The Automatic Voice Network (AUTOVON, military designation 490-L) was a worldwide

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, p ...

military telephone system. The system was built starting in 1963, based on the Army's existing Switch Communications Automated Network (SCAN) system. In June 1966, the Air Defense Command voice network was cut over to the new service. In 1969, AUTOVON switching centers opened in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, and later in other European countries,

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, the

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, and

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. It was a major part of the Defense Communications System (DCS), providing non-secure switched voice services. The system was replaced in the early 1990s by the

Defense Switched Network The Defense Switched Network (DSN) is a primary information transfer network for the Defense Information Systems Network (DISN) of the United States Department of Defense. The DSN provides the worldwide non-secure voice, secure voice, data, fac ...

Circuits

AUTOVON used a combination of its own constructed circuits and other lines operated by

AT&T Corporation AT&T Corporation, an abbreviation for its former name, the American Telephone and Telegraph Company, was an American telecommunications company that provided voice, video, data, and Internet telecommunications and professional services to busi ...

and smaller independent telephone companies, connected by high-speed switching centers produced by

Automatic Electric Company Automatic Electric Company (A.E. Co.) was an American telephone equipment supplier primarily for independent telephone companies in North America, but also had a worldwide presence. With its line of automatic telephone exchanges, it was also a lo ...

to exchanges located far from other civilian or military targets. In the US the cables were predominantly

L-carrier The L-carrier system was one of a series of carrier systems developed by AT&T for high-capacity transmission for long-distance communications. It was the first designed to handle hundreds of Voice frequency, voice frequency telephone lines, compared ...

coaxial multiplex built by AT&T, who also used them to carry about one third of all civilian long-distance calls, as their capacity was much higher than the military needed. Although unused, some of the cables remain today and the routes are visible on satellite photos. The system's traffic was transported over many media other than underground cable, including

microwave link Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz (1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signal ...

s, open wire and, near the end of the system's life,

fiber optic An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

. Most of the cable was directly buried without added concrete, relying instead on the natural protection of soil. In some areas, however, cables from the AUTOSEVOCOM network were laid in parallel. These were often concrete-encased when the traffic they were carrying was not

encrypted In cryptography, encryption (more specifically, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as plain ...

. The

telephone switches A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...

used were initially a 4 wire version of

Number Five Crossbar Switching System The Number Five Crossbar Switching System (5XB switch) is a telephone switch for telephone exchanges designed by Bell Labs and manufactured by Western Electric starting in 1947. It was used in the Bell System principally as a Class 5 telephone swi ...

, replaced in the early 1970s after the more versatile

1ESS switch The Number One Electronic Switching System (1ESS) was the first large-scale stored program control (SPC) telephone exchange or electronic switching system in the Bell System. It was manufactured by Western Electric and first placed into servi ...

had shown its reliability. Most of the cable repeater huts have been sold to private interests, to round out existing parcels, or as possible build-to-suit tower sites, etc. AT&T has been filling the small underground portion before sale, unless they sell to a major company. The junctions for AUTOVON are also being sold into private ownership, with a few exceptions. Most are stripped of all the equipment, although the AUTOVON junction in

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was sold with all the old equipment in place.

Multilevel precedence and preemption

The AUTOVON system provided a facility for placing calls with multilevel precedence and preemption (MLPP). If in the public switched telephone network a caller encounters congestion because no circuits are available, the caller typically receives the

reorder tone The reorder tone, also known as the fast busy tone, or the congestion tone, or all trunks busy (ATB) tone is an audible call progress tone in the public switched telephone network (PSTN) that is returned to a calling party to indicate that the cal ...

("fast-busy" signal) and is unable to reach the

called party The called party (in some contexts called the "B-Number") is a person who (or device that) answers a telephone call. The person who (or device that) initiates a telephone call is the calling party. In some situations, the called party may numbe ...

