FIRE CONTROLMAN, VOLUME 6--DIGITAL COMMUNICATIONS

digital data pulses into a form acceptable to the various types of communications channels. The equipment most often transmits digital data over a distance by varying a continuous analog signal in amplitude, frequency, or phase. Communications channels that can pass data in two directions (transmit and receive) are known as duplex channels. Single-direction channels are simplex channels. Duplex channels may operate in one of the following two modes: half-duplex or fill-duplex. Half-duplex channels transmit data in one direction, pause, and then receive data coming from the opposite direction. Full-duplex channels, on the other hand, can transmit and receive data simultaneously. TYPES OF COMMUNICATIONS CHANNELS (TRANSMISSION MEDIA) In the fleet and at shore activities, you will encounter several forms of communications channels. The most common channels are landlines and radio communications. Landlines Landlines are physical lines or cables that connect the digital equipment. Originally, landlines referred to telephone lines and were limited to carrying analog audio frequencies (voice frequencies). For digital information to be carried over these lines, the limits. The signal can be varied in amplitude (amplitude modulation), frequency (frequency modulation), or phase (phase modulation) to convey the data. We will discuss each type of modulation later in this chapter. A digital signal has a limited set of values (1 or 0, true or false, etc.). A limited number of discrete pulses can be transmitted in a fixed period. The unique sequence of the bits represents the data. Digital equipments (computers and peripherals) within a system normally communicate with each other in pure digital pulses (serial and parallel). Transmitting digital information over a distance requires the use of special equipment to convert characteristics of one or more tones or carriers in the audio-frequency range had to be modified in amplitude, frequency, or phase. Today, telephone lines are commonly used in many network applications. Bulletin boards, such as BUPERS ACCESS, use existing telephone lines; but many landline-based systems use dedicated lines. Dedicated lines are common in local area networks (LANs). In a LAN system, several computers are joined together to share information with all the users on the system. System connections are made using coaxial, dual-coaxial, fiber-optic, or twisted-pair cable. The type of cable depends on several factors, such as the number of users on the LAN and the maximum distance between workstations. The device used to convert the digital data into a form usable by the communications channel and back to digital data is known as a modem. Modem is an acronym for MOdulator Demodulator. The modulator function converts the data of the transmitting system into discrete modifications of the tone or carrier signals. The de- modulator converts the data-carrying tone or carrier signal into digital data for the receiving system. Radio Radio waves have been used for teletype and voice communications for many decades. The advantages of radio-based systems are that they are more mobile and can communicate over barriers such as large bodies of water. Tactical information links, like those we will cover in chapter 2, are almost exclusively radio-based. Radio communications are based on frequency ranges or radio-frequency bands. The frequency range of the carrier frequency determines the operational characteristics of the system. Table 1-1 illustrates the international frequency bands and their uses. The tactical digital information systems used by the Navy generally use portions of the hf and uhf bands. 1-2

Table 1-1.—Frequency Bands and Their Applications In the radio transmitter, the data signals (discrete or tones) are modulated (impressed) on to the carrier frequency and transmitted into space when the transmitter is keyed. A receiver tuned to the carrier frequency picks up the signal and demodulates the data-carrying signals from the carrier. The data signals can then be converted to digital data by the appropriate devices. For more information on radio operations, refer to Navy Electricity and Electronics Training Series (NEETS), Module 17— Radio-Frequency Communications Principles. THE DECIBEL MEASUREMENT SYSTEM Technicians who deal with communications equipment often speak of the gain of an amplifier or a system in units called decibels (dB). Decibels are used as an indication of equipment performance; therefore, you need a basic understanding of the decibel system of measurement. As the actual calculation of decibel measurement is seldom required in practical applications, the explanation presented in this text is somewhat simplified. Most modern test equipment is designed to measure and indicate decibels directly. This design eliminates the need for complicated mathematical calculations. Nevertheless, because many data link system alignment procedures center around dB readings and references, you need to understand the significance of an equipment gain rating as expressed in decibels. The equipment used in communications systems consists of several components, such as amplifiers, communications lines, antennas, couplers, and switches. Each component in the system will affect the signal by introducing a signal loss or gain. These losses and gains can be described by a ratio of the power input and output by the equipment or cable. The ratio can be calculated formula: Output power = Input power by using the following Power ratio If a communications system has four components, the gain or loss at each component must be calculated and these ratios multiplied. The following is an example of the gain/loss calculation of a four-component system: 1-3

In this system, the output of the signal is twice as strong as the input to the system. As you can see, this constant multiplication of the ratios can be wearisome, and the products can be extremely small or large. Therefore, the discovery that adding the logarithms of the numbers would yield the same result as this calculation led early scientists to develop the unit of measure called the bel. The bel, named in honor of Alexander Graham Bell, expresses the logarithmic ratio between the input and output of any given component, circuit, or system. The bel maybe expressed in voltage, current, sound levels, or power. The formula is as follows: The gain of an amplifier can be expressed in bels (N) by dividing the output (P1) by the input (P2) and taking the base 10 logarithm (log 10) of the resulting quotient. Thus, if an amplifier doubles the power, the quotient will be 2. When you consult a logarithm table, you will find that the base 10 logarithm of 2 is 0.3; so the power gain of the amplifier is 0.3 bel. Experience has shown that the bel is a rather large unit that is difficult to apply. A more practical, easier unit to apply is the decibel (1/10 bel). Any figure expressed in bels can be converted to decibels by multiplying the value by 10. Thus the ratio of 0.3 bel is equal to 3 decibels. The reason the decibel system is used to express signal strength is shown in table 1-2. For example, saying that a reference signal has increased 50 dB is much easier than saying that the output has increased 100,000 times. The basis of the decibel measuring system is the amount of increase or decrease from a reference level. Whether the input power is increased from 1 watt to 1-4 100 watts or from 1,000 watts to 100,000 watts, the amount of increase, or gain, is still 100 times or 20 dB. Examine table 1-2 again, taking particular note of the power ratios for source levels 3 dB and 6 dB. As the table illustrates, an increase of 3 dB represents a doubling of power. The reverse is also true. If a signal decreases by 3 dB, half of the power is lost. For example, a 1,000-watt signal decreased by 3 dB will equal 500 watts, while a 1,000-watt signal increased by 3 dB will equal 2,000 watts. Table 1-2.—Decibel Power Ratios When you speak of the dB level of a signal, you are actually speaking of the logarithmic comparison between the input and output signals. The input signal is normally used as the reference signal. In some instances, a standard reference signal must be used in place of the input signal. The most widely used reference level is a 1-milliwatt signal (600-ohm load). When the 1-milliwatt reference is used, the standard decibel abbreviation of dB is changed to dBm; dBms are used as an indication of power, while dBs are used to indicate the ratio between the input and output. A signal level of +3 dBm is 3 dB above 1 milliwatt, and a signal level of –3 dBm is 3 dB below 1 milliwatt. Whether you are using dB or dBm, a plus sign (+) or no sign indicates that the output level is

Figure 1-2.—Asynchronous character code. greater than the reference (power gain), while a minus sign (–) indicates that the power level is less than the reference (power loss). The value 0 dBm indicates that the output power is equal to the 1-milliwatt reference. It is also used to express a definite amount of power (1 milliwatt). The value 0 dBm equates to 1 milliwatt. DIGITAL DATA COMMUNICATIONS TECHNIQUES Data signals transmitted over communications channels need to follow specific protocols to ensure they are synchronized. In normal I/O data exchanges, this process is accomplished by the system of requests and acknowledges. In addition, the data signals have to be properly formatted for the receiving computer to decode them properly. ASYNCHRONOUS AND SYNCHRONOUS COMMUNICATIONS Two major data-formatting methods are used to make sure the transmitting computer and the receiving computer(s) are synchronized: asynchronous (character framed) and synchronous (message framed). Both methods are used to identify intelligence transmitted in the form of serial bit streams. Asynchronous Transmission Asynchronous transmission of data is commonly found in landline communications systems and some forms of teletype communications. Generally, asynchronous, or character-framed, transmission is used to transmit seven- or eight-bit data, usually in ASCII character format. Each character has a specific start and end sequence —usually one start bit and one or two end (stop) bits. Figure 1-2 illustrates the transmission format of an asynchronous data stream. A parity bit (even or odd) maybe included to ensure the accuracy of the transmitted data. Asynchronous characters may be transmitted one at a time or as a string of characters; however, each character transmitted will have start and end bits. When data signals are transmitted in this format, synchronization occurs on a character-by-character basis between the transmitting and receiving devices and provides some allowance for timing inaccuracies. Any inaccuracy in timing is corrected with the arrival of the next character. Synchronous Transmission Most tactical digital information links communicate using synchronous messages. Synchronous transmission is a more sophisticated method of data transmission. It sends data in long uninterrupted streams, with a predefine start and stop sequence. The start sequence is generally referred to Figure 1-3.—Synchronous message format. 1-5

as the preamble. The principal function of the preamble is to alert the receiver of incoming data and provide a reference to synchronize the receiver with the transmitted signal. Following the preamble is a start code that informs the receiving equipment of the beginning of the message data. The basic format of the synchronous data message is shown in figure 1-3. The incoming bit stream is then used to synchronize the receiver or demodulator timing. A stop code follows the message data to indicate the end of transmission. MODULATION/DEMODULATION Modulation modifies a signal so it can carry data over the communications channel. The demodulator removes the data from the carrier. For most data communications applications, the carrier is a continuous sinusoidal waveform (sine wave). The frequency of the carrier varies, depending on the application. Landline transmission generally uses the audio-frequency bandwidth signals (300 to 3,000 Hz). Radio channels use audio-frequency tones as data carriers modulated to a radio-frequency signal, or they modulate the radio-frequency signal itself to convey data. The three basic modes of modulation are amplitude modulation, frequency modulation, and phase modulation. Each of these modes modifies the carrier signal in some manner to convey data. Amplitude Modulation When amplitude modulation is used for digital transmissions, the amplitude of the carrier signal represents the two discrete data states (1 or 0). The signal represents a logic 1 when the amplitude (peak-to-peak), at the same frequency, is greater at a different time, as shown in figure 1-4. The decrease in signal amplitude, below a predetermined threshold, indicates a change from a logic 1 to a logic 0. Frequency Modulation The frequency of the carrier signal or audio tones modulated to the carrier signal can be modified to indicate the two discrete states. As shown in figure Figure 1-4.—Amplitude modulation. 1-5, a selected frequency can be used to indicate the 1 state of a bit, and another selected frequency can be used to indicate the 0 state. The change in frequency, or frequency shift, indicates the same relationship as the change in amplitude did in amplitude modulation. Figure 1-5.—Frequency modulation. Shifting the frequency of the carrier signal is called frequency-shift keying (FSK) or binary frequency-shift keying (BFSK). FSK usually involves shifts to frequencies above or below a selected center frequency. Transmission of the frequency above the center frequency indicates a binary 1; the frequency below the center frequency indicates a binary 0. The center frequency is not transmitted. FSK is used in systems such as link 4A. Another method of using frequency shifts involves audio-frequency tones. Two discrete audio tones may be modulated to a constant frequency carrier signal. One of the tones is used to indicate a mark, or binary 1, the other a space, or binary 0. This method of frequency modulation is called audio-frequency tone shift (AFTS). Phase Modulation Phase modulation is modulation. It is based 1-6 a more complex mode of on the relationship of the

