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The World-wide DSN Numbering Plan uses 140 area codes (KYXs). Of these, six are used to define the major geographical areas for the DoD's regular DSN voice communications: Continental United States (CONUS) and Puerto Rico are covered by 312; Europe, 314; Pacific, 315; Alaska, 317; Central Command (Southwest Asia), 318; and Canada, 319. Fifty-three codes are reserved for interfacing to the tactical network. Area codes 50X and 51X are assigned to the major geographic areas for dial-up data transfer. Area code 50X is ISDN capable and is used for high speed digital data/fax (switched 56/64 kbps). Area code 51X is used for ADPCM avoidance high speed digital data/fax (switched 56/64kbps).

Each geographical area includes nodal switches that provide long-haul service for Private Branch Exchange (PBX), End Office (EO) and Remote Switching Units (RSU) subscribers. Some of these nodal switches have intertheater connectivity and serve as gateways for access to other theaters. The World-wide Numbering Plan addresses only KYX codes assigned by geographical area and NNX codes assigned to Multi-Function Switches.


DISA has overall management responsibility for the DSN and is responsible for all KYX and NNX number assignments within the DSN and also specifies the interface criteria for networks connected to the DSN per CJCSI 6215.01C, Policy for Department of Defense Voice Networks.


The Switched 56/64 Kbps (SW56/64) high speed digital services are being implemented in the DSN. To reduce costs, DSN applies compression methods to derive more channels from a given transmission link. Also, to enhance performance, echo cancellers are introduced in very long circuit connections. Both compression and echo cancellers are incompatable in SW56/64 services. To implement SW56/64, circuits are being identified and procured without compression or echo cancellers. Designated DSN switches are then being programmed to route SW56/64 calls only over such circuits. This approach is creating a virtual SW56/64 network that is part of the DSN and has its own numbering and routing plan. SW56/64 services, such as high speed FAX, computer-to-computer transfer, and video teleconferencing, vary by area codes. Area code 50X is used with clear channel trunks without echo cancellers or compression.


Area code 51X is for high speed modem/FAX calls, with echo cancellers tone cancellation and without compression. The service is specifically designed for ADPCM compression avoidance. The NNXs digits dialed with area code 51X are the same as 31X digits which are theater specific.