular areas to provide alternative pathways for rerouting traffic that has become disrupted by an inoperative working link.
• a link can become inoperative in a number of ways, but most often, when it is cut. This usually occurs, for example, when excavation occurs over an underground link, or when a traffic accident or severe storm damages a utility pole carrying a link.
• the nodes connected to the inoperative link immediately notify the controller.
• the controller determines whether either enough spare links, spare capacity on working links, or combinations of the two, are available to reroute the disrupted traffic. Once an alternative traffic path is determined, the controller then sends appropriate instructions to those nodes that can interconnect the identified spare links and working links to form the alternative traffic path.
• Typical recovery time from such a disruption is approximately two seconds. This recovery time was once hailed as a decade of technology; today, however, it is no longer acceptable. A two-second outage would adversely affect, for example, the transmission of computer data. In fact, an entire computer center could be adversely affected by such an outage.
• Another known network that improves upon the mesh network described above is a ring network.
• Nodes are connected in a circular fashion to form rings, and multiple rings are interconnected to form the complete network.
• Nodes are either add/drop multiplexers (ADMs) or cross-connect switches.
• An ADM adds or drops traffic from the network or simply forwards traffic to the next node.
• a cross-connect switch interconnects one ring with another. Control in this network is decentralized, enabling nodes to make limited traffic routing decisions.
• each ring operates independently of the others thus desirably reducing the possibility of a network-wide failure.
• Ring 200 includes nodes 202, 204, 206, 208, 210, and 212.
• the connections between each node are made with one working link and one spare link. If a working link becomes inoperative (e.g., is cut), the traffic transported by that link will be rerouted back around the ring through the spare links.
• a disadvantage of this ring network is that restoration is limited to substantially only one inoperative working link per ring. If, for example, two working links were cut in the same ring, traffic flow could not be restored until at least one of the links was physically repaired. (One exception is the case where one of the two inoperative working links occurs between the nodes of an interconnecting ring, as shown in FIG. 3. Traffic can be restored by including spare link 324 of ring 322 with spare links 306, 308, 310, 312, 314, and 316 of ring 302 to restore traffic disrupted by breaks 301 and 303.
• a further disadvantage of this ring network is the high percentage of links that are set aside as spare — a full 50%. Thus, half the links in the network will either sit idle, or, at best, be underutilized with nonessential or low priority activity until needed to restore disrupted traffic flow. This high percentage of underutilized link capacity is undesirable in today's environment of ever increasing demand for computing and communications power and flexibility, which accordingly increases demands on network resources and reliability.
• a mesh telecommunications network with improved reliability for transporting traffic from a source to a destination.
• the network has high restorative capacity and includes nodes for adding, dropping, and directing traffic, and links for transporting traffic between nodes.
• Each connected pair of nodes has at least three links between them; at least two, known as working links, provide dedicated traffic transport, and at least one, known as a spare link, provides selectable alternative traffic transport should a working link become inoperative.
• the network advantageously has decentralized control for reducing the likelihood of network-wide failures and for improving restoration time. Decentralized control improves restoration time by enabling nodes affected by inoperative working links to communicate directly with adjacent nodes to quickly establish alternative paths comprised of spare links.
• the allocation of spare links throughout the network is generally sufficient to provide complete restoration of typically disrupted traffic flow, while also reducing the typical amount of underutilized link capacity.
• FIGS. 1A, IB, and 1C are each a representational diagram of a network configuration
• FIG. 2 is a representational diagram of a portion of a prior art ring network
• FIG. 3 is a representational diagram of a larger portion of a prior art ring network
• FIG. 4 is a representational diagram of a link connecting two nodes
• FIG. 5 is a representational diagram of a portion of a first embodiment of the present invention
• FIGS. 6A and 6B are representational diagrams of a portion of a preferred embodiment of the present invention.
• FIG. 7 is a representational diagram of a portion of a third embodiment of the present invention.
• FIG. 8 is a representational diagram of a portion of a fourth embodiment of the present invention.
