JP2742540B2 - Optical network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical-electrical converter and an electric-electrical converter in which each node is a set.
For optical networks that have optical converters and electrical signal processing units and perform ring-type access, and are concerned with a method for troubleshooting optical networks with low optical loss during ring reconfiguration due to cable failure. It's about networks.

[Prior Art] FIG. 6 (a) is a schematic diagram showing a conventional optical network, in which 1 to 8 are nodes, and P and S are working fibers and protection fibers, respectively. The fibers P and S are accommodated in a single cable CA connecting two nodes. Hereinafter, illustration of the cable is omitted as appropriate. The arrow attached to the cable P indicates the flow of information. This network usually includes node 1 → node 2 as shown in FIG.
Communication is performed by transmitting signals in the order of → node 3 →... → node 8 → node 1 (ring type communication).

FIG. 1B is a schematic diagram showing a state where the node 3 has failed. Built-in optical switch at node 3 (described later)
Is switched, the optical signal is bypassed, and the communication system as a whole is not affected.

FIG. 1 (c) is a schematic diagram showing a state in which the cable between the nodes 2 and 3 has a disconnection failure. In this case, by switching the optical switch in each node, the return of the optical signal is bypassed at the nodes 2 and 3, and the optical signal passing through the backup fiber is bypassed at the other nodes (hereinafter, referred to as loopback). Call).

Next, a configuration example of two nodes for realizing a conventional optical network will be described in detail.

FIG. 7 is a schematic diagram showing an example of the internal configuration of a first node in a conventional optical network. In the figure, PI, PO, SI, SO
Is a first input side, a first output side, a second input side, and a second output side optical fiber, respectively, and MAC is an electric signal processing unit, OE,
EO is the optical-electrical converter, the electrical-optical converter, SW1,
SW2 is a 2 × 2 optical switch, and F is an optical fiber connecting SW1 and SW2.

Normally, the optical switches SW1 and SW2 are in a parallel mode so that light passes in a parallel direction as shown in FIG. 7A. The optical signal input from PI is SW1 → OE → MAC → SW2 → P
Communicated with O.

FIG. 7 (b) is a schematic diagram showing a node state when the MAC fails. When the abnormality of the MAC is detected, both of the optical switches SW1 and SW2 are switched from the parallel mode to the cross mode in which light passes in the cross direction as shown in FIG. 7B. As a result, the optical signal input from PI is SW1 → F → SW2
→ Communicated with PO. In other words, the failed MAC is bypassed, and the failure does not affect the entire system. The above operation is the same for OE and EO failures. Actually, there is a control system for detecting a failure and instructing switching to an optical switch, but this is out of the gist of the present invention, so that illustration and description are omitted here.

FIG. 7 (c) is a schematic diagram showing a node state when the right PO and SI are disconnected due to a cable failure. At this time, as shown in the figure, SW1 is in the parallel mode, SW2 is in the cross mode, and the optical signal input from PI is SW1 → OE → MAC → EO → SW
It is transmitted back to 2 → SO. Other nodes not connected to the faulty cable maintain the normal state shown in FIG. 7 (a), and the turned-back signal is transmitted through the route SI → SW1 →
It is transmitted through F → SW2 → SO. At the node (not shown) on the left where PI and SO are disconnected, SW1 is in the cross mode and SW2 is in the parallel mode, and the signal is similarly folded back. As a result, the loopback state described with reference to FIG. 6 (c) is realized.

The first example of the internal configuration of the node in the conventional optical network has the above-described configuration. Therefore, node failure and cable failure are dealt with by bypass and loopback, respectively.
System down can be avoided. Therefore, there is an advantage that a highly reliable system can be configured. However, in this node internal configuration, the optical signal switched in the loopback state is transmitted while continuously bypassing the optical switches SW1 and SW2 in a plurality of nodes, so that the optical loss of the optical switch is accumulated. Problem. For this reason, the conventional optical network using this type of node has an application limitation of about ten nodes.

FIG. 8 is a schematic diagram showing an example of the internal configuration of a second node in a conventional optical network that has solved the above-described problem of optical loss. The same symbols are used for common elements. In the figure, RP is an optical repeater that amplifies an attenuated optical signal to a certain power level.

By the way, in normal times, the optical switches SW1 and SW2 are set as shown in FIG.
It is in the parallel mode as shown. The optical signal input from the PI is transmitted in the order of SW1, OE, MAC, EO, SW2, and PO as in the first configuration example.

