Abstract: A series of nodes in a telecommunications network are connected by a bi-directional transmission path. An outgoing signal passes each of the intermediate nodes in the path and sets a counter timing at each intermediate node. The outgoing signal then returns from the loop node with time information attached to it. As the returning trigger signal passes the intermediate nodes, the intermediate nodes stop counting the elapsed time since the trigger signal passed the intermediate node, and latches the time information. Precision time synchronization information is then determined for each intermediate node by halfing the two way travel time from the intermediate node to the loop node, adjusting for propagation and processing delays, and adding it to the time information from the loop node.

Abstract: A characteristic of a signal received via a receive line is monitored and used for automatic control of a line buildout circuit in a transmit signal path. The characteristic is conveniently an amplitude level, or differential amplitude levels for different signal bandwidths, of the received signal. The transmit line buildout circuit includes a transversal filter in which multiplier coefficients or delay times are controlled. The arrangement is particularly useful for digital signal interfaces on a digital cross connect.

Abstract: A digital signal, such as a t.d.m. PCM signal, is redundantly encoded in that sequences of n bits of the signal are transmitted as sequences of m bits, where m>n. Different sets of m-bit sequences are used to transmit the n-bit sequences in dependence upon the state of an additional signal, which may be a superframe indication signal. At a receiver, the digital signal and additional signal are reproduced. In the described embodiment =n+2, providing further redundancy to facilitate providing such desirable transmission code properties as maintaining d.c. balance and detecting errors on the transmission link.

Abstract: 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.

Abstract: In a high-speed fiber-optic transmission system, data streams are synchronized using fixed stuffing before being multiplexed for transmission. The fixed stuffing information is replaced with forward error correction (FEC) information, whereby FEC is effected without any increase in transmission speed. FEC information blocks of each data stream can be synchronized to the frame timing of the transmission system, or they can be relatively unsynchronized. In the latter case, an FEC decoder acts in a self-framing manner to synchronize itself to the FEC information blocks of the respective data stream.

Abstract: In a broadcast transmission system, in which in normal operation messages and terminal addresses are transmitted between a master station and a plurality of terminals each having an assigned address, the master station initially assigns the addresses to the terminals. In order to isolate each terminal in turn to assign it an address, the master station varies one or more parameters which affect the bit error rate of the terminals while polling the terminals, and each terminal which receives the poll with an acceptable bit error rate responds to the poll. When the master station receives only one response to a poll, it assigns an address to the responding, isolated, terminal which thereafter does not respond to the poll. This procedure is repeated until addresses have been assigned to all of the terminals. The parameter may, in particular, be the strength of the signal transmitted by the master station.

Abstract: Frame synchronization to the frame pattern of a DS3 bit stream is achieved by detecting the framing pattern and producing a synchronizing slip in the absence of such detection. In order to avoid long frame times as a result of unconfigured adjacent DS1 transmission links producing data which mimic the DS3 framing pattern, redundantly transmitted stuff information (tributary justification control) bits are also checked to ensure that appropriate bits, relative to the position of the framing pattern bits, have expected properties (e.g. triplicated values), and a synchronizing slip is also produced if this is not the case. Short framing times are also achieved by storing in each of the framing pattern and stuff information bit detectors not only the particular bits which are currently to be checked, but also consecutive bits which are selected in dependence upon the occurrence of previous synchronizing slips.

Abstract: Asynchronous packets for a plurality of channels, each packet comprising a channel address and two information bytes, are stored in a FIFO. The address in the packet is used with a first pointer to address a RAM for storing the bytes therein. The RAM is cyclically addressed by a channel address together with a second pointer to read the bytes out synchronously to the relevant channel. Updating of the second pointer is inhibited for each channel initially to prime the RAM with bytes for the channel, and if the pointers become equal. The bytes may comprise speech samples or data. A mapped memory may be provided for converting between channel addresses in the packets and output channel addresses.

Abstract: At a transmitter of a digital transmission system which uses a redundant transmission code to transmit data, at least one predetermined code combination which occurs randomly in the encoded data is selectively modified, to form a predetermined code violation, in dependence upon an additional signal which is to be transmitted. At a receiver, the predetermined code violation is detected and corrected to reproduce the additional signal and the data. By selection of appropriate code combinations and violations more than one additional signal can be transmitted. The arrangement is particularly suitable for transmission of additional signals, which may comprise protection switching signals or a digital voice channel signal, via fiber optic transmission links using 2AMI encoding.

Abstract: A periodically reset flip-flop is set when an error is detected in the bit stream of a digital transmission link being monitored. A counter is incremented in response to each period during which the flip-flop is set and is decremented in response to a plurality of periods during each of which the flip-flop is not set. An alarm signal is produced if the count reaches a certain value. In the presence of the alarm signal, the number of error-free periods which must occur to decrement the counter is increased. The arrangement is less sensitive to error bursts causing false alarms than bit-error-rate monitoring arrangements.