SE507415C2 - Wavelength multiplexed optical network with name node - Google Patents

Abstract

The invention relates to a wavelength routed optical communication network in a hubbed configuration. The network comprises a hub node (H) and a number of satellite nodes (A, B, C...) connected to two optical fibre means (F1, F2) in an optical ring architecture. Each satellite node works in an individual wavelength channel. The satellite nodes (A, B, C...) are connected to the fibres (F1, F2) by passive multiplexers and demultiplexers (4' to 7') and all kinds of switching in the network is provided in the hub means (H).

Description

roads from the name node with only one optical fiber cable comprising two fibers, so that if a fiber break occurs in one direction, the traffic can be redirected to the other direction.

Thus, in the event of a cable error, the name node may receive the incoming signals from certain satellite nodes from one direction and transmit the outgoing signals in the same direction as the incoming signals.

Description of the Related Art An optical ring network is described in an article "Novel Optically Restorable WDM Ring Network", by B. Glance, C. Doerr, IP Karninow, R. Montagne, AT & Bell Laboratories, Crawford Hill Laboratory, Holmdel, New Jersey 0773. 3, Published in OFC '96 Technical Digest. In this network, each satellite node is provided with a switching system for transmitting and receiving signals on the network.

Purposes of the invention. Summary An object of the invention is to provide a method and an apparatus for establishing an optical telecommunication network comprising a name node and a plurality of satellite nodes, which network has a simple and inexpensive structure.

Another object of the invention is to provide a method and apparatus for connecting many satellite nodes and a name node in an optical, logical control network connected in a ring and with so few critical components, i.e. prone to errors, as possible.

Another object of the invention is to provide a method and apparatus for performing a transmitting and receiving traffic between the name node and each of the other nodes, even if a cable fault has occurred in an optical network. 10 20 25 50 7 4 1 5 3 Yet another object of the invention is that cable failure may be a double, single fiber break or damage to a fiber or both fibers, where still some of the light flows through the damaged part, and still use the same wavelength set for both upstream and downstream communications. Yet another object of the invention is to provide a method and apparatus for maintaining a traffic in an optical telecommunication network comprising a name node and a number of satellite nodes, even when a component of the network has been damaged. Yet another object of the invention is to provide a method and apparatus for an optical telecommunication network which normally has a network interruption only at the name node. At least some of these objects are achieved with a network having the characterizing features of claim 1. Further features and improvements of the invention are provided in the dependent claims.

According to the invention, satellite nodes are connected to the transmitters by passive multiplexers and demultiplexers, for example including transducer couplers. All kinds of switching in the network are achieved in the hub unit.

Advantages of the design When using two fibers for network communication, the theoretical minimum number of wavelength channels could be used, i.e. only one wavelength channel per satellite mode connected to the network.

No optical switches are used in the bearing, they are arranged only in the name node.

The satellite nodes can then have an extremely simple design without requiring any intelligence.

(J \ lO l5 20 25 507 415 The cable protection can be handled by the name node. At least one spare name node for support function could be installed at any time without any modifications to the already installed hardware. objects and advantages thereof are now made with reference to the following description made in conjunction with the accompanying drawings, in which Fig. 1 schematically shows a first embodiment of a communication network according to the invention; Figs. 2A-2E schematically show different propagations of the traffic for different kinds fault in the network, and fi g. 3 schematically shows a second embodiment of a communication network according to the invention.

Detailed description of embodiments As shown in fi g. 1, the physical communication network comprises a central node, called name node H, and a number of satellite nodes A, B, C ... All the nodes are connected by means of a twin ring, with the fibers F1 and FZ, with oppositely propagating traffic on the two fibers.

The fibers are preferably single modes. Logically, the network is a star node because each satellite node has a unique, fixed wavelength channel, on which it transmits and receives. Each satellite node is capable of communicating directly only with the name node H.

Thus, tracks between two satellite nodes, such as A and B, must always go via the name node H. The name node transmits and receives on each wavelength channel belonging to each satellite node A, B, C ... connected to the network. Thus, each fi ber has a number of N wavelength channels in a network with a number of N satellite nodes. The channels in the name node can then via the electrical interfaces on its transmitter Tx 'and receiver Rx' in a per se known manner also be connected to other communication networks either of the same design as those described here or with another per se known other shaping.

According to the invention, each satellite node A, B, C ... is connected to the fibers by passive multiplexers and demultiplexers to avoid coupling components.

Coupling elements need to be controlled individually and are consequently prone to faults.