360-degree carrier sine wave to the baseline of the sine wave. The carrier signal starts on the baseline, as illustrated in figure 1-6, and continues to form a curve called the sine wave. When the sine wave reaches its maximum positive amplitude, it is at the 90-degree point. When it returns to the baseline, it is at 180 degrees. When it reaches its maximum negative amplitude, it is at 270 degrees; and when it returns to the baseline, it is at 360 degrees or the 0-degree point for the start of the next cycle. This process occurs over a period, with the number of full cycles per second (Hz) being the frequency of the signal. A full cycle is the transition from the 0-degree point to the 360-degree point. Figure 1-6.—Carrier sine wave, For a particular frequency this process continues without interruption. Phase modulation involves interrupting the cycle at one or more degree points and instantaneously changing the direction or amplitude of the sine wave. Figure 1-7 shows how a 180-degree phase shift is used to indicate two discrete states. The third cycle of the carrier is interrupted at the 180-degree point. Instead of continuing in the negative direction, the sine starts at the 0-degree point again. The resultant signal has the same frequency and amplitude as the original signal but is 180 degrees out of phase. This phase shift can be directly related to a digital input at a modulator in which one particular phase represents the 0 bit and the other phase represents the 1 bit. Multibit Modulation While the 180-degree phase shift can be used to indicate two discrete states, many points on the sine wave can be defined to represent different bit configurations. Individual phase changes of 0 degrees, 90 degrees, 180 degrees, and 270 degrees from a reference phase can each represent two separate data bits. For example, a 0-degree phase shift or no phase shift could indicate a binary 00; a 90-degree phase shift, a binary 01; a 180-degree phase shift, a binary 10; and a 270-degree phase shift, a binary 11. This type of modulation is known as a multibit, or quadrature (four-state) phase-shift modulation, as shown in figure 1-8. Keep in mind that only one continuous frequency and amplitude signal is being phase-modulated to transmit two bits of data for each phase shift. Figure 1-8.—Multibit phase modulation. A modification of the quadrature phase-shift modulation, called differential quadrature phase-shift keying, uses the difference between a phase-shifted signal and its preceding sine wave to represent data. When a phase shift is detected, the current signal is compared with the previously transmitted phase signal. The difference between the two signals is computed to determine the amount of phase shift. The previously transmitted signal is used as the reference phase for demodulating the data bits. Two binary digits are represented by phase changes of -45, -135, -225, and -315 degrees. The -45 degree shift indicates a binary 11; the -135 degree shift, a binary 01; the -225 degree shift, a binary 00; and the -316 degree shift, a binary 10. Figure 1-7.—Phase modulation. 1-7

Figure 1-9.—Full-duplex modem. MODEMS Transmitter Section Modems come in a variety of configurations. Their design depends including the following: Asynchronous transmissions on a number of factors, or synchronous data Simplex, half-duplex, or full-duplex communications Type of communications channel Type of modulation/demodulation used Modems may be stand-alone devices with their own power supplies and indicators. They may also be integrated into the design of larger equipments in which the modulations or demodulations are only one of the functions performed by the device. A functional block diagram of a modem is shown in figure 1-9. A full-duplex modem consists of two sections: the transmitter and the receiver sections. These two sections are functionally separate from each other. The transmitter section consists of a data encoder, the modulator, the band-pass filter, and the transmit control logic. The data encoder takes the digital data signal to be transmitted, and when necessary, converts it into the bit pattern acceptable to the modulator circuit. The modulator converts the data into the carrier signal. The most popular forms of modulation are frequency-shift keying (FSK), phase-shift keying (PSK), and quadrature phase-shift keying. After the data signals are modulated, they are fed to the band-pass filter circuitry. The band-pass filter then allows only the desired frequency to pass through the communications channel. The transmit control logic provides the timing signals necessary for the transmission of data to take place. Receiver Section The receiver section consists of a band-pass filter, a demodulator, a data decoder, and the receiver control circuit. The band-pass filter allows only the desired carrier signal to be received from the communications channel. The demodulator removes the data from the carrier signal and feeds the data to 1-8

Figure 1-10.—A time-division multiplexer (TDM) system. the decoder. The decoder reassembles the data into a be designated in a single modulation change. If two form compatible with the receiving system. In the receiver section, the incoming signal is often fed to the receiver timing logic to control the receiver timing circuitry. MULTIPLEXING One requirement of a data communications system is for it to transmit as many intelligent signals as possible in a fixed period using a single- communications channel. The rate of data transmission is measured in the number of bits per second (bps) transmitted. The bps rate is often confused with the baud rate. Baud refers to the rate at which a modulated signal between two devices changes in 1 second. For example, if the signal between two modems changes frequency or phase at a rate of 2,400 times per second, the baud is 2,400. If you are using a modulation method in which a single modulation change carries one bit, the 2,400 baud is also 2,400 bits per second. Using more sophisticated modulation methods, several bits of information can bits of data are transmitted with each modulation change, the data transfer rate is 4,800 bits per second at 2,400 baud. The data signals being transmitted are normally multiplexed to increase the transmission rate of data over the communications channel or to increase the efficiency of the channel by allowing multiple users of the same channel. The two methods commonly used to multiplex communications channels are time-division multiplexing and frequency-division multiplexing. Time-Division Multiplexing Time-division multiplexing (TDM) grants each user full channel capacity, but assigns time slots to each user. Each user is connected to a time-division multiplexer. Data signals from the user are fed to the time-division multiplexer buffer, and the time slots are rotated among the users and scanned for data. Figure 1-10 illustrates the typical construction of a 1-9

time-division multiplexer system. The data from each user can be in the form of bits, bytes, or blocks. The data signals from all users are compiled into frames for transmission on a single, high-speed communications channel. Transmit and receive frames are used for half-duplex communications. Transmit frames are sent and a receive time slot is enabled for return information. In this manner, a single carrier frequency and modem may be used to transmit and receive information at a fairly high rate of speed. Since time slots are preset and assigned, if a user has no data to transmit, the time slot is wasted. Advantages of a TDM system include the following: its ability to handle devices with varying speeds, its effectiveness when used with devices that transmit data almost continuously, and its simple implementation. Frequency-Division Multiplexing Frequency-division multiplexing (FDM) divides a band of frequencies into several distinct channels or tones. Each tone carries a portion of the data being transmitted. FDM devices can be complex because a separate modulator/demodulator circuit is required for each tone used. The composite tones are then modulated to a single carrier frequency for radio transmission. FDM allows for the parallel transmission of data over a single communications channel. For example, the Link-11 communications system uses 15 audio tones to transmit 30 bits of parallel data. Each tone transmits two bits of differential quadrature phase-shift keyed data. SUMMARY—FUNDAMENTALS OF DATA COMMUNICATIONS This chapter introduced you to the building blocks of a data communications system. The following information summarizes the important points you should have learned. COMMUNICATIONS SYSTEMS— Digital data devices that exchange data over distances are known as communications systems. A basic communications system consists of the following three components: a transmitter, a receiver, and a communications channel. The transmitter converts digital data into a form (digital or analog) useable by the communications channel. The receiver accepts data from the communications channel and converts the data back to its pure digital form. Communications systems that can transmit and receive data are known as duplex systems, while communications systems that are limited to transmit only or receive only are simplex systems. Duplex systems that transmit data, pause, and then receive data are half-duplex systems. Full-duplex systems can transmit and receive data simultaneously. COMMUNICATION CHANNELS— Several types of communications channels are in use today. The most common are landlines and radio communications. Landlines are physical cables that connect computers; they are common in local area networks. Radio communications use the radio-frequency bands to exchange information. The most common bands used in the Navy are the HF and UHF bands. DECIBEL MEASUREMENT SYSTEM— The decibel measurement system is used to measure the gain or loss of amplifiers, antennas, communications lines, and other types of communications equipment. A gain of +3 decibels (dB) indicates that the output power of the circuit, compared to the input power, has doubled. Each +3 dB gain indicates a doubling of power. For example, a signal that has a gain of 6 dB is twice as strong as a signal that has a gain of 3 dB. ASYNCHRONOUS TRANS- MISSION— Asynchronous transmission refers to data sent without the use of timing pulses. Data signals are sent a byte at a time, with start, stop, and parity bits added to each byte. SYNCHRONOUS TRANS- MISSION— Synchronous transmission refers to the sending of long, uninterrupted streams of data with a predefined start and stop sequence. 1-10

MODULATION/DEMODULATION— Modul- ation is the modifying of a signal to carry intelligent data over the communications channel. Several types of modulation are available, depending on the system requirement and equipment. The most frequently used types of modulation are amplitude modulation, frequency modulation, and phase modulation. Demodulation is the act of returning modulated data signals to their original form. AMPLITUDE MODULATION— Amplitude modulation refers to modifying the amplitude of a sine wave to store data. FREQUENCY MODULATION— Frequency modulation refers to changing the frequency of a signal to indicate a logic 1 or a logic 0. One frequency indicates a logic 1, and the other frequency indicates a logic 0. PHASE MODULATION— Phase modulation is more complex than amplitude modulation or frequency modulation. Phase modulation uses a signal frequency sine wave and performs phase shifts of the sine wave to store data. A modification of phase modulation involves the use of several discrete phase shifts to indicate the state of two or more data bits. MODEMS— A modem is a device that MOdulates and Demodulates data in a digital communications system. Modems are available in a variety of types, with various speeds and capabilities. A modem consists of two functionally separate areas—the transmitter section and the receiver section. The transmitter section prepares, or modulates, the data for transmission. The receiver section demodulates, or returns, incoming data to its original form. MULTIPLEXING— Multiplexing refers to processes used in digital communications systems to make the most efficient use of system time. Multiplexing can involve time-sharing of the communications channel by several users or assigning several frequencies for the parallel transmission of data. 1-11

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CHAPTER 2 THE LINK-11 SYSTEM INTRODUCTION Tactical data links are usually limited to a specific area of operation and are used for command and control of specific forces. Link-11 is the U.S. Navy shipboard version of NATO’s Tactical Data Information Link “A” (TADIL A). The Link-11 system is used to provide high-speed, computer-to-computer exchange of digital tactical information among ships, aircraft, and shore installations, as shown in figure 2-1. Figure 2-1.—Tactical digital information links. Link-11 data communications can operate with either high-frequency (HF) or ultra-high-frequency (UHF) radios. In the HF band, Link-11 provides gapless omnidirectional coverage of up to 300 nautical miles from the transmitting site. In the UHF band, the Link-11 system is capable of line-of-sight omnidirectional coverage, approximately 25 nautical miles between ships and 150 nautical miles for ship-to-air links. To understand the operation of the Link-11 system fully, you must be able to identify the hardware components that compose it and the functions they perform. Keep in mind that although the specific equipment used on board your ship may differ from the examples used in this chapter, the purpose of your Link-11 setup is still the same, that is, to pass tactical data to other units. 2-1

