ds generator which identifies the calling line or junction and stores this to connect itself to the indicated supervisory. When the wanted number in a free register. The register then takes over and applies number has been received by the register it applies to the decoder to for access to call control to set up a connection from the calling line set up an equivalent EN marking. Connection from the incoming or junction to itself. The register marks all free supervisories of the supervisory then proceeds, as already described, except that an first choice route and, simultaneously, sends the calling line's num- additional stage of switching (the D stage) is involved. ber to the called line marker. This decodes the number and marks the line concerned. The path selection apparatus now selects and establishes a path between the calling line and a free supervisory with access to the register already allotted. 32.4 The TXE4 system This method of control greatly improves flexibility in use, since it takes advantage of the high speed of the system and permits origin- TXE4 is designed for local exchanges ranging from 2000 to 40000 ating calls to be released and set up again to a different point within lines and with calling rates from 0.02 to 0.35 erlangs per line. The the inter-digital pause and without the knowledge of the caller. system is readily extensible up to an overall limit of approximately 10000 erlangs of bothway traffic. The system uses a reed relay switching network with electronic 32.3.4 System operation stored program control. The fundamental concept underlying the design is that it should consist of an assembly of a limited number Each customer's line is connected via the MDF to a line circuit of types of sub-system, hardware or software, arranged so that the providing the exchange line termination. Junctions are terminated exchange capacity in terms of connections, traffic or facilities can on supervisory equipments. Each line circuit or incoming supervi- be extended by simple addition of similar subsyste