WO2000042739A1

WO2000042739A1 - System and method of simulating a star network topology

Info

Publication number: WO2000042739A1
Application number: PCT/US1999/027066
Authority: WO
Inventors: Near Margalit
Original assignee: NEW ACCESS COMMUNICATIONS
Current assignee: NEW ACCESS COMMUNICATIONS
Priority date: 1999-01-16
Filing date: 1999-11-12
Publication date: 2000-07-20
Anticipated expiration: 2001-07-16
Also published as: AU1726300A

Abstract

A system and method of simulating a star network topology on a ring network (300) is described. Embodiments of the invention make use of a ring topology in combination with wavelength division multiplexing (WDM) to create a virtual star network with a central node (302) for connection to external destinations. Branch nodes (310A-310D) transmit on one or more signal channels to the central node (302) which analyzes the information and forwards it to the destination on the network (300) or to an external destination. Embodiments of the invention implement a recovery plan to ensure that information may be transmitted via the network in the event of a break in the transmission media. The recovery plan at least doubles the amount of bandwidth while still ensuring that information can reach its destination.

Description

SYSTEM AND METHOD OF SIMULATING A STAR NETWORK TOPOLOGY

1. FIELD OF THE INVENTION

This invention relates to a network communication systems, and more specifically to a system and method of simulating a star network topology.

2. BACKGROUND ART

A communications network consists of a number of stations that want to talk to each other, and some medium (such as a wire) over which they can talk. There are two typical configurations for networks, a star topology (the layout of the network looks like a star) and a ring topology (looks like a ring). The star configuration is good for fast communication, but uses a lot of wire. The ring configuration uses less wire but can be limited in communication. These limitations can be understood by reviewing networks and network topology.

Examples of communications networks include telecommunications systems (that can communicate voice, video, facsimile, electronic mail, etc.), cable television systems, and local area networks or other computer networks. The traffic associated with current communications systems, or networks, has increased markedly especially with the increased use of the world wide web (WWW or Internet). The communication infrastructure (e.g., the transmission media such as optical fiber, cable, wire, etc.) is reaching, or has reached, capacity as a result. While it may be possible to install new or additional transmission media to accommodate the increased load, this is costly. It would therefore be beneficial to be able to increase the volume of information that may be handled by the existing communications infrastructure. The communications infrastructure has a physical configuration that is referred to as a topology. A ring topology, for example, connects network nodes in a loop, or ring. Information is transmitted from node to node around the loop to reach the destination node. A ring topology has the advantage of minimizing the amount of transmission medium (e.g., fiber) that must be used to connect the nodes as compared. However, the amount of information that can be transmitted (the bandwidth) is limited in a ring topology.

In contrast to a ring topology, a star topology connects branch nodes to a central node in a spoke-like fashion. Information is transmitted from one branch node to another via the central node. A star topology has the advantage of having a central node that can be used to link to another communications systems. Further, a branch node that is connected to the central node can use the full bandwidth of the connection (e.g., 100 megabits) between it and the central node. That is, a branch node does not need to share any bandwidth between itself and the central node.

The star topology has the advantage of providing full bandwidth between a branch node and the central node. However, it uses a greater amount of transmission media (e.g., fiber optic cable) than a ring configuration.

Ring Bandwidth

The bandwidth limitations of a ring topology are an issue given the increasing demand for bandwidth. In a traditional ring communication system, a single communication channel is shared between the nodes connected on the ring. In an effort to increase the bandwidth of a ring configuration, two mechanisms have been developed for proportioning the network's bandwidth. These two mechanisms are time-division multiplexing (TDM) and wavelength division multiplexing (WDM). In TDM, the transmission bandwidth of the ring's single communication channel is broken up into intervals or slots of time. In a given time interval, a node is given the single channel's full bandwidth. Where there are "n" nodes, there are "1/n" time slots. Thus, each of the "n" nodes may transmit information "1/nth" of the time. Each node sends that amount of information that may be sent in its time slot. This may result in information being split up into multiple transmissions that are combined to form a complete transmission at the destination node.

