Patent Grant
7170852
This application is related to patent application Ser. No. 09/232,397, entitled “A CONFIGURABLE NETWORK ROUTER,” having A. Saleh, H. M. Zadikian, J. C. Adler, Z. Baghdasarian, and V. Parsi as inventors, filed on Jan. 15, 1999. This related application is assigned to Cisco Systems, Inc., the assignee of the present invention, and is hereby incorporated by reference in its entirety.
This application is related to Patent Application Ser. No. 09/232,395, entitled “A METHOD FOR ROUTING INFORMATION OVER A NETWORK,” having Zareh Baghdasarian, Vahid Parsi, Ali Saleh, and Michael H. Zadikian as inventors, filed on Jan. 15, 1999. This related application is assigned to Cisco Systems, Inc., the assignee of the present invention, and is hereby incorporated by reference in its entirety.
1. Field of the Invention
This invention relates to the field of information networks, and more particularly relates to a protocol for configuring routes over a network for protection channel communication.
2. Description of the Related Art
Today's networks carry vast amounts of information. High bandwidth applications supported by these networks include streaming video, streaming audio, and large aggregations of voice traffic. In the future, these demands are certain to increase. To meet such demands, an increasingly popular alternative is the use of lightwave communications carried over fiber optic cables. The use of lightwave communications provides several benefits, including high bandwidth, ease of installation, and capacity for future growth.
The synchronous optical network (SONET) protocol is among those protocols employing an optical infrastructure. A similar standard to SONET is the Synchronous Digital Hierarchy (SDH) which is the optical fiber standard predominantly used in Europe. There are only minor differences between the two standards. Accordingly, hereinafter any reference to the term SONET refers to both SDH and SONET networks, unless otherwise noted. SONET is a physical transmission vehicle capable of transmission speeds in the multi-gigabit range, and is defined by a set of electrical as well as optical standards. SONET's ability to use currently-installed fiber optic cabling, coupled with the fact that SONET significantly reduces complexity and equipment functionality requirements, gives local and interexchange carriers incentive to employ SONET. Also attractive is the immediate savings in operational cost that this reduction in complexity provides. SONET thus allows the realization of a new generation of high-bandwidth services in a more economical manner than previously existed.
SONET networks have traditionally been protected from failures by using topologies that dedicate something on the order of half the network's available bandwidth for protection, such as a ring topology. Two approaches in common use today are diverse protection and self-healing rings (SHR), both of which offer relatively fast restoration times with relatively simple control logic, but do not scale well for large data networks. This is mostly due to their inefficiency in capacity allocation. Their fast restoration time, however, makes most failures transparent to the end-user, which is important in applications such as telephony and other voice communications. The existing schemes rely on 1-plus-1 and 1-for-1 topologies that carry active traffic over two separate fibers (line switched) or signals (path switched), and use a protocol (Automatic Protection Switching or APS), or hardware (diverse protection) to detect, propagate, and restore failures.
A SONET network using an SHR topology provides very fast restoration of failed links by using redundant links between the nodes of each ring. Thus, each ring actually consists of two rings, a ring supporting information transfer in a “clockwise” direction and a ring supporting information transfer in a “counter-clockwise” direction. The terms “east” and “west” are also commonly used in this regard. Each direction employs its own set of fiber optic cables, with traffic between nodes assigned a certain direction (either clockwise or counter clockwise). If a cable in one of these sub-rings is damaged, the SONET ring “heals” itself by changing the direction of information flow from the direction taken by the information transferred over the failed link to the sub-ring having information flow in the opposite direction.
The detection of such faults and the restoration of information flow thus occurs very quickly, on the order of 10 ms for detection and 50 ms for restoration for most ring implementations. The short restoration time is critical in supporting applications, such as current telephone networks, that are sensitive to quality of service (QoS) because it prevents old digital terminals and switches from generating red alarms and initiating Carrier Group Alarms (CGA). These alarms are undesirable because such alarms usually result in dropped calls, causing users down time aggravation. Restoration times that exceed 10 seconds can lead to timeouts at higher protocol layers, while those that exceed 1 minute can lead to disastrous results for the entire network. However, the price of such quickly restored information flow is the high bandwidth requirements of such systems. By maintaining completely redundant sub-rings, an SHR topology requires 100% excess bandwidth.
