Autovon

The Automatic Voice Network ( AUTOVON ) was a global military phone network in the U.S.. The construction of the system began in 1963 on the basis of the existing Switch Communications Automated Network ( SCAN) of the U.S. Army. In June 1966, the Air Defense Command - phone network was transferred to the new system. 1969 AUTOVON switching centers in the United Kingdom and later other European States, Asia, the Middle East and Panama opened. It was a major component of the Defense Communications System (DCS ) and responsible for the provision of non -secured automatically switched voice services. The system was developed in the early 1990s, replaced by the Defense Switched Network.

Lines

AUTOVON used a combination of exclusive routed cables and such, which were rented at AT & T and small independent telephone companies. The leads were connected to switching centers which were built off of other civilian or military targets. This mainly L -carrier coaxial cable multiplexer were used in the U.S., which were built by AT & T. AT & T also used excess capacity to handle civilian long-distance connections. Even if they are unused today, there are some of the cable today and their routes can be seen in satellite photos. The contents of the net were - also transmitted through other media, including microwave links, overhead lines and - - next to underground cables just before detachment of the system - fiber optic cables. In contrast to stories about concrete concrete ducts, cables are routed in reality most directly in the ground and were only protected by a layer of oil.

Most repeater buildings were sold to private investors in order to strengthen existing capacities or rebuild it in telecommunications rooms, etc. AT & T had underground parts before buying refill, unless they sold to a large company. With a few exceptions, the nodes of the network AUTOVON were sold. Most case, the technology was completely removed, even if the node in Mounds, Oklahoma was sold with the entire equipment.

As services with a 4- wire version of the 5XB switch was used at the beginning, which was in the early 1970s, replaced by the more versatile switch 1ESS after it was able to prove its reliability.

Multilevel presedence and preemption

The AUTOVON system provided a function to pause and force of talks ready which was called multilevel precedence and preemption ( MLPP ). In the public telephone network, it could happen that a line between the caller and called was not available and therefore the call was not made ​​. The caller then got a special kind of busy tone ( " reorder tone" ). In a military telephone network, such behavior was not acceptable, as some phone calls tolerated no delay.

Therefore got four AUTOVON Before computing facturing levels: Routine, Priority, Immediate and Flash, there was also a higher-level stage with the designation Flash Override. These stages were activated by keys in an additional column on the number switch through which the DTMF signals A, B, C and D were generated:

• A ( 679 and 1633 Hz): Flash Override ( FO)
• B ( 770 and 1633 Hz): Flash ( F)
• C ( 852 and 1633 Hz): Immediate (I)
• D ( 941 and 1633 Hz): Priority ( P)

Routine was the stage without priority and did not require a special signal - the user simply had to choose only the phone number. For calls with priority the said priority level had to be dialed before the telephone number. Calls with a higher priority as to interrupt lower talks if it was needed. For example, if a conversation with the precedence level flash was set up and on the route was no free line longer present in a trunk group, the switch finished a telephone call with the priority level routine or - if no such was active - a call to the Priority or Immediate stage. Only if all the lines were already occupied with Flash or Flash Override calls, the caller will hear a busy signal.

Who was allowed to use which priority levels, was the subject of a complex set of rules. Flash override was not designed as a preemption level but should the U.S. President or other members of the National Command Authority the opportunity to interrupt any other telephone traffic in an emergency.

The International Telecommunication Union accepted the MLPP specification as a recommendation Q.955.3 in March 1993.

Numbering plan

AUTOVON used a numbering plan, which was similar to the North American Numbering Plan. The telephone network had its own three-digit area numbers (area codes) for various geographic regions worldwide. Each area was divided into various three-digit "exchange codes" which were usually associated with a central office in a military facility. This allowed almost every military facility be called directly via AUTOVON. A select number of phones were four wire phones, which could directly build calls to AUTOVON network. Others could build AUTOVON talks with the help of an operator.

Although the numbering plan was similar to the civilian plan was the routing structure - in contrast to the hierarchical civilian variant - a very complex, highly meshed system. It was at the limit of the 5XB exchanges on which it was implemented. The non-hierarchical routing structure was necessary in order to still achieve any goal, when a greater number of exchanges was destroyed during a war. This system inspired similar viable systems for the exchange of messages, including the future Internet.

Local switching centers were connected via a few manifolds on the AUTOVON system, which could be reached by selecting the number 8 (in some cases 88 or ). To make local calls, had to be chosen 9. For commercial wide-area connections - if supported - had the 1 will be selected. The Ministry of Defense of the United States (DoD ) calculated from connections to AUTOVON system via a complicated billing system, and each facility according to local guidelines expected from.