Figure 1 provides an example of a ring network configuration that uses TDM. LANs 112, 114, 116 and 118 are interconnected via ring network 104 and TDMs 102. TDM 102 is a time division multiplexer such as a Synchronized Optical Network (SONET) device that is capable of transmitting a packet on ring network 104 in a given time slot. The total amount of ring network 104's bandwidth is divided into time slots such that each of LANs 112, 114, 116 and 118 share ring network 104's bandwidth. That is, each is able to use l/4th of the ring network 104's bandwidth. If a user of LAN 112 wants to communicate with a user on LAN 114, for example, the information must be sent using one or more packets sent to LAN 114 via TDM 102 during LAN 112's time slot. Uplink 106 is a node on ring network 104 that can be used to transmit and /or receive signals to /from an external communications system.

A disadvantage of TDM is that the nodes must share a fraction of the total available bandwidth of the communication system. The more nodes, the smaller the amount of time allotted to each node. Instead of dividing a network's bandwidth into time slots, WDM divides a network's bandwidth into channels, each channel is assigned a particular channel wavelength. This allows multiple signals (each at a different wavelength) to be carried on the same transmission medium. For example, multiple optical channels can be used with fiber optic cable to transmit multiple signals on the same cable. Each signal channel operates at the network's full bandwidth. Thus, a node can use the full bandwidth of the network by sending information one of these signal channels.

The channels are multiplexed at a transmitting end and transmitted to a receiving end where they are demultiplexed into individual signals. In the existing systems, the transmitting and receiving ends must be tuned to the same wavelengths to be able to communicate. That is, the transmitting and receiving ends use a device such as an add/drop multiplexer to transmit /receive a fixed signal channel.

In the case of fiber optic cable, an optical add /drop multiplexer is used at the transmitting and receiving ends to generate a fixed wavelength (e.g. using lasers) and to receive a fixed wavelength. Existing systems have as many as 16-40 signal channels. While not commercially available to date, this has been extended to as many as 100 signal channels on a single fiber.

Figure 2 provides an example of a ring network using WDM. Signal channel 216 of ring network 204 is used by LANs 206 to communicate. Signal channel 218 is used by LANs 208 to communicate. The connections via LAN 204 are fixed point-to-point connections. WDMs 226 are capable of generating and receiving a fixed wavelength via signal channel 216. WDMs 228 are capable of generating and receiving a fixed wavelength via signal channel 218. However, WDMs 226 are not capable of generating or receiving signals on signal channel 218, nor are WDMs 228 capable of generating or receiving signals on signal channel 216. Thus, it is not possible for LANs 206 and LANs 208 to communicate.

Variable add/ drop multiplexers provide a possible alternative to fixed add /drop multiplexers to allow a source or destination node to generate or receive different wavelengths. For example, a variable wavelength laser may be used on one node to generate a wavelength that can be received by a fixed wavelength receiver on another node. Thus, to communicate with a destination node, a source node tunes its wavelength laser to the destination node's wavelength to generate a signal that can be received by the destination nodes fixed wavelength receiver. Alternatively, it is possible to use a fixed wavelength laser with a variable wavelength receiver. The reliability of tunable wavelength lasers and /or receivers has not yet been proven. Further, variable add /drop multiplexers are costly.

Therefore, existing WDM approaches do not allow for dynamic, or variable, communications. Further, ring communication systems that employ WDM do not have a central uplink or node to connect to an external station or communications systems. This is primarily a result of the inability to provide a mechanism for variable connections between nodes. Thus, it would be beneficial to be able to employ a variable communication scheme such as that provided by the star topology while still being able to take advantage of the low cost, increased bandwidth of a ring topology using WDM.

SUMMARY OF THE INVENTION

A system and method of simulating a star network topology on a ring network is described. Embodiments of the invention make use of a ring topology in combination with wavelength division multiplexing (WDM). A virtual star network is created on the physical ring configuration to create a central node for connection to external destinations (e.g., another communication system or node). Each node on the network is assigned one or more signal channels. A mechanism such as an add /drop multiplexer is used to generate and receive signals via a given signal channel. Branch nodes transmit on one or more signal channels to a centralized node which analyzes the information and forwards it to the destination on the network or to an external destination.

