What Is a DSN Fax Number?

By Irene A. Blake , last updated March 13, 2012
The Defense Switched Network (DSN) is the primary global private-line voice and data services circuit-switch transfer network for the United States Defense Information Systems Network. The DSN is used by the Department of Defense, approved DoD contractors, other government departments and agencies and approved U.S. allies. The network is used for day-to-day standard communications such as voice calls, video teleconferencing and faxes, as well as for high-priority and emergency communications during crises.

DSN Fax Service

DSN provides all the same services that the Public Switched Telephone Network (PTSN) provides. As a result, a DSN fax number, simply put, is a dedicated number for sending and receiving faxes via equipment linked directly to a DSN line.

Fax Service Setup

Per the DoD's Defense Information Systems Agency (DISA), employees approved for DSN usage must follow certain procedures to set up a DSN fax line and equipment. To set up fax equipment at an existing DSN line location, they must contact their telecommunications control officer. To set up services for the first time, or for answers to questions, they must contact the DISN Global Service Center at 800-554-3476 or 312-850-4790.

Fax Equipment

Two types of equipment are permitted for use in sending faxes via the DSN: standard fax machines and Secure Telephone Unit, Third-Generation/Secure Terminal Equipment. STU-III/STE is preferred for voice and data transmissions such as faxes, as the equipment provides encryption for unsecured lines. Because standard fax machines don't offer this encryption, a standard machine has a one-minute transmission restriction. With either type of equipment, other types of calls are allowed to preempt transmissions.


A DSN fax number is used in much the same way as a regular fax number, with only a few differences. Calls made to a DSN fax number via fax equipment not attached to a DSN line are routed to the commercial non-DSN equivalent if available. Calls made from a DSN line fax machine to an 800 fax number require a transfer. You must dial 809-463-3376, wait for a tone and then dial the fax number. If you need to contact a location that uses the DSN to follow up on a fax, you must dial directly using a DSN voice line. If you don't have a DSN voice line, you must contact a base operator to see if he can transfer you to the person or office you're attempting to reach.
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