Abstract: A framer-demultiplexer circuit provides means for reducing the high serial bit-stream rate of byte-interleaved low level signal frame structures proposed by the Synchronous Optical Network (SONET) signal hierarchy to speeds which can be processed with low-power low-cost CMOS VLSI technology, while establishing and maintaining basic byte integrity. In this circuitry the incoming high-rate serial bit stream is divided alternately between shift registers 43, 44 under the control of a single high-precision clock-division circuit to provide a multi-bit formatting that enables parallel delivery of stage bytes with the multifold reduction in transmission to a rate within the processing capabilities of CMOs devices.

Abstract: A demultiplexer circuit which extracts from an incoming time division multiplexed digital bit stream any combination of PCM encoded words or data bits, irrespective of the rate of latter or the position of the data bits in a given channel or channels. The demultiplexer circuit includes a random access memory (12) for storing information as to the bit(s) to be demultiplexed out of the incoming digital bit stream. A counter (13) operates in synchronism with the received bit stream and the output thereof serves to access the random access memory to provide output signals indicative of the bit(s) carrying information for the subscriber station. These output signals are utilized to read the digital signals intended for said station into other random access memory (31, 41). A summing circuit (16-19) is coupled to the input of said other memory so that conference calls are summed in real time.

Abstract: A demultiplexer circuit which extracts from an incoming time division multiplexed digital bit stream any combination of PCM encoded words (in separate channels), or data bits irrespective of the rate of the latter or the position of the data bits in a given channel. The demultiplexer circuit includes a random access memory (12) (RAM) for storing information as to the channel(s) to be demultiplexed out of the incoming digital bit stream. A counter (13) operates in synchronism with the received bit stream and the output thereof serves to access the RAM to provide output signals indicative of the channel(s) carrying information for the subscriber station. These output signals are utilized to read the digital signals intended for said station into a shift register (16). A summing circuit (17, 18) is interconnected with the register so that conference calls are summed in real time. Before the next frame of digital signals, the contents of the register are transferred to a second shift register (21).

Abstract: A transmitter of information to be communicated in secure form is optically coupled to a composite optical fiber at one end, the fiber being connected to a receiver of the secure information at the other end. The composite optical fiber has cores including a central core for carrying the secure information, one or more guard signal cores, a cladding matrix surrounding all the cores, and a metallic or other nontransmissive film surrounding the central core but not the guard cores. A guard signal optical transmitter section is coupled to the guard cores for jamming any leakage of secure information through the film, and a guard signal receiver section is provided at the other end of the fiber for monitoring purposes. The optical transmitter apparatus employs pulse code modulation (PCM) and sends related security bits in the guard and secure signals.

Abstract: In a duplex optical communication system employing, at each location, the same electrooptic device alternately as a source and as a detector of optical wave energy, and using a single optical fiber to connect pairs of locations, interference produced by reverse Rayleigh scattering along the fiber is minimized by means of R-C equalizers. The modulation signal applied to the electrooptic device (11) during its transmitting period is simultaneously applied to the equalizer (20). During the receiving period, the signal stored in the equalizer is coupled to the local receiver (18), along with the signal from the electrooptic device, wherein it combines destructively with the reverse Rayleigh scattered signal produced along the fiber by the original transmission.