Synchronization arrangements for digital switching centers

Claim 2

A communication network including a first centre and at least a second centre connected together by a two-directional link having a multi-channel t.d.m. transmission system using p.c.m. techniques for each direction of transmission, wherein each said centre includes a substantially-stable oscillator for the control of a local clock which controls the bit-rate of the outgoing transmission of the centre and other possible outgoing transmissions of the centre, and wherein each centre includes at least one link equipment responsive to the incoming transmission and operative to synchronise the outgoing transmission of the particular centre with the local clock, said at least one link equipment in each centre including: (a) first detecting means for assessing the position bit-rate of the incoming transmission in relation to the acceptable threshold limits of a position datum, said bit-rate being set according to the frequency of the oscillator of the other centre and arranged to produce one of three output signals indicating that the position of the incoming transmission is, by comparison with said datum, lagging or leading within said limits or equal to said datum, (b) second detecting means responsive to one of three mutually-exclusive control signal patterns is included in said incoming transmission for producing an output signal appropriate to a request from said other centre for advancement or retardation or no-change of the frequency of the local oscillator, (c) means for injecting into the outgoing transmission, in dependence upon the output signals from said first and second detecting means, one of three control-signal patterns, including an advancement signal, a retardation signal and a no-change signal signifying requests for advancement, retardation and no-change, respectively, of the frequency of the oscillator at the other centre, and (d) first logic means controllable by said first and second detecting means for producing a first signal to increase the local oscillator frequency as a result of the first detecting means signifying that the incoming transmission is leading said datum and said second detecting means requesting advancement, or for producing a second signal to decrease the oscillator frequency as a result of said first detecting means signifying that the incoming transmission is lagging said datum and said second detecting means is requesting retardation.

Claim 3

A communication network as claimed in claim 1, wherein the signal produced by said first logic means is connected to an input lead of a voting circuit serving the local oscillator and having an input lead for each link equipment provided at the centre; said voting circuit being actuated to disable said first signal for increase or said second signal for decrease of the oscillator frequency as appropriate but only if a signal of opposite significance is also received from any other said link equipment.

Claim 4

A communication network including a first centre and at least a second centre connected together by a two-directional link having a multi-channel t.d.m. transmission system using p.c.m. techniques for each direction of transmission, wherein each said centre includes a substantially-stable oscillator for the control of a local clock which controls the bit-rate of the outgoing transmission of the centre and other possible outgoing transmissions of the centre, and wherein each centre includes at least one link equipment responsive to the incoming transmission and operative to synchronise the outgoing transmission of the particular centre with the local clock, said at least one link equipment in each centre including: (a) first detecting means for assessing the position of the incoming transmission at a predetermined bit-rate in relation to acceptable threshold limits of a position datum, said bit-rate being set according to the frequency of the oscillator of the other centre and arranged to produce one of three output signals indicating that the position of the incoming transmission is, by comparison with said datum, lagging or leading within said limits or equal to said datum, (b) second detecting means responsive to one of three mutually-exclusive control signal patterns included in said incoming transmission for producing an output signal appropriate to a request from said other centre for advancement or retardation or no-change of the frequency of the local oscillator, (c) means for injecting into the outgoing transmission, in dependence upon the output signals from said first and second detecting means, one of three control-signal patterns, including an advancement signal, a retardation signal and a no-change signal signifying requests for advancement, retardation and no-change, respectively, of the frequency of the oscillator at the other centre and (d) first logic means controllable by said first and second detecting means for producing a first signal to increase the local oscillator frequency as a result of the first detecting means signifying that the incoming transmission is leading said datum and said second detecting means requesting advancement, or for producing a second signal to decrease the oscillator frequency as a result of said first detecting means signifying that the incoming transmission is lagging said datum and said second detecting means is requesting retardation; wherein the signal produced by said first logic means is connected to an input lead of a voting circuit serving the local oscillator and having an input lead for each link equipment provided at the centre; said voting circuit being actuated to disable said first signal for increase or said second signal for decrease of the oscillator frequency as appropriate but only if a signal of opposite significance is also received from any other said link equipment; wherein said means for injecting said one of three control-signal patterns into the outgoing transmission of the link comprises a signal combiner for deriving the appropriate signal-pattern data from a signal generator controllable by the outputs of said first and second detecting means via delay means for introducing delay, and which, in the absence of any modifying control signal from the input lead of the signal generator, causes the no-change signal injected into the outgoing transmission to be replaced by an advancement or retardation signal if the output of the first detecting means signifies that the incoming transmission is lagging or leading, respectively, regardless of the state of the second detecting means.