Embodiments of the invention comprise a system having a central node that is capable of receiving and generating on each of the signal channels used by the network nodes. Upon receipt of a signal, the central node analyzes the signal to determine its destination. Where the signal is intended for a node of the network, the central node generates a signal having a wavelength of the destination node. Where the signal is intended for a destination outside the network, the central node transmits the signal to the external destination via one or more of the destination's signal channels. At each node of the network, an add /drop multiplexer is used to generate and /or receive signals on each of its assigned signal channels.

Embodiments of the invention implement a recovery plan to ensure that information may be transmitted via the network in the event of a break in the transmission media. The recovery plan at least doubles the amount of bandwidth that is available from existing recovery approaches while still ensuring that information can reach its destination. The recovery approach uses two virtual star networks that are interconnected to allow information to cross-over between the virtual star networks. Thus, when information cannot reach its destination via the virtual star network on which it resides, the information can be transferred to the other virtual star network for transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 provides an example of a ring network configuration that uses TDM.

Figure 2 provides an example of a ring network using WDM.

Figure 3A provides an example of a virtual star network according to one or more embodiments of the invention.

Figure 3B provides another illustration of the virtual star topology according to one or more embodiments of the invention.

Figure 4 provides a block overview of central node 302 according to an embodiment of the invention.

Figure 5 provides an example of external links accessible via a central node according to one or more embodiments of the invention.

Figure 6 provides a process flow for transmitting a packet using the virtual star topology according to one or more embodiments of the invention.

Figure 7 provides an example of two virtual star networks interconnected via a single central node according to one or more embodiments of the invention.

Figure 8 provides an illustration of a recovery configuration according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

A system and method of simulating a star network topology is described. In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.

Virtual Star Topology

One or more embodiments of the invention simulate a star network topology (i.e., virtual star network) using a ring network configuration.

Embodiments are described herein with reference to a optical fiber transmission medium. However, it should be apparent that the teachings herein can be adapted for use with other transmission mediums as well.

According to one or more embodiments of the invention, the virtual star network comprises at least one central node and at least one branch node. The virtual star network topology uses wavelength division multiplexing (WDM) such that multiple transmission channels (or wavelengths) may be established on a single fiber optic cable. Figure 3A provides an example of a virtual star network according to one or more embodiments of the invention. Branch nodes 304 and central node 302 are interconnected via virtual star network 340 whose transmission media (e.g., fiber optic cable) is in a physical ring configuration.

Each of branch nodes 304 is capable of generating optical signals using one or more wavelengths that are separate from the one or more wavelengths generated by the other of branch nodes 304. Therefore, the same fiber transmission media can be used to simultaneously transmit signals between branch nodes 304 and central node 302 on separate signal channels. In an embodiment of the invention, each of branch nodes 304 comprise a fixed optical add /drop multiplexer capable of generating and receiving a fixed set of optical signal for transmission on the signal channels. Alternatively, a variable optical add /drop multiplexer can be used to transmit and receive optical signals of variable wavelengths. Any of the currently available optical add /drop multiplexers may be used with embodiments of the invention.

At central node 302, the signals that are received on signal channels of transmission media 306 are demultiplexed into individual signals that may be analyzed by central node 302 to determine the destination of the signal. Alternatively, branch nodes 304 can perform the analysis and include a destination tag in the transmission to (e.g., a packet) identify the destination. If the destination is one of branch nodes 304, central node 302 forwards the signal using one or more signal channels of the destination branch node.

Central node 302 is capable of forwarding a transmission to an external destination such as another communication system (e.g., an external LAN or the Internet). In this case, central node 302 forwards the transmission via link 318 to its external destination. Similarly, central node 302 can receive external signals via link 318 that may be forwarded to branch nodes 304. Central node 302 forwards an external signal to the intended destination using one or more signal channels associated with the destination branch node.

Using WDM, each of branch nodes 304 can communicate at different wavelengths at the full bandwidth of virtual star network 340. This is in contrast to time division multiplexing (TDM) that limits "n" branch nodes to "1/nth" of the bandwidth of network (i.e., each of branch nodes 304 would be limited to 1/4 of the total transmission bandwidth). Like a traditional star topology, each of branch nodes 304 in the virtual star topology communicates with central switch 302 using the total bandwidth of virtual star network 340. Further, since each of branch nodes 304 uses a different wavelength, a signal can travel past uninvolved branch nodes (i.e., those of branch nodes 304 that are not the intended destination branch node) to the destination branch.

