METHOD AND APPARATUS FOR DETECTING A FAULT ON AN OPTICAL FIBER
Mechanisms for operating a network element in an optical network are disclosed. A network element has a plurality of ports, each port including a respective receive input for receiving an optical signal from another network element and a respective transmit output for transmitting an optical signal to the other network element. Each port is configured with a respective fault detection mode of a plurality of fault detection modes. The plurality of fault detection modes include a first fault detection mode in which interruption of the optical signal received from the other network element on the respective receive input is interpreted as indicating interruption of an optical path from the respective transmit output to the other network element, and a second fault detection mode in which detection of a predetermined signal pattern from the other network element on the respective receive input is interpreted as indicating interruption of the optical path from the respective transmit output to the other network element.
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This application is a continuation of co-pending U.S. patent application Ser. No. 11/314,678, filed on Dec. 21, 2005, entitled METHOD AND APPARATUS FOR DETECTING A FAULT ON AN OPTICAL FIBER, which is hereby incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to communication networks and, more particularly, to a method and apparatus for detecting a fault on an optical fiber.
2. Description of the Related Art
Communication networks may include various routers, switches, bridges, hubs, and other network devices coupled to and configured to pass data to one another. These devices will be referred to herein as “network elements.” Data is communicated through the communication network by passing logical associations of bits/bytes of data in the form of packets between the network elements over one or more communication links between the devices.
When optical fibers are used to provide communication links between two devices, they are usually deployed in pairs, with each fiber in the pair providing a unidirectional path between the two devices. The optical fibers are connected to the network elements at communication ports, such that an optical transmitter of one port is connected to an optical receiver of another port and vice versa. Since fibers are generally used for unidirectional communication, when a fiber fails or when a far end receiver fails, the transmitting device will not naturally know that the data it is transmitting is not reaching its peer receiver. Accordingly, remote fault indication mechanisms have been developed to enable the network element on the opposite end of the optical fiber to notify the transmitting network element via a second optical fiber that there is a fault on the other fiber.
Generally, link failure detection is performed in hardware using Far End Fault Indication (FEFI) or Remote Fault Indication (RFI), both of which are industry standards for detecting link failure using pre-configured hardware circuits. Where hardware detection of a failure is not available or is cost prohibitive to implement, a software method may be used.
There are currently two ways in which software has been implemented in optical networking equipment to detect a failure on a link. In both of these methods, when a port, such as port 12b, detects a failure on a fiber, it will turn its transmit laser off and on at a specified frequency and duty cycle. Specifically, the port that detects a failure will oscillate power to its transmit laser off and on so that the transmit laser periodically stops sending light over the fiber. The frequency and duty cycle of the transmit laser oscillations may be, for example, one oscillation every 12 seconds with the signal being off for 4 seconds and on for 8 seconds, as shown in
The difference between the two ways of using software to detect a failure on a link is in how the receiver 18a interprets a loss of signal on the fiber 14b. In either instance, a loss of signal on the receive interface 18a will cause the port 12a to determine that the receive interface 18a is down. However, since the loss of signal may be an isolated loss of signal or a periodically generated loss of signal intentionally being generated by the far end port 20b as an attempt to signal a failure on the fiber 14a, the loss of signal is monitored by the port so that it can determine how to operate its transmit interface.
In one method (immediate mode), a loss of signal on the receive interface 18a is immediately assumed to be intentionally generated as part of the oscillating off/on pattern associated with a failure on fiber 14a, so that the transmit interface 16a is immediately shut down upon detection of a loss of signal on fiber 14b. Using this method allows the transmit interface 16a to be shut down quickly in the event of a failure on fiber 14a so that minimal data will be lost should a failure occur on that fiber. However, this mode of operation also causes the transmit interface to be shut down any time a fiber is disconnected for a short period of time, which may occur for maintenance such as re-routing of cables and for other common reasons. For example, if fiber 14b were to be disconnected in
In another method (multiple cycle detection mode), a loss of signal on the receive interface 18a is not assumed to be part of the off/on pattern associated with a failure on fiber 14a until five off/on cycles have been received. This method enables a fiber to be disconnected for a short period of time without causing the port 12a to unnecessarily disable the peer fiber by shutting down the transmit interface 16a. However, since it takes five cycles to recognize the off/on pattern as indicating a fault on fiber 14a, a significant amount of data may be lost while the port is waiting to determine if there is a fault on the fiber.