An alternative to the ring topology is the mesh topology. The mesh topology is similar to the point-to-point topology used in inter-networking. Each node in such a network is connected to one or more other nodes. Thus, each node is connected to the rest of the network by one or more links. In this manner, a path from a first node to a second node uses all or a portion of the capacity of the links between those two nodes.
Networks based on mesh-type restoration are inherently more capacity-efficient than ring-based designs, mainly because each network link can potentially provide protection for fiber cuts on several different links. By sharing the capacity between links, a SONET network using a mesh topology can provide redundancy for failure restoration at less than 100% of the bandwidth capacity originally required. Such networks are even more efficient when traffic transits several links. One study found that for an 11-node, 22-span network, only 51% redundant net capacity was required for 100% restorability, as reported in, “The design and simulation of an intelligent transport network with distributed control,” by T. Chujo, H. Komine, K. Miyazaki, T. Ogura, and T. Soejima, presented at the Network Operations Management Symposium, San Diego, Feb. 11–14, 1990, which is included herein by reference, in its entirety and for all purposes. The corresponding ring-based design required five rings and a total DS-3 redundancy of 330%. However, path restoration often consumes several minutes in such a topology. This is much slower than the restoration times exhibited by ring topologies and is so long that connections are often lost during the outage.
Various kinds of networking equipment can be used to support the ring and mesh topologies just described. Options include:
WDMs may be connected in back-to-back configurations to allow the connection of various wavelength routes to one another (also known as “patching” or “nailing up” connections). Provisioning paths in such architectures is done manually using a patch panel. Thus, provisioning is slow and prone to mistakes due to human error and equipment failure. In the event of a failure, restoration is performed manually in such architectures, and is again slow and error-prone. Such architectures scale poorly because additional bandwidth is added by either adding to the number of wavelengths supported (requiring the replacement of equipment at nodes, and possibly the replacement of fiber optic cables as well) or adding new fiber optic cables and supporting node equipment. Such architectures are also inherently unmanageable, due to the lack of centralized control. And while the initial capital investment tends to be relatively low (as a result of their simplicity), operating expenses for such architectures tends to be relatively high because of the costs associated with configuration, expansion, and management. Thus, a mesh topology employing back-to-back WDMs will tend to be slow to deploy and difficult to manage due to the need for manually “nailing up” paths and lack of centralization.
Another architectural element that may be used to create a mesh topology is the optical cross connect (OXC). OXCs allow provisioning using a centralized scheme to accomplish provisioning in a matter of minutes. Restoration in the event of a failure may be performed manually or may be effected using a centralized management system. However, restoration still requires on the order of minutes per wavelength route restored. As with the back-to-back WDM architecture, a mesh topology that employs OXCs scales poorly due, in part, to the large increase in size and cost such scaling entails.
An OXC can be either transparent (purely optical, in which the signals are never converted from optical signals) or opaque (in which the optical signals are converted from optical signals into electrical signals, switch, and then converted back into optical signals). Transparent optical cross connects provide little in the way manageability because the information is never made accessible to the OXC's operator. In contrast, opaque OXCs can be configured to permit access to the information being switched. However, neither type of OXC maintains information regarding the topology of the network and, in fact, OXCs possess no intrinsic network intelligence. Moreover, OXC technology is expensive, making initial investment quite high, as well as the cost of future expansion.
