International Business Machines Corporation

Francois Gabriel Caron

Dominique N Godard

Andre E Desblache

Emile Morlec

Jean Cholat-Namy

Francis Paul Maddens

Firmin Bigo

A data transmission system is described which includes a switching circuit that enables the connection of a tributary modem to a control modem via the public switched network. Switching occurs when it is no longer possible to transmit data on the leased network because the line connected to the tributary modem has failed. The switching circuit can connect either the permanent leased line or the switched network to the receiver of the control modem. It comprises a narrow pass-band filter and detector which is permanently connected between the reception side of the switched network and the control modem receiver. When the tributary modem answers a call from the control modem, it sends a tone ahead of the data message, the frequency of which tone corresponds to the frequency of the pass-band filter and is out of the data band. When such a tone is detected by the detector and pass-band filter, the control modem toggles a two position switch which isolates the leased line and connects the switched network to the receiver of the control modem.

Switching device for connecting a data transmission system to the

This invention relates to a process for automatically allocating appropriate communication rates to different data communication lines connected to a common multiplex channel, in terms of the traffic on these lines and the available maximum rate S on this channel, so as to improve the data throughput on the common channel. To this end, Traffic T.sub.i.sup.n is, first, valuated on each line at time t.sub.n, according to formula: T.sub.i.sup.n =.beta.F.sub.i.sup.n +(1-.beta.)T.sub.i.sup.n-1 In this formula:

Odynamical operating rate allocation process in a multiplex

A method and device which, in a receiver forming part of a data transmission system using DSB-QC modulation and wherein the transmitter generates a first sequence of successive carrier phase changes of 180.degree. taking place at the signaling rate 1/T followed by a second sequence of pseudo-random carrier phase changes of 0.degree. and 180.degree., with the first of these being a 0.degree. phase change, permit detecting the beginning of said second sequence. The received signal is filtered to extract therefrom its components at frequencies f.sub.1 and f.sub.2 defined as

Method and device for detecting a pseudo-random sequence of carrier

A clock setting circuit is provided at a receiving modem for adjusting the phase of a timing signal defining the signal sampling instants. The received signal is filtered in two filters to derive a first signal having a phase .phi..sub.1 and a frequency f.sub.1 equal to f.sub.c - 1/2T, f.sub.c being the carrier frequency and 1/T being the transmission baud rate, and a second signal having a phase .phi..sub.2 and a frequency f.sub.2 equal to f.sub.c + 1/2T. The first and second derived signals are combined to derive an error signal indicative of the phase difference .phi..sub.2 - .phi..sub.1 which difference is used for adjusting the phase of a phase locked oscillator which provides the timing signal.

Growing community of inventors

Cagnes-sur-Mer, France

Francois Gabriel Caron