ing
equipment.

Center checking originated long before the invention of common-battery
systems. It requires merely that no waystation shall have a generator
which can ring a bell. The method most widely used is to equip the
waystations with magneto generators which produce direct currents only;
such a generator cannot operate a polarized ringer. It is not usual to
produce the direct current by actually rectifying the alternating
current, but merely by omitting half the impulses, sending to the line
only alternate half-cycles of the current generated. Any drop or relay
adapted to respond to regular ringing current will respond to this
modified form of generator.

CHAPTER XXXVII

TELEPHONE TRAFFIC

The term "traffic," with reference to telephone service, has come to
mean the gross transaction of communication between telephone users.
This traffic may be expressed in whatever terms are found convenient for
the particular phase considered.

=Unit of Traffic.= With reference to payment for local telephone
service, the conversation is the unit of traffic. In the daily
operations of telephone systems there are fewer conversations than there
are connections and fewer connections than there are calls, because
lines are found busy and all calls to subscribers are not answered.

For these reasons, in traffic inquiries which have to do with the amount
of business which subscribers attempt to transact, the total traffic in
a given time usually is considered as so many calls originated by the
subscribers in the community. From this condition arises the term
"originating calls."

For the reason that the purpose of the switching equipment in a central
office is to make connections, the abilities of operators and of
equipments frequently are measured in terms of connections per hour or
per other unit of time.

For the reason that in charging for service all unavailing calls are
omitted, the conversation is the unit of traffic.

=Traffic Variations.= Telephone-exchange traffic is subject to such
general variations as are noted in the way a compass needle points
north, the migrations of birds, the blowing of the trade winds, and
other natural phenomena. There are variations in traffic which occur
each day, others which change with the seasons, and still others which
are related to holidays and other special commercial and social events.
For instance, the day before Thanksgiving Day, in many regions, is the
busiest tel