Alternatively, a SONET network may be configured in a ring (SHR) topology by using add/drop multiplexers (ADMs). An ADM is a SONET multiplexer that allows signals to be added into or dropped from a higher rate signal. ADMs have two bidirectional ports, commonly referred to as an east and a west port. Using ADMs, a SONET network in a SHR topology uses a collection of nodes equipped with ADMs in a physical closed loop such that each node is connected to two adjacent nodes with a duplex connection. Any loss of connection due to a single failure of a node or a connection between nodes is automatically restored. The traffic terminated at a failed node, however, is lost. Two types of SHRs are unidirectional (UPSR) and bidirectional (BLSR), as defined by the traffic flow in normal conditions. Bidirectional rings have a capacity carrying advantage over unidirectional rings because of the ability to share protection capacity among the links between nodes, as opposed to unidirectional rings, which dedicate capacity all the way around the ring.
Provisioning in such architectures is centralized and can be performed in minutes. While restoration can also be performed quickly (on the order of 50 ms, as previously noted), 100% spare bandwidth is required. For all intents and purposes, then, the user must install fiber optic cabling for two networks, one for normal traffic and one to be used in the event of a failure. Moreover, the cabling for each link should be physically diverse in order to minimize the possibility that a cause of physical damage will damage both links and cause both directions of a ring to fail. These issues detrimentally affect cost, manageability, and scalability. With regard to expansion, ADMs are stacked in an SHR in order to increase capacity. However, stacked ADMs are blocking. In other words, the switching function may not be transparent as a result of the ADMs not being available on a full-time basis (i.e., occasionally blocking). Thus, an architecture employing ADMs is best suited for small offices or other situations that do not require the relatively large amounts of bandwidth (implying the need for stacked ADMs). As noted, stacked ADMs are also difficult to manage and expensive due to the extra hardware required for 100% spare capacity.
Other combinations can also be employed. For example, WDMs can be combined with OXCs (either transparent or opaque) in order to create a network having a mesh topology. Such an architecture supports the cross-connection of wavelength routes by either manual connection or under centralized control. However, such an architecture is also difficult to expand due to the need to add WDMs/fiber optic cables and the increase in size of the OXC, and cannot restore failed links quickly enough to avoid dropping or interrupting telecommunications connections.
Another option is the use of a digital cross-connect system (DCS). A DCS is used to terminate digital signals and cross-connect them, integrating multiple functionalities such as signal adding and dropping, cross-connection capabilities, and multiplexing and demultiplexing of signals. DCS based networks enjoy an advantage over networks employing back-to-back WDMs because the use of DCS eliminates the need for additional back-to-back electrical multiplexing, thus reducing the need for labor-intensive jumpers. Operational cost savings are realized by a DCS through electronically controlling cross-connections, test access and loopbacks, and maintenance. Two types of DCSs are wideband DCSs and broadband DCSs. Wideband DCS (W-DCS) terminates full duplex OC-Ns and DS3s, has VT cross-connection capability, and provides DS1 interfaces. A broadband DCS (B-DCS) terminates full-duplex OC-N signals and provides DS3 interfaces. The B-DCS makes two-way cross connection at the DS3, STS-1, and concatenated STS-Nc levels. STS-Nc may be used, for example, in broadband services such as high definition television (HDTV), where an STS-3c cross connection may be used to cross connect the signal as a single, high-capacity channel.
Thus, as described above, communications providers have a number of different techniques available to provide network restoration in the event of a failure. The SONET ring architectures described above generally provide protection switching in less than 50 msec, provided the maximum number of nodes in the ring, or the circumference as specified in the standard is not exceeded.
The SONET provisioning for automatic protection and reconfiguration in case of failure is called APS (Automatic Protection Switching), and MSP (Multiplex Section Protection) in the SDH systems. Both APS/MSP configuration refer to the redundant systems as those that include at least one protection interface circuit and at least one working interface circuit. One such APS configuration is known as “1+1 linear APS”. In a 1+1 linear APS configuration, any data transmitted by a network element is transmitted to both the working circuit and the protect circuit connected to the network element.
