of
trunks and also as applied to traffic, always refer to the direction in
which the trunk handles traffic or the direction in which the traffic is
flowing with respect to the particular office under consideration at the
time. Thus an _incoming trunk_ at one office is an _outgoing trunk_ at
the other.

_Two-Way Trunks._ Two-way trunks are nearly always employed where the
traffic is very small and they are nearly always operated by having the
_A_-operator plug directly into the jack at her end of the trunk and
displaying a signal at the other end by ringing over the trunk as she
would over an ordinary subscriber's line. The operator at the distant
exchange answers as she would on an ordinary line, by plugging into the
jack of that trunk, and receives her orders over the trunk either from
the originating operator or from the subscriber, and then completes the
connection with the called subscriber. Such trunks are often referred to
as "ring-down" trunks, and their equipment consists in a drop and jack
at each end. In case there is a multiple board at either or both of the
offices, then the equipment at each end of the trunk would consist of a
drop and answering jack, together with the full quota of multiple jacks.
It is readily seen that this mode of operation is slow, as the work that
each operator has to do is the same as that in connecting two local
subscribers, plus the time that it takes for the operators to
communicate with each other over the trunk.

_One-Way Trunks._ Where one-way trunks are employed in the double-track
system, the trunks, assuming that they connect multiple boards, are
provided with multiple jacks only at their outgoing ends, so that any
operator may reach them for an outgoing connection, and at their
incoming ends they terminate each in a single plug and in suitable
signals and ringing keys, the purpose of which will be explained later.
Over such trunks there is no verbal communication between the operators,
the instructions passing between the operators over separate order-wire
circuits. This is done in order that the trunk may be available as much
as possible for actual conversation between the subscribers. It may be
stated at this point that the duration of the period from the time when
a trunk is appropriated by the operators for the making of a certain
connection until the time when the trunk is finally released and made
available for another connection is called the _holding time_, and th