• the present invention provides a mesh telecommunications network with improved reliability.
• the network transports information, known as "traffic, " in one form or another, from a source to a destination.
• Traffic can represent, for example, computer data, voice transmissions, or video signals.
• the network includes a plurality of nodes and links. Nodes route traffic into the network, out of the network, and from one portion of the network to another. Such nodes are generally known as cross-connects. Links interconnect the nodes to provide a system of traffic paths, each link being connected to two nodes. A "mesh" network is configured such that most nodes are connected via links to three or more other nodes. Examples of mesh networks are shown in FIGS. 1A and IB.
• Traffic enters the network usually at a node, is transported via a plurality of links and other nodes to a destination, and then exits the network usually at another node.
• Traffic refers both to a single communication being transported through the network from a source to a destination, and to all communications being transported through the network from a plurality of sources to a plurality of destinations.
• Links are advantageously fiber-optic cable for transport of traffic in optical signal form. Other transmission media, such as, for example, coaxial cable for electronic signal transport, could also be used.
• Each link provides two separate paths for transporting traffic between two nodes. As shown representationally in FIG. 4, link 401 has a first path 402 for transporting traffic from a first node 404 to a second node 406, and a second path 408 for transporting traffic from second node 406 to first node 404. For simplicity, each link is shown in the drawings as a double-headed arrow.
• Links are allocated as working links and spare links. Most links are working links that provide dedicated traffic transport between the two nodes connected thereto. Spare links, which do not normally transport traffic, provide selectable alternative traffic transport for restoring traffic flow between nodes that have had one or more working links between them become inoperative. Thus, spare links, while enhancing network reliability, also constitute an underutilized network resource. Therefore, providing a sufficient number of spare links such that the network is adequately protected and yet not unduly burdened is one of the more advantageous features of the invention.
• Nodes are complex structures containing thousands of devices and controls for routing and preferably managing traffic flow. The design of such nodes, and the components used within, are well known in the art. Nodes are implemented preferably electronically, but can also be implemented, for example, optically, mechanically, or in any combination thereof. Besides performing basic traffic routing functions, nodes are also in communication with a network controller via links, providing status and other control information.
• Network control is advantageously decentralized, enabling nodes to communicate with adjacent nodes and make limited traffic routing decisions. This reduces the time needed to restore traffic flow disrupted by inoperative working links, because the nodes affected by the disruption can cooperate directly with adjacent nodes to establish alternative traffic paths, rather than having to first communicate the disruption to a controller, await instructions while the controller, which is likely handling other tasks as well, determines an alternative path, and then execute the received instructions.
• Decentralized control also reduces the likelihood of network-wide failures. By distributing traffic management functions to nodes throughout the network, problems arising in a controller, such as hardware failures or software errors, are much less likely to affect the entire network.
• Restoration of disrupted traffic flow is advantageously accomplished by connecting together a minimum number of spare links to form one or more alternative traffic paths to the nodes affected by inoperative working links.
• inoperability occurs when a link has been cut or severed, such as when excavation cuts through an underground conduit carrying a link, or when severe weather severs a link being carried on an overhead utility pole.
• An inoperative working link is sensed by the two nodes connected to that link.
• the two affected nodes then communicate the disruption to the network controller so repairs can be scheduled, and then cause the traffic from the inoperative links to be routed to spare links.
• Communication from the affected nodes to adjacent nodes is accomplished via spare links.
• the communication is detected by receivers in the spare links that cause the adjacent nodes to activate the appropriate switches to connect the spare links with other spare links to form the alternative traffic path. Programming within the nodes selects the most direct available alternative path.
• Typical recovery times from such link disruptions are desirably in the microsecond to nanosecond range, dependent, in part, on the switching technology of the nodes.
• FIG. 5 A portion of a first embodiment of a network according to the present invention is shown in FIG. 5.
• Network 500 has a plurality of nodes that are advantageously electronic, and a plurality of links that are advantageously fiber-optic, connected in a symmetrical mesh configuration. Symmetry results from each node being connected to an equal number of other nodes (except at the periphery) .
