A digital message transmission system has a transmit side wherein two pulse sequences are sampled at the rate of two plesiochronic data clocks and the sampled sequences are expanded by the insertion of additional information in the manner of "positive stuffing." The two pulse sequences including the additional information are transmitted to the receive side in a pulse frame, the procedure being reversed at the proceed side to decode the message. The momentary phase relationship between the two plesiochronic data clocks, in the form of a binary phase word, is inserted as a portion of the additional information. An auxiliary clock signal is derived from a reference data clock signal for use in transforming the phase measurement (difference between a higher and a lower frequency level) into the binary phase word. An auxiliary plesiochronic clock signal, which is plesiochronic relative to the auxiliary clock signal, is derived from the reference data clock signal and the plesiochronic data clock signal (plesiochronic relative to the data clock signal), the auxiliary plesiochronic clock signal being compared in phase to the auxiliary clock signal.
In a method of transmitting digital signals using so-called pulse stuffing, in which plesiochronous (nearly-synchronous) data signals are transmitted in a main channel of a sum signal channel as synchronous data and in an auxiliary channel of a sum signal channel as additionl data together with stuffing data, it is proposed that the stuffing data should consist of phase words which contain, in digital form, the phase relationship between the sum signal and the plesiochronous data signals.
A method for the recovery of a plesiochronic data signal is provided, whereby the received sum signal generated upon application of what is referred to as pulse stuffing is divided into a synchronous data signal and into an additional data signal in a demultiplexer. A data bit likewise transmitted in the additional data signal is inserted into the synchronous data signal in a format converter on the basis of stuffing information transmitted in the additional data signal or, respectively, a bit is purged from the synchronous data signal. The stuffing information is composed exclusively of phase words which, in digital form, contain the momentary phase relationship between the sum signal and the plesiochronis data signal. A command evaluation stage forwards control signals to the format converter when the extreme values of the phase words are transgressed, the bits being inserted into the synchronous data signal or, respectively, purged from the synchronous data signal by way of the control signals.
In a synchronous network, asynchronous data signals are synchronized using positive/negative stuffing under the control of stuff request signals which are produced in dependence upon the phase difference between the asynchronous and synchronized data signals as compared to respective threshold values. The phase difference is, or the threshold values are, cyclically changed in a manner to produce additional stuffing, not necessitated by the asynchronous frequency difference, whereby the frequency of jitter, due to stuffing, in the synchronized data signal is increased. The increased frequency jitter is filtered out in an already-provided phase locked loop.
Apparatus and methods for distributing synchronization throughout a network is disclosed. The distribution of the synchronization is through the use of generating a reference timing signal, and by counting the line clock pulses between the start of a frame and the timing reference signal pulse at a first office and that count is then encoded and transmitted to the next office. At the next office, the transmitted count is decoded and used for regenerating synchronization by counting a number of received line clock pulses from the start of the frame to regenerate the reference timing signal. Particular criteria for selecting the frequencies for the timing reference signal are disclosed.
Apparatus and methods for distributing synchronization throughout a network is disclosed. The distribution of the synchronization is through the use of generating a reference timing signal, and by counting the line clock pulses between the start of a frame and the timing reference signal pulse at a first office and that count is then encoded and transmitted to the next office. At the next office, the transmitted count is decoded and used for regenerating synchronization by counting a number of received line clock pulses from the start of the frame to regenerate the reference timing signal. Particular criteria for selecting the frequencies for the timing reference signal are disclosed.