Figure 3B provides another illustration of virtual star network 340 according to one or more embodiments of the invention. Virtual star network 340 of Figure 3A is shown in Figure 3B as network 300 in its actual ring or loop configuration. Branch nodes 310A-310D comprise one or more fixed add/drop multiplexer capable of generating and receiving one or more signal wavelengths that are unique as to the other branch nodes 310A-310D. For example, an add/drop multiplexer model WD1515-AD1 from JDS Fitel Inc., Nepean, Ontario, Canada may be used with branch nodes 310A-310D in one or more embodiments of the invention. Other add/drop multiplexers may also be used.

Branch nodes 310A-310D may act as a link between network 340 and another communication system such as a local area network, for example, via lines 312A-312D and 314A-314D. Where, for example, network 300 is a metro-ring that connects buildings within a given geographic area, branch nodes 310A-310D link LANs within these buildings to the metro-ring. Thus, a LAN in one building can be dynamically connected to a LAN in another building using the variable connection capabilities of network 300.

When information is received via line 312 A for transmission via network 300 to another LAN, for example, branch node 310A generates a optical signal having a wavelength associated with branch node 310 A and adds the signal via line 316A onto network 300. The signal generated by branch node 310A travels, via one of branch node 310A's signal channels, at the full bandwidth of network 300, past branch nodes 316B-316D to central node 302.

Central node 302 receives the signal as well as those signals generated by branch nodes 310B-310D. The signal generated by branch node 310A is separated from the other signals and analyzed by central node 302 to determine its destination. Once central node 302 determines the destination, central node 302 forwards the signal to its destination using one or more of the destination node's signal channels. If, for example, central node 302 determines that the signal's destination is branch node 310C, central node 302 generates a signal on a signal channel (i.e., at a given wavelength) assigned to branch node 310C. The signal is transmitted via network 300 at full bandwidth past branch nodes 310A-310B to branch node 310C. If central node 302 determines that the destination is external to network 300, central node 302 uses uplink connection 318 to forward the information to its external destination.

Central Node Configuration

Central node 302 is capable of generating and receiving each of the wavelengths that may be generated /received by branch nodes 310A-310D, analyzing addresses contained in the information received from branch nodes 310A-310D and forwarding the information to its intended destination. Thus, while it is possible to use variable add /drop multiplexer technology with embodiments of the invention, there is no need for any of branch nodes 310A-310D to use variable add/drop technology.

Figure 4 provides a block diagram of central node 302 according to an embodiment of the invention. In the example of Figure 4, it is assumed that four signal channels or wavelengths may be transmitted via network 300 (e.g., one wavelength for each of branch nodes 310A-310D). Central node 302 may be configured to accommodate more or less than four signal channels. For example, central node 302 may accommodate one signal channel for each branch node. As is discussed in more detail below, more than one signal channel may be assigned to a branch node.

Demultiplexer 404 of central node 302 separates the signal wavelengths received on signal channels of network 300 into individual signals. Demultiplexer 404 may be, for example, a JDS Fitel demultiplexer model WD15016-D1. It should be apparent that other demultiplexers may also be used with embodiments of the invention. Demultiplexer 404 forwards the individual signals 406A-406D to switch 412 via ports 408A-408D, respectively. In one or more embodiments of the invention, the signals that are transmitted via network 300 represent a packet of information that contains address data.

Switch (or router) 412 is configured to analyze a packet received via one of ports 408A-408D to determine the destination of the information. Switch 412 is configured to analyze the header information, determine the destination of the packet and forward the information to a output port of switch 412. Switch 412 may be, for example, a encore switch from PMC-Sierra, Inc. located in Burnaby, British Columbia, Canada. However, it should be apparent that other switches may be used with embodiments of the invention.

