 Most trunks had three wire spring relays and two scan points.They could supply regular battery or reverse battery to a line, and on-hook or off-hook supervision to the distant end, or be put into a bypass state allowing all functions (usually sending and receiving address signals) to be performed by common control circuits such as digit transmitters and receivers.Slightly more complex trunks, for example those going to TSPS offices for operator control, were packaged as only one per plugin unit.