• Control of network 500 is advantageously decentralized. Each node can sense the operability of the links connected to it, and can communicate with adjacent nodes and the controller. Each connected pair of nodes has three links therebetween. Two of the links are working links and the other is a spare link. Thus, there is a spare link between every pair of connected nodes and only one-third of all links are spare links. This allocation of spare links is a 33.3% improvement in underutilized link capacity as compared to the previously known ring network.
• Alternative traffic path 520 is made up of spare links 522, 525, and 527 and node switches 524 and 529.
• Alternative traffic path 510 is formed by node 502 communicating with node 513 via spare link 512 to activate switch 514.
• Switch 514 connects spare link 512 with spare link 515.
• node 504 communicates with node 518 via spare link 517 to activate switch 519.
• Switch 519 connects spare link 517 with spare link 515, thus completing alternative traffic path 510.
• Alternative traffic path 520 is formed similarly. Node 523, after receiving communication from node 502 via spare link 522, activates switch 524 to connect spare link 522 with spare link 525. Meanwhile, node 528, after receiving communication from node 504 via spare link 527, activates switch 529 to connect spare link 527 with spare link 525, thus completing alternative traffic path 520. Traffic flow previously provided by severed working links 505 and 507 is now restored to nodes 502 and 504.
• Network 600 is a symmetrical mesh network with decentralized control of traffic flow.
• each connected pair of nodes has four links connected therebetween, three working links and one spare link.
• every pair of connected nodes has a spare link connected therebetween, and only one- fourth of all links are spare links.
• This allocation of spare links represents a 50% improvement in underutilized link capacity as compared to the previously described ring network.
• each spare link in FIGS. 6A and 6B is shown as two separate unidirectional paths, each represented by a single-headed arrow, which indicates the direction of traffic flow.
• spare links are preferably pre-connected in a standby mode as shown in FIG. 6A.
• spare link 602a is connected by switches 623 and 603 to spare links 642b and 612a, respectively.
• Spare links 642b and 612a are then connected to spare link 632b via switches 643 and 633, respectively, to form a selectable unidirectional standby alternative path between nodes 610, 630, 640, and 620.
• Such selectable standby alternative paths are formed between each group of nodes. These standby paths significantly improve restoration time by providing established alternative traffic paths for substantially immediate transport of disrupted traffic flow. Furthermore, these standby paths can be modified as needed by reconnecting the node switches to other spare links to form other alternative paths.
• a third alternative traffic path is preferably formed as follows: node 640, after receiving communication from node 620 via spare link 642a, activates switch 645 to connect spare link 642a with spare link 632a. Substantially simultaneously, node 630, after receiving communication from node 610 via spare link 612a, activates switch 635 to connect spare link 632a with spare link 612b, thus completing a third alternative traffic path between nodes 620 and 610.
• a fourth alternative traffic path is preferably formed as follows: node 650, after receiving communication from node 610 via spare link 652b, activates switch 655 to connect spare link 652b with spare link 662b. Meanwhile, node 660, after receiving communication from node 620 via spare link 622b, activates switch 665 to connect spare link 662b with spare link 622a, thus completing a fourth alternative traffic path between node 610 and 620.
• a fifth alternative traffic path is formed also substantially simultaneously as the third and fourth alternative paths preferably as follows: node 630, after receiving communication from node 610 via spare link 612a, activates switch 637 to connect the standby alternative path formed by spare links 614a, 672a, and 634b with the standby alternative path formed by spare links 682a, 684b, and 686b. Meanwhile, node 640, after receiving communication from node 620 via spare link 642a, activates switch 647 to connect the standby alternative path formed by spare links 682a, 684b, and 686b with the standby alternative path formed by spare links 644b, 692b, and 624a, thus completing a fifth alternative traffic path.