At the time of bypass, both the optical switches SW1 and SW2 are switched from the parallel mode to the cross mode as shown in FIG. 8 (b), and the optical signal input from the PI is relayed as SW1 → RP → SW2 → PO. Is transmitted.

At the time of cable failure, as shown in FIG. 8 (c), SW1 is in the parallel mode and SW2 is in the crossing mode, and the optical signal input from PI is transmitted in the order of SW1 → OE → MAC → EO → SW2 → SO. You. Other nodes not connected to the faulty cable maintain the normal state shown in FIG. 8 (a), and the returned signal is transmitted while being relayed along the route SI → SW1 → RP → SW2 → SO. The roof back state as described with reference to FIG.

Conventionally, in this type of optical network, an optical signal is relayed in a node at the time of bypass as described above, so that the problem of optical loss has been solved. Therefore, there is an advantage that a system having a large number of nodes can cope with a node failure and a cable failure, and a large-scale and highly reliable system can be configured. However, the conventional optical network using this type of node has a problem that the cost of the network increases because each node has an optical repeater RP. In particular, when an ultrahigh-speed transmission system of a class of several hundred Mbps to several Gbps using a single mode fiber is formed, the optical repeater becomes extremely expensive, so that this problem becomes more serious. Further, in the second configuration example, compared to the first configuration example, the reliability of the network is reduced by the insertion of the optical repeater RP.

[Problems to be Solved by the Invention] As described above, the conventional optical network copes with node failure and cable failure by bypass and loopback, respectively, thereby avoiding a system down. Although there is an advantage that a reliable system can be configured, there are the following problems.

In the case where the optical repeater is not provided: Since the optical loss of the optical signal looped back at the time of loopback is accumulated as much as the optical signal passed through the optical switch, the number of applicable nodes is limited.

In the case of having an optical repeater ... The cost of the network is large, and the reliability of the optical repeater insertion decreases.

An object of the present invention is to solve the above-mentioned problems, and to realize a communication method capable of coping with a node failure and a cable failure without having an optical repeater and reducing optical loss at the time of bypass. Accordingly, an object of the present invention is to provide a highly reliable and low-cost optical network independent of the number of nodes.

[Means for Solving the Problems] In order to achieve the above object, according to the first aspect of the present invention, a set of an optical-electrical converter, an electrical-optical converter, and an electric signal N communication nodes (hereinafter, referred to as nodes) each including a processing unit (hereinafter, referred to as OE, EO, MAC) and an optical switch, and the n nodes are connected in a double ring via the optical switch. A first optical transmission line and a second optical transmission line having different transmission directions from each other, and an optical fiber cable that accommodates the first and second optical transmission lines and connects two adjacent nodes. When ring communication is performed using the first optical transmission line in the order of node numbers (in the order of 1 → 2 → 3... → n → 1), if the OE, EO, or MAC of the node fails, the failed part is Means for switching the optical switch so as to be bypassed, i-th (0 <i <n) If the optical fiber cable connecting the node and the (i + 1) th node fails, the ai-th node receives from the first optical transmission line and transmits to the second optical transmission line, and b.i + 1-th node , Receiving from the second optical transmission line and transmitting to the first optical transmission line, and for the nodes except the ci-th and i + 1-th nodes, receiving from the first optical transmission line and transmitting to the first optical transmission line, Signals passing through the optical transmission line are optically bypassed, and signals received from the second optical transmission line and transmitted to the second optical transmission line, and signals passing through the first optical transmission line are optically bypassed. Each optical switch is switched so as to have a configuration, and a single ring is formed as a whole network.

According to the second aspect of the present invention, there are provided n pieces of optical-to-electrical converters, electrical-to-optical converters, electric signal processing units (referred to as OE, EO, and MAC) and optical switches therein. And a first node for connecting the n nodes in a single ring through the optical switch.
An optical transmission line, a second optical transmission line for connecting every other node in a ring shape via the optical switch, and a housing for accommodating the first and second optical transmission lines, and a connection between two adjacent nodes. And an optical fiber cable for linking. Normally, ring communication is performed in the order of node numbers using the first optical transmission line. If the node fails, the failed node optical bypass is used using the second optical transmission line. Means for switching the optical switch so that the optical fiber cable connecting the i-th node and the (i + 1) -th node is broken down if the optical fiber cable connecting between the i-th node and the (i + 1) -th node fails. For the nodes of the above, a state of receiving from the first optical transmission path and transmitting to the second optical transmission path, or a state of receiving from the second optical transmission path and transmitting to the first optical transmission path, bi-1 to i + 2 For nodes other than the
Each optical switch is switched so that the signal is received from the second optical transmission path and transmitted to the second optical transmission path, and a single ring is formed as a whole network.