As illustrated in station D in Fig. 1, each satellite period comprises an access point 1 with a transmitter and a receiver (not shown), two 1-to-2 fiber couplers 2 and 3, two passive multiplexers 4 and 5 and two passive demultiplexers 6 and 7. .

The function of the fiber coupler 3 is to distribute the transmitter signal from the transmitter at the access point 1 to the two multiplexers 4 and 5. The function of the carrier coupler 2 is to merge the received signals from the two demultiplexer series 6 and 7 to the receiver at the access point 1. The transmitted and received the signals are within the same wavelength channel for each station.

The multiplexers 4 and 5 connect the transmitter signal to the bus fibers F1 and FZ.

The demultiplexers drain the desired wavelength channel for the satellite mode in question from the bus fibers to the receiver in the workstation 1.

As can be seen from station C, which illustrates the satellite node design in a simplified form, the multiplexers may comprise simple fiber couplers 4 'and 5'. The demultiplexers can be replaced with fiber couplers 6 'and 7' and a bandpass filter 8 adapted to the wavelength channel of the station in question.

The name node device (H) is provided with an interrupt for the fibers F1 and F2 and the transmitting and receiving devices 9, 10, 13 and 11, 12, 14 connected to each end of the fibers F1 and F2. Therefore, the name node H includes a light emitter Tx ', such as a wavelength stabilized, modulated laser, and an optical receiver per satellite node connected to the network. Each fiber has an interrupted connection in the name node. A demultiplexer 10 and a multiplexer ll are connected to each end of fi bern F1.

In the same way but on opposite sides, a demultiplexer 9 and a multiplexer 12 are connected to fi bern F2.

An individual switching unit 13 comprising a P1N diode and a Z-to-Z optical coordinate selector switch is connected to each light transmitter Tx 'and the two multiplexers 9 and 10. The "1" direction of the 2-to-2 coordinate selectors on the receiver side is that choose which of the two demultiplexers 9 or 10 the receiver in question should listen to, ie from which fi its associated satellite node signal should be given.The selector unit could of course be replaced by another selector device with the same function, but a coordinate selector structure with PIN the diode provides a cheap application.

One of the demultiplexers, 9 in fi g. 1, is the one that is in operation when there is no ñber interruption in the leg. The P1N diode automatically listens to the second demultiplexer 10 on the same wavelength channel and provides a switch to provide signal information from the demultiplexer 10 when there is an incoming signal information only on the demultiplexer 10. Thus, the two demultiplexers are connected in the coordinate selector. the selector units 13, hereinafter also called the switches, so that a certain selector and thereby a certain receiver / PIN diode pair always listens on the same wavelength channel regardless of the position of the selector.

The satellite nodes always send transmitter signals on both fi brema F1 and FZ but in different directions, as shown by fi g. l. The satellite receivers are connected to listen in both directions, although the same channel will never come simultaneously on the two fibers F1 and P2.

LI: 10 15 20 25 507 415 In each channel in the name node, an optical 1-to-2 distance switch 14 is connected between the transmitter, indicated only by the reference Tx ', and the two multiplexers 11 and 12 for transmitting either on ñbem Fl or on ñbem F2.

Transmitter / receiver pairs in the name node work on the same wavelength channel and thereby handle the bidirectional communication with a certain satellite node so that it always transmits to and listens from the same direction. In other words, if the receiver switch 13 for a particular channel changes from a first position, hereinafter referred to as left, to a second, hereinafter referred to as right, the transmitter switch 14 for the same wavelength channel shall do the same. Thus, each transmitter switch unit 14 is controlled by the position of the corresponding receiver switch 13.

If a fi ber error occurs, for example at 15, on at least one of fi brema F1 and / or FZ, the nominal node will lose the incoming signals from at least some channels either on the receivers or on the PIN diodes. The name node will then work to reconstruct the transmitter and receiver switches in accordance with the following two rules. l) Change the positions of the switches for the channels that have been lost on the receivers. 2) If channels have been lost on the PIN diodes, change the positions of all the switches except those that have been lost.

The rules above assume that all switches have the same position, for example on the left. The name node can, of course, mix left- and right-hand communication, even if the network is in order. However, the simple rules of protection described above cannot be used in that case.

With reference to ñg. 2A, if there is no cable fault for any of the channels in the ring architecture, the name node H will only transmit through its left multiplexer 11 by having all the transmitter switches set to the left. All the receiver switches 13 are in the forwarding position, so that all communications start from 10 and enter the name node H on its left side. Each satellite node is normally designed to receive and transmit only on an individual channel. However, there is nothing to prevent having multi-channel satellite nodes communicating with the name node. Each satellite mode will receive a channel from the name node and transmit the same (or other) wavelength channels in both directions through its multiplexers 4 and 5 (4 'and 5'). The signal propagation of the different channels for the satellite nodes A, B, C ... has been illustrated with common node references but in small letters. Only those signals multiplexed on the clockwise propagating bus fi bern will reach the real receiver in the name node, while those multiplexed on the other fi bern will reach the corresponding, monitoring PlN diode in the name node switch unit 13.

