GB2109654A

GB2109654A - Apparatus for transferring data between two positions

Info

Publication number: GB2109654A
Application number: GB8133470A
Authority: GB
Inventors: Philip Edward Stephens; David Glyndwr White; Martin John Collier
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1981-11-06
Filing date: 1981-11-06
Publication date: 1983-06-02
Also published as: GB2109654B

Abstract

Data from a computer 1 and from a spurious signal generator 3 is switched at 4 between lines 4A and 4B before being converted to optical form at 6A and 6B. The two channels of optical signals 7A and 7B are multiplexed onto a common line 8 to a demultiplexer 9. The outputs of the demultiplexer are converted back to electrical form at 10A and 10B and a switch 11, acting in synchronism with switch 4, separates the data from the spurious signals. The data is fed to a second computer 2. Because the line 8 is an optical line it is difficult to tap and this is made even more difficult by the presence of the spurious signals. In this way the invention makes it possible to reduce problems previously encountered in monitoring security of information transmitted between computers located at different positions. <IMAGE>

Description

SPECIFICATION Apparatus for transferring data between two positions This invention relates to apparatus for transferring data between two positions, and arose with a view to providing a data link which is secure against illicit tapping.

This invention provides apparatus for transferring data between two positions comprising mixing means at one of the positions for mixing the data with a spurious signal and applying the data and the spurious signal to one end of a path extending between the positions, and means at the other position for separating the data from the spurious signal.

The use of an optical path (e.g. a line such as a glass fibre line) itself can provide security against tapping since it is difficult to tap information from an optical line. Furthermore, by mixing the data with the spurious signal even greater security can be achieved.

The data to be transferred may initially be in electrical form in which case the apparatus includes means for converting the data from electrical signals into optical form. Alternatively the data may be generated initially in optical-form, e.g., by an optical code generating device such as are conventionally used to deliver signals representing the position of a moveable member.

The data, when in optical form is preferably of a wavelength which is different from the wavelength or wavelengths of the spurious or false signal at any one time. However, the possibilities exist for distinguishing between the data and the spurious signals. For example they could have characteristic frequency or amplitude changes. Alternatively they could have different phases or different phase changes.

If the data and the spurious signal have different wavelengths it is possible to mix them using a colour multiplexer, which multiplexes the signals onto the optical line between the two positions.

The wavelengths of the data and spurious signal may advantageously be changed repeatedly. This can be accomplished by using a change-over switch which allocates different optical wavelengths to the data, and preferably also to the false signals at respective different times. Also it is preferable to have a control signal generator in order to control the change-over switch, preferably in a random or pseudo-random way.

A number of false signals may be employed, each having a different wavelength from the others and from the data. Preferably the data and the spurious signals are in pulse form.

When the data has been transmitted with the spurious signals from one position to the other it can be separated from the spurious signals by using a demultiplexer and a change-over switch similar to that mentioned previously.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawing in which: Figure 1 is a block diagram of a device constructed in accordance with the invention.

The apparatus shown in the drawing has two computers 1 and 2 at two respective positions between which it is required to transfer information. Data is transmitted from the first computer 1 via input line 1 A to a changeover or cross-over switch 4.

Faise signals from a spurious signal generator 3 are also applied to the switch 4 on input line 3A. Both the data and the spurious signals are digital signals represented by a train of electrical pulses.

The switch 4 is controlled by a control signal generator 5 and operates to switch between a first condition in which input line 1A is connected to an output line 4A and the input line 3A is connected to an output line 4B, and a second condition in which input line 1 A is connected to output line 4B and input line 3A is connected to output line 4A.

The electrical signals carried by lines 4A and 4B are converted into optical form by electricalto-optical transducers 6A and 6B, each of whose outputs 7A and 7B has a given optical wavelength different from the other. These outputs 7A and 7B are fed to mixing means in the form of a colour multiplexer 7 and then transmitted along an optical line constituted by a fibre 8. Thus the elements 4 and 5 constituted means for changing the optical wavelengths of the data and the spurious signal.

A colour multiplexer 9 receives the signals from the optical fibre 8 and demultiplexes them onto outputs 9A and 9B corresponding to the outputs 7A and 7B of the transducer.