Conventionally, if a network element included the ability to detect a fault on a fiber using software, the network element would be configured to implement only one of these methods. Specifically, depending on the particular network element, the network element would be programmed to use either the multiple cycle detection mode or the immediate mode. Accordingly, it would be advantageous to provide a way to choose an immediate mode or multiple detection mode, or in general, any intermediate setting to detect a fault on a communication link.
SUMMARY OF THE INVENTIONAccording to an embodiment of the invention, a network administrator is provided with the option to switch the mode of operation for a given port, group of ports, I/O card, or network element, so that the particular failure detection method is user selectable and changeable during operation. By making the fault indication mode user selectable and changeable, the manner in which a network detects and reacts to failures on an optical fiber may be selected independent of the network element on which the port is implemented. By making the fault detection method dynamically changeable, the mode may be altered to enable the network element to operate in an optimum manner under different conditions. For example, the network element mode may be placed into the multiple cycle detection mode during routine maintenance and may be placed into immediate mode during normal operation.
Aspects of the present invention are pointed out with particularity in the appended claims. The present invention is illustrated by way of example in the following drawings in which like references indicate similar elements. The following drawings disclose various embodiments of the present invention for purposes of illustration only and are not intended to limit the scope of the invention. For purposes of clarity, not every component may be labeled in every figure. In the figures:
The following detailed description sets forth numerous specific details to provide a thorough understanding of the invention. However, those skilled in the art will appreciate that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, protocols, algorithms, and circuits have not been described in detail so as not to obscure the invention.
According to an embodiment of the invention, a mode selector is provided in a network element to set the mode in which the fiber fault detection software operates so that one of a plurality of modes may be used to detect a fault on an associated fiber.
As described above, when a port 12 detects a loss of signal at its receiver 18, it will toggle the laser associated with the transmitter 16 on and off at a specified frequency and duty cycle whenever the port is not receiving laser light from the far end of the link. For example the transmitter 16 may turn off its laser for 4 seconds and on for 8 seconds, as shown in
The far end of the link receiving the oscillating signal will detect and identify the oscillations as being generated by the fiber fault detection application using one of the modes (multiple cycle detection mode, immediate mode, or another user-defined mode) selected using the mode selector. When a fault is confirmed on the fiber, the port will report the fiber as down to its associated network element, and stop transmitting and receiving until the oscillations stop. Note that although it is possible for a signal to be present on a fiber for part of the cycle, and thus may appear to the far end that the link is up, the far end will not report the link as “up” to the network element until it is certain that the oscillations have stopped.
The multiple cycle detection mode is configured to allow normal network maintenance operations, such as cable moves, to occur with little or no impact on the regular link up/down processing times. Specifically, since the far end must see an oscillating off/on patter with a particular periodicity and duty cycle, the fiber may be temporarily disconnected so that work may be performed on a fiber without causing the other fiber in the fiber pair to be shut down. Accordingly, the network administrator may determine that the network element on the far end of a fiber to be replaced should be set into multiple cycle detection mode during routine maintenance to prevent other fibers from being affected by the work on the network.
In operation, when the port is set to operate in the multiple cycle detection mode, the port controller 86 (see
Using the signaling pattern described herein in connection with
The mode selector 22 enables multiple cycle detection mode to be selected as an operational mode for the port. This mode enables the fiber 14 to be disconnected temporarily without causing the ports at the ends of the fiber to associate the disconnection with a failure on another fiber. Accordingly, using this mode the ports will be able to transmit data on the other fiber in an uninterrupted manner while allowing normal maintenance to be performed on the network element. Similarly, where links are not likely to be intentionally disconnected, the mode selector enables the immediate mode to be selected as an operational mode for the port in which any loss of signal will be interpreted as not only a problem on the optical fiber connected to the receiver but also as an indication as a fault on the fiber associated with the transmit interface. In this mode the transmit interface may be shut down more quickly to minimize the loss of data that may occur where there is a fault on the fiber.
The I/O cards in this embodiment contain the ports 12 configured in accordance with an embodiment of the invention. As shown in
The network element also includes a control plane 52 configured to control operation of the network element. One aspect that may be controlled, according to an embodiment of the invention, is how the individual ports handle loss of signal on their attached fibers. The control plane may contain a CPU 64 containing control logic 66 configured to implement a network management interface 68 such as a command line interface or other user interface that may be used to set the mode for particular ports. The invention is not limited to the particular manner in which the network administrator is allowed to input mode selection information for particular ports on the network element.