[Operation] According to the first aspect of the present invention, even if an optical cable fails due to switching of an optical switch of each node, a simple link is not required at each node because the entire network forms a single link. become.

According to the second aspect of the present invention, the entire network forms a single link by appropriately using the first optical transmission line and the second optical transmission line even when the optical cable fails. Therefore, the problem of the transmission loss in the invention of claim 1 is further solved, and the efficiency is further improved.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a first embodiment of the present invention.
In the figure, P (outer ring: clockwise), S (inner ring:
Counterclockwise) are the first transmission path and the second transmission path, respectively.
Nodes 1, 5, and 7 receive from the first transmission path and transmit to the first transmission path, and nodes 4, 6, and 8 receive from the second transmission path and transmit to the second transmission path. The node 2 receives from the first transmission path and transmits to the second transmission path, and the node 3 receives from the second transmission path and transmits to the first transmission path. As a result, even if the cable between the nodes 2 and 3 breaks down, the optical signals are all transmitted in the order of node 1 → node 2 → node 8 → node 6 → node 4 → node 3 → node 5 → node 7 → node 1. Is forwarded to the node.

FIG. 2 is a schematic diagram showing a state inside the node in this embodiment. FIGS. 2A and 2B show a normal state and a bypass state of the network, respectively. The normal state and the bypass state are exactly the same as the first configuration example of the related art.

FIGS. 2C to 2F show the state of each node at the time of loopback in FIG. If each node operates as shown in (c) to (f) of FIG. 2, the loopback of FIG. 1 can be realized.

As can be seen from FIGS. 1 and 2, according to this embodiment, the loss (about 2 to 3 dB) of the optical switch in at most one node increases between the two nodes in any state. It is. From the viewpoint of a normal system that expects a transmission margin of about 5 dB, the effect of this optical loss on practical use is small. In the above description, the case where the number of nodes is 8 has been described as an example. Therefore, according to this embodiment, the conventional problem that the loss of the optical switch accumulates at the time of loopback is solved, and an optical network having an unlimited number of nodes can be provided.

FIG. 3 is a schematic view showing a second embodiment of the present invention.
Node 1 is connected to Node 8 and Node 2 from the viewpoint of the cable, but Node 7 and Node 2 from the viewpoint of the fiber.
8, connected to nodes 2 and 3. L1 and R1 are the input fiber, output fiber, and L of the first transmission line, respectively.
Reference numerals 2 and R2 denote an output fiber and an input fiber of the second transmission path, respectively, and M denotes a bypass fiber. FIGS. 3 (a), (b), and (c) show a normal state, a bypass state, and a cable failure state, respectively.

FIGS. 4A to 4D are schematic diagrams showing the state inside the node in this embodiment. This node is MAC and one set of OE, EO
And 2 × 4 optical switches. Under normal conditions,
As shown in FIG. 2A, the signal enters the 2 × 4 optical switch from L1 as shown by the thick line, passes through the OE → MAC → EO → 2 × 4 optical switch, and exits from R1. If the next node has failed, the 2 × 4 optical switch is switched, and FIG.
The signal is output from R2 as shown in FIG. R2 in FIG.
The fiber is the same as the fiber M in FIG. 4C, and is connected to the L2 in FIG. FIG. 3C shows a node bypassed due to a failure. In this way, when the signal is bypassed, the optical signal passes directly through the fiber without passing through the optical switch, so that the optical loss is smaller than in the first embodiment. FIG. 4D shows a node next to the bypassed node.

5 (e) to 5 (j) show the state of each node at the time of the cable failure in FIG. 3 (c). Node 2
When it is detected that the right cable has failed, the signal is output to L2 as shown in FIG. The node 3 in which the cable on the left side has failed inputs from R1 and outputs to R2 as shown in FIG. Hereinafter, nodes 5 and 7 are as shown in FIG. 2G, nodes 6 and 8 are as shown in FIG. 2H, node 1 is as shown in FIG. 2I, and node 4 is as shown in FIG. As a result, the ring-shaped transmission path shown in FIG. 3 (c) is secured.

Therefore, as can be seen from FIGS. 4 and 5, according to this embodiment, since the signal directly passes through the fiber at the time of bypass and loopback, the transmission loss is smaller than that of the first embodiment. is there. Therefore, the second embodiment is more suitable for a system that performs long-distance communication than the first embodiment. Also, a failure in only the first transmission line and a failure in the optical switch have been dealt with by loopback in the prior art and the first embodiment, but can be dealt with by the optical bypass in the second embodiment. There is an advantage that stable communication can be provided. In the above description of the second embodiment, the case where the number of nodes is eight and the case where the number of optical fiber cables is three are described. However, when the number of nodes is different (including the odd number), the multi-core optical fiber cable is used. The same can be realized when used. A multi-core optical fiber cable may be used to connect up to a plurality of nodes, but in this case, the network and the optical switch become complicated.

