Abstract: The invention relates to a digital loop sharing telephone system and also to a digital telephone for connection into such a system. The loop may be for a parallel telephone system or a party-line system. Each telephone is adapted to transmit data in an upstream direction on the loop, that is towards an exchange of the system, which data may originate from the telephone itself or a further telephone downstream thereof. Each telephone includes code detector circuitry and logic circuitry whereby if the telephone is the first to change to an off-hook or active condition it "seizes" the loop for exclusive data transmission to the exchange. In the case of a parallel telephone system any telephone going off-hook can receive incoming data from the exchange but only the first telephone to go off-hook can send data. In the case of a party-line system only the telephone which seizes the loop can receive data.

Abstract: The invention relates to method of interconnecting terminal devices in a digital telephone network wherein either the terminal devices in question normally operate at different data rates or they are to be interconnected over data links in the network which normally operate at different data rates. The method involves firstly determining, by processor means at a switching point in the network, the normal data bit rate of two terminals to be interconnected as well as the normal data bit rate of the or each data link over which the connection is to be made. In the case where there is a difference in the normal data bit rates the processor initiates a procedure to send a digital bit stream to one or both of the terminals to cause the terminals to operate, in the course of the connection, at a common data rate equal to the lowest of the normal data bit rates of said terminals and said data link.

Abstract: A digital switch for switching word formatted PCM digital data is disclosed. The data of each PCM word is serially bit switched rather than being switched in parallel as in conventional PCM switches. This is achieved by time multiplexing corresponding word bits of respective incoming channels or inlets onto a single data highway to form a bit interleaved digital bit stream. Data on the highway is switched through a RAM under control of a control memory according to the required connections so as to rearrange the order of the data bits. The rearranged data is demultiplexed to the respective outgoing channels or outlets. To avoid less of alignment of word boundaries at the outlets, as between respective channels, the switch determines those connections which incur a switch cycle delay relative to those which do not.

Abstract: The invention relates to a digital data switch for serially bit-switching word synchronized Pulse Code Modulated (PCM) data from inlets to outlets of the switch. The switch is particularly intended for use in situations wherein PCM data words arriving at the switch on different inlets are not aligned in so far as word boundaries are concerned. The PCM data is bi-polar or diphase modulated and the synchronization information of each word consists of a violation of the modulation. The switch includes a demodulator on each inlet for demodulating the data and a synchronization detect circuit associated with each demodulator for detecting the synchronization information in each incoming data word. The switch has two functionally identical time division multiplexed switch paths; one being a data path and the other being a by-path for switching the synchronization information.