LOCAL-AREA NETWORK HARDWARE The basic hardware components of a LAN are cables, network interface cards, network servers, peripherals, and workstations. These components are covered in the material that follows. CABLES Several types of cables can be used in LAN applications. The selection of the type of cable depends on several factors, such as maximum length of a single cable run, security requirements, and the capacity and speed of the system. Twisted-Pair Cable The twisted-pair cable is easy to install and costs little on a per-foot basis. In some cases, existing telephone cable may be used. Its disadvantages include limitations in capacity and speed. It is also susceptible to electrical interference unless it is shielded. Shielded Twisted-Pair Cable The shielded twisted-pair cable is encased in an RFI shield. The stranded wire used as a conductor is manufactured with greater precision and is capable of greater data transmission rates and longer cable runs. Coaxial Cable Coaxial cable networks have gained in popularity because of their use in cable television. The quantities of cable and connectors produced for cable television have greatly reduced the prices of these components for network users. Coaxial cable comes in various thicknesses and is designated by a number: RG-11, RG-58, RG-59, RG-62, and so forth. You can use either baseband or broadband transmission methods with coaxial cable. Baseband coaxial systems transmit digital signals unchanged over a single channel and have several advantages. They are inexpensive, easy to install, and have low maintenance. They also allow very high data transmission rates. One disadvantage is that they are limited to transmitting digital signals only. In contrast, broadband coaxial systems require the digital signal to be converted to an analog signal before transmission and then back to digital by modem at the receiving device. Broadband systems support data, voice, and video signals that may be transmitted simultaneously. Disadvantages of broadband systems are their higher installation costs and complex maintenance. Fiber-Optic Cable Fiber-optic cable is the best choice if a secure network is needed. Because the cable transmits light, the transmissions are immune to interference caused by electrical or electronic devices. Also, if your network will run through an area of heavy industrial activity or a work place with strong radio frequency interference, fiber-optic cable is the most appropriate choice. Other advantages of the fiber-optic cable are that it lasts longer than other types of cable and can carry many more channels. Its disadvantages include its high price, poor connectivity, and low flexibility. NETWORK INTERFACE CARD To attach personal computers to the LAN, you must connect a network interface card (NIC) to each PC and attach the network cable to the NIC. The NIC is nothing more than a circuit board that normally plugs directly into one of the expansion slots inside a PC. Sometimes, the NIC comes as a separate unit. In this case, you plug it into the back of the PC. Most NICs have their own built-in microprocessor(s) designed to take care of network communications. This relieves the PC’s main processor of this responsibility. The type of cable used on the network is determined by the type of LAN to be installed. NETWORK SERVERS Your understanding the concept of a server is important to understanding how LANs work. A server is a combination of hardware and software that is used to manage the shared resources of the network. The hardware may be a PC or a computer designed 6-2

specifically to act as a server. In either case, the computer normally has a hard disk and the software needed to run the network system. A network server is able to control network traffic as well as the sharing of other resources, such as application programs, disk space, data files, and printers. There are several different types of servers, and each has a particular function. In newer systems, some separate server functions are combined into a central file server. The servers we will look at are the disk server, the file server, and the print server. Disk Server The disk server was the first of the network operating systems. In the early days of PC networks, very few computers were equipped with a hard disk. When the hard disk became affordable, manufacturers were asked to develop a system to allow several users to share a single hard drive. The earliest disk servers were multiplexer that polled each connected computer for requests to write a file on the hard drive or to retrieve a file from the disk. The multiplexer then responded accordingly. A major problem with this process was that it did not allow for any type of security, data organization, or disk management. As LAN technology evolved, the development of the disk server software in the early 1980s addressed some of these issues. The disk server is a software routine that was installed on each computer in the network. The disk server software allowed each PC to access the shared hard drive as if it were a local drive. In other words, the computer thought the drive was installed in the computer, but in reality, the drive was remotely located on the network. The disk server also provided for some information sharing. One purpose of a network is to allow multiple users access to the same information. One problem encountered with early disk servers occurred when two or more users updated the same file at the same time. When the file was saved by both users, the updates of one of the users was lost. A method of preventing this information loss is file locking. File locking means that when one user accesses a file, all the other users are prevented from accessing that file until the first user is finished with it. As you can see, this method severely limits the number of users able to access the information. Another method used to prevent data loss is record locking. In a data-base environment, many users could access the same data file, but when a record was being modified by one user, the other users were locked out of the record being modified. A data file can be updated by several users without threatening the integrity of the data by using this technique. Although the disk server was used in most LANs developed before 1985, a major problem still existed in maintaining data integrity. The two methods covered in the previous paragraphs provided for data management, but not for reliable disk management. A disk drive stores information on the next available block on the disk. When the disk server was used, it was not uncommon for two users to try to write data to the same block at the same time. When this happened, the second user would overwrite the data just written by the first user, causing a loss of data. The development of the file server in 1983 solved all of the problems encountered with the disk server. File Server Currently, all local-area networks require some type of file server. In most cases, the file server is a dedicated PC or minicomputer. The file server performs the processing of the network control software and the central processing and storage point of the application software and data files of the network. The file server has a hard disk with a very large storage capacity. The file server manages the hard disk and ensures that multiple requests for the same file do not conflict with each other. In the disk server environment, each PC workstation manages its I/O with the disk through low-level sector calls. In the file server environment, each workstation communicates with the central disk through the use of high-level calls to the file server. A high-level call can be a request to open a particular file or to store a file, while a low-level call maybe to write this file to sector xyz on the disk. The file server converts the high-level calls from the users to low- 6-3

level disk commands, thus providing effective disk management. The file server maintains the list of privileges and authorizations for each user. This protects the data files from unauthorized access and protects the data. An example of this is that one user may be authorized total access to a data-base file to update the file, while another user may be authorized read-only access to the information. Still a third user may be denied access to the file altogether. A network file server is a special-purpose unit that can reside in either a dedicated computer, or one of the workstations (a PC) that has a hard disk containing the software of the network. When the network server is used solely for serving the network and is NOT used as a workstation, it is referred to as a dedicated server. If the server can also be used as a workstation, it is referred to as a nondedicated server. Some networks do NOT have a single dedicated file server. Instead, they use a distributed approach in which any of the nondedicated servers may make available files that reside on their hard disks. Under these circumstances, any workstation on the network can use or copy these files. Moving files back and forth on such a network establishes a temporary relationship, you might say, between the two PCs involved. One PC acts as the server, and the other PC acts as the receiving workstation. Print Server The print server is a software routine that allows all the workstations on the LAN to use a single printer. When the laser printer was introduced to the market, the extremely high-quality print and multiple fonts made it desirous for all correspondence. Unfortunately, the cost of a laser printer often exceeded that of an individual workstation and made it impractical for each workstation to have a dedicated printer. The print server solved that problem by accepting requests for print jobs from the network users and directing them to the printer. The print server makes sure one job is completed before a new job is started. Print server routines are included in almost all network operating systems on the market today. WORKSTATIONS Workstations is another name for the PCs used on a network. The PCs can be of the same brand, such as Zenith, or they can be a combination of different brands, such as IBM, Zenith, Compaq, along with other PC compatible computers (clones). Each PC can be configured differently. Some might have their own hard disk drives; others might have expanded memory. Still others might NOT even have diskette drives or printer ports of their own. Instead, these less expensive workstations use the storage and printing resources available through the network. Even though a PC may be part of a LAN system, you can use it independently as a stand-alone PC at any time or you can use it as part of the LAN. THE OPEN SYSTEM INTERCONNECTION (OSI) REFERENCE MODEL Over the past few years, a number of network standards or protocols (rules to live by) have been developed by the International Standards Organization (OSI) to provide some level of uniformity among computer manufacturers and network vendors. OSI is one of several governing organizations in this field that has developed such protocols. These seven layers of standards, shown in figure 6-1, define a generalized architecture called the Reference Model of Open Systems Interconnection. It is also known as the OSI reference model or OSI model. The primary purpose of the OSI model is to provide a basis for coordinating the development of standards that relate to the flexible interconnection of incompatible systems using data communications facilities. The OSI model does NOT define any one vendor’s particular network software as such, nor does it define detailed standards for any given software. It simply defines the broad categories of functions that each of the seven layers should perform. The OSI model can include different sets of standards at each layer that are appropriate for given situations. For example, in a very simple data communications system, one that uses a simple point-to-point link, the software at the higher level layers (say 5, 6, and 7) might be very simple or possibly nonexistent. However, in a very complex data communications 6-4

Figure 6-1.—The OSI model showing the seven layers. system, all seven software layers may be implemented. Although there is no requirement for any hardware or software vendor to adhere to the principles set forth in the OSI model, there is a worldwide trend in the computer industry toward acceptance and conformance to these standards. Ideally, if the hardware, network software, application software, and cabling were all supplied by the same manufacturer, there would be relatively few problems for users to contend with when designing and implementing a network. Everything would work together rather smoothly. However, a computer manufacturer’s architecture can make it difficult to interconnect hardware offered by other competing manufacturers or vendors. The protocols used by communications devices are also highly complex and are often completely different from one manufacturer to another. Then there is the network software. Usually, the network software from one LAN vendor will not work with that of a competitor; neither will the application programs. Even the cabling must be selected for a specific local-area network. HARDWARE LEVEL The hardware level contains the first two layers of the OSI reference model. They are the physical layer and the data-link layer. These are concerned primarily with the actual hardware used in a network. Physical Layer The physical layer is concerned with the transmission of the unstructured raw bit stream over a physical medium. It describes the electrical, mechanical, and functional interfaces to the carrier. The physical layer carries the signals for all the higher layers as follows: Voltages and pulse encoding of bits Media and media interface (cables, connectors, NIC, and so on) Line discipline (full- or half-duplex) Pin assignments Data-Link Layer The data-link layer provides error-free transmission of information over the physical medium. This allows the next higher layer to assume virtually error-free transmission over the link. The data-link layer is responsible for getting data packaged and onto the network cable. It manages the flow of the data bit stream into and out of each network node as follows: Creates and recognizes frame boundaries Checks received messages for integrity Manages channel access and flow control Ensures correct sequence of transmitted data The data-link layer detects and, when possible, corrects errors that occur in the physical layer without using the functions of the upper layers. It also provides flow-control techniques to ensure link-buffer capacity is not exceeded. TRANSPORT LEVEL The next three layers of the OSI reference model make up the transport level, also known as the subnet. The transport level defines the software protocols 6-5

