DEFENSE SWITCHED NETWORK

The Defense Communications System (DCS) Defense Switched Network (DSN) is a telecommunications telephone interconnected network. This system is found on most military and other Federal Government installations in the United States and overseas.

This system upgraded the Automatic Voice Network (AUTOVON) and will evolve into an all-digital network in the 1990s. The DSN incorporates capabilities that were not available in the AUTOVON system, such as automatic callback, call forwarding, call transfer, and call waiting.

Precedence of Calls

The precedence of a call indicates the degree of preference to be given a call relative to all other calls in progress. A preemption feature provides the ability to disconnect a call of lower precedence and seize the access line or interswitch trunk to complete a call of higher precedence. A unique aspect of the DSN is that switches have been programmed to determine what precedence treatment must be given each call.

The combined features of precedence and preemption used in DSN are called multilevel precedence and preemption (MLPP). The effectiveness of this system depends on the proper use of the precedence system by the users.

All users should be familiar with the system and the types of calls assigned to each precedence. Each user should ensure that his or her call is not assigned a precedence higher than that justified by the circumstance or information involved.

The DSN offers five types of call treatment. The precedences and their applications are listed below in relative order of priority in handling.

FLASH OVERRIDE (FO) -FO 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.

FLASH (F) -FLASH calls override 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 preattack conditions.

IMMEDIATE (1) -IMMEDIATE precedence 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 essential to national security, widespread civil disturbance, and vital information concerning aircraft, spacecraft, or missile operations.

PRIORITY (P) -PRIORITY precedence is for calls requiring expeditious action or furnishing essential information for the conduct of government operations. Examples of PRIORITY calls are intelligence; movement of naval, air, and ground forces; and important information concerning administrative military support functions.

ROUTINE (R) -ROUTINE precedence is for official government communications that require rapid transmission by telephone. These calls do not require preferential handling.

Security

Local command policy normally states that the DSN is to be used only for the most essential official calls. The DSN system must never be used to make personal or unofficial calls.

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.

TRANSMIT MESSAGES VIA MANUAL CIRCUITS

In these days of super speed burst message transmission the use of manual relaying or transmitting of messages is not the norm. You should locate, identify, and use locally produced instructions, publications, and References.

ENEMY CONTACT REPORTING

Enemy contact reports are normally made only once when you are in direct communications with the officer in tactical command (OTC), a higher authority, or a shore radio station. Enemy contact reports are signaled using basic R/T procedures as modified by chapter 6 of ACP 125. Details of enemy contact

reporting are contained in Allied Maritime Tactical Instructions and Procedures, ATP 1, Volume I. There are two conditions under which enemy contact reports are to be made more than once:

When DO NOT ANSWER procedures are used (texts are transmitted twice in this procedure).

When the text consists of emergency alarm signals. In this case, the text is transmitted twice, separated by the proword I SAY AGAIN, with a time group in the ending.

When required, authentication is used in contact reports. Lack of proper authentication, however, should not prevent retransmission or relay of the message to higher authority.

There are two types of contact reports: initial and amplifying. As you would expect, initial reports are used to report initial contact or sightings. These reports should be sent as expeditiously as possible with immediate, pertinent information (type vessel, location, basic track, and so forth). The amplifying reports contain all necessary amplifying information to be fully analyzed by higher authority or command.