Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-07-15
2001-07-17
Chan, Jason (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C370S217000, C370S216000, C370S222000, C370S223000, C370S224000
Reexamination Certificate
active
06262820
ABSTRACT:
TECHNICAL FIELD
This invention relates to restoration of transmission systems and, more particularly, to restoration of optical transmission systems.
BACKGROUND OF THE INVENTION
Optical transmission systems and, especially, those employing Dense Wavelength Division Multiplexing (DWDM) are desirable because they provide extremely wide bandwidths for communications channels. Each communications channel in the DWDM transmission system carries a plurality, for example, 16, 40 or even 80, optical channels (wavelengths) on a single optical fiber and single optical repeater. However, there is a trade off between providing wider bandwidth communications channels, with their corresponding lower cost of transport, and their vulnerability to large-scale disruption of communications services because of transmission medium failure. Therefore, the ability of an optical transmission system, for example, those employing DWDM, to restore itself after a transmission medium failure is very important because of its wider impact on communications services. The DWDM optical transmission systems are of particular interest because of their restoration capabilities.
Prior attempts at providing adequate restoration in optical transmission systems have focused on so-called 1+1 optical protection switching and on optical cross connect systems. The 1+1 optical protection switching is limited in its application and does not efficiently use optical fiber. Known optical cross connect systems, require the use of a relatively large optical switching fabric to accommodate the capacity of the optical transmission system. Unfortunately, current technology may not support providing such a large switching fabric having an acceptable optical performance level. Moreover, use of such a large switching fabric in the optical cross connect comes with a relatively high cost. Furthermore, the optical cross connect system will be slower in terms of restoration speed than provided by prior known SONET/SDH ring transmission systems. In order to protect all wavelengths used in the optical transmission system the prior arrangements had to switch one wavelength at a time. Such switching is very inefficient.
More recently, an optical restoration system has been proposed in which efficient restoration of optical communications between optical nodes in the ring, after an optical transmission media failure, is realized by employing a relatively simple and efficient optical switch matrix having a first number of possible switching states and, then, by utilizing only a second number of the switching states fewer than the first number to switch optically from the optical service transmission capacity of the failed or faulted optical transmission media to the optical protection transmission capacity of another optical transmission media. Optical switching states of the optical switch matrix are blocked that are not actively used for switching from the active optical service capacity of the faulted optical transmission media to the standby optical protection capacity of the other optical transmission media. Use of this relatively simple optical switch matrix allows for the bulk switching of the optical wavelengths as contrasted with the one-to-one switching of the optical wavelengths used in prior arrangements. However, switch control signals must be transmitted via a maintenance channel to effect proper switching in other nodes in the optical ring transmission system.
SUMMARY OF THE INVENTION
These problems and other limitations of prior known optical restoration systems are overcome in an optical communications system that employs a plurality of optical nodes interconnected in an optical ring transmission configuration by at least two optical transmission media, for example, optical fiber. The at least two optical transmission media, in this example, provide optical service transmission capacity and optical protection transmission capacity. Efficient restoration of optical communications between optical nodes in the optical ring transmission configuration, after an optical transmission media failure, is realized by employing an autonomous optical restoration arrangement and technique. To this end, each node autonomously controls an optical switch matrix in the node in effecting the desired restoration without the need of switch control signals transmitted from any other node in the ring, from a main controller or from a central controller.
Specifically, each optical node in the optical ring transmission configuration has the capability to detect the presence or absence of optical signals at its input optical ports. Upon detecting a loss of optical signal on an incoming service capacity port, the node autonomously switches its optical switch matrix configuration to route a copy of its outgoing optical signal in a direction away from the fault. Then, upon detecting the presence of an optical signal on an incoming protection capacity port, the node autonomously switches its optical switch matrix configuration to supply the optical signal incoming on the protection capacity port to terminal equipment associated with the node. Additionally, each node has the capability of detecting a change of signal state at its protection capacity input ports. Upon a change from no signal to detection of an optical signal at a protection capacity input port, the node autonomously switches the switch matrix to pass the detected optical signal through to a protection capacity output port.
A technical advantage of the invention is that through the autonomous switching of the node optical switch matrix, transitions between switching states are faster, thereby resulting in faster overall restoration in the optical ring transmission configuration. Furthermore, restoration is still effected even if the node main controller is out of service for maintenance or otherwise.
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patent: 6046833 (2000-04-01), Sharma et al.
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Chan Jason
Lucent Technologies - Inc.
Nguyen Chau M.
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