Secure Terminal Equipment (STE) is the U.S. government's current (), encrypted telephone communications system for wired or "landline" communications. STE is designed to use
ISDN
Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Wor ...
telephone lines which offer higher speeds of up to 128 kbit/s and are all digital. The greater bandwidth allows higher quality voice and can also be utilized for data and fax transmission through a built-in
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' ('' data terminal equipment'') suc ...
port. STE is intended to replace the older
STU-III
STU-III (Secure Telephone Unit - third generation) is a family of secure telephones introduced in 1987 by the NSA for use by the United States government, its contractors, and its allies. STU-III desk units look much like typical office telephone ...
office system and the
KY-68 tactical system. STE sets are backwards compatible with STU-III phones, but not with KY-68 sets.
STE sets look like ordinary high-end office desk telephones and can place unsecured calls to anywhere on the
public switched telephone network
The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...
(PSTN), as well as secured calls on it via the phone's backwards compatible STU-III mode. There is a
PC Card
In computing, PC Card is a configuration for computer parallel communication peripheral interface, designed for laptop computers. Originally introduced as PCMCIA, the PC Card standard as well as its successors like CardBus were defined and devel ...
slot in the STE that allows a
Fortezza Plus (
KOV-14) Crypto Card or
KSV-21 Enhanced Crypto Card to be inserted. When an
NSA configured Crypto Card is present, secure calls can be placed to other STE phones. STE phones are "releasable" (unlike STU-III sets). All cryptograp