When routers are configured as network elements in a SONET system configured for APS, the interface circuits connecting the routers to the working and protect circuits may be configured to be located in separate routers or the same router. Protection occurs at the SONET line level (in SDH terminology, protection occurs at the SDH section level). Protection control bytes transmitted between line terminating equipment LTEs, the end points of a SONET line, communicate APS protection information. This protection information relates to whether the protect or working circuit is currently active for transmitting working channel data. Normally, when all equipment is functioning correctly, traffic is carried by the working circuit. In APS configurations involving routers, the working interface is active and the protect interface is inactive. If the working circuit fails, an “APS switch” occurs, causing deactivation of the working circuit and activation of the protect circuit. In APS configurations involving routers, the working interface is deactivated and the protect interface is activated.
SONET architectures with redundant transmission paths require both working and protection equipment to transmit the same payloads identically to tail-end working and protection equipment. The receiving equipment chooses either the working or the protection signal as the one from which to select traffic based on switch initiation criteria. Typically, SONET architectures do not allow unprotected extra traffic to be provided. Another architecture similar to the 1+1 architecture is the 1:n architecture, which requires that any of “n” working channels be bridged to a single protection line. In each architecture that requires working and protection equipment, a working and dedicated protect path is provided whereby traffic is switched between these facilities on an as needed basis. In this approach, the protect path is unutilized and kept available for network restoration.
Although the protect path is typically unutilized and available, the SONET Specification permits the protection channel described above to be used for traffic on a preemptable basis for pre-defined architectures in what is referred to as protection channel access (PCA). However, traffic over the protection channel is dropped and not recovered until the initial cause of the failure is corrected. Thus, service providers do not utilize the protection channel due to the inherent lower availability of services to customers. What is needed is a system and method of using the protection channel for services that is more robust in the event of a working channel failure.
A method and apparatus employs mesh restoration to protect channel data, thereby maintaining network reliability while substantially increasing the traffic carrying capacity of a network. The mesh restoration increases overall capacity of a network by 30–70% with no additional cost in fiber plant or dense wave division multiplexing (DWDM) costs. More particularly, an apparatus and method is presented for a communications network that includes a protect channel transmitting protect channel data and working channel transmitting working channel data. The method includes transmitting the working channel data via the protect channel upon a disruption in the working channel, and restoring the transmitting of protect channel data, wherein the restoring includes applying a mesh restoration protocol to the communications network to restore the transmittal of the protect channel data. The restoring includes finding one or more alternate channels to transmit the protect channel data, the one or more alternate channels including connected working and protect channels.
In one embodiment, the communication network includes a plurality of interconnected nodes that transmit a disruption signal upon receiving a signal indicating the disruption, the disruption signal flooding the communication network to determine alternate routes for the protect channel data, the interconnected nodes having at least one of a working channel and a protect channel.
In another embodiment, the mesh restoration protocol includes communicating status and control messages across a physical network layer of the communication network using SONET frame overhead bytes. Another embodiment includes communicating status and control messages across out-of-band communication channels. In either embodiment, the status and control messages are communicated via either centralized or distributed intelligence.
One embodiment is directed to an apparatus disposed in a communication network having a protect channel and a working channel. The apparatus includes a node controller, a route processor coupled to the node controller, the route processor implementing a mesh restoration protocol, and a circuit coupled to the node controller and the route processor, the circuit including a logic gate for receiving signals identifying disruptions in transmissions in the protect channel and the working channel and a switch responsive to the signals identifying disruptions in transmissions in the protect channel and the working channel, the switch communicating with the route processor to implement mesh restoration of protect channel data.
In one embodiment, the circuit is coupled to at least one line card, the line card transmitting the signals identifying disruptions in transmissions in the protect channel and the working channel. The circuit further includes an input/output circuit for receiving instructions identifying criteria for applying mesh restoration to protect channel data. For example, in one embodiment the criteria are a function of the type of data being transmitted as the protect channel data, such as voice, video and internet protocol (IP) data.
The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.
