US 5,311,551 A · Digital signal hardware protection switching

Abstract

Protection switching of digital signal transmitting and receiving hardware is realized in a "hitless" manner. The hitless switch is obtained by employing hardware switching units which can individually determine the instant to switch from an active state to a standby state and vice versa. A switch is initialized by supplying a switch request signal from a control unit to a hardware switching unit in the active state. The active hardware switching unit, upon detecting a prescribed bit condition, for example, a predetermined bit state, of the digital signal being supplied as an output therefrom, supplies a predetermined synchronization pulse to the standby hardware switching unit. In response to the synchronization pulse, the standby hardware switching unit forces the bit condition of a bit of the digital signal to be supplied as an output therefrom resulting from a current input bit to be in the same bit condition as that detected in the active hardware unit. Output circuits in both the active hardware switching unit and standby hardware switching unit are simultaneously turned OFF and ON, respectively, in the individual units by observing the digital signal being supplied as an input to both units. Upon detection of a predetermined bit condition of the input digital signal individually by each of the hardware switching units, the active unit output circuit is turned OFF and the standby unit output circuit is turned ON at the same instant. The instant of turning OFF and On of the output circuits is determined individually in each hardware switching unit.

Claims16

Dependent claims

A protection switching unit for use in a hardware protection switching arrangement and being adapted for controllably supplying and receiving a digital signal to and from, respectively, a digital transmission line, the protection switching unit comprising:

means for multiplexing a digital data signal into a prescribed digital signal having a predetermined framing format;
means responsive to a switch request signal for detecting a next bit having a first predetermined bit condition of a digital signal being supplied as an output from the unit,
means for generating a first control signal in response to said means for detecting indicating that a bit having said first predetermined bit condition has been detected of said digital signal being supplied as an output D from the unit;
means for supplying said first control signal as an output from the unit;
means responsive to a received first control signal for synchronizing to said first predetermined bit condition of a digital signal to be supplied as an output from the unit to the digital transmission line;
means for generating a second control signal based on a second predetermined bit condition of a digital signal being supplied as an input to the unit;
and
output circuit means for supplying said digital signal as an output, said output circuit means having an ON state and an OFF state and being responsive to said control signal to select either the ON state or the OFF state.

5 more elements

A hardware protection switching arrangement including at least first and second apparatus each adapted for controllably supplying and receiving a digital signal to and from, respectively, a digital transmission line, each of the first and second apparatus comprising:

means for multiplexing a digital data signal into a prescribed digital signal having a predetermined framing format;
means responsive to a switch initiation signal for detecting an occurrence of a first predetermined bit condition of a digital signal being supplied as an output from the apparatus and
means for generating a first control signal representative of said first predetermined bit condition upon detection of said occurrence, said first control signal being supplied as an output from the apparatus;
means responsive to a received first control signal for synchronizing to said first predetermined bit condition of a digital signal to be supplied as an output from the apparatus to the digital transmission line;
means for detecting a second predetermined bit condition of a digital signal being supplied as an input to the apparatus and for generating a second control signal upon detecting said second predetermined bit condition of said formatted digital signal being supplied as an input to the apparatus;
and
output circuit means for supplying said digital signal as an output, said output circuit means having an ON state and an OFF state and being responsive to said second control signal to select either the ON state or the OFF state.

4 more elements

Dependencies are inferred from the claim text.

Digital signal hardware protection switching

Life of this patent

Digital signal hardware protection switching

Life of this patent

Abstract

Claims16