necessary to exchange data on the network. The three layers of the transport level are the network layer, the transport layer, and the session layer. Network Layer The network layer decides which physical pathway the data should take based on network conditions, priorities of service, and other factors. Software on the network interface card must build the data packet, so the network layer can recognize and route the data to the correct destination address. It relieves the upper layers of the need to know anything about the data transmission and switching technologies used to connect the systems. It is responsible for establishing, maintaining, and terminating connections across the intervening communications facility as follows: Addresses messages Sets up the path between communicating nodes on possibly different networks Routes messages among networks Is concerned with the sequence delivery of data packets Controls congestion if too many packets are on the network Translates logical addresses or names into physical addresses Has accounting functions to count packets or bits sent by users to produce billing information Transport Layer The transport layer makes sure data units are delivered error-free, in sequence, without losses or duplications. It relieves higher layer protocols from any concern with the transportation of data between them as follows: Message segmentation. Accepts data from the session layer, splits it up into smaller units, and passes the units down to the network layer Establishes and deletes host-to-host connections across the network Multiplexes several message streams onto one channel and keeps track of which message belongs to which connection Provides reliable end-to-end delivery with acknowledgment Provides end-to-end flow control and window management Session Layer The session layer allows users on different machines to establish sessions between one another. It performs the functions that enable two or more applications to communicate across the network, performing security, name recognition, logging, administration, and other similar functions. Unlike the network layer, this layer deals with the programs in each machine to establish conversations between them as follows: Allows two applications processes on different machines to establish, use, and terminate a connection (or session) Performs synchronization between end-user tasks by placing checkpoints in the data stream so that if the network fails, only the data after the last checkpoint has to be retransmitted Provides dialogue control (who speaks, when, how long, and so on) PRESENTATION LEVEL/LAYER The presentation level consists of the presentation layer. The presentation layer formats data to be presented to the application layer. It can be viewed as the translator for the network. This layer provides a 6-6

common representation for data which can be used between the application processes. The presentation layer relieves the applications from being concerned with data representation, providing syntax independence as follows: Encodes data in a standard way (integers, floating point, ASCII, and so on) Provides data compression to reduce the number of bits that have to be transmitted Provides data encryption for privacy and authentication APPLICATION LEVEL/LAYER The final level is the application level, which consists of the application layer. The application layer serves as the window for the application process to access the OSI environment. This layer represents the services that directly support users and application tasks. It contains a variety of commonly needed protocols for the following items: Network virtual terminals File transfers Remote file access Electronic mail Network management USING THE OSI MODEL A communications system that does not use a layered architecture can be designed. A specifically designed communications system is faster, more efficient, requires less software code, and eliminates redundant functions and activities. Why, then, is the OSI reference model considered the standard in designing networks and writing software? It is considered the standard primarily because the use of a layered architecture, such as the OSI reference model, provides the network with flexibility and migration. The greatest advantage of your using layer architecture in a network is hardware independence. As advances in technology continue, it is not necessary to scrap a network completely because one component has been superseded. For example, if you have a network and need to upgrade the cable to a type that can handle increased data at a faster rate, the layered architecture of the OSI model will allow you to make this replacement to the physical layer without changing the other layers. LAN TOPOLOGIES The physical arrangement of the components of a LAN is called its configuration or topology. The three major types of configurations, or topologies, of a LAN are the linear bus, the star, and the ring. You can also create hybrid topologies by combining features of these configurations. For example, several bus networks can be joined together to form a ring of buses. Each topology requires the components of a LAN to be connected in a different arrangement. These components are also referred to as nodes. A node is any point on a network where data can be sent (transmitted) or received—a workstation, a server, and so on. LINEAR BUS NETWORK The linear bus topology is like a data highway. That is, all components or nodes are connected to the same cable, and the far ends of this cable never meet, as shown in figure 6-2. Linear bus LANs are best suited to applications involving relatively low usage of the bus coupled with the need to pass relatively short messages from one node to another. In many such networks, the workstations check whether a message is coming down the cable before sending their messages. Since all nodes share the bus, all messages must pass through the other workstations on the way to their destinations. Each node checks the address attached to the message to see if it matches its own address. Bus topologies allow individual nodes to be out of service or to be moved to new locations without disrupting service to the remaining nodes. 6-7

Because of the way linear bus cabling is laid out, this type of cabling is simple. The bus topology is very reliable, because if any node on the bus network fails, the bus itself is NOT affected, and the remaining nodes can continue to operate without interruption. Many of the low cost LANs use a bus topology and twisted-pair wire cabling. Figure 6-2.—A bus network topology. A disadvantage of the bus topology is that generally there must be a minimum distance between workstations to avoid signal interference. Another disadvantage is that the nodes must compete with each other for the use of the bus. Simultaneous transmissions by more than one node are NOT permitted. This problem, however, can be solved by using one of several types of systems designed to control access to the bus. They are collision detection, collision avoidance, and token passing, which we will cover shortly. Also, there is no easy way for the network administrator to run diagnostics on the entire network. Finally, the bus network can be easily compromised by an unauthorized network user, since all messages are sent along a common data highway. For this reason, it is difficult to maintain network security. STAR NETWORK In a star network, each component is connected directly to the central computer or network server, as shown in figure 6-3. Only one cable is required from the central computer to each PC’s network interface card to tie that workstation to the LAN. The star is one of the earliest types of network topologies. It 6-8 uses the same approach to sending and receiving messages as our phone system. Just as a telephone call from one person to another is handled by a central switching station, all messages must go through the central computer or network server that controls the flow of data. New workstations can be easily added to the network without interrupting other nodes. This is one of the advantages of the star topology. Another advantage of star topology is that the network administrator can give selected nodes a higher priority status than others. The central computer looks for signals from these higher priority workstations before recognizing other nodes. The star topology also permits centralized diagnostics (troubleshooting) of all functions. It can do this because all messages must first go through the central computer. This can prove invaluable in making sure that network security has not been breached. The main disadvantage of the star topology is its reliance on the central computer for performing almost all the functions of the network. When the central computer fails, all nodes also stop functioning, resulting in failure of the entire network. Figure 6-3.—A star network topology.

DISTRIBUTED STAR Figure 6-4.—A distributed star (tree) network topology. The distributed star, or tree, topology is shown in figure 6-4. It provides many of the advantages of both bus and star topologies. It connects workstations to a central point called a hub. This hub can support several workstations or hubs which, in turn, can support other workstations. Distributed star topologies can be easily adapted to the physical arrangement of the facility site. If the site has a high concentration of workstations in a given area, the system can be configured to more closely resemble a star topology. If the workstations are widely dispersed, the system can use inexpensive hubs with long runs of shared cable between hubs, similar to the bus topology. RING NETWORK In a ring network, all the components or nodes are connected to the main cable, and the cable forms a ring, as shown in figure 6-5. This topology allows a node to send a message to another node on the ring. However, the message must be transmitted through each node until it reaches its destination. Messages proceed from node to node in one direction only. Should anode fail on the network, data can no longer be passed around the ring unless the failed node is either physically or electronically bypassed. Using bypass software, the network can withstand the failure of a workstation by bypassing it and continuing to maintain the integrity of the network. One of the major issues in a ring topology is the need for making sure all workstations have equal access to the network. One of the major disadvantages of ring topologies is the extreme difficultly of adding new workstations while the network is in operation. Normally, the entire network has to be brought down while a new node is added and cabling reattached. However, this particular problem can be overcome by the installation of additional connectors when the network is initially set up. These connectors enable you to add or remove nodes while the network remains intact and in operation. ACCESS METHODS Another decision the designer makes is that of which access method to use. Access methods are the Figure 6-5.—A ring network topology. 6-9

Figure 6-6.—A bus network using the CSMA/CD access method. arrangements used to make sure each workstation has fair and equal access to the network. The access method used is governed primarily by the topology and the protocol of the network. The principal access methods are contention and token passing. Contention The contention method features Carrier Sense Multiple Access (CSMA) and Carrier Sense Multiple Access with Collision Detection (CSMA/CD). The CSMA/CD method is shown in figure 6-6. Access for both is on a first-come, first-served basis. The CSMA access scheme is very similar to that of a citizens band (CB) radio. Stations with data to send listen to the channel and wait until it is clear to transmit. With CSMA/CD, when two or more workstations transmit simultaneously, their messages will collide. As soon as a workstation detects a collision, it ceases transmission, monitors the network until it hears no other traffic, and then retransmits. Most contention networks assign a unique retry algorithm to vary the wait-and-retry period. This algorithm reduces the likelihood that after a collision, two workstations will transmit retries simultaneously. Token Passing Token passing is an orderly access method and is shown in figure 6-7. Each workstation passes on the opportunity to transmit to its closest neighbor until a station is found with a message to send. This permission to transmit is called a token. When a workstation with data to send is handed a token, part of the token is changed, indicating it is carrying a message, and then data is transmitted with the token. The token is then passed around the network, and every station checks whether the message is intended for it. The receiving station copies the message from the token, but then passes the unchanged token along the network. When the transmitting station receives the same token, it knows the message has been passed around the network. The transmitting station erases the message and puts the empty token back into circulation on the network. The amount of information that maybe transmitted during possession of the token is limited so that all workstations can share the cable equally. PROTOCOLS Network protocols are an important component because they define how networks establish communications between elements, exchange information, and terminate communications. Protocols have two major operational functions. They establish the circuit for transmission (handshaking) and for the transmission itself. Transmission is conducted subject to the line discipline. The line discipline is the sequence of operations that actually transmits and receives the data, handles the error-control procedures, handles the sequencing of message blocks, and provides for validation for information received correctly. 6-10

Figure 6-7.—A ring network using the token passing access method. Two representative protocols, which control line discipline, are the Binary Synchronous Communications Protocol (Bisync) and the Synchronous Data Link Control (SDLC). Bisync Bisync is a half-duplex protocol that transmits strings of characters at lower speeds over dial-up circuits. The information movement is in one direction at a time, with each data transfer being answered by an acknowledgement. SDLC SDLC is a control procedure that sends multiple blocks of data and returns a single acknowledgement for many blocks, thereby increasing the amount of time spent transmitting data. The bits that are put before and after the message at the transmitting end are removed at the receiving end, so only the message is presented to the user. The hardware chosen for the network plays a part in the choice of network protocol. Most users and many of the vendors who build the clone type of equipment would like to see universal interfaces, while others think that the availability of different specifications will lead to a proprietary set of equipment, even though they favor the overall OSI specifications. LAN SYSTEMS When you decide to install a LAN system, the type of topology used in the initial wiring of the system will have a major effect on the type of system that can be used. There are many LAN systems available, each with advantages and disadvantages. In the following paragraphs, we briefly examine some of the available LAN systems. The Institute of Electrical and Electronics Engineers (IEEE) has developed a set of standards for local-area networks. These standards encourage the use of common approaches for LAN protocols and interfaces. The IEEE LAN standards were developed by a committee of engineers and classified as the 802 standards. The 802 standards are broken down even further to define the protocols and topology used in a LAN. Some of the standards we are concerned with are the following: IEEE 802.3—Carrier sense multiple access/collision detection (CSMA/CD) IEEE 802.4—Token Bus IEEE 802.5—Token ring ETHERNET The EtherNet local-area network was developed by Xerox, the Intel Corporation, and the Digital Equipment Corporation. It became the model for the development of the IEEE 802.3 standard. The original standard defined a maximum throughput for EtherNet of 10 Mbit/s, but it has been revised to support throughput of much higher rates. When operating over coaxial cable, EtherNet has a 20-Mb per second throughput speed. For high-demand environments, such as engineering or graphics, EtherNet is often the choice. It is a bus topology and uses CSMA/CD protocol. It is available in the following three versions: standard EtherNet, ThinNet, and twisted-pair EtherNet. Standard EtherNet and ThinNet both use coaxial cable. Standard EtherNet is somewhat more expensive and more difficult to install than ThinNet, 6-11

