Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-01-19
2001-02-27
Evans, F L (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S205000, C356S073100, C359S199200, C359S199200
Reexamination Certificate
active
06194707
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for AUTOMATIC LASER SHUTDOWN METHOD IN OPTICAL TRANSMISSION SYSTEM earlier filed in the Korean Industrial Property Office on the 16
th
of January 1998 and there duly assigned U.S. Ser. No. 1115/1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a line loss handling method and apparatus in an optical transmission system, and in particular, to a method for controlling an automatic laser shutdown (ALS) function upon detection of a line loss.
2. Description of the Related Art
An automatic laser shutdown (hereinafter referred to as ALS) function is generally used to automatically shut the laser down in order to protect the eyesight of a worker who repairs a defective optical line between optical repeaters or between an optical repeater and a terminal station in an optical transmission system.
For example, in an optical transmission system exemplary of contemporary practice in the art an optical line between optical repeaters has a line loss, with the optical repeaters having working lines and protection lines in either direction, respectively. In this regard, in a method exemplary of contemporary practice in the art of performing an ALS function specified by ITU-T Recommendation, it is assumed that a first optical line which is a working line in a direction from a second optical repeater to a first optical repeater has the line loss. Upon detection of the line loss on the defective optical line, the first optical repeater determines whether the line loss state continues for a preset time of 550 ms, for example. If the line loss state continues for the preset time 550 ms, the first optical repeater performs line switching to shut down the defective working line. After the line switching, the first optical repeater designates an optical line in an opposite direction of the defective optical line and performs the ALS function for the designated optical line. That is, upon detection of the line loss, the first optical repeater performs the ALS function for an optical line in the opposite direction if the line loss state continues for the exemplary preset time of 550 ms.
Here, the method exemplary of contemporary practice in the art of designating the optical line in the opposite direction can be classified into two methods: the first method exemplary of contemporary practice in the art is to designate a working line in the opposite direction if the defective optical line is the working line and designate a protection line in the opposite direction if the defective optical line is the protection line; and the second method exemplary of contemporary practice in the art is to match the optical lines on the one-to-one basis such that, for example, first and second optical lines are fixedly matched with third and fourth optical lines, respectively.
A description will be made as to an operation of designating the optical line in the opposite direction according to the first method exemplary of contemporary practice in the art and then performing the ALS function. It is assumed that the first and fourth optical lines are set to the working lines W and the second and third optical lines are set to the protection lines P.
Upon detecting a defect on the first optical line (which is the working line) between the second and first optical repeaters, the first optical repeater switches the defective first optical line before performing the ALS function. That is, upon detection of the line loss, the first optical repeater switches the first defective optical line having the line loss from a working state to a protection state before the passage of the exemplary preset time of 550 ms. After the line switching, the first optical repeater performs the ALS function for the protection third optical line in the opposite direction of the switched first optical line to shut down the laser.
Next, a description will be made as to an operation of designating the optical line in the opposite direction according to the second method exemplary of contemporary practice in the art on the assumption that the first and second optical lines are matched with the third and fourth optical lines, respectively, and then performing the ALS function. Upon detecting a defect on the working first optical line between the second and first optical repeaters, the first optical repeater performs the ALS function for the working third optical line matched with the working first optical line to shut down the laser if the line loss on the defective working first optical line continues for the exemplary present time of 550 ms. In the meantime, during the shutdown of the laser, the third and fourth optical lines switch their operating states. Here, in the case that the third optical line is the working line, the third and fourth optical lines make an unnecessary switching, which can cause a deterioration of the system performance.
As the first optical repeater performs the ALS function according to the first or second method exemplary of contemporary practice in the art as stated above, the second optical repeater then recognizes the line loss through the protection third optical line. Subsequently, the second optical repeater shuts down the laser by performing the ALS function for the optical line corresponding to the protection third optical line.
That is, in recognizing the line loss by the first method exemplary of contemporary practice in the art, the ALS function is performed for the protection first optical line paired with the protection third optical line. Also, in recognizing the line loss by the second method exemplary of contemporary practice in the art, the ALS function is performed for the first optical line matched with the third optical line.
As stated above, however, the second method exemplary of contemporary practice in the art can cause an unnecessary switching of the defect-free working third optical line and the defect-free protection fourth optical line, which can deteriorate the transmission performance of the optical transmission system. In addition, assume that the first optical line is in a lock-out state due to its previous transmission state. Here, the lock-out state refers to a state in which the line switching is not performed. That is, the first and second terminal stations perform a compulsory command to prevent the line switching by the internal affairs (e.g., the repeated line switching for a specified time) and the control option, and the state caused by performance of this command is referred to as the lock-out state. For example, if the first terminal station issues a lock-out command to prevent the line switching from the first optical line to the second optical line, the first optical line continues to be a working line and the second optical line continues to be a protection line, until the lock-out state is released. In the lock-out state, the operation result according to the first method exemplary of contemporary practice in the art does not turn out as expected.
The ALS function exemplary of contemporary practice in the art in the optical transmission system which is set to the lock-out state is described as follows. If the first and second terminal stations issue the lock-out command to prevent the switching from the first optical line to the second optical line, the first optical line continues to be a working line serving as a primary channel and the second optical line continues to be a protection line serving as a secondary channel, until the lock-out state is released. Although the first optical repeater should switch, upon detection of the line loss, the defective first optical line having the line loss from the working state to the protection state before the passage of the exemplary preset time of 550 ms, it cannot perform the switching operation because the first optical line continuously maintains the working state. Accordingly, the first optical repeater performs the ALS function f
Bushnell , Esq. Robert E.
Evans F L
Samsung Electronics Co,. Ltd.
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