Figure 6-39.--The rotary switch in the selector, simplified block diagram.

--A calling station initiates finder action by

Figure 6-39 is a block diagram of a typical MDM

removing the handset from the cradle, causing shared

system, having 300 telephone stations in three groups

switching equipment to be placed under the control of

(switchboards) of 100 each. One finder/selector, one

the calling line by way of a connection in the wire

a l l o t t e r , and one connector represent each

bank.

switchboard. Each selector terminates into a connector

circuit. The selector (using a rotary switch) is the link

--Dialing from the calling station extends the

between the linefinder and the connector. Although

switching link to a wire bank position that terminates

the rotary switch has 20 positions, only 10 are shown

the audio leads of the called station.

The sample call diagramed in figure 6-40, view

B, is between station 262 (the calling party) and

Sample Call

station 474 (the called party). Assume that station 474

is not busy at the time of the call and that the idle

Figure 6-40 is a simplified block diagram tracing

connector is connector No. 13 in the switchboard of

a sample call from one station to another. As an aid

the called station.

toward understanding the actions involved in

completing this call, keep in mind the following facts

The T and R leads for line 262 terminate in

concerning the MDM system:

switchboard cabinet No. 1 and extend to wire bank

position 62 by way of the line circuit serving level 6,

--Each telephone station has audio (tip and ring)

line 2. When the calling party operates the hook

leads that terminate in the wire bank of a switchboard

switch, line circuit 262 extends two sources of battery

cabinet.

Figure 6-39.--The rotary switch in the selector, simplified block diagram.