but it allows networking over greater distances with more users. Twisted-pair EtherNet uses a distributed star topology with wiring concentrator hubs, not the bus topology characterizing standard EtherNet and ThinNet. Connecting more than 100 users on a standard EtherNet trunk or on a series of twisted-pair concentrators is not uncommon, while ThinNet LANs usually support less than 50 users. All versions of EtherNet create a LAN with high interconnectivity options. A number of products are available for connecting EtherNet LANs to minicomputers and mainframe computers and for bridging to other LANs; examples are STARLAN, ARCnet, and IBM Token Ring Network. STARLAN STARLAN uses a star topology with a CSMA/CD protocol. Its throughput speed is 1Mb per second over twisted-pair cable. If buildings are already wired with twisted-pair cable meeting AT&T premise cabling specifications, STARLAN can be installed easily. It is considered to be a low cost-per-user network and its star topology makes it a flexible network. ARCnet ARCnet is a distributed star topology that uses a token passing protocol and either twisted-pair or coaxial cabling. Its throughput speed is 2.5Mb per second. Although ARCnet does not conform to an IEEE standard, it closely resembles the 802.4 standard for a token bus system. It can easily handle up to 75 users. If user demand is low, it can handle additional users. It is considered an extremely reliable network and is easy to install, expand, and modify. IBM Token Ring Network The IBM Token Ring Network uses a star ring topology, and is defined by the IEEE 802.5 specification. It has a throughput speed of 4 Mbits per second and 16 Mbit per second. This allows for flexible expansion of very large networks. Because of its speed and token passing protocol, it is a good choice to meet high-volume requirements. It is a 6-12 sophisticated LAN technology developed by IBM to be used with an IBM cabling system and is currently the fastest growing installed network base. The star ring topology also makes use of redundant circuits and loopbacks to handle breaks in the ring and results in high-fault tolerance on the network. NETWORK OPERATING SYSTEMS Network operating system software is necessary to control the overall operations of the network. Careful consideration must be given to the various packages on the market to ensure the operating software is fully compatible with your system, topology, and needs. NETWORK OPERATING SYSTEM BASICS The two basic components of the network operating system are the network operating system server and the workstation. The network server is usually a dedicated computer that runs the operating system software and processes all requests for services. The workstation computer runs the application software needed by the workstation user and establishes communications with the network server. The network server operating system consists of the following five subsystems: the control kernel, the network interfaces, the file systems, the system extensions, and the system services. Control Kernel The control kernel is the main subsystem of the network operating software. The control kernel coordinates the various processes of the other subsystems. Some of the functions performed by the control kernel are as follows: Optimizing access to services by users Maintaining status information of many of the processes Error reporting

Service initialization and service termination of workstations Network Interfaces The network interfaces provide the low-level subnet protocols and basic translation for bridging hardware drivers with the network operating system. In sophisticated systems, the network interfaces can also provide for bridging a new network into an operating network without having to rebuild the operating system. File Systems The file system controls the way the data is organized, stored, and retrieved from the storage systems available to the network. The files may be stored on hard drives, RAM disks, or optical storage devices, such as CD-ROM or write once, read many (WORM) drives. File systems are generally designed to provide universal applicability. This means that the file system can be compatible with any application program’s expectation of file input/output protocol. When adaptable interfaces are used, the file system can appear to emulate a number of different file systems. System Extensions The system extensions define the openness of the network operating system and are used by third party developers to produce add-on products. The extensions are usually high-level protocol handlers that perform operations, such as file access protocol translations required by different operating systems. The extensions available also include network management, system tools, and data-base services. System Services Network system services contain all services that are not easily defined by any of the other areas of the network. Examples of network services are security, system reliability features, error conditions, and access violations. NETWORK OPERATING SYSTEMS SOFTWARE The most important job of a network operating system (NOS) is to provide file service for the attached computers. This allows information retrieval and usage and the storage of data in a shared environment. A NOS manages the other resources shared by the network and provides the following functions: Directory structure for shared hard disk storage devices File service for sharing and using data Interface to the network for application software/programs The means by which the network manager manages the network and its users Network security and data protection Communications with other networks The types of network operating systems include full-featured, low-cost, and zero-slot operating systems. Full-Featured Network Operating Systems Most full-featured network operating systems allow for high performance, flexibility, and excellent security measures. They require a LAN administrator. They require network interface cards. Also, they can be quite costly. Examples of a fill-featured NOS are EtherNet, Novell’s NetWare, 3Com’s 3+Share, IBM’s Token Ring Network, and Banyan’s Vines. Low-Cost Network Operating Systems Most low-cost network operating systems differ from full-featured systems only in the maximum number of users accommodated on the network and the number of security levels incorporated into the operating system. In general, they are much lower in cost and are easier to install and use. Examples of 6-13

low-cost systems are STARLAN, ARCnet, 10Net, and LANtastic. Zero-Slot Network Operating Systems Zero-slot network operating systems are appropriate only for networks with very few users and light usage. They are an inexpensive and simple alternative to the NOSs that require expensive network interface cards. Rather than requiring each workstation computer to have a NIC, the computer’s RS-232 serial communications port and twisted-pair cables are used. Because of this, they are very slow and offer limited file transfer abilities. They may not provide disk sharing. An example of a zero-slot system is LANLink. SUMMARY—LOCAL-AREA NETWORKS This chapter introduced you to local-area networks. The following information summarizes the important points you should have learned. LOCAL-AREA NETWORKS— LANs are a combination of hardware and software which allows personal computers to share information. The total number of computers and the total distance the network can cover are determined by several factors, including the type of cable used and the network operating system software. CABLES— Several types of cables can be used to create a local-area network. They are twisted-pair, shielded twisted-pair, coaxial, and fiber-optic. The type of cable used determines maximum data transfer rates and can be a factor when the number of nodes in the network is determined. NETWORK INTERFACE CARD— The network interface card attaches the PC to the network. Most network interface cards have built-in microprocessors that control network communications. This frees the PC’s main processor of time-consuming I/O operations. NETWORK SERVERS— The modern network server controls all operations of the network. These operations include controlling network communications, storing and retrieving files from shared memory resources, and controlling common printers. In older systems, each of these functions required a separate server. WORKSTATIONS— Workstations are the personal computers connected to the network. Even if a PC is part of a network, it can still be used in a stand-alone configuration. OPEN SYSTEM INTERCONNECTION OSI REFERENCE MODEL— The open systems interconnection reference model defines the protocols network hardware and software manufacturers use to create a network operating system. There are seven layers in the OSI model. These layers are contained in the five levels. HARDWARE LEVEL— The hardware level contains the first two layers of the OSI reference model. These are the physical layer and the data link layer. The physical layer defines the electrical, mechanical, and functional interfaces for the transmission of data through the cable. The data link layer is responsible for error detection and correction of the transmitted data. TRANSPORT LEVEL— The next three layers of the OSI reference model are contained in the transport level, also referred to as the subnet. The three layers of the transport level are the network layer, the transport layer, and the session layer. The network layer monitors network activity and controls which path the data is to be transmitted over. The software, controlling the network interface card, stores the data to be transmitted, builds the data packets, and routes the data to the correct destination. The transport layer ensures the integrity of the data packets. The session layer provides for the interface between two or more applications to communicate across the network. PRESENTATION LEVEL/LAYER— The presentation level contains the presentation layer. The presentation layer formats the data presented to the application level. The presentation layer provides 6-14

standardized data encoding, data compression, and data encryption and decryption as required. APPLICATION LEVEL/LAYER— The final level of the OSI reference model is the application level and it consists of the application layer. This layer directly supports the users and application tasks. USING THE OSI MODEL— When you use a layered architecture (such as the OSI reference model) to design a communications network, it is possible to update specific items in the network without having to replace the entire system. LAN TOPOLOGIES— The physical arrangement of the components of a LAN is called its topology. The three basic topologies used in building a LAN are the linear bus, the star, and the ring. Hybrid topologies can be created by combining different features of each. LINEAR BUS— The linear bus topology connects all the nodes to a common straight cable. All the nodes on the network share the common bus. This topology is very reliable since a failure of one or more nodes does not affect the bus. The disadvantages of the linear bus are the need for minimum distances between nodes to avoid signal interference, and the loss of data caused by the simultaneous transmission by two nodes. STAR NETWORK— In a star network, each node is connected directly to the central computer. All communications between the nodes have to pass through the central computer. Star networks allow the network administrator to give selected nodes higher priority and also allow centralized running of diagnostic programs. RING NETWORK— In a ring network, all nodes are connected to a common cable, and the cable starts and ends at the network server. In this type of network, communications are always in one direction, and the data being transmitted is passed through each node in the ring. A major disadvantage of this network is that when a node fails, it can completely halt all communications on the network. 6-15 ACCESS METHODS— Once the topology of a network is determined, the method by which the nodes access the network must be determined. In some cases, the access method is determined by the topology of the network. Some of the access methods used in networks are as follows: carrier sense multiple access (CSMA), carrier sense multiple access with collision detection (CSMA/CD), and token passing. In the CSMA method, each node monitors the network line for activity. When the node detects that there is no activity on the network, it will send its data. A problem occurs when two or more nodes attempt to use the network at the same time. This situation causes a collision of the data packets and a possible loss of data. In the CSMA/CD method, when a collision is detected, each node ceases transmission and retransmits when it senses that activity on the network is completed. In token passing, a software token is passed to each node in an orderly manner. The method is similar to the Roll Call mode of operation of the Link- 11 system described in chapter 2. When the node with the token has no data to transmit, it passes the token to the next unit. When the node has data, it transmits it when it receives the token, and when it completes its transmission, passes the token to the next node. LAN SYSTEMS— There are several types of systems that can be installed in a LAN. The topology used has a major effect on the system the LAN will be capable of using. A few of the LAN systems available are as follows: EtherNet, STARLAN, ARCnet, and the IBM Token Ring. EtherNet is generally a linear bus network using the CSMA/CD protocol for network access. STARLAN is a star topology that also uses the CSMA/CD access protocol. ARCnet is a distributed star network that uses a token passing access protocol. The IBM Token Ring network is a star ring network that uses the token passing access protocol. NETWORK OPERATING SYSTEM BASICS— The network operating system has five basic subsystems to control the operation of the

network. These are the control kernel, the network interfaces, the file systems, the system extension, and the system services. The control kernel coordinates the various functions and processes of the network. The network interfaces provide the low-level subnet protocols for bridging hardware devices with the network operating system. The file systems module controls the methods of organizing, storing, and retrieving data from the various types of storage systems used by the network. System extensions are defined by the network operating system manufacturers to allow third party modifications to the operating systems. This allows the network user to customize the network. The network services module contains all the functions that do not fit in any of the other subsystems. These include, but are not limited to, system security, system reliability, error conditions, and access violations. 6-16