A further set of transducers 1 OA and 1 OB convert the optical signals back into electrical form. These signals are fed to a second cross-over switch 11 which is controlled by a control signal generator 12. The control signal generator 12 operates in a way corresponding to and in synchronism with the first control signal generator 5 and its action is such that the channel carrying the data is selected from the other channel carrying the spurious signal, enabling only the required information to be transmitted to the second computer 2. Thus the elements 9 and 11 constitute means for separating the data from the spurious signal.

For the purpose of this Specification the word 'optical' is defined as including not only visible wavelengths of light but also infra-red and uitraviolet radiation. Similarly, 'colour' is defined as including wavelengths of radiation in these ranges.

Whilst the illustrated embodiment of the invention includes only one spurious signal generator 3 it may be desirable, in order further to improve security, to include two or more such generators in which case the switches 4 and 11 would have to be modified accordingly.

Claims

1. Apparatus for transferring data between two positions comprising mixing means at one of the positions for mixing the data with a spurious signal and applying the data and spurious signal to one end of a path extending between the positions, and means at the other position for separating the data from the spurious signal.

2. Apparatus according to claim 1 in which the path is an optical path and in which the apparatus includes means for applying the data and spurious signals to the path in optical form.

3. Apparatus according to claim 2 in which the optical path is defined by a light guide.

4. Apparatus according to claim 2 or 3 including means for converting the data from electrical form to optical form at a given optical wavelength.

5. Apparatus according to claim 4 including means for converting the spurious signal to optical form at a given optical wavelength different from that of the data.

6. Apparatus giving a data link secure against tapping comprising: a multiplexer; a demultiplexer; a common optical line between the multiplexer and the demultiplexer; a plurality of input lines to the multiplexer; means for generating spurious signals; switching means for switching the data and the spurious signals onto different input lines at different times; a plurality of output lines from the demultiplexer being connected to demultiplex the signals from the common optical line onto the output lines; and second switching means for switching between the output lines to separate the data from the spurious signals.

6. Apparatus according to claim 5 in which the mixing means is a colour multiplexer arranged to receive the data and the spurious signal in optical form and to apply them to the optical line.

7. Apparatus according to claim 6 including means for changing the optical wavelengths of the data and the spurious signal.

8. Apparatus according to claim 7 in which the said means for changing is a change-over switch connected to receive the data and the spurious signal when in electrical form.

9. Apparatus according to claim 8 including a control signal generator for controlling the change-over switch.

1 0. Apparatus according to any preceding claim including means for generating and applying to separate electrical lines, a plurality of respective spurious signals.

11. Apparatus according to any preceding claim in which the data and spurious signals are trains of pulses.

12. Apparatus according to claim 1 and substantially as described with reference to the drawings.

1 3. Apparatus giving a data link secure against tapping comprising: a multiplexer; a demultiplexer; a common optical line between the multiplexer and the demultiplexer; a plurality of input lines to the multiplexer; means for generating spurious signals switching means for switching the data and the spurious signals onto different input lines at different times; a plurality of output lines from the demultiplexer being connected to demultiplex the signals from the common optical line onto the output lines; and second switching means for switching between the output lines to separate the data from the spurious signals.

New claims or amendments to claims filed on 16 November 1982.

Superseded claims 1 to 13.

New or amended claims:

1. Apparatus for transferrring data between two positions comprising: means for converting the data from electrical form to optical form at a given optical wavelength; means for converting a spurious signal to optical form at a given optical wavelength different from that of the data; a colour multiplexer arranged to receive the data and the spurious signal in optical form and to apply them to one end of an optical line extending between the two positions; a first change-over switch at the said one end at the line connected to interchange the optical wavelengths of the data and the spurious signal applied to the optical line; a colour demultiplexer arranged to receive the data and the spurious signal from another end of the optical line; means for converting the data and the spurious signal from optical form to electrical form; and a second change-over switch at the said other end of the optical line connected to interchange the data and the spurious signal.

2. Apparatus according to claim 1 including a control signal generator for controlling one of the change-over switches.

3. Apparatus according to claim 1 or 2 including means for generating and applying to separate electrical lines, a plurality of respective spurious signals.

4. Apparatus according to any preceding claim in which the data and a spurious signal are trains of pulses.

5. Apparatus according to claim 1 and substantially as described with reference to the drawings.