Cryptography – Key management – Having particular key generator
Patent
1990-05-21
1992-02-04
Tarcza, Thomas H.
Cryptography
Key management
Having particular key generator
380 49, 370 953, H04L 902
Patent
active
050864700
DESCRIPTION:
BRIEF SUMMARY
This invention related to scrambling in digital communications networks such as optical fibre networks serving single line telephony outstations and to central stations and outstations for use in such networks.
In digital networks where outstations generate their clock from the received signal it is known to scramble the signal before transmission to avoid long sequences of the same bit value, which would disturb the operation of the clock recovery circuit, and to descramble in the outstations in accordance with the predetermined scrambling sequence to recover the original signal.
The present invention concerns the use of a synchronisation signal in the form of a predetermined pattern of bits in each frame of a stream of frames transmitted from a central station, and the avoidance of an outstation erroneously recognising an identical pattern of bits in an adjacent housekeeping part of the frame.
In accordance with a first aspect of the present invention there is provided a central station for a digital communications network, arranged to transmit data to outstations in the form of a stream of frames, each in the form of a first portion containing a synchronisation signal in the form of a predetermined pattern of bits at least n bits in length, and a second portion, the central station comprising a binary sequence scrambling means for scrambling the frames, characterised by the binary sequence scrambling means being arranged such that the first portions and at least part of the second portions adjacent to the first portions are scrambled with the same predetermined binary sequence, and by means for inverting successive nth bits in said at least part of the second portions, but not inverting successive nth bits in the scrambled first portions themselves, thereby preventing false recognition of sychronisation due to an identical pattern of bits in said at least part of the second portions.
Thus any part of the frame which is scrambled with the same binary sequence as the synchronisation signal has its scrambled form perturbed whereby a descrambler operating in accordance with this binary sequence can descramble the synchronisation signal correctly but is prevented from outputting any identical pattern of bits which do not constitute a synchronisation signal.
Since no part of the second portions of the frames is scrambled with the same predetermined binary sequence as the first portions without being subject to the perturbation of the inversion process, an unauthorised user attempting to descramble the frames will not, unless he uses sophisticated equipment, be able to synchronise and decode message data.
In a preferred form of this first aspect of the invention each second portion comprises a first section containing housekeeping data for the outstations, and a second section containing message data for the outstations, the scrambling means is arranged to scramble said first portions and said first sections with a first predetermined binary sequence and to scramble said second sections with a second predetermined binary sequence, and the inverting means is arranged to invert successive nth bits of only said first sections.
According to a second aspect of the present invention there is provided an outstation for a digital communications network, arranged to receive frames from a central station as defined in the first aspect of the invention, the outstation comprising binary sequence descrambling means for descrambling the frames, characterised by the binary sequence descrambling means being arranged to descramble the first portions and at least part of the second portions adjacent to the first portions with the same predetermined scrambling binary sequence, by means for identifying the synchronisation signal in the output of the descrambling means, and by means arranged to correct the inverted nth bits of the descrambled said at least part of the scrambled second portions thereby to reconstitute the original form of said at least part of the scrambled second portions.
In a preferred form of this second aspect
REFERENCES:
patent: 3920894 (1975-11-01), Shirley
patent: 3931472 (1976-01-01), Gill et al.
patent: 4527195 (1985-02-01), Cheung
patent: 4575755 (1986-03-01), Schoeneberger et al.
patent: 4642806 (1987-02-01), Hewitt et al.
patent: 4817144 (1989-03-01), Citta et al.
patent: 4890321 (1989-12-01), Seth-Smith et al.
patent: 4977593 (1990-12-01), Ballance
Electronic Letters, 23 Apr. 1987, vol. 23, No. 9, "Novel Fibre Break Locator For Optical Duplex Transmission Systems," Cochrane, pp. 440-442.
Elektronik,5/8.3.1985, Thomas Hermes, "Einfache Fehlerlokalisierung in Digitalen Ubertragungssystemen," pp. 60-62.
Patent Abstracts of Japan, vol. 6, No. 37 (E-97), [915], 6th Mar. 1982; JP-A-56 156 045 (Fujitsu K.K.) 02-12-1981.
Electronics Letters, vol.23, No. 24, 19th Nov. 1987, pp. 1255-1257, Stevenage, Herts, GB; J. R. Stern et al.: "Passive Optical Local Networks for Telephony Applications and Beyond" pp. 1255-1257.
Patent Abstracts of Japan, vol. 5, No. 137 (E-72)[809], 29th Aug. 1981; JP-A-56 73 941 (Fujitsu K.K.) 19-06-1981.
British Telecommunications public limited company
Swann Tod
Tarcza Thomas H.
LandOfFree
Scrambling in digital communications network using a scrambled s does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Scrambling in digital communications network using a scrambled s, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scrambling in digital communications network using a scrambled s will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-350938