The following is intended to provide a detailed description of an example of the invention and should not be taken to be limiting of the invention itself. Rather, any number of variations may fall within the scope of the invention, which is defined in the claims following the description.
Referring to
Referring to Table 1, a portion of a SONET frame, 9 rows and 270 columns, shows the organization of a SONET OC-3c (concatenated) frame, according to the BellCore STS-3c standard for SONET, which is incorporated herein by reference. The frames are transmitted row by row, from top to bottom, column byte by byte, 8000 frames/sec.
The OC-3c designation indicates that the carrier is not multiplexed, but carries data from a single source. Thus, the data stream is from a single source at 155.52 Mbps with three OC-1 streams within an OC-3c stream interleaved by column. The interleaving of streams produces a frame 270 columns wide and 9 rows deep. An OC-3c stream produces more actual user data than an OC-3 stream due to the path overhead column being included inside an SPE once instead of three times as is the case for three independent OC-1 streams. Accordingly, as shown in Table 1, 260 of the 270 columns within the frame are available for user data in OC-3c as compared to 258 columns available in OC-3. A similar protocol to OC-3c is provided for European systems in ITU G.783. Although the OC-3 standard is presented, one of ordinary skill in the art with the benefit of the disclosure herein appreciates that the embodiments herein described apply to other SONET and SDH standards.
As shown in Table 1, the first ten bytes of a SONET OC-3c frame constitute transport overhead, followed by 260 bytes of Synchronous Payload Envelope. The ten bytes of transport overhead include section overhead, line overhead and path overhead bytes. In general, certain bytes of the transport overhead only travel between each section, and are reconfigured at each section boundary. Other transport overhead bytes travel through section boundaries and are reconfigured at line boundaries. For example, an Add-Drop Multiplexer (ADM) receiving a SONET frame will interpret the line overhead bytes. These line overhead bytes will not be sent on through the network. Instead, the ADM generates new line overhead bytes for transport through the network. Unlike the line overhead and section overhead bytes, path overhead bytes are received and interpreted at the ends of a path. Accordingly, frames received by an ADM will neither remove nor reconfigure path overhead bytes.
Referring now to
Normally, in 1+1 linear APS, ADM 210 bridges all data to be transmitted to the working and protect interface circuits 214 and 216 via the fiber optic lines 205.
In system terminology, the connection between router 202 and ADM 210 is a line level connection. The connection between router 201 and router 209 is a path level connection. The connection between an ADM such as ADM 210 and any other elements in a SONET network consists of one or more line level connections.
A routing protocol running in each router, such as the higher-level routing protocols “Intermediate System to Intermediate System” (IS—IS), or “Border Gateway Protocol” (BGP), based on the Internet Protocol (IP), maintains one or more routing tables. The routing tables associate outgoing interfaces with destination network addresses. Ideally, when a network configuration changes, as it does because of an APS switch, every involved router receives immediate notification of the new configuration.
Referring now to Table 1 and
According to the SONET specification for a 1+1 linear APS or MSP system, any data transmitted to ADM 210 from ADM 212 is transmitted to working interface 214 housed in router 202 and to the protect interface 216 also housed in router 201. Likewise, ADM 212 transmits data to the remote working interface 218, and to remote protect interface 220, both housed in router 209. A SONET network implementing APS uses bytes K1 and K2 in the line overhead portion of the frame to identify the interface, either working or protect, from which an ADM is currently receiving data. Thus, for example, ADM 210 bridges all transmissions equally to two separate interfaces, working interface 214 and protect interface 216, but “listens” to only one of the two interfaces. The working and protect interfaces 214 and 216 are managed by logic running in the router containing the protect interface, such as router 201, which contains protect interface 216. The APS logic activates for transmitting only the interface currently selected for “listening” by the ADM. The non-selected interface is held in a “Protocol Down” state by the router to prevent transmission of data packets on the circuit. For example, if ADM 210 selects the working interface 214, the APS logic in router 201 commands router 202 to activate the working interface 214. Regardless of whether a protect interface or a working interface is currently selected, the protect interface 216 conducts an ongoing protocol dialog with ADM 210, using SONET bytes K1 and K2 or appropriate SDH bytes in the line overhead.
