Multiplex communications – Wide area network – Packet switching
Patent
1986-11-20
1988-06-28
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 13, 370100, H04J 302
Patent
active
047544562
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement of a multiplex system used in a hierarchical data transmission system in which a plurality of signals output by multiplexers are further multiplexed and transmitted to a transmission line, especially an optical transmission line.
2. Description of the Related Art
A hierarchical transmission system is known in which, for example, 9-channel data trains, each having a transmission rate of 45 Mb/s, are multiplexed by low group multiplexers to obtain a multiplexed data train of 405 Mb/s and, for example, two of these multiplexed data trains are further multiplexed by a high group multiplexer to obtain a multiplexed data train of 810 Mb/s, and this high group multiplexed data train is electro-optic converted by an optical interface circuit and transmitted to an optical transmission line, whereby a large amount of data transmission is performed. In this system, the output signals of the low group multiplexers are scrambled at the highest speed now possible, whereby the ratio of "1" and "0" of the output signal becomes almost equal.
In such a system, when one of the low group multiplexers becomes unavailable through a fault occurrence, the unavailable multiplexer outputs "0" or "1" continuously. Accordingly, the ratio of "0" and "1" of the output signal does not become equal.
However, when the unavailable low group multiplexer outputs, for example, "0" continuously, if the transmission rate of the system is very high and the number of low group multiplexers is small, for example, two, it is difficult to extract a timing clock from a received signal in the receiver side, therefore normal reception becomes impossible. On the other hand, when the unavailable low group multiplexer outputs "1" continuously, if this system is used in the optical transmission system, the lighting time of a light emission element, for example a semiconductor laser, becomes long in comparison with the case in which a fault does not occur, and accordingly, the lifetime of the light emission element is shortened.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an improved multiplex system which can facilitate the extraction of the timing clock at the receiver side and prolong the lifetime of the light emission element at the transmitter side.
According to a fundamental aspect of the present invention, there is provided a multiplex system comprising a plurality of first multiplexers, a second multiplexer for further multiplexing signals output by the first multiplexers, means for generating an alternating pattern in synchronization with the signals output by the first multiplexer, and switching means provided for each of the first multiplexers for selectively outputting the signals output by the related first multiplexer or the alternating pattern to the second multiplexer, wherein the switching means related to the first multiplexer, the output signal of which is cut off, outputs the alternating pattern signal in place of the signal output by the first multiplexer.
According to another aspect of the present invention, there is provided a multiplex system comprising a plurality of first multiplexers, a second multiplexer for further multiplexing signals output by the first multiplexers, a generator for generating an alternating pattern signal in synchronization with the signals output by the first multiplexers, and a plurality of selectors provided for each of the first multiplexers for selecting the signal output by the related first multiplexer when the related first multiplexer assumes a normal state, and selecting the alternating pattern signal when the related first multiplexer assumes a fault state and outputting the selected signal to the second multiplexer.
According to another aspect of the present invention, there is provided a multiplex system comprising a plurality of first multiplexers, a second multiplexer for further multiplexing signals output by the first multiplexers, and means for
REFERENCES:
patent: 4535451 (1985-08-01), Drupsteen
patent: 4701912 (1987-10-01), Bueno et al.
IEEE International Conf. on Communications, May 14-17, 1984, New York; Stevenson et al.; "A 280 Mbit/s Monomode Optical Trunk Transmission System" pp. 790-795.
Elektronik, vol. 31, No. 22, Nov. 1982, Munchen; Marten: "Optische Sender Mit Halbleiterlasern Fur Hohe Bitraten" pp. 89-94.
Fujimoto Naonobu
Fukushima Takeo
Yato Yoshiaki
Fujitsu Limited
Olms Douglas W.
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