Volume Ii Part 19 (2/2)

[Ill.u.s.tration: Fig. 452. Load Curve]

_Busy-Hour Ratio._ If the story told by Fig. 452 were to be turned into a table of calls per hour, the busiest hour of the day would be found to correspond to the highest portion of the figure, and in that busiest hour of the day, if a number of selected days were to be compared, would be found a very constant traffic. The number of calls made, or the number of connections completed, in that particular hour, day by day, would be found to be much the same. The ratio of the number of units in that hour to the number of units in that entire day would be found to be practically the same ratio day by day. This ratio of busy hour to total day would be found to be much more nearly constant than the gross number of calls per hour or per day.

In a large, busy city, about one-eighth of the total daily calls are in some one hour; in a smaller, less active city, probably one-tenth are so congested. This is reasonable when one remembers that in the larger city the active business of the day begins later and ends earlier.

=Importance of Traffic Study.= A knowledge of the amount of traffic in an exchange, and its distribution as to time and as to the divisions of the exchange, is important for a number of reasons. Traffic knowledge is essential in order that the equipment may be designed and placed in the proper way and the total load distributed properly on that apparatus and its operators.

For example, in an office equipped with a manual multiple switchboard, the length of the switchboard is governed entirely by the number of operators who must work before it. It is mechanically possible to make a switchboard for ten thousand lines only 15 feet long, seating seven operators. The entire multiple of ten thousand lines could appear three times in such a switchboard. The seven operators could not handle the traffic we know would be originated by ten thousand lines, with any present system of charging for service. Even a rough knowledge of the probable traffic would enable us to approximate the number of operators needed and to equip each position, not only with access to the ten thousand lines to be called, but also with just enough keyboard equipment, serving as tools, and just enough answering jacks, serving as means of bringing the traffic to her. It is foreknowledge of traffic which enables a switchboard to fit the task it is to perform.

=Rates of Calling.= The rates of calling of different kinds of lines vary. The lines of business stations originate more calls than do the lines of residences. Some kinds of business originate more calls than others. Some kinds of business have a higher rate of calling in one season than in others. Flat-rate lines originate more calls than do message-rate lines. When a line changes from a flat rate to a message rate, the number of originating calls per day decreases. An operator's position, handling message-rate lines only, can serve more lines than if all of them were at flat rates. The number of message-rate or coin-prepayment lines which an operator's position can care for depends not only on the traffic but on the method of charging for service, whether by tickets or meters and upon the kind of meters; or it depends on the method of collecting the coins. In some regions, the rate of calling, on the introduction of a complete measured-service plan, has been reduced to one-fourth of what it was on the flat-rate plan.

In manual switchboards of early types, wherein the position of the subscriber's answering jack was fixed by his telephone number, the inequality of traffic became a serious problem. Most of the subscribers who first installed telephones when the exchange was small, retained their telephones and numbers; as their use of the telephone grew with their business, it was customary to find the positions answering the lower numbers much more busy than the positions answering the higher numbers, the latter belonging to later and usually less active business places.

_Functions of Intermediate Distributing Frame._ The intermediate distributing board was invented to meet these conditions of unequal traffic upon lines and of variations in traffic with changes of seasons and of charges. The intermediate distributing board enables a line to retain its number and its position in the multiple, but to keep its answering jack and lamp signal in any desired position. If a flat-rate subscriber changes to a message rate, his line may be moved to a message-rate position and be answered, in company with others like it, by an operator serving many more lines than she could serve if all of them were flat rate.

=Methods of Traffic Study.= The best way to learn traffic facts for the purposes of designing and operating equipment is to conduct systematic series of observations in all exchanges; to record them in company with all related facts; and to compare them from time to time, recording the results of the comparisons. Then when it is required to solve a new problem, the traffic data will enable the probable future conditions to be known with as great exactness as is possible in studies with relation to transportation or any other human activity.

TABLE XIII

Calling Rates

+-------------------------+-------------------------------+

CALLS PER DAY WITH DIFFERENT

KIND OF SERVICE

METHODS OF CHARGE

+-------------+-----------------+

FLAT RATE

MESSAGE RATE

+-------------------------+-------------+-----------------+

Residence

8

4

Business

12 to 20

8 to 14

Private Exchange Trunk

40

25

Hotel Exchange Trunk

50

30

Apartment House Trunk

30

18

+-------------------------+-------------+-----------------+

There are three general ways of observing traffic. A record of originating calls is known as a ”peg count,” because the counting formerly was done by moving a peg from place to place in a series of holes. The simplest exact way is to provide each operator with a small mechanical counter, the key of which she can depress once for each call to be counted. A second way is to determine a ratio which exists, for the particular time and place, between the number of calls in a given period and the average number of cord circuits in use. Knowing this ratio, the cord circuits can be counted, the ratio applied, and the probable total known. The third method, which is applicable to offices having service meters on all lines, is to a.s.sociate one master meter per position or group of lines with all the meters of that position or group, so that each time any service meter of that position is operated, the master meter will count one unit. This method applies to either manual or automatic equipments.

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