The SONET Specification permits the protection channel to be used for traffic on a preemptable basis for pre-defined architectures in what is referred to as protection channel access (PCA). Generally, however, traffic over the protection channel is dropped and not recovered.
Alternative Restoration Topologies
Mesh network topologies are an alternative approach for restoration of communications networks. Mesh networks share protection bandwidth across all facilities instead of dedicating protection bandwidth. In this manner, the protection routes change with the configuration and working state of the underlying services.
According to an embodiment, the mesh restoration topology is used in conjunction with working and protect equipment. More specifically, a protection paradigm hereinafter referred to as Mesh Protection Channel Access (MPCA) allows carriers to use SONET rings that have protect and working rings and SONET ring protection channel access without the penalty of dropping traffic when the rings preempt the protection channel. For example, a communications provider builds a mesh restoration topology connected to the PCA channels of the SONET rings. As a result, the overall capacity of a network to transmit voice, video and data increases without degradation during network failures.
Referring to
During a network failure, if a SONET ring switch occurs, such as an APS switch, the protection channel traffic is dropped on those facilities by the SONET architecture. More particularly, a network failure includes occurrences such as a fiber cut, multiple equipment failures, “chopped” channel characteristics, degradation of service, noisy channel and the like resulting in a determination by the network that a failure occurred. A failure typically results in a loss of signal (LOS) message across the network and typically causes automatic switching to occur. A network failure includes at least one of a section level, a line level or a path level failure of equipment. However, as other failures related to quality of service (QOS) also affect transmission lines and are generally related to bit error rates.
Referring to
Referring to
More specifically, the SONET network 500, according to an embodiment, uses an alternate protocol for PCA traffic to restore transmissions of traffic between node 360 and node 362 across protection rings. Thus, as shown in
According to an embodiment of the present invention, a method of using one of the restoration protocols enables a carrier to complete a SONET ring network and restore PCA transmissions. More specifically, one of the restoration protocols connects traffic switches, such as wavelength routers, digital cross-connects, optical cross-connects, IP routers, and ATM switches to connect to PCA ports on the rings and mesh restoration is enabled. In one embodiment, the PCA is restored using a mesh status and control system that is communicated in-band. In-band refers to communications carried by the physical network layer, such as a SONET frame overhead byte. However, out-of-band communication channels can also be configured to carry status and control messages between network nodes.
In one embodiment of the invention, restoration of PCA is accomplished using a distributed intelligence for end-to-end provisions. In accordance with distributed intelligence, in one embodiment, event pipelining and parallel execution of protocol processes enables a distributed routing protocol, thereby minimizing event delays. Distributed routing optionally includes a distributed database with distributed control thereover.
In another embodiment of the invention, restoration of PCA is accomplished using a centralized intelligence. For example, according to an embodiment, a topology database contains information about all network nodes, their links, and available capacity. The topology database enables data to be transmitted using a mesh protocol.
Referring now to
Block 620 provides that the working channel data be transmitted via the protect channel, as is known in the SONET specification for automatic protection switching (APS). Block 630 provides for restoring the protect channel data. In one embodiment, the method provides for a choice in whether to restore protect channel data. For example, according to the SONET specification, protect channel data is lost in accordance with bock 640. According to another embodiment of the invention, protect channel data is not lost, but is restored using a restoration protocol. Whether to implement a restoration protocol depends on a user or predetermined criteria for interpreting a disruption signal. For example, the numerous types of disruption signals may be categorized as requiring implementing a mesh restoration protocol or not requiring implementing a mesh restoration protocol for restoring the protect channel data.
