The Defense Information Systems Network (DISN) is
"The DISN is the major element of the GIG (see Figure II-2). It has three segments: sustaining base, long haul, and deployed. It is DOD's worldwide enterprise-level telecommunications infrastructure providing end-to-end information transfer for supporting military operations. For the most part, it is transparent to the joint force. The DISN facilitates the management of information resources, and is responsive to national security, as well as DOD needs. It provides GIG network services to DOD installations and deployed forces. Those services include voice, data, and video, as well as ancillary enterprise services such as directories and messaging. DOD policy mandates the use of the DISN for wide-area network (WAN) and metropolitan networks."