Table 1-1.—DSN Telephone Network Precedence System

Government telephones are intended for official business only. Most commands permit limited, brief, local telephone calls to be made to take care of personal matters that cannot be conducted during off-duty hours. However, the use of commercial long-distance services for personal business is prohibited and is always investigated. Detailed records of every commercial long-distance call (telephone bills) are forwarded monthly to each command for verification with the long-distance phone call records. DEFENSE SWITCHED NETWORK.—The Defense Switched Network (DSN) is a telephone network servicing most military installations in the continental United States and overseas. This system is an upgraded, all-digital network that has replaced the former Automatic Voice Network (AUTOVON). The DSN incorporates many special features, such as automatic callback, call forwarding, call transfer, and call waiting. Instructions for use of the service and special options are included in the DSN User Services Guide, DISA Circular 310-225-1. All telephone connections on the DSN are connected and maintained on a precedence basis (see table 1-1). Low precedence calls are initially connected only if there are free circuits available between the caller and the destination. Higher precedence calls may initially be connected even if all circuits are in use by a process called "preemption." When no free circuits are found, the computer checks the precedence on calls in progress. A lower precedence call in progress will be terminated by the system to allow a higher precedence call to proceed. The calling parties of the lower precedence call hear a brief high-pitched tone on the line just before the line goes dead to indicate that their call has been preempted. The effectiveness of this system depends on the proper use of the precedence system. Each user should ensure that his or her call is not assigned a precedence higher than that justified by the circumstance or information involved. Local command policy normally states that the DSN is to be used for official calls only. Personal or unofficial calls must never be initiated into the DSN system. Telephone circuits, particularly those routed by high frequency and microwave, are susceptible to monitoring and interception. The DSN is not a secure system! Users must take care and use common sense to avoid divulging classified information. Giving hints or talking "around" a classified subject can lead to the compromise of classified information. Table 1-1.—DSN Telephone Network Precedence System PRECEDENCE FLASH OVERRIDE (FO) FLASH (F) IMMEDIATE (O) PRIORITY (P) ROUTINE (R) DESCRIPTION Takes precedence over and preempts all calls on the DSN and is not preemptible. FO is reserved for the President of the United States, Secretary of Defense, Chairman of the Joint Chiefs of Staff, chiefs of military services, and others as specified by the President . Preempts lower precedence calls and can be preempted by FLASH OVERRIDE only. Some of the uses for FLASH are initial enemy contact, major strategic decisions of great urgency, and presidential action notices essential to national survival during attack or pre-attack conditions. Preempts PRIORITY and ROUTINE calls and is reserved for calls pertaining to situations that gravely affect the security of the United States. Examples of IMMEDIATE calls are enemy contact, intelligence reports essential to national security, widespread civil disturbance, and vital information concerning aircraft, spacecraft, or missile operations. Preempts only ROUTINE calls. For calls requiring expeditious action or furnishing essential information for the conduct of government operations. Examples of PRIORITY calls are intelligence reports, movement of naval, air, and ground forces, and important information concerning administrative military support functions. For official government communications that require rapid transmission by telephone. These calls do not require preferential handling. 1-4