The restoration of protect channel data allows for communications companies and other carriers to transmit video, voice or internet protocol data via a protect channel, thereby increasing the throughput of data of the system over a more robust traffic channel than prior SONET systems. More specifically, block 650, in one embodiment, includes finding one or more alternate channels to transmit the protect channel data, the one or more alternate channels including connected working and protect channels. The alternate channels may include a plurality of interconnected nodes, such as those found in a ring formation with at least one of a working channel and a protect channel. Thus, protect channel data may be transmitted over working channels. For example, a carrier that desires a higher throughput of data being transmitted over the protect channel may opt for a mesh restoration protocol that includes redirecting protect channel data over less-used or available working channels.
According to one embodiment, the mesh restoration protocol includes receiving a signal indicating the disruption, the disruption signal flooding the communication network to determine alternate routes for the protect channel data. The disruption signal includes communicating status and control messages in overhead bytes of packets across a physical network layer of the communication network. When using overhead bytes, the communication system alternatively uses a distributed intelligence using a distributed routing protocol.
Another embodiment communicating the status and control messages across out-of-band communication channels. Thus, for example, instead of using a SONET network layer to communicate the disruption signals, an embodiment uses non-SONET communication systems to indicate disruptions and transmit status and control messages. Such out-of-band communications channels include internet protocol (IP) channels across non-SONET rings, as well as other SONET rings.
Referring now to
At the bottom of the hierarchy is what is referred to herein as a group matrix, or a Group Ethernet Repeater in a system using Ethernet communications, and depicted in
Shelf switches 720(1)–(N) and 721(1)–(N) are the next higher level of the control hierarchy in the exemplary router, and are located on the shelf processor module (exemplified by line racks (730(1)–(N)). Each copy of shelf switches 720(1)–(N) and 721(1)–(N) interconnects six connections from the three groups in each shelf, another connection from the shelf processor, and one connection from system switch 740 (and 741). Shelf switches 720(1)–(N) and 721(1)–(N) can be implemented, for example, using an 8-port Ethernet configured to handle 10 Mbps Ethernet traffic and a single-port, dual-rate switch (e.g., 10 Mbps/100 Mbps Ethernet).
The next level of the hierarchy is the system switch, of which there are two copies in each router. These are shown as system switches 740 and 741. This fully redundant scheme prevents failures on one switch from taking down the entire control bus. In one embodiment, a system switch manages connections from the following sources:
1. High-speed connection(s) from shelf switches 720(1)–(N) and 721(1)–(N);
2. High-speed connection(s) to higher-level processors (e.g., redundant node controllers 750 and 751, and redundant route processors 760 and 761); and
3. High-speed connection(s) to matrix shelf processors 770(1)–(N) and 771(1)–(N) which, in turn, control matrix cards 780(1,1)–(1,N)), located in main matrix racks 790(1)–(N).
It will be noted that main matrix 714 includes matrix cards 780(1,1)–(1,N), and that, more generally, main matrices 714 and 718 are included matrix racks 790(1)–(N).
System switches 740 and 741 are located in a management bay. As noted, the fully redundant switches manage connections from various router elements, such as I/O and matrix bays, node controllers, and route processors. Each of node controllers 750 and 751, and route processors 760 and 761 is preferably connected to system switches 740 and 741 using 100 Mbps Ethernet connections in a configuration that creates an expandable, efficient, and fully redundant control bus.
Each of line cards 720(1,1)–(N,N) receives optical signals from other network elements via a line-side optical receiver and from a local router's system via a system-side optical receiver. Each of these receivers implements an optical-to-electrical (O/E) conversion function. Each line card transmits optical signals to other network elements using a line-side optical transmitter and to the group matrices using a system-side optical transmitter. Each of these transmitters implements an electrical-to-optical (E/O) conversion function. It will be noted that line-side refers to the side of the line card coupled to other network elements and system-side refers to the side of the line card coupled to the group matrices.
Also shown in
Circuits 701 and 702 are optionally controlled by user input to determine appropriate restoration criteria as described above with reference to
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention.
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