Synchronization related to data streams

A remote terminal for a subscriber loop carrier network operates by flow from one to another of units in the terminal of time division multiplexer data streams of binary valued digital bits. Each stream has the format of periodic frames of time slots of which each frame consists of (a) a service time slot containing only service bits, and (b) a plurality of customer slots which contain mostly bits coded with data from customers of the network, but which also include a less number of service bits. Each unit includes encoding means responsive to local synchronizing and clock pulses derived from data incoming to the unit to encode on each frame of the outgoing data stream synchronizing information consisting of (c) a synchronizing pattern comprising a coded sequence of service bits localized in the frame's service slot and (d) a spoiler pattern formed of service bits distributed over customer slots in the frame. The spoiler pattern is interrelated with the synchronizing pattern so that no fortuitous bit sequence occurring in the stream and including any bit beating customer data can falsely duplicate the synchronizing pattern. Each unit also includes decoding means responsive to the presence of synchronizing patterns in an incoming data stream to produce signals for synchronizing the operation of that unit with the pre-established timing of the incoming stream. Such units may be circuit cards having mounted thereon encoding and decoding means in the form of semiconductive integrated circuits and including binary counters used to implement the encoding and decoding functions.