|Publication number||USRE42095 E1|
|Application number||US 11/902,368|
|Publication date||Feb 1, 2011|
|Filing date||Sep 30, 1998|
|Priority date||Feb 20, 1998|
|Also published as||DE19807069A1, DE59808202D1, EP1057289A1, EP1057289B1, US6947668, WO1999043106A1|
|Publication number||11902368, 902368, PCT/1998/2885, PCT/DE/1998/002885, PCT/DE/1998/02885, PCT/DE/98/002885, PCT/DE/98/02885, PCT/DE1998/002885, PCT/DE1998/02885, PCT/DE1998002885, PCT/DE199802885, PCT/DE98/002885, PCT/DE98/02885, PCT/DE98002885, PCT/DE9802885, US RE42095 E1, US RE42095E1, US-E1-RE42095, USRE42095 E1, USRE42095E1|
|Inventors||Jan Koeppen, Guenter Neumann, Helmut Tiltmann|
|Original Assignee||Nola Semiconductor Llc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Non-Patent Citations (1), Classifications (43), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a method for transmitting useful optical signals in an optical transmission device having optical line paths and relates to an optical network.
Optical glass fiber lines have proven to be particularly suitable for the low-loss transmission of information having high information density. Usually information signals in electrical form are converted into optical signals, for example, using light-emitting diodes or laser diodes, and they are coupled into a corresponding optical fiber-optic line. At appropriate locations in the network, the signal is detected, for example, using a photodiode and is once again converted into an electrical signal, such as can be further processed in the customary manner. This signal transmission is well suited for overcoming large distances. At suitable intervals in the appropriate lines, amplifiers and/or regenerators are inserted, which are designed to assure that the signal arrives at the signal sink configured, for example, by the photodiode in an easily receivable form. Just as in the case of electrical networks, it is necessary to provide nodes, through which signals are conveyed to a specific desired receiver and as a result of which it is possible to provide an alternative path for a main line path in the event that the transmission on the main line path is disturbed. As a result of appropriately provided bytes in an overhead of the useful signal to be transmitted, it is also possible to undertake automatic alternative line switching operations. One disadvantage in this method is that the switching operation of an alternative path is only possible within an established transmission standard for the useful signals and that, in a conventional system, an optoelectronic conversion of the signal is necessary at the ends of the segment that is protected by an alternative path. These ends do not necessarily coincide with the sources/sinks of the useful signals.
European Patent No. 0 440 276 describes adding, outside of the useful signal band, a communication signal, using optical couplers. As a result, control and command signals can be transmitted between the nodes of the transmission device. Whereas the transmission of useful signals takes place in the so-called “third window,” the “second window” has been provided for the transmission of communications signals. The “windows” arise from from the damping characteristics of the glass fiber material for certain wavelength ranges. In the “third window,” the damping is minimal, whereas the “second window” is formed using a different damping minimum, in which the lower damping values of the “third window” are not attained. For service communications on the line network, a dedicated transmission band is therefore made available.
The present invention provides for transmitting bidirectional test signals on the line paths, connected to each other, of an optical path between signal source and sink and, if appropriate, on individual line segments of the line paths, the reception or non-reception of the test signals being evaluated as an indicator for a line disturbance on a line segment. By forestalling the transmission of the test signal in the opposite direction, it is possible to initiate an alarm upstream in the transmission direction or to trigger a switchover of a node to an alternative path. The decentralized switchover to alternative paths, made possible in this manner, can be carried out orders of magnitude faster than is the case via a centralized control system. This advantage, however, is linked to the problem that even slight and predictable disturbances trigger switchover operations and, as a result, activate alternative paths that are not necessary or not helpful, so that the alternative paths may be used for a communication having lower priority or as a protective measure for a different normal line path, for example. In particular, there is nothing to prevent switchover operations from taking place on an optical path that, in any case, is no longer usable due to a detected disturbance, so that unnecessary switchover operations and unnecessary occupations of alternative paths occur.
The present invention is based, at least in part, on the general problem of making possible a rapid switchover to alternative line paths, while at the same time avoiding pointless switchover operations. For solving this problem, according to the present invention, a method for optical transmission includes at least one of the following features:
The method according to the present invention provides that test signals of at least two types are generated and that the switchover depends not only on the absence of a test signal—as an indicator of the disturbance—but rather on the type of test signal previously received. In this manner, the present invention makes it possible in a controlled manner to avoid switchover operations, as result of the fact that test signals of the second type are transmitted over a line path, because these test signals of the second type suppress protective measures such as switchovers on the line path. As result of the transmission of a test signal of the second type, it is possible, for example, to prevent switchover operations in an optical path which, on the basis of an already detected disturbance, is currently no longer usable. In addition, the present invention makes it possible to undertake the supplying of the test signal of the second type from a superordinate control system and, for predictable disturbance events, for example, transit a further useful signal channel in the network, to avoid interference signals that are brought about in the present useful signal channels and that experience shows are short-term.
