US 4,683,567 AGranted

Asynchronous signaling system for digital communication channel

AssigneeBritish Columbia Telephone Company

InventorsMichael J. Green, James B. McKay

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Abstract

A selected one of a plurality of unique N-bit digital code words that corresponds to an associated signaling message is continuously transmitted until it is desired to transmit a different signaling message. Decoder logic in the receiver looks at a new group of N-signaling bits during each signaling bit interval, without reference to the start of a transmitted code word, and makes a decision during each signaling bit interval as to what signaling message was transmitted. In this manner a keep-alive signal is virtually continuously provided in the receiver. Latch circuitry repeats the previous decision from the decoder logic when the current group of N-signaling bits does not correspond to one of the unique code words or an ordered permutation thereof. In an alternate embodiment a memory circuit requires that the decoder logic repeat the same decision as to what signaling message was transmitted for P consecutive groups of N-signaling bits (i.e., for P consecutive signaling bit intervals) before the latch circuit will indicate that a different signaling message is being transmitted.

Apparatus for performing asynchronous signaling in a digital communications system including transmitter and receiver equipment for multiplexing and demultiplexing digital signaling information signals and digital traffic information signals, each of said signaling information signals defining a different one of a plurality of signaling states S1-SM, said apparatus comprising:

means for storing a plurality of M unique N-bit primary digital code words Sm1 each defining a different one of the signal states S1-SM and each having N-1 additional ordered permutations of the order of the N-bits thereof, said additional ordered permutations being designated as secondary code words;
first means responsive to a particular status/control input signal for causing said storing means to serially produce an output signal comprising serial bits B1-BN of one of the primary and secondary code words for a particular signaling state Ss at a signaling clock rate;
means for multiplexing the serially produced bits from said storing means with traffic information bits at signaling time slots in a bit stream, said signaling time slots occurring at the signaling clock rate;
means for transmitting the multiplexed bit stream to receiver equipment;
means for extracting a signaling clock signal from the multiplexed bit stream in the receiver equipment;
means for demultiplexing the multiplexed bit stream in the receiver equipment for producing a stream of serial signaling bits;
and
means for producing during each signaling bit interval a first indication that the transmitted signaling state is a prescribed signaling state Sp when there is a match between the most recently received N signaling bits of the serial signaling bit stream and one of the N-bit primary and secondary code words associated with the prescribed signaling state Sp;
and producing a second indication when there is not a match between the most recently received N signaling bits of the serial signaling bit stream and any of the primary and secondary code words.

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Abstract

Claims11