digits to the cyclic store for network arrangement in which the several individual control ele- a code translation and will store any routing digits which may be ments (microprocessors) associated with different network ports are returned together with the identity of the route and, where required, able to set up digital paths through the network simultaneously without a need for some central network controller. the number length. The MCU then carries out a further search over the cyclic stores The distributed control implementation in System 12 results in a to identify a free junction within the required route and when this is number of system characteristics representing direct benefits to both found by comparison, its identify is stored within the MCU. Two network operators and users, e.g. robustness against total system paths are now set up in sequence in the same way as already failure, capability for smooth incremental growth both in traffic and described, one between the sending side of the register and the control capacity, high degree of system uniformity leading to the selected outgoing junction, and the other between the calling line need for only a very limited set of printed board types to build up an and the outgoing junction, the latter path having a split function in exchange. All these aspects make System 12 an outstanding product in the world of telecommunications. the link circuit. The MCU then instructs the register to send the appropriate routing digits over the junction, followed by the numeri- Finally, good indications exist that for the next major evolutionary cal digits identifying the wanted customer. When this has been done, step in switching, the so called Broadband ISDN, fully distributed the split is removed from the final conversation path and the con- control systems based on end-controlled switching networks are the nections between the calling customer and the register and the obvious solution. In this sense, System 12 is already prepared for this transition. register and the out