APPENDIX I GLOSSARY This glossary defines abbreviations and acronyms as they are used in this training manual. ACDS— Advance combat direction system AFTS— Audio-frequency tone shift ASCII— American Standard Code for information interchange BER— Bit error rate BFSK— Binary frequency-shift keying CAINS— Carrier Aircraft Inertial Navigation System CCA— Circuit card assembly C 2 — Command and Control C 2 P— Command and Control Processor CDG— Control/display group CDS— Combat Direction System CRT— Cathode-ray tube CPS— Continuous phase shift CS— Carrier suppression CSMA— Carrier sense multiple access CU— Control unit dB— Decibel dBm— Milliwatt reference (600-ohm load) DDC— Digits!-to-digital converter DDPG— Digital data processor group DIV— Diversity DLRP— Data link reference unit DPG— Data processing group DTS— Data Terminal Set EDAC— Error detection and correction elf— Extremely low frequency ehf— Extremely high frequency EMMSD— Embedded mass memory storage device EMS— Embedded memory subsystem ETA— Estimated time of arrival ETD— Estimated time of departure FDM— Frequency-division multiplexing FFT— Fast Fourier transform FSK— Frequency-shift keying Ghz— Gigahertz GRU— Gridlock reference unit hf— High frequency HPAG— High power amplifier group HPIB— Hewlett Packard Interface Bus Hz— Hertz ID— Track identification AI-1

IDA— Input data acknowledge IDR— Input data request IEEE— Institute of Electrical and Electronics Engineer I/O— input/output ISO— International Standards Organization JTIDS— Joint Tactical Information Distribution System JU— JTIDS unit kHz— Kilohertz lf— Low frequency LAN— Local area network log— Logarithm LMS— Link monitor system LSB— Lower sideband mf— Medium frequency MHZ— Megahertz MODEM— MOdulator Demodulator MCM— Monitor control message MRM— Monitor reply message MUF— Maximum useable frequency NATO— National Alliance Treaty Organization NIC— Network interface card NICP— Network interface computer program NCS— Net control station NTR— Network time reference ODR— Output data request OSI— Open system interconnection AI-2 POFA— Programmed operational and fictional appraisal PIU— Power interface unit PU— Participating unit R/T— Receiver/transmitter group RGB— Red, green, and blue RCV— Receive SDLC— Synchronous data link control SDU— Secure data unit SNR— Signal-to-noise ratio SGS— Shipboard Gridlock System shf— Superhigh frequency SINS— Ship’s Inertial Navigation System TADIL— Tactical Data Information Link TDM— Time-division multiplexing TDMA— Time-division multiple access TQ— Track quality uhf— Ultra-high frequency USB— Upper sideband µsec— Microsecond UTM— Universal test message vhf— Very high frequency vlf— Very low frequency XMT— Transmit

APPENDIX II REFERENCES USED TO DEVELOP THE TRAMAN NOTE: Although the following references were current when this TRAMAN was published, their continued currency cannot be assured. Therefore, you need to be sure that you are studying the latest revision. Chapter 1 Black, Uyless D., Data Networks, Concepts, Theory, and Practice, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1989. Navy Electricity and Electronics Training Series, Module 11, Microwave Principals, NAVEDTRA 172-16-00-84, Naval Education and Training Program Management Support Activity, Pensacola, FL, 1984. Navy Electricity and Electronics Training Series, Module 17, Radio-Frequency Communications Principles, NAVEDTRA 172-17-00-84, Naval Education and Training Program Management Support Activity, Pensacola, FL, 1984. Understanding Link-11, A Guidebook for Operators, Technicians, and Net Managers, Navy Center for Tactical Systems Interoperability, San Diego, CA, 1991. Chapter 2 Data Communication System AN/USC-30, NAVSEA 0967-563-9010, Government Telecommunications Division, Collins Radio Group, Rockwell International, Dallas, TX, 1975. Instruction Manual, Data Terminal Set, AN/USQ-59(V)2, SPAWAR 0967-LP- 563-9020, Space and Naval Warfare Systems Command, Washington, D. C., 1973. Link-11 Seminar for Operators and Technicians, Instructor Notes, Link-11 Waterfront Seminar, Logicon, Inc., San Diego, CA, 1990. Operation and Maintenance Instructions, Organizational Level, Link 11 Data Terminal Set AN/USQ-76(V)3, SPAWAR EE640-DW-OMI-01B/E110- USQ76V3, Space and Naval Warfare Systems Command, Washington, D.C., 1990. System Operation and Maintenance Manual, AN/USQ-74, 74A, Data Terminal Set, SPAWAR EE600-AA-OMI-010, Space and Naval Warfare Systems Command, Washington, D. C., 1990. AII-1

Technical Manual, Operation, and Maintenance with Illustrated Parts Breakdown, Data-Terminal Set Control, C-9063/USQ-59, NAVSEA 0967- LP-563-9050, Naval Sea Systems Command, Washington, D. C., 1977. Technical Manual, Operation, Maintenance Manual with Illustrated Parts Breakdown, Digital To Analog Converter, CV-2969A(P)/U, NAVSEA 0967- LP-563-9070, Naval Sea Systems Command, Washington, D. C., 1977. Technical Manual, Installation, Operation, and Maintenance with Illustrated Parts Breakdown, Computer Adapter MX-9222/U, NAVSEA 0967-LP-563- 9060, Naval Sea Systems Command, Washington, D. C., 1977. Technical Manual, Operation, Maintenance with Illustrated Parts Breakdown, Address Control - Indicator, C-9062/U, NAVSEA 0967-LP- 563-9040, Naval Sea Systems Command, Washington, D. C., 1977. Understanding Link-11, A Guidebook for Operators, Technicians, and Net Managers, Navy Center for Tactical Systems Interoperability, San Diego, CA, 1991. Chapter 3 LMS-11 Troubleshooter’s Guide for Link-11 Operations, Logicon, Inc., San Diego, CA, 1990. Operator/O-Level Maintenance Training Course, Trainee Guide for the Link Monitor System, AN/TSQ-162(V)1, Logicon, Inc., San Diego, CA, 1990. Technical Manual, System Operation and Maintenance Instructions, Organization Level, Link Monitor System, AN/TSQ-162(V)1, SPAWAR EE- 190-AB-OMI-010/TSQ-162(V)1, Space and Naval Warfare Systems Command, Washington, D. C., 1989. User’s Manual, Link-11 Monitor System, Rack-mountable (LMS-11R), Logicon, Inc., San Diego, CA, 1990. Chapter 4 Operation and Maintenance Manual for the Link Monitor System (LMS-4) for Link-4A, Logicon, Inc., San Diego, CA, 1990. Technical Manual, Volume 1, Digital Data Communications Control Set, AN/SSW-1D(U), NAVSEA 0967-LP-555-4010, Naval Sea Systems Command, Washington, D. C., 1973. Chapter 5 Operating and Service Manual, C-12428/USQ-125 Control Unit, Cedar Technology Inc., Longmont, CO, 1995. AII-2

Operation and Maintenance Instructions, MK512PV, Link-11 Data Terminal, General Atronics Corp., Philadelphia, PA, 1992. Preliminary Technical Manual, System Maintenance, Organization Level, AN/UYQ-62(V)1, 2, Command and Control Processor (C 2 P) Subsystem, SPAWAR EE600-AB-SLM-010, Space and Naval Warfare Systems Command, Washington, D. C., 1992. Understanding Link-16, A Guidebook for New Users, Logicon, Inc., San Diego, CA, 1994. Chapter 6 Black, Uyless D., Data Networks, Concepts, Theory, and Practice, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1989. Hancock, Bill, Designing and Implementing Ethernet Networks, QED Information Sciences, Inc., Wellesley, MA, 1988. Heath, Steve, Effective PC Networking, Butterworth-Heinemann Ltd., Oxford, England, 1993. Woodward, Jeff, The ABC’s of Novell NetWare, Sybex Inc., Alameda, CA, 1989. Durr, Michael, Networking Personal Computers, 3d ed, Que Corp., Carmel, IN, 1989. AII-3

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INDEX A Access methods, 6-9 Arcnet, 6-12 Air traffic control, 4-2 Amplitude modulation, 1-6 Antennas, 2-4 Antenna couplers, 2-4 AN/USQ-125 Data Terminal Set, 5-1 Asynchronous transmission, 1-5 Audio tone generation, 2-11 Automatic Carrier Landing System, 4-2 B Building a link message, 2-7 Broadcast, 2-7 C Carrier Aircraft Inertial Navigation System (CAINS), 4-6 CDS computer, 2-3 CP-2205 (P)(V) USQ-125 Data Terminal, 5-1 Command and Control Processor, 5-11 purpose, 5-11 system configuration, 5-12 Communications systems, 1-1 D Data Terminal Set (DTS), 2-3 Decibel measurement system, 1-3 Digital data communications techniques, 1-5 Distributed star network, 6-9 E Error detection and correction (EDAC), 2-10 Ethernet, 6-11 Establishing a LINK-11 net, 2-5 F Frequency modulation, 1-6 H Hamming bits, 2-11 I IBM Token Ring Network, 6-12 Information segment, 2-8 Intercept vectoring, 4-2 J Joint Tactical Information Distribution System (LINK-16), 5-4 architecture, 5-6 capabilities, 5-6 data exchange, 5-6 equipment configuration, 5-8 features, 5-4 model 5, 5-8 nets, 5-5 terminal, 5-9 transmission protocols, 5-5 L Landlines, 1-2 LANS, 6-1 hardware, 6-2 network interface card, 6-2 network servers, 6-2 systems, 6-11 topologies, 6-7 workstations, 6-4 Linear bus network, 6-7 Link protocol & interface control, 2-12 LINK-4A CDS system, 4-1 components, 4-4 control messages, 4-3 message formats, 4-3 overview, 4-1 reply message, 4-3 LINK-11, 2-1 INDEX -1

communication switchboard, 2-4 controls & indicators, 2-13 DTS, 2-9 functions, 2-10 message formats, 2-8 myths & facts, 3-1 net operational modes, 2-5 overview, 2-2 POFAs, 3-3 security device, 2-3 LMS-4, 4-6 LMS-11, 3-6 accessory group, 3-9 carrier suppression, 3-18 control/display group, 3-8 data processing group, 3-7 link monitor mode, 3-9 net display, 3-12 operation & displays, 3-9 L LMS-11 (cont) pu display, 3-15 spectrum display, 3-17 status display, 3-11 system configuration, 3-7 system initialization, 3-9 M Message data frames, 2-8 Modems, 1-8 Modulation/demodulation, 1-6 Multibit modulation, Multiplexing, 1-9 N 1-7 Net Control Station (NCS) input/output operations, 2-18 modulator/demodulator, 2-18 radio set interface, 2-19 Net synchronization, 2-6 Net test, 2-6 Network Operating Systems control kernel, 6-12 file systems, 6-13 network interfaces, 6-13 system extensions, 6-13 system services, 6-13 Network operating system O software, 6-13 Online & offline system test options, 5-3 Open system interconnection reference model, 6-4 application, 6-7 hardware level, 6-5 presentation level, 6-5 transport level, 6-5 P Phase reference frame, 2-7 Preamble, 2-7 Programmed Functional and Operational Analysis (POFAs), 3-3 analyzing multistation, 3-5 analyzing single station, 3-3 multistation, 3-4 multistation procedures, 3-5 setup, 3-3 Precision course direction, 4-2 Protocols, 6-10 R Radio silence, 2-7 Recognizing LINK-11 net problems, 3-18 Receive cycle, 2-5 Ring network, 6-9 Roll call, 2-6 S Shipboard Gridlock System, 2-3 Short broadcast, 2-7 Starlan, 6-12 Star network, 6-8 Start code, 2-8 Stop code, 2-8 Synchronous transmission, 1-5 T Transmission cycle, 2-4 Types of communication channels, 1-2 INDEX-2

Assignment Questions Information: The text pages that you are to study are provided at the beginning of the assignment questions.