On the counterclockwise propagating bus bear, "unnecessary channel signing" will accumulate. However, these are different from the useful one by wavelength filtering in the bandpass filter 8 in the satellite nodes.

Also, the same information from the same satellite nodes could be obtained twice in the propagation direction ring on ema brema F1 and FZ, when it reaches the name node on its right side. However, this will not cause any problems, as the name node is adjusted to receive only irrigation migrants coming from the left side.

Own. 2B illustrates that a double cable interruption has occurred between the satellite nodes C and D. In this case, the name node H loses the incoming channels of the satellite nodes A, B and C. The effect of the name node is to change the receiver switches for these channels from throughput to cross-connect state, and the transmitter switches of the same channels from the left to the right position.

Full communication is restored, which according to ñg. 2B means that the name node communicates with the nodes E and D on the left incoming and outgoing buses fi b-rem as before and with the satellite nodes A, B and C on the right bus fi brema, Ut 10 15 20 25 507 415 9 as illustrated by the node references in small letters. (Even without a cable break, this could of course be a normal way of operating the network.) In the event of a simple ñber break on ber bern clockwise between satellite nodes C and D, the name node loses the incoming channels a, b and c. The effect of the name node will be the same as for the double cable break, as illustrated in fi g. ZC.

In the event of a simple fi interruption on fi bem counterclockwise between satellite nodes C and D, the name node will not lose any incoming traffic channels, as shown in fi g. 2D which shows the state of the network just when the error has occurred.

However, it will lose the channels d and e of the PlN diodes in the receiver switch devices 13, which monitor fi bem with counterclockwise propagation. It will therefore change all the switches except those that have not been lost on the PlN diodes. The effect will be the same as in tig. 2B, i.e. changing the receiver switches 13 for channels a, b and c from switch-through to cross-switching mode and the transmitter switches 14 of the same channels stra from the left to the right position. The channel signal propagation after this switching is shown in ñg. 2E.

Since all traffic passes through the name node H, this is a very sensitive part of the network. Therefore, according to a second form of utterance shown in ñg. 3 where the elements in fi g. 1 with the same function has been given the same reference numerals, a spare name node SH be located anywhere along the bus fi leg and is shown inserted between the satellite nodes D and E. This tea service name node SH is illustrated as a simple type of node node with the same kind of connection to the two F1 and FZ as the satellite nodes A, B, C ..., ie fi the berk chain should not be broken by the spare name node SH, only by the name node H.

As in the ordinary name node H, the spare name node SH has as many transmitters and receivers as there are satellite transmitter receivers (normally equal to the number of satellite nodes) connected to the bearing. However, it has only one multiplexer 17 and one demultiplexer 18, each of which is connected to both fibers F1 and FZ by fiber couplers 4 "and 5" in the same manner as for each satellite node. In the normal case, when the ordinary name node H is functional, the transmitters Tx "in the spare name node SH are switched off. The spare node node is then completely transparent and does not affect the traffic passing on the network, except for certain power losses caused by fi berkopplama 4", 5 " , 6 "and 7" _ Optical amplifiers could of course be installed anywhere in the network (not shown).

The backup name node SH is activated as soon as an error on the name node H occurs. Once activated, the signals from the transmitters Tx "are transmitted in both directions through the opp carrier switches 4" and 5 ". The receivers Rx" listen simultaneously on both bus numbers F1 and F2. If no other error in the network has occurred at the same time as the error of the name node H, which should be rare, all satellite modes have full communication with the reference name node SH. The signals from the satellite nodes arrive at the reserve node SH either from the left or from the right. All signals from the spare name SH are transmitted in both directions. Some of those transmitted to the right are received by the satellite modes, and the rest are received from the signals transmitted to the left. The signals are prevented from circulating completely around the bearing due to the design of the ordinary name node H, which has a fiber break.

If a fi interrupt occurs when the backup node SH is in working order, then it can communicate with all the satellite nodes except those located between the interrupt and the regular name node H. Although it is stated above that each satellite mode uses the same wavelength channel for both its transmitted and received traffic, it is within the scope of the invention to have separate wavelength channels for both, without the need to change the network. It is then possible to change the network so that only one fi ber for both the transmitted and the received traffic is used. However, the use of the same fiber for both downstream and upstream traffic means that realized optical amplifiers need to operate in both directions. This is quite cumbersome, and therefore an application of this kind will only be used on very rare occasions.

