US3622993A
Expired / Lapsed
US
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Digital communication system
Assignee: Post Office
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Filing: 1969-12-15
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Granted: 1971-11-23
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Expires: 1989-12-15
Abstract
Abstract A digital communication system is described in which the local oscillators of the different switching centers of the system are synchronized by selectively increasing or decreasing the frequencies of the oscillators by preset amounts in response to phase advancing and retarding control signals respectively. Each switching center includes for each incoming channel an aligner for absorbing phase differences between incoming digits and local digit times as determined by the oscillator. Each switching center includes for each link joining it to another switching center a comparator for comparing the phase differences between incoming digits and local digits in the centers at the ends of the link, the comparator producing a phase advancing or retarding control signal whenever the difference between the phase differences exceeds a threshold value, the sense of the difference determining the type of control signal. To avoid blocking of the control system due to the simultaneous generation of conflicting control signals in any center the control signals from the different links are progressively inhibited in ascending order of importance of the links whenever the comparators detect excessive differences, until control signals of a single sense only are produced. To minimize the disturbance of the more important switching centers the threshold value above which the control signals are produced are larger links to such centers than for links to centers of lesser importance only, and the preset frequency shifts may be smaller for the more important centers. In any closed loop the threshold value of a direct links between two centers is less than the sum of the threshold values in any series of links joining them.
Inventors
- 👤 Winston Theodore Duerdoth
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 18:17
CPC Classifications
H; H04; H04J; H04J3/00; H04J3/02; H04J3/06; H04J3/062; H04J3/0626; H04J3/0635; H04J3/0676; H04J3/0638; H04J3/0641
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
340 words
A communication system for digital information including a plurality of switching centers joined by links, each switching center having individual oscillator means and means for aligning information receive on the or each link connected to the particular switching center with the oscillator means of that switching center by temporarily storing the received information, each aligning means having means for comparing the phase of the information received over the respective link with the phase of the oscillator means of the particular switching center to produce a signal representing the phase difference, the particular switching center including a plurality of further comparing means respective to the links connected to the switching center for comparing the phase difference signals from the comparing means in the aligning means at both ends of the link, each further comparing means being able to produce a first output signal when the phase difference signals applied to it differ by more than a first threshold value in a first sense, and a second output signal when the phase difference signals applied to it differ by more than a first threshold value in the opposite sense, means responsive to a first output signal to cause a predetermined increase in the frequency of the oscillator means of the particular switching center and a predetermined reduction in the frequency of the oscillator means of the switching center at the other end of the link, and means responsive to the second output signal to cause a predetermined reduction in the frequency of the oscillator means of the particular switching center and a predetermined increase in the frequency of the oscillator means of the switching center at the other link, the first and second output signals being produced to change the frequencies of the oscillator means in such sense as to reduce the difference detected by the the further comparing means, in which means are provided for disabling the control of the oscillator means by the first and second signals when both are present simultaneously from the same or different further comparing means.
Claim 2
Dependent Claim
340 words
A communication system for digital information including a plurality of switching centers joined by links, each switching center having individual oscillator means and means for aligning information receive on the or each link connected to the particular switching center with the oscillator means of that switching center by temporarily storing the received information, each aligning means having means for comparing the phase of the information received over the respective link with the phase of the oscillator means of the particular switching center to produce a signal representing the phase difference, the particular switching center including a plurality of further comparing means respective to the links connected to the switching center for comparing the phase difference signals from the comparing means in the aligning means at both ends of the link, each further comparing means being able to produce a first output signal when the phase difference signals applied to it differ by more than a first threshold value in a first sense, and a second output signal when the phase difference signals applied to it differ by more than a first threshold value in the opposite sense, means responsive to a first output signal to cause a predetermined increase in the frequency of the oscillator means of the particular switching center and a predetermined reduction in the frequency of the oscillator means of the switching center at the other end of the link, and means responsive to the second output signal to cause a predetermined reduction in the frequency of the oscillator means of the particular switching center and a predetermined increase in the frequency of the oscillator means of the switching center at the other link, the first and second output signals being produced to change the frequencies of the oscillator means in such sense as to reduce the difference detected by the the further comparing means, in which means are provided for disabling the control of the oscillator means by the first and second signals when both are present simultaneously from the same or different further comparing means.
Claim 3
Dependent Claim
112 words
A system according to claim 1, in which each further comparing means can produce a third output signal when the phase difference signals applied to it differ by more than a second threshold value greater than the first threshold value in either sense, each switching center including means responsive to a third output signal from any of the further comparing means of that center to disable the production of either a first or a second output signal from the further comparing means of the links connected to that switching center, one link at a time taken in a predetermined order, when both first and second signals are present simultaneously on separate links.
Claim 4
Dependent Claim
89 words
A system according to claim 1, in which each aligning means includes means for transmitting a signal representing the phase difference from the comparing means over the link to the further comparing means for the aligning means at the other end of the link, and means for receiving from the link a signal representing the phase difference from the comparing means to the aligning means at the other end of the link and for applying the received phase difference signal to the further comparing means for the particular link.
Claim 5
Dependent Claim
75 words
A system according to claim 1, in which the links joining the switching centers form one or more closed paths and the first threshold values of the further comparing means for the different links are so arranged that in any closed path the first threshold value of a direct link between two switching centers is less than the total of the first threshold values of tHe links forming another path between the two switching centers.
Claim 6
Dependent Claim
108 words
A system according to claim 1, in which the switching centers are divided into groups according to rank depending on their position in the network, the magnitude of the first threshold value of the further comparing means depending on the lower of the ranks of the switching center joined by the respective link, the first threshold value being larger for switching centers of high rank, and the magnitude of the change in the frequency of the oscillator means of a switching center being inversely dependent on the rank of the switching center so that the switching centers of high rank are disturbed less than those of lower rank.
Claim 7
Dependent Claim
54 words
A system according to claim 2, in which each of certain of the switching centers includes means responsive to the third output signal from any of the further comparing means of the particular center for disabling the production of the first and second signals from one or more links connected to that switching center.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-11-22 | 1975-05-24 | 1975-11-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-11-22 | 1979-05-24 | 1979-11-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-11-22 | 1983-05-24 | 1983-11-23 | $7700.00 | Window Closed / Lapsed |