• a sixth alternative path is formed substantially simultaneously as the other alternative paths preferably as follows: node 660, after receiving communication from node 620 via spare link 622b, activates switch 667 to connect the standby alternative path formed by spare links 624b, 694b, and 664a with the standby alternative path formed by spare links 666b, 696a, and 654a. Meanwhile, node 650, after receiving communication from node 610 via spare link 652b, activates switch 657 to connect the standby alternative path formed by spare links 666b, 696a, and 654a with the standby alternative path formed by spare links 656a, 674a, and 614b, thus completing a sixth alternative traffic path.
• FIG. 7 illustrates a portion of a third embodiment of a mesh network according to the present invention.
• Network 700 is an asymmetrical network with decentralized control and a plurality of nodes, preferably implemented electronically, interconnected with a plurality of links, which are advantageously fiber-optic cable.
• Each connected pair of nodes has three links therebetween, two working links and one spare link. Spare links are again shown as bidirectional paths represented by double-headed arrows.
• restoration of traffic flow is as follows: assume a break 701 severs the links between nodes 710 and 720.
• Alternative traffic paths 731 and 753 can be formed substantially simultaneously to restore the traffic flow of working links 711 and 713 in the same manner as previously described for the embodiments shown in FIGS. 5 and 6B.
• Alternative path 731 is formed by connecting spare link 732 to spare link 734 via switch 736 at node 730.
• Spare link 734 is connected to spare link 742 via switch 744 at node 740, thus completing alternative path 731.
• alternative traffic path 753 is formed by connecting spare link 752 to spare link 756 via switch 754 at node 750.
• Spare link 756 is connected to spare link 766 via switch 762 at node 760.
• Spare link 766 is connected to spare link 774 via switch 772 at node 770.
• Spare link 774 is connected to spare link 784 via switch 782 at node 780, thus completing alternative path 731.
• FIG. 8 illustrates a portion of a fourth embodiment of a mesh network according to the present invention.
• Network 800 includes a plurality of electronically implemented nodes 802 interconnected by a plurality of fiber-optic links 804. However, instead of each link 804 transporting traffic sequentially, as in the previous embodiments, each link 804 transports a plurality of traffic in parallel. Parallel traffic transport is accomplished by transporting each plurality of traffic through the link at a unique transporting parameter. This parameter is preferably wavelength and the manner in which transport is accomplished is wavelength-division-multiplexing (WDM) , which is known in the art.
• WDM wavelength-division-multiplexing
• Wavelength multiplexers 806, located at each node, provide the necessary wavelength modulated traffic multiplexing and demultiplexing, and translation from optical signal form to electronic signal form and vice versa.
• Restorative capacity is established by setting aside at least one wavelength per direction as a spare.
• traffic can be transported at three wavelengths per direction per link.
• the percentage of "spares" can be as low as 25% of the total number of wavelengths available for transporting traffic, the same percentage of spare links as in the preferred embodiment of the present invention.
• Spare wavelengths are then available for use in selectable alternative traffic paths. Nodes still provide the connections between links for transporting disrupted traffic, and the wavelength multiplexers provide the proper routing of wavelength modulated traffic into and out of the nodes.
• standby alternative paths can also be provided by appropriately presetting the multiplexers and node switches to accommodate traffic flow at a spare wavelength. Such paths would enable disrupted traffic flow to be substantially immediately rerouted.
• spare links can also be used to reduce traffic density. For example, if a particular working link or group of working links becomes saturated, that is, traffic is being transported at the maximum rate and more traffic awaits to be transported, spare links, if available, could be used to transport the additional traffic. Such situations could occur in peak demand situations, such as, for example, in a telephone network on Mother's Day when there is typically a significant increase in the number of calls. This flexibility improves network performance and further reduces underutilized link capacity.

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• 1998
  • 1998-01-05 EP EP98902388A patent/EP0997043A2/de not_active Withdrawn
  • 1998-01-05 WO PCT/US1998/000058 patent/WO1998031159A2/en not_active Application Discontinuation
  • 1998-01-05 CA CA002276518A patent/CA2276518A1/en not_active Abandoned

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