In the embodiment shown in
The network administrator may perform mode selection to select between multiple cycle detection mode and immediate mode for individual ports, groups of ports, or for the network element as a whole. Additionally, the network administrator may be provided with the option of selecting the number of cycles that should be received before declaring a fault on the transmit fiber 14a when the mode selected is the multiple cycle detection mode. Other modes of operation may be programmed as well, and selected using the mode selector, and the invention is not limited to an embodiment that implements only these described modes of operation.
The port 12 also includes a loss of signal detector 84 configured to detect when laser light is not being received from the fiber 14b. If there is a loss of signal on the fiber 14b, as registered by the receive interface 18, the loss of signal detector 84 will provide an input to a controller 86. The controller 86 is configured in this embodiment to enable the port to interpret a loss of signal at the receiver differently depending on the mode signal or data 88 that has been transmitted to control the manner in which the port is to operate. The mode signal 88 is transmitted to the port 12 from the mode selector 22.
Upon detection of a loss of signal at the detector, the loss of signal detector 84 will output a loss of signal to the control 86. The control 86 will notify its applications that the receive link is down. Depending on the mode of operation, the loss of signal on the receive fiber 14b may be immediately interpreted as a fault on the transmit fiber 14a, or may instead may be allowed to continue for a period of time, e.g. a set number of cycles. The manner in which the loss of signal is interpreted with respect to fiber 14a will depend on the mode 88 as set by the mode selector 22 (see
If the loss of signal detector 84 sees the signal on the fiber 14b return, the mode in which the port is operating may make a difference as to how the port operates. Specifically, if the port 12 is in a first mode in which any loss of signal is to be interpreted as a fault on the transmit fiber 14a, the port will, immediately upon receipt of a loss of signal at the loss of signal detector, cause the transmit laser in the transmit interface 16 to stop transmitting data on the transmit fiber 14a. To verify whether the loss of signal is transient or part of a pattern intentionally being transmitted by a port on the other end of the optical fiber bundle, the control will require the signal on the receive fiber to be up for more than 8 seconds prior to enabling the transmit laser to resume transmitting data. An advantage of this mode of operation is that data may be stopped immediately upon detection of a loss of signal on the receive fiber so that a minimal amount of data may be lost on the transmit fiber 14a. A down-side is that the immediate mode causes the transmit interface to be shut down for several seconds during normal maintenance on the other fiber 14a.
If the multiple cycle detection mode is selected, when the loss of signal detector 84 detects a loss of signal at the receive interface 18, the controller 86 will wait to determine if the loss of signal is transient or part of a pattern intentionally being transmitted by a port on the other end of the optical fiber bundle. If the control 86 determines that the loss of signal is repeating with the appropriate frequency and duty cycle for a number of cycles, the control will interpret the pattern as a fault on the transmit fiber and cause the transmit interface 16 to be shut down.
In the described example, the frequency of the pattern is 12 seconds and the duty cycle is ⅔ with the laser off for 4 seconds and on for 8 seconds. Other frequencies and duty cycles may be used as well and the invention is not limited to an embodiment that uses these particular frequencies and duty cycles. Also, in the multiple cycle detection mode, the control will look for five cycles before interpreting the received pattern as a fault on the transmit fiber. The invention is not limited in this manner as other numbers of cycles may be used to identify a fault on the transmit fiber. Although the previous example has focused on a situation in which the software is used to detect a fault on the fiber 14a, the invention is not limited in this manner as the software may also be used to detect a fault on the transmit interface 16a or on the receive interface 18b.
It should be understood that all functional statements made herein describing the functions to be performed by the methods of the invention may be performed by programmable logic such as software programs implemented utilizing subroutines and other programming techniques known to those of ordinary skill in the art. Where the programmable logic is implemented as software, the software may be stored as one or more sets of program instructions that are stored in a computer readable memory 69 within the network element and executed on one or more processors within the network element. Programmable logic can be fixed temporarily or permanently in a tangible medium such as a read-only memory chip, a computer memory, a disk, or other storage medium. Programmable logic can also be fixed in a computer data signal embodied in a carrier wave, allowing the programmable logic to be transmitted over an interface such as a computer bus or communication network. The invention is not limited to a software embodiment, however, as the programmable logic may also be implemented in a Field Programmable Gate Array (FPGA) or other programmable hardware implementation. All such embodiments are intended to fall within the scope of the present invention.
It should be understood that various changes and modifications of the embodiments shown in the drawings and described in the specification may be made within the spirit and scope of the present invention. Accordingly, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not in a limiting sense. The invention is limited only as defined in the following claims and the equivalents thereto.