The present invention provides rapid, decentralized switchover by coupling nodes while simultaneously controlling for the sensibleness of a switchover of this type and also simultaneously avoiding pointless switchovers.
In order to carry out the present invention, test signal nodes are provided at the ends of each line segment, through which specific test signals are received, new test signals are formed and transmitted, or test signals are conveyed further.
In this context, consideration is given to the fact that the test signal nodes, depending on the prevailing configuration of an optical path, sometimes border a line segment that is simultaneously a test signal segment, and sometimes, within a test signal segment, are not supposed to exercise the function of influencing the test signals. In an exemplary embodiment according to the present invention, the test signal nodes are constructed so as to be substantially identical and, through software, are configured as transit nodes, inception nodes, or end nodes. In an end node, test signals in both transmission directions are received, evaluated, generated once again, and transmitted. An end node is located at a signal sink or signal source and is effective, from the point of view of the end node, for reception and transmission in one direction. A transit node does not alter the received test signals, but it can determine whether a test signal has not been received, since it, in this case, produces and transmits a particular test signal, for example, of the third type.
In order to avoid switchover operations on an optical path that is no longer usable due to a detected disturbance, in an exemplary embodiment according to the present invention, it is provided that, from a plurality of line paths connected to each other, one optical path between the two signal sources or sinks is formed and, in response to a detected disturbance on a line path, a test signal of the second type is transmitted on all other line paths of the optical path.
If the test signal nodes recognize a test signal of a third type, or if no test signal at all is received at the test signal node, then a switchover to an alternative line path is undertaken if a transition is detected from the test signal of the first type to the test signal of the third type.
The test signal nodes are connected via signals to a superordinate control system, which controls the configuration of the test signal nodes in the individual case. The superordinate control system can be configured in a decentralized manner by control systems of the coupling nodes located closest to the test signal node.
An application area of the present invention lies in communications networks, in which the transmission of useful optical signals takes place in a bidirectional manner, the transmission of the useful optical signals being able to take place over separate optical fiber optic lines in both transmission directions.
The test signals according to the present invention are transmitted together with the useful signals transmitted in the direction in question.
In general, a plurality of useful signals is transmitted on optical fiber lines in a multiplex operation, for example, in wavelength division multiplexing. In this context, each transmitted useful signal has assigned to it its own test signal and is transmitted in a separate test signal channel. The test signals are combined electrically in the time-division multiplex operation and are then optically added to the useful signals in wavelength division multiplexing. For solving the above-mentioned general problem, an optical network including at least one of the following features functions according to the present invention:
In this context, the control system may be part of the corresponding coupling node.
The test signal nodes are preferably configured for transmitting three types of test signals and are able, at the test signal receivers, to detect four different states, namely, the reception of the three test signals and a non-reception of a test signal, in that, using a test signal detector, for example, the undershooting of a level of the test signal, or an insufficient edge steepness, or an entirely false test sum is detected as a disturbance and a corresponding disturbance recognition signal is generated. At the disturbance recognition signal, an alarm device can be triggered.
The other end of fourth coupling node OCC4 is connected to transmitter/receiver TxRx, terminating the optical path in test signal node LS6.
The test signal segments are formed according to the following rules:
All test signal nodes that are not required at the ending of a test signal segment are configured as transit nodes, i.e., the test signal is only conveyed further.
If the absence of a test signal LS is established on test segment 1-3, then no alternative path is available, so that an alarm is transmitted to a central network control system (Telecommunication Management Network). The user of the network control system reacts to the line failure.
On the other hand, if the test signal on normal line path 3-6 fails, coupling nodes OCC2 and OCC4 are induced to switch over and the test signal nodes are reconfigured, so that now test signal nodes LS4 and LS5 are configured as inception nodes for testing the repair of test segment 4-5, whereas test signal nodes LS7 and LS10, heretofore active as inception nodes, can be configured as transit nodes. Test segment 3-6 now forms the active alternative line path, whereas normal line path 4-5 is no longer used.
A third coupling node OCC3′ brings together at line point 6′ the two line paths that arrive at line points 5′, 10′ having test signal nodes LS5′, LS10′.
