COMMUNICATIONS FUNDAMENTALS

Now that we have learned the Navy's fundamental use of the various frequency bands, we should look at the types of communications links and their modes of operation. The Navy uses many modes of operation; the type used is based upon the function of the circuit or network. These modes (or functions) are combined to form a communications link. We will also discuss some of the actual networks the Navy uses on a daily basis.

COMMUNICATIONS LINKS

A complex of links forms a major communications system. The naval communications system is broken down into strategic and tactical groups.

Strategic

Strategic communications are generally world-wide in nature. They are operated on a common-user (Navy, Army, Department of Defense, and so on) or special-purpose basis. A strategic system may be confined within a specified area or limited to a specific type of traffic, but the configuration is designed so that combined operations with other strategic systems are possible. As an example, we will look at the automatic voice network, automatic digital network, and the defense special security communications system later in this chapter.

Tactical

Tactical communications are usually limited to a specific area of operations and are used to direct or report the movement of specific forces. Some tactical networks are used only for operational traffic; others may be used for operational and administrative traffic. For instance, the task force, task-group, and air-control networks are ordinarily used for operational traffic. Ship-to-shore networks and broadcast networks serve both types of traffic.

Modes of Operation

Communications links have numerous modes of operation. In our discussion, a mode of operation is identified as a link or path between two or more points that is capable of providing one or more channels for the transmission of intelligence. Let's take a look at the five most common modes of operation.

SIMPLEX. - The simplex (splx) mode uses a single channel or frequency to exchange information between two or more terminals. Communications is in one direction only.

HALF DUPLEX. - The half-duplex (hdx) mode has one-way flow of information between terminals. Technical arrangements often permit transmission in either direction, but not simultaneously. This term must be qualified to show s/o (send only), r/o (receive only), or s/r (send or receive).

SEMIDUPLEX. - The semiduplex (sdx) uses an arrangement of equipment where one terminal is simplex configured and the other uses two channels or frequencies in full duplex. A clarifying example is a ship in a simplex mode terminated full duplex with a shore station. The ship may send or receive but not do both at the same time.

FULL DUPLEX. - The full-duplex (fdx) mode is a method of operation in which telecommunications between stations takes place simultaneously in both directions using two separate frequencies. In other words, a ship may send and receive different messages at the same time. The term "full duplex" is synonymous with "duplex."

BROADCAST. - Broadcast (bc) is the type of operation in which one station transmits information on one or more channels directed to more than one station and/or unit. The broadcast system has no provision for receipt or reply; however, special arrangements may require the receiving station to reply or receipt for the message at a later time by other means. Broadcasts are the primary means of delivering messages to the fleet. Since Navy units copying broadcasts are not required to receipt for messages received, they can maintain radio silence while still receiving essential messages.

Message traffic is normally sent to the fleet by three methods: broadcast, intercept, and receipt. The first two are "do not answer" methods; the third, as its name implies, requires a receipt from the addressee (addee) for each message. Broadcast and intercept methods allow the fleet to preserve radio silence, which is a great advantage from the standpoint of security. By the intercept method, a shore radio station transmits messages to another shore station that repeats them back. Ships intercept and copy all of this message traffic.

Broadcast is preferable to intercept chiefly because it is faster. It is the method by which nearly all fleet traffic is handled. It uses radiotelegraph, radiotelephone, radio teletypewriter, and facsimile.

There is some similarity between civilian and naval broadcasts. Just as commercial stations in the broadcast band transmit programs to radio receivers in the homes in their communities, Navy communications stations broadcast messages to fleet units in their particular geographic areas. The resemblance between Navy and commercial stations ceases there. Information broadcast by naval communications stations is contained in chronologically numbered messages addressed to the ships. The messages are copied by the fleet units, which check the serial numbers to ensure they have a complete file. This checks and balances system ensures the ship has not missed any of the broadcast message traffic.

Fleet broadcasts follow regular schedules. Messages are placed on the schedules in order of precedence. If a message of higher precedence is given to a transmitter station while a lower precedence message is being transmitted, the latter message may be interrupted to transmit the message of higher precedence. All ships copy all messages appearing on the broadcast schedule they are guarding.

Messages are normally transmitted on several frequencies to make sure they are received. This gives the receiving station the choice of frequency selection when considering time of day and atmospheric conditions for best reception.