Claim 5

A communication network including a first centre and at least a second centre connected together by a two-directional link having a multi-channel t.d.m. transmission system using p.c.m. techniques for each direction of transmission, wherein each said centre includes a substantially-stable oscillator for the control of a local clock which controls the bit-rate of the outgoing transmission of the centre and other possible outgoing transmissions of the centre, and wherein each centre includes at least one link equipment responsive to the incoming transmission and operative to synchronise the outgoing transmission of the particular centre with the local clock, said at least one link equipment in each centre including: (a) first detecting means for assessing the position of the incoming transmission at a predetermined bit-rate in relation to acceptable threshold limits of a position datum, said bit-rate being set according to the frequency of the oscillator of the other centre and arranged to produce one of three output signals indicating that the position of the incoming transmission is, by comparison with said datum, lagging or leading within said limits or equal to said datum, (b) second detecting means responsive to one of three mutually-exclusive control signal patterns included in said incoming transmission for producing an output signal appropriate to a request from said other centre for advancement or retardation or no-change of the frequency of the local oscillator, (c) means for injecting into the outgoing transmission, in dependence upon the output signals from said first and second detecting means, one of three control-signal patterns, including an advancement signal, a retardation signal and a no-change signal signifying requests for advancement, retardation and no-change, respectively, of the frequency of the oscillator at the other centre and (d) first logic means controllable by said first and second detecting means for producing a first signal to increase the local oscillator frequency as a result of the first detecting means signifying that the incoming transmission is leading said datum and said second detecting means requesting advancement, or for producing a second signal to decrease the oscillator frequency as a result of said first detecting means signifying that the incoming transmission is lagging said datum and said second detecting means is requesting retardation; wherein the signal produced by said first logic means is connected to an input lead of a voting circuit serving the local oscillator and having an input lead for each link equipment provided at the centre; said voting circuit being actuated to disable said first signal for increase or said second signal for decrease of the oscillator frequency as appropriate but only if a signal of opposite significance is also received from any other said link equipment; wherein said means for injecting said one of three control-signal patterns into the outgoing transmission of the link comprises a signal combiner for deriving the appropriate signal-pattern data from a signal generator controllable by the outputs of said first and second detecting means via delay means for introducing delay, and which, in the absence of any modifying control signal from the input lead of the signal generator, causes the no-change signal injected into the outgoing transmission to be replaced by an advancement or retardation signal if the output of the first detecting means signifies that the incoming transmission is lagging or leading, respectively, regardless of the state of the second detecting means.

Claim 6

A communication network as claimed in claim 3, wherein the link equipment incorporates a second logic means which is controllable by the output of the first and second detecting means and from an output lead of said voting circuit, which output lead has a dissent signal connected to it when the voting circuit is receiving input signals of opposite significance, whereas said signal generator is also controlled over its input lead by the output of said second logic means; the second logic means in conjunction with the signal generator being operative, in the presence of said dissent signal and an advancement or retardation signal in the incoming transmission whilst the output of said first detecting means is signifying that the incoming transmission position lies evidently within said limits, for injecting a signal identical with that of the incoming transmission into the outgoing transmission.

Claim 7

A communication network as claimed in claim 4, wherein the link equipment also includes an off-set device for supplying said threshold limits and set to provide an off-set for said threshold limits to compensate for the propagation delay of the incoming transmission medium, and said first detecting means is controlled jointly from a first condition derived from a frame alignment signal derived from the incoming transmission and a second condition derived from said off-set device.

Claim 8

A communication network as claimed in claim 5, comprising third logic means included in the link equipment and controllable by the outputs of said first and second detecting means for effecting adjustment of the setting of both threshold limits of said off-set device in the event of each direction of transmission being subjected to a change in propogation time of the same sense.