Gpt Limited

Gec Plessey Telecommunications Limited

Marconi Communications Gmbh

Stephen P Ferguson

Allan D Berry

Antony M Thorley

In an optical telecommunications system using wave division multiplexing (WDM) a wavelength add-drop multiplexer (WADM) has an array of adjacently connected filters, each for selecting light of a respective wavelength being transmitted in a multiplexed data stream along an optical fibre, each of the array of filters being adjacently connected to a portion of the array which is a nominally transparent filter and having means for moving the array so that movement between filters in use occurs via the nominally transparent filter portion of the array. Further, in a method of operating a WADM the transition between two filters of an array of filters each for selecting light of a respective wavelength being transmitted in a multiplexed data stream along an optical fibre occurs by way of a nominally transparent filter portion of the array.

Filter Selector

Data is protected in a data transmission system operating on the synchronous digital hierarchy. The data is transmitted in multiplex form between ports in the system and protection is applied between ports at different or the same aggregate bit rates. This protection is achieved by selecting between individual portions of the payload within the aggregate signals and each part of mutually protective portions has the same nominal traffic capacity. By duplexing an alternative signal path is created to ensure a continuity of traffic through the system in the event of a fault in one path.

Dual connections

A data transmission system in which multiplex data is created in accordance with the Synchronous Digital Hierarchy standard includes an add-drop multiplex having a switch across which data streams are switched between a pair of multiplexers and each input and output for a stream has a rejustifier circuit the timing of which is extracted from a timing extract from the other side of the switch.

Multiplex data ring transmission

Bus bypassing matrix switch in add-drop multiplexer

A digital communications apparatus for receiving a plurality of parallel digital input signals (IN1 . . . IN1 6) all at one rate, and for interleaving multiple bit sequences of a predetermined length from each of the input data streams into a single data stream at a higher rate. The apparatus has a plurality of first stage blocks (BIC1) each adapted to receive a plurality of the input data streams and to output a similar number of data streams at the same bit rate but with the bits of the incoming data signals interchanged. The first stage blocks are connected to a plurality of second stage blocks (BIC2) each connected to said first stage blocks (BIC1) in such a manner that each secondary stage block is connected to a first stage block by a single data stream so that the secondary stage blocks (BIC2) interchange the bits of the already bit-interchanged input signal to generate a plurality of digital output data streams. Depending on the number of input signals to be interleaved the second stage blocks may be similarly connected to third stage blocks, and so on. Finally the apparatus has circuitry (IL) for interleaving the output data streams from the second or final stage blocks to produce the higher rate output data stream.

PCM communication system

A transmission system in which a plurality of data streams are to be multiplexed and sent between receiving and transmitting equipment. At the transmit end the system comprises a plurality of worker tributary cards (51, 52) each having an input port (57) connected to an individual tributary to be sent to an associated multiplexer, and a stand-by tributary card (56) operative to replace a failed worker card. All the worker tributary cards (51-55) are interconnected by a common line (60) leading to the iput port (57) of the stand-by tributary card (56) but in normal operation being isolated from said line by a controllable unity-gain buffer 58. Each tributary to be transmitted is connected to an input port (57) of a worker tributary card and has a branch line which is connected to said common line (60) via the buffer (58) carried on another tributary card, detection of failure of a worker tributary causing the buffer (58) of the associated worker tributary card to be enabled to connect the tributary to said stand-by tributary card.

Data path protection

A system for transmitting digital data by time division multiplex (TDM) includes a transmission terminal for transmitting a TDM data stream having a frame structure which includes fixed stuff bytes and/or frame overheads forming part of the payload but not normally available to the user. The system includes a processor for locating said fixed stuff bytes, and overwriting at least some of the fixed stuff bytes to introduce mark parity, and a receive terminal having a processor for detecting the introduced parity bytes and determining whether or not there has been an error in transmission. The processor at the receive terminal includes an AND-gate to which the transmitted TDM signal containing mark parity is fed, a clock for supplying a clock signal to the AND-date, a bistable flip-flop connected to the output of the AND-gate, and a band pass filter for filtering the output of the AND-gate.

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Coventry, United Kingdom

Stephen P Ferguson