The Secure Telephone Unit - Third Generation (STU-III) is a low-cost, user-friendly, secure telephone device. The terminals are designed to operate reliably, with high voice quality, as both ordinary telephones and secure instruments over the dial-up public switch telephone network. STU-III operates in full-duplex over a single telephone circuit using echo canceling modem technology. STU-IIIs come equipped with 2.4 and 4.8 kbps code-excited linear prediction (CELP) secure voice. Secure data can be transmitted at speeds of 2.4, 4.8, and 9.6 kbps. There are many manufacturers each having different maximum throughput rates. The data throughput between two STU-IIIs can only be as great as the slowest STU-III connected. After, 31 March 1998, General Dynamics (Formerly AT&T) became the only producer of STU-III terminals.
The STU-III Family consists of some of the following
- The STU-III/Low Cost Terminal (LCT) was designed for use in the office environment among a broad spectrum of military, civil, government, and selected private sector users. It is compatible with standard modular or multiline (key system) connectors and operates full-duplex over a single telephone circuit.
- The STU-III/Cellular Telephone is interoperable with all other versions of the STU-III Family. It combines cellular mobile radiotelephone technology with advanced secure voice/data communications. The unit includes a message center that is integrated with the standard cellular handset; it can be conveniently mounted inside a vehicle and provides all STU-III functions, including authentication/classification display.
- The STU-III/Allied (A) is a specialized version of the STU-III/LCT that is compatible with the STU-II. It retains all basic STU-III functions and capabilities and incorporates STU-II BELLFIELD Key Distribution Center (KDC), STU-II net, and STU-II multipoint modes of operation.
- The STU-III/Remote Control Interface (RCU) provides RED enclave subscribers with STU-III compatible secure communications in a rack-mounted remotely controlled line encrypting unit. When used in conjunction with a RED switch or conferencing director, the STU-III/R allows STU-III users to confer with multiple STU-III users or others who have secure functions. It is capable of encrypting/decrypting voice or data over two-wire or four-wire telephone systems and incorporating a 2.4 kbps BLACK digital (external modem) interface.
- The MultiMedia Terminal (MMT) 1500 is a diversified STU-III capable of clear or secure voice and data communications over both analog and digital mediums. The MMT interfaces to the commercial telephone system via a standard RJ-11 telephone jack and to digital systems through a Black Digital Interface (BDI). The BDI port will support both half-and full-duplex communications, precedence dialing, black digital network signaling, and multiple satellite hopsWhen unattended the MMT can automatically answer an inbound call without operator intervention and establish a secure link with any user on a preprogrammed Access Control List (ACL).
- The Inter Working Function (IWF) is the shore gateway device that provides the digital to analog conversion between the MMT and the analog STU-III. The IWF supports half and full duplex voice and data communications with rates of 2.4, 4.8, and 9.6Kbps. The IWF improves secure voice and data synchronization over multiple satellite hops with programmable extended time-outs and pre-staging of STU-III call information. The IWF supports all necessary network-signaling functions to enable call setup and status messages including canned voice messaging to the analog user.
- The STU-III Secure Data Device (SDD) is designed with the same capabilities as other members of the STU-III family including Secure Access Control System (SACS), remote authentication (RA), remote control, auto-answer secure data, and capable of operating in both attended and unattended environments. The SDD provides protection for facsimiles, e-mail, and computer communications.
- The Motorola CipherTAC 2000 (CTAC) STU-III family compatible secure voice communications via cellular phone. CTAC without an inserted CipherTAC 2000 security module is unclassified and functions as a non-secure commercial off the shelf (COTS) telephone product. The CTAC CiphterTAC security module is certified for all levels of classified discussions up to and including SECRET in an adequate operating/security environment.