Multiplex communications – Wide area network – Packet switching
Patent
1984-05-18
1987-06-30
Orsino, Jr., Joseph A.
Multiplex communications
Wide area network
Packet switching
370 3, H04B 900
Patent
active
046776087
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to a method of transmitting data and more particularly a method of transferring additional information, e.g. across an optical fibre line transmitting regular telephony signals. The proposed method is primarily for use with a 34 Mbits/s fibre optic conductor or a 140 Mbits/s fibre optic conductor.
The problem solved by the invention is that of transmitting an extra low-frequency information channel on an optical fibre at low cost. The low-frequency information channel may be for service telephony for example.
BACKGROUND
The problem of transmitting an extra information channel further on ordinary telephony channels has previously been solved in several ways:
(1) A service channel can be transmitted by integrating a copper pair in a fibre cable, for example. This is cheap and relatively reliable, but such a solution is not accepted by certain telephone administrations nor in certain markets.
(2) A service channel can be transmitted by using bits in the regular bit flow, e.g. by manipulating data as is described in Swedish patent application No. 8105914-9. In this case the transmission of the extra information channel is entirely digital, and coders/decoders or complicated synchronizing circuits are required to enable injection or extraction of the extra information bits.
(3) A further method of transmitting a service channel is described in "Electronic Letters" July 31, 1980, Vol. 16 No. 16 "Novel Supervisory Channel for Fiber Optic Transmission System".
(4) Finally, there is described in Philips Telecommunication Review, Vol. 40, No. 2, July 1982, "Philips Optical Fiber Transmission System: II. The Equipment Family", a method of transmitting an information channel by modulating the amplitude of the bit flow which is to transmit the regular data signals. The transmission of both service channel and data signals is performed with the aid of light pulses amplitude-modulated by the information channel.
According to item 2 above, it would in principle be possible to transmit a service channel by adding an extra telephone channel to the other channels transmitted by the regular bit flow. In this case, the extra channel must be coupled through all the repeaters in the connection to fill its function as a service channel, which causes problems by further demands having to be made on the transmission medium and the switching functions in the respective exchanges.
DISCLOSURE OF INVENTION
In low-frequency amplitude modulation according to method (4) above, there are the following disadvantages:
(a) Vibrations in the optocontact and fibre channel, which can disturb the transmission.
(b) Poor signal-noise ratio in the transmission of telephone calls.
(c) Heavy low-frequency 1/f noise from certain semi-conductor lasers, used in generating the light pulses.
(d) Sensitivity to non-linearities in the light-emitting element in the transmission of analogue baseband signals.
SUMMARY OF INVENTION
In accordance with one embodiment of the invention, the signal corresponding to the service channel is first frequency-modulated with a middle frequency substantially lower than the bit frequency of the bit flow. There is thus transmitted an FM channel having a higher frequency than the service channel, resulting in that the disadvantages according to items (a) and (d) of method (4) are reduced.
An object of the present invention is to provide a method of transmitting an extra information channel, preferably for a fibre optical system line, which transmits a data flow of high bit frequency such that the service channel can be reached by all repeaters along the system line without unnecessary multiplication and without making the system line transmission properties more complicated.
BRIEF DESCRIPTION OF DRAWINGS
The invention will now be described in detail with reference to the accompanying drawing in which:
FIG. 1 is a frequency diagram of the code used and the extra information channel;
FIG. 2 is a block diagram of a sender unit for an extra information channel in accordance with
REFERENCES:
patent: 3603882 (1971-09-01), Wilson
patent: 3718766 (1973-02-01), Stover
"Novel Supervision Channel"--Cochran et al--Electronic Letters, Jul. 31, 1980, vol. 16, #6-pp. 624-620.
Buijs--"Philips Optical Fibre Transmission"--Philips Telecommunication Review-vol. 40, #2, Jul. 1982, pp. 71-88.
Orsino Jr. Joseph A.
Telefonaktiebolaget LM Ericsson
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