France Telecom

L'etat Francais Represente Par Le Ministre Des Postes, Des

Minister of the Post Telecommunications and Space (centre National

L'etat Francais Represente Par Le Ministre Des Poste, Telecommunications

Jacques Abiven

Fabrice Bourgart

Gilles Ramel

Alain Rebours

A tree-structured star telecommunication network of the wavelength division multiplex transmission type includes multirate periodic downstream and upstream frames transmitted at different wavelengths in full-duplex mode, thereby to connect a central terminal with a plurality of user terminals. Half-duplex transmission for each low bit rate terminal equipment uses a half-frame period shift with respect to the frame period between upstream frame data sectors and downstream frame data sectors. Data derive by the high rate equipment is transmitted in upstream and downstream sectors not occupied by low bit rate data.

Tree structured star telecommunication system including multitrate frames

The method is intended for implementation in a central station connected to digital channels having different primary rates and servicing terminal stations matched at different on-line rates respectively higher than the primary rates via a one single duplex or half-duplex communications network. The network carries a multirate frame divided into sectors having on-line rates corresponding to terminal stations communicating with the main station.

Multirate digital multiplexing demultiplexing method and device

The synchronization of a terminal station in a half-duplex tree-structured communication network consists in counting clock pulses in a central station. The pulses are counted between the emission of a forward frame including a synchronization word emission order that is intended for the terminal station, and the reception of the synchronization word emitted from the terminal station in response to the forward frame. As a function of the pulse count is computed a delay depending on the propagation time between the two stations so as to data sectors emitted by the terminal stations do not overlaps and form a backward frame whatever the different distances between the terminal stations and the central station. According to the invention, the counted pulses are pulses of a central clock signal phase-shifted to within a bit time fraction of the received words. The time intervals attributed to the sectors are thus determined more accurately. The central clock signal depends on the operating rate of the terminal station, and the network can then carry multirate frames. The invention also remedies to variations of propagation time between the stations caused by thermal drifts by modifying clock signals to regenerate sectors in the central station.

Synchronization of terminal stations in a multirate half-duplex

The invention enables extremely quick and reliable recovery of the synchronization of a communication signal transmitted in a half-duplex link. Such a communication signal comprises first time intervals including useful data, and second time intervals devoid of useful data and in a given logic state. At the beginning of each of the first time intervals is included a digital synchronization pattern which is then considered as associated with the second time intervals to form synchronization words of great length. The synchronization of the communication signal is recovered by detecting the synchronization words of great length in the communication signal.

Synchronization method and synchronization recovery devices for

A loop-back device is particularly designed to fit line terminals in half-duplex optical transmission systems thereby facilitating fault location in these transmission systems. An optical fiber coupler having a high crosstalk generates an echo in a reception channel of the terminal, from a test signal transmitted in a transmission channel of the terminal, to an optical transmission medium. Means are provided for cancelling transmission of the echo in the reception channel when the loop-back is de-activated, i.e. when a data signal is carried in the transmission medium, and for amplifying and regenerating said echo when the loop-back is activated, i.e. when said test signal is transmitted. A memory is used for delaying the echo and for transmitting it to a receiving circuit in the terminal during a signal reception period of the half-duplex transmission.

Loop-back device for half-duplex optical transmission system

An information encryption method particularly intended for a communication system in which bidirectional multiplexed communications of the point-to-multipoint type are derived between a switching exchange and plural terminal stations. The switching exchange transmits first multiplexed words respectively destined for the terminal stations. The terminal stations supply second words which are multiplexed and transmitted towards the switching exchange. In the switching exchange, informations concerning transmission errors detected in the second words are derived and transmitted towards the terminal stations, and the first words are encrypted as a function of second words previously received free of transmission error in the switching exchange. In each of the terminal stations, the informations concerning the transmission errors are detected, and the second words transmitted from the terminal station and received free of transmission error by the switching exchange are memorized. The first words received are decrypted in the terminal station as a function of transmission errors and the memorized second words.

Growing community of inventors

Plouaret, France

Jacques Abiven