Engine seizure due to improper fuel and oil mixing is one of the most common failures of 2-stroke power equipment. The interface between remote concentrators and telephone switches has been standardised by ETSI as the V5 protocol. Their purpose was to eliminate the need for human switchboard operators who completed the connections required for a telephone call. Examples of signals communicating supervision or call progress include E and M signaling, SF signaling, and robbed-bit signaling. In physical (not carrier) E and M trunk circuits, trunks were four wire. This made it possible for subscribers to call each other at homes, businesses, or public spaces.
See nonblocking minimal spanning switch for a discussion of the Charles Clos algorithm, used in many telephone switches, and a very important algorithm to the telephone industry. Nortel now Genband DMS100 is very popular with operators all over the world. NEC NEAX used in Japan, New Zealand and many other countries. Fifty trunks would require a hundred pair cable between switches, for example.
Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, X-Y, panel switch and the crossbar switch. For wire spring relay markers these noises resembled hail falling on a metallic roof. On a pre-dawn Sunday morning, call processing might slow to the extent that one might be able to hear individual calls being dialed and set up. Multi-frequency (MF) was the last of the pre-digital methods. It used a different set of tones sent in pairs like DTMF. Dialing was preceded by a special keypulse (KP) signal and followed by a start (ST). Variations of the Bell System MF tone scheme became a CCITT standard. These systems could use the old electromechanical signaling methods inherited from crossbar and step-by-step switches. Плюс расположены они глубоко, чтобы увидеть, что за температура выбрана, надо стоять строго над плитой, чуть шагнул в сторону и выбранную цифру не видно! Examples of these systems included the Western Electric 1ESS switch, Northern Telecom SP1, Ericsson AKE, Philips PRX/A, ITT Metaconta, British GPO/BT TXE series and several other designs were similar.