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ASSIGNMENT 1 Textbook Assignment: “Fundamentals of Data Communications,” chapter 1, pages 1-1 through 1-13; “The Link-11 System,” chapter 2, pages 2-1 through 2-8. 1-1 . 1-2. 1-3. 1-4. Which of the following are components of a communications system? 1. Receivers 2. Transmitters 3. Communications channels 4. All of the above The conversion of da. to a form that can be sent over a communications channel is a fiction of which of the following communication system components? 1. The transmitting equipment 2. The receiving equipment 3. The communications channel 4. The computer Data sent over a communications channel may be in which of the following forms? 1. Analog only 2. Digital only 3. Either analog or digital, depending on the type of system 4. Alphanumeric characters A communications channel signal that varies continuously between a minimum and a maximum value is what type of signal? 1. Analog 2. Digital 3. Numeric quantities 4. Alpha characters 1-5 . 1-6. 1-7. 1-8. To convey data, analog signals can be varied in which of the following ways? 1. Phase only 2. Amplitude only 3. Frequency only 4. Phase, amplitude, or frequency Which of the following communications signal types have a limited set of values and 1. 2. 3. 4. are transmitted as discrete pulses? Analog Digital Both 1 and 2 above Alphanumeric characters In which of the following types of communications channels is data in a single direction ONLY? 1. Simplex 2. Duplex 3. Half duplex 4. Full duplex Which of the following communications channels can transmit and receive data simultaneously? 1. Simplex 2. Duplex 3. Half duplex 4. Full duplex 1

1-9 . Which of the following types of communications channels transmits data in one direction, pauses, and then receives data coming in the opposite direction? 1. Simplex 2. Duplex 3. Half duplex 4. Full duplex 1-10. What device converts digital data signals to tones and converts tones back to digital data signals? 1-11. 1-12. 1. Modem 2. Modulator 3. Demodulator 4. Data converter The modulator of a modem performs which of the following functions? 1. It converts data to be transmitted into discrete modifications of the tone or carrier signal 2. It converts data-carrying tones into digital data 3. It receives digital data from the demodulator 4. It receives analog data from the computer The operational characteristics of a radio communications system are determined by what means? 1. Low frequency 2. High frequency 3. Carrier frequency 4. Radio frequency band 1-13. 1-14. 1-15. 1-16. 1-17. The tactical digital information links that the Navy uses generally require which of the following radio frequency bands? 1. LF 2. HF 3. UHF 4. Both 2 and 3 above The data signals must be (a) to the carrier signal at the transmitter and (b) from the carrier signal in the receiver. 1. (a) Modulated (b) modulated 2. (a) Modulated (b) demodulated 3. (a) Demodulated (b) modulated 4. (a) Demodulated (b) demodulated A radio frequency of 8,090 KHz is in which of the following frequency bands? 1. LF 2. MF 3. HF 4. UHF Which of the following radio frequency bands is limited to line-of-sight communications? 1. LF 2. MF 3. HF 4. UHF Decibels are the unit of measure of what function of an amplifier, communications equipment, or a system? 1. Gain 2. Power 3. Output 4. Input 2

1-18. The bel most often expresses what value of any component, circuit, or system? 1. Power 2. Input 3. Output 4. Ratio of input to output power 1-19. In the formula for bel, which of the following symbols would represent the output of an amplifier? 1. N 2. PI 3. P2 4. Log10 1-20. In the formula for bel, which of the following symbols would represent the gain of an amplifier in bels? 1. N 2. P1 3. P2 4. Log10 1-21. The decibel is equal to what total number of bels? 1 . 1/10 bel 2 . 1/100 bel 3 . 1 bel 4 . 10 bels 1-22. A value of 1.5 bels is equal to what total number of decibels? 1 . 15. 2 . 15 3 . 150 4. 1,500 1-23. What is the power ratio of an increase of a reference signal of 30 dBs? 1. 10 2. 100 3. 1,000 4. 10,000 1-24. A power gain of -6 dB from a reference signal of 1,000 watts results in what maximum value of output signal? 1. 250 watts 2. 500 watts 3. 2,500 watts 4. 5,000 watts 1-25. When dBm is measured, which of the following signals is normally the reference signal? 1. Input 2. Output 3. 1 milliwatt 4. 1 millivolt 1-26. Which of the following signal levels indicates that the output signal is greater than the input signal? 1 . 5 dB 2 . +3 dB 3 . Either 1 or 2 above 4 . -2 dB 1-27. A reading of 0 dB indicates that the output signal has what relationship to the reference signal? 1. Equal to 2. Less than 3. Greater than 4. Not equal to 3

1-28. A reading of 0 dBm indicates an output value equal to which of the following signal values? 1 . 0 dB 2. 1 milliwatt 3 . 500 watts 4. 1,000 watts 1-29. What framed transmission method is used to transmit ASCII characters? 1. Asynchronous 2. Synchronous 3. Message framed 4. Alphanumeric framed 1-30. What framed transmission method is used to transmit long streams of uninterrupted data bits? 1. Asynchronous 2. Synchronous 3. Character framed 4. Alphanumeric framed 1-31. When the asynchronous transmission method is used, each character sent has which of the following control bits? 1. Start bit(s) only 2. Stop bit(s) only 3. Both start and stop bits 4. Parity bits 1-32. When the asynchronous transmission method is used, synchronization between the transmitting and the receiving devices is achieved by which of the following methods? 1. Synchronization reference signal in the preamble 2. Synchronization reference in the stop codes 3. Character-by-character synchronization 4. External timing signals sent concurrently on a separate line 1-33. Which of the following codes indicates the beginning sequence of a synchronous message? 1. Sync bits 2. Stop code 3. Parity code 4. Preamble IN ANSWERING QUESTIONS 1-34 THROUGH 1-38. MATCH THE TERM OR STATEMENT IN COLUMN A WITH THE BASIC MODE OF MODULATION LISTED IN COLUMN B. RESPONSES IN COLUMN B MAY BE USED MORE THAN ONCE. A. TERMS/ STATEMENT B. MODES 1-34. The change in 1. Phase signal amplitude modulation indicates a change in the 2. Amplitude 1 or 0 bits modulation being transmitted 3. Frequency modulation 1-35. Differential quadrature phase-shift keying 4

1-36. 1-37. 1-38. 1-39. 1-40. 1-41. 1-42. BFSK AFTS Interrupting the cycle at a degree point and changing the direction or amplitude of the sine wave Which of the following modes of modulation can be used to modify carrier signals to convey data? 1. Phase modulation 2. Frequency modulation 3. Amplitude modulation 4. All of the above In which of the following modulation methods are frequencies above and below a center frequency used to indicate a logic 1 or 0 bit? 1. Amplitude modulation 2. Frequency-shift keying 3. Audio frequency tone shift 4. Differential quadratic phase-shift keying Which of the following modulation methods uses two discrete audio tones that are modulated to a constant frequency carrier signal? 1. FSK 2. BFSK 3. AFTS 4. Phase-shift keying When quadrature phase-shift modulation is used, a single tone transmits what total number of binary bits of data for each phase Shift? 1. One 2. Two 3. Three 4. Four 1-43. When quadrature phase-shift modulation is used, which of the following phase shifts indicates a binary 00? 1 . +135 degrees 2. –135 degrees 3 . +225 degrees 4. –225 degrees 1-44. Which of the following components of a modem converts the data bits into a carrier signal? 1. The transmitter 2. The receiver 3. Both 1 and 2 above 1-45. Each modem transmitter circuit outputs several carrier signals. 1. True 2. False 1-46. Which of the following circuits allows ONLY the desired carrier signal to be received from the communications channel? 1. The demodulator 2. The data decoder 3. The band pass falter 4. The receiver control circuit 1-47. The term baud describes the number of characters per second transmitted over a communications channel. 1. True 2. False 5

1-48. 1-49. 1-50. 1-51. 1-52. Multiplexing data being transmitted over a communications channel performs which of the following functions? 1. It increases the baud rate 2. It allows multiple users of the same channel 3. Either 1 and 2 above 4. It changes the carrier frequency Which of the following multiplexing methods divide(s) the asynchronous message into a fixed number of time slots? 1. Time division 2. Frequency division 3. Both 1 and 2 above 4. Quadrature phase-shift Which of the following multiplexing methods transmits several tones over a single communications channel? 1. Time division 2. Frequency division 3. Both 1 and 2 above 4. Quadrature phase-shift Link-11 is designated as which of the following types of tactical data information link? 1. TADIL A 2. TADIL C 3. TADIL J 4. Teletype Link-11 communications can operate with which of the following radios? 1. HF only 2. UHF only 3. Either HF or UHF 4. VHF only 1-53. When Link-11 is operated with UHF radio, it is capable of over-the-horizon communications. 1. True 2. False IN ANSWERING QUESTIONS 1-54 THROUGH 1-61, SELECT FROM THE FOLLOWING LIST THE EQUIPMENT THAT PERFORMS THE FUNCTION DESCRIBED IN THE QUESTION. ITEMS IN THE LIST MAY BE USED MORE THAN ONCE. A. B. C. D. E. F. CDS Digital Computer SGS Computer Cryptographic Device Data Terminal Set Communications Switchboard Radio Set 1-54. Selects the HF or the UHF transceiver. 1. B 2. C 3. D 4. E 1-55. Encrypts parallel data from the CDS computer and passes the encrypted data to the data terminal set. 1. A 2. B 3. C 4. D 1-56. Correlates reported positions of local and remote tracks. 1. A 2. B 3. C 4. D 6