. In military networks such an event was not acceptable, as some calls must always be completed. AUTOVON included four

message precedence Message precedence is an indicator attached to a message indicating its level of urgency, and used in the exchange of radiograms in radiotelegraph and radiotelephony procedures. Email header fields can also provide a precedence flag. Early teleg ...

levels: ''Routine'', ''Priority'', ''Immediate'' and ''Flash'', and had an additional capability called ''Flash Override''. These levels were activated using the buttons in an additional column of the keypad, which produced the dual-tone multi-frequency (DTMF) signals A, B, C, and D: *A (697/1633 Hz): Flash Override (FO) *B (770/1633 Hz): Flash (F) *C (852/1633 Hz): Immediate (I) *D (941/1633 Hz): Priority (P) ''Routine'' was the level of calls without priority and required no special signaling; the user would only dial the telephone number. Calls with precedence required preceding the telephone number with the desired precedence signal. Calls of increasing precedence could preempt calls of lower priority, giving them a special tone, if need be. For example, if a call was placed with Flash precedence and the route had no available trunks, the switch would preempt a Routine call, and if none in progress, would search for Priority and Immediate type calls. Only when all lines of a switch were already used with Flash or Flash Override precedence would the caller receive a reorder signal. The authority of a caller to use the precedence levels was granted by complex regulations. Flash Override was not designated as a precedence level, but a ''capability'' designed to allow the

President of the United States The president of the United States (POTUS) is the head of state and head of government of the United States. The president directs the Federal government of the United States#Executive branch, executive branch of the Federal government of t ...

or other National Command Authority to preempt any other traffic in the network in an emergency. The

International Telecommunication Union The International Telecommunication Union (ITU)In the other common languages of the ITU: * * is a list of specialized agencies of the United Nations, specialized agency of the United Nations responsible for many matters related to information ...

accepted the MLPP specification as recommendation Q.955.3 in March 1993.

Numbering plan

AUTOVON used a numbering scheme similar to the

North American Numbering Plan The North American Numbering Plan (NANP) is an integrated telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1, World Numbering Zone ...

. The network had its own three-digit area codes for various geographic regions around the world. Each area code covered several three-digit exchange codes, usually corresponding to the central office telephone switches serving each installation. Thus, almost any telephone on a military base could be direct-dialed via AUTOVON. A selected set of telephones were four-wire AUTOVON phones, wired directly into the AUTOVON network. Others could initiate AUTOVON calls with operator assistance. Though the numbering plan was similar to the U.S. civilian scheme, the routing structure was a very complex ''polygrid'' system unlike the civilian office classification scheme, which used a 5-level hierarchical system in which longer-distance traffic, in general, was handled by higher-level switches. It was barely within the information processing capabilities of the Number Five Crossbar switching system which implemented it. The non-hierarchical routing structure was intended to get around any number of nodes destroyed in war. This system inspired similarly survivable ones for message networks, including in future decades the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

. Local base switches would be connected to a few AUTOVON trunks, which the user would access by dialing 8 (or in some cases, 88) before the telephone number. To dial locally a user would dial 9, and to dial using commercial long-distance, 1 (where this was supported). The

United States Department of Defense The United States Department of Defense (DoD, USDOD, or DOD) is an United States federal executive departments, executive department of the federal government of the United States, U.S. federal government charged with coordinating and superv ...

(DoD) charged access to AUTOVON according to a complex billing system, and each base budgeted according to local practice.

Defense Switched Network

The digitization of and upgrade of AUTOVON began in 1992 and took several years to complete. Equipment is housed in a network of redundant and distributed deep underground facilities spread across the globe, each of which are capable of withstanding multiple direct nuclear attacks of very significant yield. All equipment is housed in such a way that it can absorb multiple blast waves propagating underground while still maintaining continuous operation. The engineering is still impressive by today's standards and it is still in use today.Suelette Dreyfus, Digital Underground, ch. 10 (edited by Julian Assange)

References

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External links