From the above rules, it can be seen that a line segment can belong to a plurality of test segments, as is demonstrated also in
If a disturbance resulting from the failure of the test signal is established on normal line 1′-4′, then a switchover is caused, which is depicted in FIG. 3d. Segment 2′-3′ is passively connected and the active transmission now takes place on alternative line path 7′-8′ from circuit point 1′ to line point 4′. Other alternative line path 9′-10′, in this case, is not needed as an alternative line path, and is therefore not made active. The test segments now run from 1′ to 4′ via line points 7′ and 8′, on the one hand, and from 8′ via 4′, 5′ to line point 6′, on the other hand. In addition, passive paths 2′-3′ and 9′-10′ are tested for the preservation or reinstatement of functionality.
As a result of the present invention, it is assured that a switchover to an alternative line path only occurs if a switchover of that type can also be expedient. If, for example, in the configuration according to
LS-HOT, e.g., as bit pattern 1010
LS-COLD, e.g., as bit pattern 0101
LOLS all other bit patterns.
Test signal nodes LSX are also furnished with test signal receivers, which include a test signal level detector, so that the absence of a test signal—of whatever type—is recognized as an individual state. Test signal nodes LSX can therefore distinguish four states on the receiving side, namely, “test signal not present” and “test signal received,” specifically corresponding to the three possible types of received test signal.
The test signals for the control of switchovers or of other protective measures are utilized according to the present invention on the basis of the rules elaborated below.
In the error-free state, test signal LS-HOT is transmitted on the entire optical path. If, within one line segment, for example, line segment 2-3 in
If the test signal failure on line segment 2-3 were to occur in the other transmission direction, i.e., if it were detected by test signal node LS3 which is configured as an inception node, then the latter would transmit the LOLS test signal only in the reverse direction, i.e., in the direction of test signal nodes LS2 and LS1.
At the ends of line path 1-3, i.e., at test signal nodes LS1 and LS3, a direct transition from test signal LS-HOT to test signal LOLS is detected, so that at these locations a switchover to an alternative line path could be undertaken if an alternative line path of this type were available (as is the case in the exemplary embodiment illustrated in
On the basis of the disturbance arising in line path 2-3 in the exemplary embodiment depicted in
The transmission of test signal LS-COLD, which, in this way, prevents a switchover to alternative line path or other protective measures, can also be controlled from outside, for example, by a coupling node computer, in order to avoid inadvisable switchover reactions in the event of a foreseeable short-term disturbance. This is advantageous, for example, if in an existing network configuration a new transmission path for useful signals (for example, a new wavelength channel) is constructed or an existing transmission path is dismantled, since, in this context, it is possible that short-term disturbances of existing transmission paths can occur. By supplying LS-COLD test signals to the optical path, potentially existing alternative path circuits are “frozen,” until the new operating state is reliably established. As a result, “chain reactions,” as a result of switchovers arising one after the other, can also be avoided. In addition, for purposes of servicing, an existing network configuration can be “frozen,” without having to dismantle protective mechanisms configured, for example, by a central computer.
In the depicted exemplary embodiment, test signal node LSX also has four inputs from superordinate control systems. Via an input SendW, a test signal to be transmitted by test signal transmitter SW can be input from outside. The same applies for an input SendO, which establishes from outside a test signal to be transmitted by test signal transmitter SO.
At a further input LSTP, LSCP, a configuration signal is input for test signal node LSX, through which it is established whether test signal node LSX is configured as a transit node (LSCP) or as an inception node (LSTP).
If test signal node LSX is an end node of an optical path (e.g., LS1 and LS6 in FIG. 1a), it is only used as an end node (LSIP) for one side E or O. This configuration is controlled through an input LSIP. The test signals received from test signal node LSX are output as test signal information via outputs EmpfW, EmpfO to a superordinate control system, for example, a coupling node computer, so that the coupling node computer can undertake evaluations for the purpose of the switchover to protective measures, the worse state of SO and EO being transmitted on EmpfO and the worse state of SW and EW being transmitted on EmpfW.
If test signal node LSX is in the configuration as a transit node (LSCP), the received test signals are retransmitted unchanged (EW=SO; EO=SW). Only if a test signal is not received, for example, at test signal receiver EW, is signal LOLS transmitted in both directions by test signal transmitters SO, SW.