Q.16 The naval communications system is made up of what two groups of communications?
Q.17 What are the five most prominent communications modes of operation?

SWITCHED NETWORKS

The defense communications system (DCS) is composed of all worldwide, long-haul, government-owned and leased point-to-point circuits, trunks, terminals, switching centers, control facilities, and tributaries of military departments and other defense activities. In essence the DCS combines into a single system all the elements that make up the naval communications system and the Army and Air Force equivalent.

The switched networks discussed in this section, automatic voice network, automatic secure voice communications, automatic digital network, and the defense special security communications system, are part of the DCS and are managed by the Defense Communications Agency (DCA). You should not confuse these DCS networks with the HICOM (high-command communications network) and NORATS (Navy operational radio and telephone switchboard) networks. We will discuss both of these Navy-only networks later in this chapter.

Automatic Voice Network (AUTOVON)

The DCS AUTOVON offers rapid, direct interconnection of DOD and certain other government installations through worldwide telephone exchanges. AUTOVON is a worldwide, general-purpose direct dialing telephone system. The goal of the AUTOVON system is to complete connections between two points anywhere in the world in about two seconds and to complete regular connections with push-button speed.

The AUTOVON system is made up of several installations comparable in function to commercial telephone exchanges. An installation is referred to as an AUTOVON switch, or simply switch. Within individual areas we have local command, control, and administrative voice communications systems. These systems connect into the worldwide AUTOVON through manually operated telephone switchboards or automatic dial exchanges by using direct in and out dialing.

Normal AUTOVON service allows your station to call other stations on a worldwide basis for day-to-day communications by using the telephone.

Automatic Secure Voice Communications (AUTOSEVOCOM)

Another close relative to the AUTOVON system is the AUTOSEVOCOM a worldwide, switched telephone network. It provides authorized users with a means for exchanging classified information over communications security (COMSEC) circuitry or over other approved circuitry. The system consists of both manual and automated networks within a single system.

For subscribers to the AUTOSEVOCOM network, telephone directories containing subscriber listings, general instructions for placing calls, and trouble-reporting procedures are provided.

Automatic Digital Network (AUTODIN)

The DCS AUTODIN is a fully automatic, digital system. The system converts word messages to digital form for transmission.

AUTODIN is used to furnish instantaneous, error-free, and secure communications around the world to several thousand directly connected subscriber terminals. Daily capacity of the system is about five-million average-length messages.

AUTODIN switching centers are interconnected through a network of high-frequency radio channels, submarine cables, microwave and tropospheric channels, and a variety of wire lines.

The whole concept of AUTODIN is to reduce manual handling of messages to a minimum by the use of automated equipment. This system has reduced message delivery times and delay anywhere in the world to a matter of seconds rather than minutes or hours.

Defense Special Security Communications System (DSSCS)

The defense special security communications system (DSSCS) was established for the purpose of integrating the critical intelligence communications (CRITICOMM) and the special intelligence communications (SPINTCOMM) networks into a single automated communications network. In effect, the integration of DSSCS subscribers into AUTODIN provides two separate systems within AUTODIN-one system for special intelligence (SI) message traffic and the other for the AUTODIN regular message traffic.

NAVY-ONLY NETWORKS

Some networks are used by the Navy only. As mentioned previously, these are the high command communications network (HICOM) and the Navy operational radio and telephone switchboard (NORATS) networks. Let's look at some of their functions and purposes.

High Command Communications Network (HICOM) The HICOM network provides a voice link between the Chief of Naval Operations (CNO) and all subordinate commands ashore, afloat, and airborne. CNO is the master control station and each fleet commander in chief has an area network control station. All naval communications stations are members.

In cases where a fleet unit is suffering communications difficulties with normal channels, HICOM is used on a not-to-interfere basis to restore communications. All naval communications stations are required to guard HICOM for their respective area networks and use this system.

Navy Operational Radio and Telephone Switchboard (NORATS)

The NORATS meets our need for a connection between Navy tactical voice systems of the operating forces and the various fixed telephone services ashore. This system extends tactical voice to shore-based operational commands. NORATS provides a connecting point in the fleet center of each communication station. This point allows us to connect or patch all ship-to-shore voice circuits and designated local shore telephone systems and extensions. A combined HICOM/NORATS console exists at many naval communications stations.

Q.18 What four switched networks are part of the defense communications system?
Q.19 What two elements support only designated Navy requirements?