Although the invention has been described with reference to particular embodiments, it is to be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit of the invention as defined in the appended claims. In addition, modifications may be made without departing from the teachings of the invention as defined in the claims.

Claims (14)

th 10 15 20 30 507 415 17 a .. Patent claim A wavelength-mounted optical communication network in a name node configuration, comprising a name node device (H) and a plurality of satellite node devices (A, B, C ...) coupled to optical means (F1, FZ) in an optical ring architecture, characterized in that the satellite node devices ( A, B, C ...) are connected to said carrier means (F1, P2) by passive multiplexers and demultiplexers (4'-7 '), and all kinds of cable protection switching in the network are provided in the name node device (H). A device according to claim 1, characterized in that in the satellite node arrangement the multiplexers comprise two transmitter couplers (4 'and 5'), through which it is connected to said transmitter part (F1, 1: 2). Network according to claim 1 or 2, characterized in that in the satellite node device the demultiplexers comprise two fi carrier couplers (6 'and 7'), through which it is connected to said fi carrier part (F1, P2), and a bandpass filter (8) arranged for the wavelength channel of the satellite node device in question. Network according to one of the preceding claims, characterized in that each satellite node device comprises an access point (1) with a satellite node transmitter and a satellite node receiver, the two passive multiplexers (4 and 5), the two passive demultiplexers (6 and 7), a coupler (3), which distributes the transmitter signal from the satellite node transmitter to the two multiplexers, and a coupler (2), which combines the received signals from the two multiplexers (4 and 5) to the satellite receiver in the workstation (1 ). Net according to any one of the preceding claims, characterized in that the name device (H) is provided with a fi interrupt and with transmitting and receiving means (9, 10, 13 and 11, 12, 14) connected to each end of said fi carrier means. 10 15 20 25 507 415 13 Network according to one of the preceding claims, characterized in that the name node device (H) comprises at least one optical transmitter (Tx '), for example a wavelength stabilized laser, and at least one optical receiver (Rx') per satellite node device (A, B, C). ..) connected to the network. Net according to claim 6, characterized in that the bearing comprises two fibers, and each bearing has a relaxation in the naming device, the naming device having a demultiplexer (9 or 10) connected to one end of each fiber (F1 or P2) and a multiplexer ( ll or 12) connected to the other end, the demultiplexer for one of the two of the two being connected to the same side of the children as the multiplexer of the other of the two. Network according to claim 6 or 7, characterized in that for each light receiver (Rx ') in the hub device (H) an individual switching unit (13) is connected to it and controllably connected to one or the other of the two the demultiplexers (9 or 10) and normally connected to a predetermined one of the demulliplexers (9 or 10), when the fiberization is in order, and changed to the other of the demultiplexers (10 or 9) in the event of a fault in the bearing, which affects the signaling to the light receiver in question (Rx). Network according to Claim 6 or 7, characterized in that for each light transmitter (Tx ') in the name node device (H) an individual switching unit (14) is connected to the light transmitter and controllably connected to one or the other of the two multiplexers ( 1 1 or 12) and normally connected to a specific one of the multiplexers (11 or 12) when the bearing is in order and connected to the other of the multiplexers (12 or 11) in the event of a fault on the bearing, which affects the signaling of the light emitter in question. (Tx '). Network according to claims 6 and 8 or 9, characterized in that the switching units of the light transmitter and the light receiver in the name node device with respect to the signaling of the same satellite modem device are connected in the same way and have their states changed at the same time. 11. ll. Network according to one of Claims 8 to 10, characterized in that the receiver switching devices in the name node device automatically listen to a second of the name node device's demultiplexers (10), and in the event of a fault the name node device reconciles the transmitter and receiver devices according to the following rules: 1) the positions of the switching devices in the naming device for the channels that have been lost on the name receivers, 2) if channels have been lost on the channels to which the switching units are automatically monitoring, changing the positions of all the name switching devices except those that have been lost . Network according to one of the preceding claims, characterized in that the transmitted and the received signals are within the same wavelength channel for each satellite mode device. Network according to one of the preceding claims, characterized in that a spare name node (SH) can be connected anywhere outside a bus which can be operated and controlled by a fault of the name node device (H). Network according to claim 13, characterized in that the spare name node device (SH) comprises only a multiplexer (17) and a demultiplexer (18), each of which is connected to said edel carrier means (F1 and FZ) by fi carrier coupler (4). "-7").