If test signal node LSX is configured as an inception node (LSTP), then in response to the failure of reception of a test signal, for example, at test signal receiver EW, it transmits signal LOLS only in the corresponding reverse direction (SW), regularly transmitting the signal (LS-COLD) in the other direction, however, unless the transmission of a worse test signal (LOLS) is indicated by a test signal from the other direction. Test signal node LSX, receiving signal LOLS transmitted by test signal transmitter SW, and configured as an inception node (LSCP), at the end of the line path that is disturbed in the other transmission direction, regularly transmits signal LS-COLD in the W direction in response to the reception of LOLS, so that all line paths not affected by the disturbance transmit signal LS-COLD in the W transmission direction. Test signal nodes LSX, which as inception nodes (LSTP) receive a signal LS-COLD, transmit signal LS-HOT in the opposite direction, if non-corresponding test signal receiver EW simultaneously registers a loss of a test signal, so that corresponding test signal transmitter SO transmits an LS-COLD test signal.
On the basis of the rule that, in the reverse direction, test signal transmitter SO or SW fundamentally transmits a test signal of a higher order (failure test signal LOLS; LOLS LS→COLD; LS→COLD LS→HOT, assuming an end node (LSIP) is present or LS-HOT has been received on transmitter side), a rapid and automatic reconnection of the normal line paths is permitted after the carrying out of a line repair.
For a transit node (LSCP), it only remains to be tested whether one of test signal receivers EW or EO signals a test signal failure (“off”) or not. If a test signal failure is established, then signal LOLS is transmitted in both directions. If both test signal receivers EW, EO have received a test signal, then the received test signal is once again transmitted unchanged (SW=EO; SO=EW).
If, on the other hand, test signal node LSX is an inception node (LSTP; an end node (LSIP) is a subcase of an inception node (LSTP)), then in response to an established test signal failure (for example, EW=off) signal LOLS (SW=LOLS) is transmitted in the opposite direction. The same applies if the test signal failure is established by other test signal receiver EO. In this case, test signal LOLS is transmitted by test signal transmitter SO.
If a test signal is received by test signal receiver EW, EO, and if this test signal is LOLS, then in accordance with the above rule, test signal LS-COLD (SW=cold or SO=cold) is transmitted in the opposite direction.
If the received test signal is not LOLS, then it can only be LS-COLD or LS-HOT. If the input signal of the other side is LS-HOT or if the test signal node is an end node (LSIP), then test signal LS-HOT is transmitted in the opposite direction, otherwise LS-COLD.
The bit patterns cited above as examples for test signals LS- HOT and LS-COLD have an advantage in that it is very difficult to confuse the two test signals.
The control system for the protective measures may be set such that in state LS-HOT only a small number of other bit patterns (LOLS) suffice to send an alarm to the control computer. In state LS-COLD, an alarm is reported only after a much larger number of falsely received test signal bit patterns. In this manner, it can be avoided that, in state LS-COLD, failures lasting briefly lead to an alarm in the central control system of the network.
If the transmission capacity of the test signal channel is selected so as to be sufficiently large, e.g., two MBit/s, then in addition to the test signals described here, other data for controlling and monitoring can also be transmitted independent of the test signals themselves.
For the test signal concept according to the present invention, it is not important how many wavelengths are transmitted simultaneously over one optical fiber, for example, in wavelength division multiplexing, because each wavelength channel has assigned to it its own test signal. Each wavelength can therefore be protected by its own alternative line path.
The protective measures depicted, according to the present invention, are locally controlled, for example, by the coupling node computer, so that the central control system of the network and the operator do not participate in acute switchover measures.
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|U.S. Classification||398/16, 398/177, 398/50, 398/140, 398/141, 370/243, 398/5, 370/247, 398/20, 398/12, 398/56, 398/30, 370/223, 370/227, 398/19, 398/45, 398/135, 398/82, 398/31, 398/33, 398/139, 370/228, 398/3|
|International Classification||H04B10/08, H04B10/24, H04B10/02, H04B10/077, H04B10/25, H04B10/032, H04B10/00|
|Cooperative Classification||H04J14/0289, H04B10/2503, H04J14/0279, H04B10/0771, H04J14/0291, H04B2210/071, H04B10/032|
|European Classification||H04J14/02P4S, H04J14/02P4, H04B10/032, H04B10/00, H04B10/0771, H04B10/2503|
|Dec 28, 2010||AS||Assignment|
Effective date: 20060119
Owner name: NOLA SEMICONDUCTOR LLC, NEVADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ROBERT BOSCH GMBH;REEL/FRAME:025540/0856
|May 3, 2013||REMI||Maintenance fee reminder mailed|
|Sep 20, 2013||LAPS||Lapse for failure to pay maintenance fees|