Claims
1. A method of operating a network element in an optical network, the network element having a plurality of ports, each port comprising a respective receive input for receiving an optical signal from another network element and a respective transmit output for transmitting an optical signal to the other network element, the method comprising configuring each port with a respective fault detection mode of a plurality of fault detection modes, the plurality of fault detection modes comprising:
- a first fault detection mode in which interruption of the optical signal received from the other network element on the respective receive input is interpreted as indicating interruption of an optical path from the respective transmit output to the other network element; and
- a second fault detection mode in which detection of a predetermined signal pattern from the other network element on the respective receive input is interpreted as indicating interruption of the optical path from the respective transmit output to the other network element.
2. The method of claim 1, wherein the predetermined signal pattern comprises an interruption of the optical signal from the other network element at the respective receive input persisting for a predetermined period of time.
3. The method of claim 1, comprising monitoring a respective receive input of a respective port for the predetermined signal pattern when the respective port is operating in the second fault detection mode.
4. The method of claim 3, comprising:
- detecting the predetermined signal pattern at the respective receive input of the respective port; and
- responsive to detecting the predetermined signal pattern, determining a presence of a fault on the optical path from the respective transmit output of the respective port to the other network element.
5. The method of claim 3, comprising:
- detecting the predetermined signal pattern at the respective receive input of the respective port; and
- responsive to detecting the predetermined signal pattern, interrupting optical transmission on the respective transmit output of the respective port.
6. The method of claim 5, wherein the predetermined signal pattern comprises intervals of optical signal interruption of a predetermined duration at the respective receive input interleaved with intervals of optical signal reception at the respective receive input.
7. The method of claim 6, wherein detecting the predetermined signal pattern comprises detecting at least a predetermined number of intervals of optical signal interruption of the predetermined duration.
8. The method of claim 7, wherein the at least a predetermined number of intervals of optical signal interruption of the predetermined duration is configurable.
9. The method of claim 1, comprising interrupting optical transmission from the respective transmit output of a respective port responsive to fault detection at the respective port.
10. The method of claim 1, comprising transmitting the predetermined signal pattern from the respective transmit output of a respective port responsive to fault detection at the respective port.
11. The method of claim 1, comprising transmitting the predetermined signal pattern from the respective transmit output of a respective port responsive to fault detection at the respective port to signal the other network element that there is a fault in an optical path from the other network element to the respective receive input of the respective port.
12. The method of claim 1, wherein:
- the plurality of ports comprises a plurality of distinct groups of ports; and
- configuring each port with a respective fault detection mode of the plurality of fault detection modes comprises configuring each group of ports with a respective fault detection mode of the plurality of fault detection modes.
13. The method of claim 12, wherein each group of ports is located on a respective input/output card of the network element wherein each input/output card of the network element has a respective fault detection mode.
14. The method of claim 13, wherein the first and second optical waveguides are optical fibers.
15. The method of claim 1, wherein each respective receive input is coupled to a first optical waveguide and each respective transmit output is coupled to a second optical waveguide.
16. The method of claim 1, wherein:
- a transmit output of a particular port of the network element is coupled to a receive input of a particular port of the other network element via a first optical path;
- a receive input of the particular port of the network element is coupled to a transmit output of the particular port of the other network element via a second optical path;
- the particular port of the network element is configured with the first fault detection mode of the plurality of fault detection modes; and
- the particular port of the other network element is also configured with the first fault detection mode.
17. The method of claim 16, comprising transmitting the predetermined signal pattern from the respective transmit output of a respective port responsive to fault detection at the respective port to signal the other network element that there is a fault in an optical path from the other network element to the respective receive input of the respective port.
18. The method of claim 17, comprising:
- detecting the predetermined signal pattern at a respective receive input of the particular port of the other network element; and
- responsive to detecting the predetermined signal pattern at the receive input of the particular port of the other network element, interrupting optical transmission on the transmit output of the particular port of the other network element.
19. The method of claim 17, comprising:
- detecting the predetermined signal pattern at a respective receive input of the particular port of the other network element; and
- responsive to detecting the particular signal pattern, determining presence of a fault on the second optical path.
Type: Application
Filed: Apr 14, 2014
Publication Date: Aug 14, 2014
Applicant: Rockstar Consortium US LP (Plano, TX)
Inventors: Jagdish S. Patel (Santa Clara, CA), Keshav Kamble (Fremont, CA), Gregory Allen Foster (Gilroy, CA)
Application Number: 14/252,474