Most weather offices are equipped with multi-line
telephones to handle normal business. Multi-line
telephones contain six or more buttons in addition to the
normal keypad. Depressing a button will switch the
telephone to the number shown by the lighted button.
Incoming calls activate a flashing light corresponding
to the number of the incoming call. Normally, these
telephones are on unprotected circuits, and classified
information may not be discussed.
Additionally, secure telephones are found in many
offices, and just about every weather activity has at least
one telephone facsimile send and receive terminal.
Telephone Unit-Third Generation (STU-III) is a
communications system that meets the need for the
protection of vital and sensitive information over a
telephone system. The STU-III is a compact, self-
contained, desktop unit capable of providing the user
with both clear as well as secure voice and data
transmissions (fig. 1-2). The STU-III is unique in that it
works as an ordinary telephone and as a secure
telephone network to other STU-III terminals. STU-III
equipment may be used to provide secure
communications on all commercial and military
telephone networks. Full feature STU-III telephone
terminals are equipped with modems that also allow
clear and secure data transfer. However, some
telephone networks do not provide the high-quality,
low-noise circuits necessary for data transmission.
The STU-III is operated the same way as any
regular telephone. That is, you pick up the handset, wait
for a dial tone, and then dial the number of the person
you want to call. Calls on the STU-III are always
initiated in the clear voice mode. Once the party you
have called (at another STU-III terminal) has answered,
you have the option of talking to that person in the clear
voice or secure voice mode.
The STU-III terminal uses special keys with a
designator of KSD-64A. The KSD-64A is a plastic
device that resembles an ordinary key. Two types of
KSD-64A keys are used with the STU-III, the seed key
and the crypto ignition key (CIK). The seed key is
special keying material used for the initial electronic
setup of the terminal. The CIK is used by the operator to
activate the secure mode. CIKs work only on the STU-
III that they are issued with, and are unusable on all
other terminals. More than one CIK may be issued with
Calls are always initiated in the clear voice mode,
exactly the same as a normal telephone call. For users to
go from clear to secure voice transmission, both the
calling and the receiving STU-III terminals must have
the CIK inserted and turned a quarter turn clockwise.
Then either caller may initiate the secure mode by
pressing the "SECURE" button. Once a secure link has
been initiated, the two STU-III terminals begin
Figure 1-2.STU-III terminal.