Number Groups - The number group translates subscriber directory numbers into line equipment locations of subscriber lines. (The line equipment location identifies the line link frame location of a subscriber line.) The number group also supplies the proper ringing control information and other in' formation concerning the called number, such as whether it is in a terminal hunting group or in a physical or theoretical office.

A number group frame serves 1000 consecutive directory numbers. For example, number group frame 1 contains directory numbers whose numericals are 1000 to 1999. Therefore, the total amount of directory numbers, in multiples of 1000, to be equipped, determines how many number group frames are required.

The number group is also used on tandem or toll through-switched calls. On these calls the number group supplies the marker with the line link frame location of the trunk seeking a path through the office. The trunks may be given regular subscriber directory numbers for use by the marker in entering the number groups. However, since this uses up available numbers (two subscriber numbers per trunk served) it may be better to furnish separate trunk number groups (two required) where the quantity of toll or tandem trunks is high. The trunk number groups are not part of the subscriber number series.

This example is where the number 2348 was classified.