Where the information is intended for a destination on network 300, switch 412 outputs the signal to multiplexer 424 via ports 418A-418B. Each of ports 418A-418D is connected to a wavelength transmitter of multiplexer 424. The wavelength transmitter that receives a signal transmits a signal at the destination's wavelength via network 300 to its destination. Multiplexer 424 multiplexes the individual signals received from switch 412 at their respective wavelengths onto network 300. Multiplexer 424 may be, for example, a multiplexer model WD15016-M1 available from JDS Fitel. It should be apparent that other multiplexers may also be used.

For example, if branch node 310A generates a packet specifying branch node 310C as its destination node, the packet is transmitted via one of branch node 310A's signal channels on network 300 to central node 302. The signal is received by demultiplexer 404 of central node 302. Referring to Figure 3 A, it is assumed for this example that ports 408A-408D and 418A-418D are associated with the signal channels of branch nodes 310A-310D of Figure 3B, respectively. Demultiplexer 404 separates out the signal received from branch node 310A and sends the packet that is represented by the signal to switch 412 via port 408A.

Switch 412 examines the packet to determine that branch node 310C is the packet's destination. Switch 412 outputs the packet on port 416C that corresponds to branch node 3 IOC. Multiplexer 424 generates a signal for transmission via network 300 that corresponds to a signal channel of branch node 310C. Like a star topology, the signals that are transmitted between branch node 310A and 310C use network 300's full bandwidth. Further, as with a star topology, the signals are passed through a central node (e.g., central node 302).

External Links

If a destination outside network 300 is specified in a packet's destination address, central node 412 forwards the packet to the external destination via external link 318. External link 318 may connect network 300 to another communications system or a node that does not reside on network 300, for example. Figure 5 provides an example of external links accessible via a central node according to one or more embodiments of the invention. Central node 702A can provide a link to the World Wide Web (WWW), or Internet, for example. A branch node that is connected to central node 702 A can communicate (e.g., upload or download) information with the Internet via link 706. For example, branch node 512 of network 500A can transmit and/or receive information from the Internet via central node 502A. Branch node 510 can be linked to central node 502A (via link 508) to communicate with a branch that is connected to central node 502B (e.g., branch node 514) as well as to the Internet.

Central node 502A is connected to central node 502B via link 504. In this case, a branch node that resides on network 500 A can communicate with a branch node that resides on network 500B. For example, branch node 512 of network 500A can transmit a packet using one or more of its signal channels to central node 502A which determines that the packet is destined for branch node 514 of network 500B. Central node 502A forwards the packet to central node 502B via link 504. Central node 502B transmits the packet via one of branch node 514's signal channels to branch node 514. As will be illustrated in more detail below with reference to Figure 7, branch nodes that reside on separate virtual star networks (e.g., branch nodes 512 and 514) may use the same signal channels.

Information Transmission

In the virtual star topology, transmission of information from one branch node on the network to another branch node is performed using the central node according to one or more embodiments of the invention. The information that is to be transmitted is contained in a packet that further contains addressing information. Examples of protocols that may be used to generate packets are Asynchronous Transfer Mode (ATM) or Internet Protocol (IP). The header and addressing information is determined according to specific protocol used. Further, a branch node may specify a destination address as a tag thereby eliminating the need for the central node to determine the destination. In this case, the addressing information is contained within the tag.

Figure 6 provides a process flow for transmitting a packet using the virtual star topology according to one or more embodiments of the invention. Figure 6 assumes that the central node identifies the destination (i.e., the source node does not provide a destination tag).

When the central node (e.g., central node 302) is initiated, central node 302 is programmed or in some way learns which header addresses are associated with which branch nodes. For example, central node 302 can retrieve a lookup table that associates header addresses with their respective branch nodes. Similarly, branch node 302 is aware of the input/output ports (e.g., ports 408A-408D and 418A-418D, respectively).

At step 602, a branch node (e.g., branch node 310A) transmits a packet using one or more of its signal channels. At step 604, central node 302 separates the branch node 310A's signal into an individual signal. It is possible for branch node 310A to be assigned more than one wavelength. In this case, branch node 310A may send the packet using more than one signal channel. This increases the amount of bandwidth that is available to a branch node. If, for example, branch node 310 uses two signal channels to send the information, the amount of bandwidth that is available to branch node 310 is doubled.