[Effects of the Invention] As described above, the present invention makes it possible to cope with a cable failure by reducing the optical loss at the time of loopback,
By eliminating the need for an optical repeater, there is an advantage that a highly reliable, low-cost, ring-type optical network with no limitation on the number of nodes can be realized. Therefore, if the present invention is applied to a high-speed optical LAN system in the class of several hundred Mbps to several Gbps, where the optical repeater is expensive, the effect can be greatly exerted.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention, FIG. 2 is a schematic diagram showing the internal configuration of a node of the first embodiment, FIG. 3 is a schematic diagram showing a second embodiment of the present invention, FIG. 4 and 5 are schematic diagrams each showing the internal configuration of a node according to the second embodiment, FIG. 6 is a schematic diagram showing a conventional optical network, and FIG. 7 is an example of the internal configuration of a first node of a conventional optical network. Schematic diagram showing the eighth
FIG. 1 is a schematic diagram showing an example of the internal configuration of a second node of a conventional optical network. 1 to 8 ... Node, P, S, PI, PO, SI, SO, F, L1, L2, R1, R2, M
…… Optical transmission line, CA …… Cable, MAC …… Signal processing unit, O
E …… Opto-electric converter, EO …… Electrical-optical converter, RP ……
Optical repeater, SW1, SW2,2 × 4SW …… Optical switch.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tetsuo Yoshizawa Nippon Telegraph and Telephone Corporation, 1-6-1, Uchisaiwai-cho, Chiyoda-ku, Tokyo (56) Reference JP-A-1-141424 (JP, A) JP-A Sho 58-140702 (JP, A) JP-A-2-199431 (JP, A)

Claims (2)

(57) [Claims] An n-communications node (hereinafter, referred to as OE, EO, MAC) and an optical switch including a set of optical-electrical converters, electric-optical converters, electric signal processing units (hereinafter referred to as OE, EO, and MAC, respectively). ), A first optical transmission line and a second optical transmission line having different transmission directions for connecting the n nodes in a double ring shape via the optical switch, and the first and second optical transmission lines. An optical fiber cable for accommodating a transmission line and connecting two adjacent nodes, and normally using the first optical transmission line in the order of node numbers (1 → 2 →
3)... → n → 1) in order to perform ring communication, and when OE, EO, or MAC of the node fails, the optical switch is switched so that the failed part is bypassed. When the optical fiber cable connecting the node (0 <i <n) and the (i + 1) th node fails, the aith node receives the signal from the first optical transmission line and transmits it to the second optical transmission line. B. The (i + 1) th node receives from the second optical transmission line and transmits to the first optical transmission line, and for the nodes other than the ci and i + 1th nodes, receives from the first optical transmission line and receives the first optical transmission line. To the transmission path,
The signal passing through the optical transmission line is optically bypassed, and the signal is received from the second optical transmission line, transmitted to the second optical transmission line,
An optical network characterized in that each optical switch is switched so that a signal passing through an optical transmission line is optically bypassed and adjacent to each other, forming a single ring as a whole network. 2. A communication node (hereinafter, referred to as a node) including a set of an optical-to-electrical converter, an electrical-to-optical converter, an electrical signal processor (referred to as OE, EO, and MAC) and an optical switch. ), A first optical transmission line connecting the n nodes in a single ring via the optical switch, and a second optical transmission line connecting every other node in a ring via the optical switch. An optical transmission line, accommodating the first and second optical transmission lines,
An optical fiber cable connecting between two adjacent nodes, wherein ring communication is performed in the order of node numbers using the first optical transmission path during normal times, and when the node fails, the second optical transmission path is used. Means for switching the optical switch so that the failed node is optically bypassed. If the optical fiber cable connecting the i-th node and the (i + 1) -th node fails, the ai-1 and i-th nodes , i + 1st, i + 2th nodes are received from the first optical transmission line and transmitted to the second optical transmission line, or received from the second optical transmission line and transmitted to the first optical transmission line, For nodes other than bi-1 to i + 2,
An optical network, wherein each optical switch is switched so as to receive a signal from the second optical transmission path and transmit to the second optical transmission path, thereby forming a single ring as a whole network.