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1998-04-20 22:36:18


U.S. Defense System's Communications May Crash in 1999



This 1993 article describes the Defennse Department's 1986 decision to switch to the Global Positioning System (GPS) to regulate its communications system.

On August 22, 1999, the GPS will lose 1,024 weeks. If all GPS-dependent telecommunications software is not recoded, tested and implemented by that date, it will go down.

Hello? Hello?

* * * * * * * *

Network synchronization in any telecommunications system in essential in order to achieve the required performance objectives. . . .


The Defense Communications System (DCS) is a worldwide communications network serving the needs of the Commanders -in-Chiefs (CINCs) and their respective areas. The network frequency reference is in the process of being switched over from the LORAN-C network to the NAVSTAR Global Positioning System (GPS). The DCS is managed by the Defense information Systems Agency (DISA).

The DCS, like other synchronous digital communications system, relies heavily on accurate frequencies being available throughout the network. Accurate and stable frequency is essential to reduce Loss of Bit Count Integrity (LBCI) and provide mission critical communications services to field operations. With the planned phase over from LORAN-C transmissions, the DCS is in the process of installing GPS frequency references at major nodes in the network to improve and maintain network stability. . . .

The Defense Communications System (DCS)

The Defense Communications Agency (renamed Defense Information Systems Agency in 1991) began converting the DCS from an analog system to a digital system in the early 1970s, much in the same way that AT&T was converting their system. During the transition period the DCS digital transmission subsystems were timed by clocks intrinsic to the equipment (e.g, internal clock) and by use of pulse stuffing and buffering, also intrinsic to the transmission equipment However, the introduction of digital switches and other subsystems required the use of synchronous transmission, which requires that an accurate clock signal accompany the digital data signal.

Network Synchronization in the DCS

After studying various network synchronization schemes which could be used to support a synchronous network, an independent clock approach was selected to maximize network survivability. . . .

LORAN-C was selected as the original reference standard for the candidate timing and synchronization subsystem primarily because of its low cost off-the-shelf availability, and virtual worldwide coverage necessary for a global communications system. . . .

By 1986, it became evident that the long-term goal of the DoD was to phase out LORAN-C and other navigation systems in favor of GPS.


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