At step 606, the central node analyzes the packet's addressing information. At step 608, a determination is made as to whether the destination is on the network. If not, processing continues at step 614 to forward the packet to its destination via the external link (e.g., external link 318). If the destination is on the network, central node 302 transmits the packet using one or more of the signal channels (or wavelengths) associated with the destination branch node. In either case, processing of a packet ends at step 612.

Multiple Virtual Star Networks

Multiple virtual star networks can be connected via one or more central nodes. Figure 5 provided one example of two interconnected virtual star networks using two separate central nodes. Figure 7 provides an example of two virtual star networks interconnected via a single central node according to one or more embodiments of the invention.

Central node 702 comprises two instances of central node 302. One instance of central node 302 handles the traffic transmitted on network 700A while the other handles the traffic that is transmitted on network 700B.

Central node 702 comprises two of switch 412 (e.g., switches 732A and 732B), demultiplexer 404 and multiplexer 424. As previously described, demultiplexer 404 and multiplexer 424 are connected to switches 732A and 732B via at least one port (e.g., ports 408A-408D and 418A-418D). Link 704 links the instances of switches 732A and 732B. Switches 732A and 732B use different instances of demultiplexer 404 and multiplexer 424 that are connected to separate networks (i.e., networks 700 A and 700B). Therefore, it is possible to use the same signal channels for two nodes where each node resides on a different network (i.e., where one node resides on network 700A while the other resides on network 700B).

A packet that originates on network 700A by branch node 710B, for example, is transmitted to central node 702 on network 700A using at least one of branch node 710B's signal channels. All of the signals received by central node 702 from network 700 A are demultiplexed into individual signals, or packets. The packet generated by branch node 710B is forwarded to switch 732 A. Switch 732A analyzes the packet's header information to determine packet's destination. The packet sent by branch node 710B is intended for branch node 760B of network 700B, for example. Switch 732A forwards the packet to switch 732B via link 704.

Switch 732B forwards the packet to the instance of multiplexer 424 associated with switch 732B. Switch 732B's multiplexer 424 generates one or more signals that represent the packet using one or more of branch node 760B's signal channels. The signals that are generated by switch 732B's multiplexer 424 are transmitted via network 700B to branch node 760B.

Since switch 732A's multiplexer 424 generates signals for transmission on network 700A and switch 732B's multiplexer 424 generates signals for transmission on network 700B, the branch node 760B's signal channels may be the same as branch node 710B.

Recovery

In a traditional fiber optic ring network, two rings are used to achieve redundancy for recovery purposes. Both fiber optic cables are usually installed in the same conduit. Thus, there is a strong likelihood that a cut in one fiber optic cable will result in a cut in the other cable. To limit the amount of down time due to a break in the fiber cables, a technique is used whereby the same packet is sent on both rings. One packet is sent in the clockwise direction on one ring while the same packet is sent in the counterclockwise direction on the other ring. If a break occurs, one of the packets will avoid the break. If, for example, the packet is intended for a node that is positioned at the six o'clock position on the rings and the break occurs at the two o'clock position, the packet that is transmitted in the clockwise direction is unable to reach the node. However, the packet that is transmitted in the counterclockwise direction is able to reach the node.

Thus, in the traditional recovery approach, use of both rings to transmit a single packet provides an approach to ensure that information is able to get through despite a break. The disadvantage of this approach is that only half of the bandwidth of the two rings is available even when there is no break, since both rings are used to send the same information.

Embodiments of the invention implement a recovery plan that does not require the transmission of redundant information. This allows both rings to be used to double the amount of bandwidth that is available for transmission when there is no break, and ensures that information can reach its destination when a break occurs.

Figure 8 illustrates a recovery configuration according to an embodiment of the invention. Branch nodes 810A-810B are connected to ring 800A via lines 816A-816B as well as being connected to ring 800B via lines 820A-820B. Central node 802A is located on ring 800A and central node 802B is located on ring 800B. Link 828 exists between central nodes 802 A and 802B.

