h exchange lines for
conversation are held longer than are the actual long-distance trunks
between cities. Knowing the probable traffic to be brought to the
long-distance switching center by the long-distance trunks from exchange
centers, the number of trunks required may be determined by knowing the
capacity of each trunk. These trunk capacities vary with the method of
handling the traffic and they vary as do local trunks with the number of
trunks in a group. Table XVII illustrates this variation of capacity
with sizes of groups.

TABLE XVII

Messages per Trunk in Long-Distance Groups

+--------------------------+-------------------------+
| NUMBER OF LONG-DISTANCE | MESSAGES PER TRUNK PER |
| TRUNKS IN GROUP | BUSY HOUR |
+--------------------------+-------------------------+
| 5 | 2 |
| 10 | 3 |
| 20 | 3.2 |
| 40 | 3.5 |
| 60 | 4 |
| 100 | 4.6 |
+--------------------------+-------------------------+

=Quality of Service.= The quality of telephone service rendered by a
particular equipment managed in a particular way depends on a great
variety of elements. The handling of the traffic presented by patrons is
a true manufacturing problem. The quality of the service rendered
requires continuous testing in order that the management may know
whether the service is reaching the standard; whether the standard is
high enough; whether the cost of producing it can be reduced without
lowering the quality; and whether the patrons are getting from it as
much value as they might.

In manual systems, the quality of telephone service depends upon a
number of elements. The following are some principal ones:

1. Prompt answering.

2. Prompt disconnection.

3. Freedom from errors in connecting with the called line.

4. Promptness in connecting with the called line.

5. Courtesy and the use of form.

6. Freedom from failure by busy lines and failure to answer.

7. Clear enunciation.

8. Team work.

_Answering Time._ There is an interrelation between these elements. Team
work assists both answering and prompt disconnection. The quality of
telephone service can not be measured alon