Packets are sent on ring 800A in the counterclockwise direction while packets on ring 800B are sent in the clockwise direction. Branch nodes 810A and 810B can communicate via either or both of rings 800A and 800B. For example, branch node 810A sends a packet via line 820A on ring 800B. Central node 802B receives the packet and determines that it is destined for branch node 810B. Absent break 830, central node 802B may forward the packet to branch node 810B via either of rings 800A or 800B.

When break 830 occurs, a packet destined for branch node 810B sent by central node 802B via network 800B cannot reach branch node 810B. However, central node 802B can send the packet to central node 802A which forwards the packet to branch node 810B via ring 800A and line 816B.

Thus, a system and method of simulating a star network topology has been described in conjunction with one or more specific embodiments. The invention is defined by the claims and their full scope of equivalents.

Claims

CLAIMSWhat is claimed is:

1. A system comprising:

a transmission medium comprising a plurality of signal channels; a first node coupled to said transmission medium, said first node configured to transmit and receive a signal via one or more of said plurality of signal channels of said transmission medium; a second node configured to receive said signal via one or more of said plurality of signal channels and transmit said signal via another one or more of said plurality of signal channels to a destination node.

2. The system of claim 1 wherein said transmission medium is configured as a ring network.

3. The system of claim 1 wherein said first node and destination node comprise at least one add/drop multiplexer.

4. The system of claim 1 wherein said second node is configured to receive and transmit signals using said plurality of signal channels of said transmission.

5. The system of claim 1 wherein said second node comprises:

a demultiplexer capable of retrieving said signal via said plurality of signal channels of said transmission medium;

a switch coupled to said demultiplexer, said switch capable of determining a destination of said signal; a multiplexer coupled to said switch, said multiplexer capable of transmitting said signal via said plurality of signal channels of said transmission medium.

6. The system of claim 1 wherein said second node is configured to transmit to and receive from a node external to said network.

7. The system of claim 1 further comprising:

a second transmission medium comprising a second plurality of signal channels; a third node coupled to said second node and said second transmission medium, said third node configured to receive said signal via one or more of said second plurality of signal channels and transmit said signal via another one or more of said second plurality of signal channels to a destination node.

8. The system of claim 7 wherein said second plurality of signal channels transmit signals in an opposite direction from said plurality of signal channels.

9. The system of claim 7 wherein said first node and said destination are capable of transmitting and receiving via said plurality of signal channels and said second plurality of signal channels.

10. A method of simulating a star network topology comprising:

transmitting a signal from a source along at least one signal channel of a ring network; receiving said signal on said at least one signal channel at a central node; determining a destination of said signal at said central node; transmitting said signal to said destination.

11. The method of claim 10 wherein said source and destination comprise at least one add /drop multiplexer.

12. The method of claim 10 wherein said central node comprises:

a demultiplexer configured to receive from a plurality of signal channels capable of being transmitted along said ring network; a switch configured to determine said destination; a multiplexer configured to transmit along a plurality of signal channels of said ring network.

13. The method of claim 10 wherein said transmitting said signal to said destination further comprises:

transmitting said signal along said destination's at least one signal channel of said ring network.

14. The method of claim 13 further comprising:

receiving said signal at said destination.

15. The method of claim 14 wherein said transmitting and receiving said signal at said destination use at least one add /drop multiplexer.

16. The method of claim 10 further comprising:

coupling a second ring network to said ring network, said ring network comprising a first plurality of signal channels and said second ring network comprising a second plurality of signal channels.

17. The method of claim 16 wherein said transmitting a signal from a source and transmitting a signal to said destination use one or more of said first plurality of signal channels and said second plurality of signal channels.

18. The method of claim 16 wherein said step of coupling comprises:

coupling a second central node to said second ring network and said central node.

19. The method of claim 16 wherein said first plurality of signal channels transmit a first plurality of signals in an opposite direction of a second plurality of signals transmitted via said second plurality of signal channels.

20. The method of claim 10 wherein said transmitting said signal to said destination further comprises:

determining whether said destination is a node of said ring network; transmitting said signal to said destination along said ring network, if said destination is a node of said ring network; transmitting said signal via an external link to said destination, if said destination is not a node of said ring network.