1-57. Outputs 24-bit data words to the security equipment via the SGS computer. 1. A 2. B 3. C 4. D 1-58. Multiplexes and modulates parallel data into audio tones. 1. A 2. B 3. C 4. D 1-59. Receives the audio tone package from the data terminal set and transmits the tones. 1. C 2. D 3. E 4. F 1-60. Demodulates the audio tones and checks the six hamming bits for transmission errors. 1. A 2. B 3. C 4. D 1-61. Decrypts the 24-bit data word and sends it to the CDS computer. 1. A 2. B 3. C 4. D 1-62. Which of the following functions is performed by an antenna coupler? 1. Amplification of the HF radio signal 2. Impedance matching of the antenna and the radio set 3. Conversion of atmospheric electromagnetic energy to RF current 4. Coupling of the data terminal set to the radio 1-63. The size of an antenna is determined by which of the following factors? 1. The operating power 2. The operating frequency 3. The range of the receiver 4. The type of data being transmitted 1-64. The frequency range of an antenna can be extended by adding which of the following factors? 1. A resistive load only 2. A capacitive load only 3. An inductive load only 4. Either a capacitive or an inductive load 1-65. Which of the following functions is NOT performed by the data terminal set? 1. Generating the radio key-line signal 2. Converting digital data to audio tones 3. Encrypting CDS computer data 4. Converting audio tones to digital data 1-66. The data terminal set communicates with the radio set via which of the following devices? 1. The communications switchboard 2. An antenna coupler 3. The cryptographic device 4. The SGS computer 7

1-67. Which of the following radio frequency modulation methods is used to minimize propagation-caused signal loss during HF Link-11 operations? 1. Quadrature phase-shift modulation 2. Frequency modulation 3. Phase modulation 4. Amplitude modulation independent sideband 1-68. Which of the following individuals is responsible for assigning primary and secondary Link-11 frequencies before the deployment of a task force? 1. The aircraft carrier commanding officer 2. The net control station track supervisor 3. The task force commander 4. The fleet CinC 1-69. When a Link-11 net is established, which of the following sequences of operations should be followed to determine readiness of all units to enter the net? 1. Net Test, Net Sync, roll call 2. Net Sync, Net Test, roll call 3. Net Sync, Net Test, Broadcast 4. Roll call, Net Test, Net Sync IN ANSWERING QUESTIONS 1-70 THROUGH 1-75, SELECT FROM THE FOLLOWING LIST THE OPERATING MODE DESCRIBED IN THE QUESTION. A. Net Synchronization B. Net Test C. Roll Call D. Broadcast E. Short Broadcast F. Radio Silence 1-70. 1-71. 1-72. 1-73. 1-74. What Link-11 operating mode establishes a uniform time base from which all net communications are normally initiated? 1. A 2. B 3. C 4. D In what Link-11 operating mode is each picket unit interrogated, in turn, by NCS? 1. A 2. B 3. C 4. D What Link-11 operating mode provides an overall evaluation of net and equipment performance? 1. B 2. C 3. D 4. E In what Link-11 operating mode will one participating unit transmit data continuously to all other net members? 1. C 2. D 3. E 4. F In what Link-11 operating mode are the radio set key line and data terminal audio output inhibited? 1. C 2. D 3. E 4. F 8

1-75. In what Link-11 operating mode is a single data transmission sent only when the operator depresses the TRANSMIT START button? 1. B 2. C 3. D 4. E 9

ASSIGNMENT 2 Textbook Assignment: “The Link-11 System,” chapter 2, pages 2-7 through 2-23; “Link-11 Fault Isolation,” chapter 3, pages 3-1 through 3-7. 2-1 . 2-2 . 2-3 . 2-4 . Net Sync continuously broadcasts which of the following signals? 1. Phase reference frames 2. Start codes 3. Stop code 4. Preamble frames When the stored sync mode is operating, the picket station uses which of the following signals to establish a time base? 1 . 2 . 3 . 4 . An external frequency standard The internal frequency standard in the DTS The sync signal received from NCS The sync signal received form another picket Which of the following functions is NOT tested when Net Test is running? 1. DTS to radio interface 2. CDS computer to DTS interface 3. Radio to antenna interface 4. Radio receiver function The preamble of a Link-11 message consists of a total of how many frames? 1. Five 2. Six 3. Seven 4. Eight 2-5 . 2-6 . 2-7 . During transmission of the preamble, the 605 Hz tone is transmitted at which of the following power levels? 1. –6 dB 2. +6 dB 3. –12 dB 4. +12 dB To enable the DTS to detect frame transitions during the preamble, the 2,915 HZ sync tone is phase shifted how many degrees at each frame? 1. 90 2. 180 3. 270 4. 360 The phase reference frame of a Link-11 header performs which of the following functions? 1. Provides synchronization between the DTS and the CDS computer 2. Provides a time reference for the DTS 3. Provides a time reference for the radio 4. Provides the reference to extract the data in the next frame 10

2-8 . During a receive cycle, the start code causes which of the following actions? 1. The CDS computer to send the prepare to receive data interrupt 2. The DTS to send the prepare to receive data interrupt 3 . The CDS computer to send the prepare to transmit data external function 4. The DTS to send the prepare to transmit data interrupt 2-9 . Exactly how many data bits are contained in each Link-11 information frame? 1. 18 2 . 24 3 . 30 4 . 32 2-10. The control stop code is generated by which of the following units? 1. NCS only 2. Picket station only 3. Either NCS or a picket station, indicating the end of a control message 2-11. During a receive cycle, the stop code (control or picket) causes which of the following actions? 1. The CDS computer to send the end of data interrupt 2 . The DTS to send the end of data external function 3 . The CDS computer to send the end of receive interrupt 4. The DTS to send the end of receive interrupt 2-12. A call-up, or interrogation message consists of a total of how many frames? 1. Five 2 . Six 3 . Seven 4 . Eight 2-13. The two frames following a control stop code indicate which of the following? 1 . The address of the NCS 2 . The next picket address in the roll call 3 . The end of the NCS message 4. The last address interrogated 2-14. A picket reply message is sent in which of the following sequences? 1 . Preamble, phase reference, data, stop code 2 . Preamble, phase reference, start code, data, control stop code 3 . Preamble, phase reference, start code, data, picket stop code 4. Phase reference, preamble, start code, data, stop code 2-15. The DTS operates in full duplex when it performs which of the following operations? 1. System testing 2. Net Test 3. Normal operations 4. Short Broadcast 2-16. The DTS performs which of the following functions? 1. Data encryption 2. Error detection and correction 3. Track gridlock 4. Transmitting data tones on a carrier frequency 11

2-17. The six hamming bits added to the data word enables the DTS to correct what maximum number of data bits? 1. One 2. Two 3. Three 4. Four 2-18. The DTS is operating in the detect and correct mode. A data word is received by the CDS computer with bit 24=0, and bit 25=1. Which of the following conditions is indicated by this bit combination? 1. No errors detected 2. Parity error(s) detected 3. Odd bit error(s) detected, correction attempted 4. Even errors detected, no correction attempted 2-19. The DTS develops a composite signal consisting of what total number of frequency division multiplexed audio-frequency tones? 1 . 2 2. 11 3 . 16 4. 30 2-20. Bits 4 and 5 of a 30-bit data word are carried by which of the following audio tone frequencies? 1 . 935 Hz 2. 1,155 Hz 3 . 1,265 Hz 4. 1705 Hz 2-21. What is the basic unit of the Link-11 transmission? 1. Bit 2. Tone 3. Frame 4. Doppler 2-22. In a single frame, the DTS can tolerate what maximum phase shift error without generating an error code? 1. + 44 degrees only 2. – 44 degrees only 3 . ± 44 degrees 4. ±135 degrees 2-23. A phase-shift error of +105 degrees in any one of the data tones will cause a single bit to be erroneous. 1. True 2. False 2-24. Which of the following Link-11 signals allows the receiving unit to correct errors caused by the relative motion between the sending and receiving units? 1. Sync tone 2. Doppler tone 3. Data carrying tones 4. Motion correct tone 2-25. During the preamble, the 2,915 Hz tone sets which of the following references? 1 . Frame timing when the DTS is in corrected timing 2. Signal power levels when the DTS is in corrected timing 3 . Frame timing when the DTS is in stored timing 4. Signal power levels when the DTS is in stored timing 12

2-26. During the reception of the data segment of a Link-11 message, the 605 Hz Doppler tone should be at which of the following power levels? 1. +12 dB 2 . + 6 dB 3 . – 6 dB 4 . 0 dB 2-27. When the DTS is in the OPERATE mode, exactly how many fault-sensing sensors can cause the SUMMARY FAULT lamp to light? 1. 11 2. 14 3. 23 4. 27 2-28. The LAMP TEST switch on the Mode Control Panel will cause all of which of the following lamps to light? 1. Those on the mode control panel only 2. Those on the TADIL A control panel only 3. Those on the address control unit only 4. Those on the mode control panel, the TADIL A control panel, and the address control unit 2-29. When the FULL-DUPLEX/HALF-DUPLEX switch is in the FULL-DUPLEX POSITION, the transmit sidetone is processed for input to the computer. 1. True 2. False 2-30. When the SIDEBAND SELECT switch is in the DIV position, which sideband signal is processed for input to the computer? 1. USB only 2. LSB only 3. The combination of the USB and LSB signals 4. Either the USB or the LSB, depending on the signal quality of each sideband 2-31. During normal Link-11 operations, the DATA RATE switch on the mode control panel should be in which of the following positions? 1 . 1,200 bps 2 . 2,400 bps 3 . DUAL 1,200 bps 4 . TADIL A 2-32. The SYNC MODE switch on the mode control panel is used in conjunction with which of the following switches on the TADIL A control panel? 1. OPERATE/RADIO SILENCE switch 2. NET CONTROL/PICKET switch 3. TIMING STORED/CORRECTED switch 4. ERROR CORRECT/LABEL switch 13

2-33. When the SYNC MODE switch is placed in the FAST position, synchronization is obtained by which of the 1 . 2 . 3 . 4 . following methods? Use of the frame timing reference stored during Net Sync Use of the frame timing reference obtained from the preamble of the current message only Use of the frame timing reference obtained at each data frame of the current message only Use of both the frame timing 2-34. 2-35. reference obtained during the preamble and the frame timing of each frame of the current message The NET BUSY indicator of the TADIL A control panel is activated by which of the following signals? 1. Signal presence 2. Receive mode 3. Transmit mode 4. Start code detected When the SYNC COMPT indicator is lighted after the DTS has achieved which of the following conditions? 1 . It is in sync with the radio 2 . It is using stored synchronization signals 3 . It is in sync with NCS 4. It is testing the internal sync circuits 2-36. The TIMING/STORED/CORRECTED switch is set to the STORED position. Which of the following signals will the DTS use for frame timing synchronization? 1 . 2 . 3 . 4. The frame timing reference stored during Net Sync The frame timing reference obtained from the preamble of the current message only The frame timing reference obtained at each data frame of the current message only Both the frame timing reference obtained during the preamble and the frame timing of each frame of the current message 2-37. When the ERROR CORRECT/LABEL switch is in the CORRECT position, the DTS is capable of performing which of the following operations? 1. Detecting and correcting an even number of bit errors in the received data word 2. Detecting and correcting an odd number of multiple bit errors in the received data word 3. Detecting and correcting a single bit error in each received data word 4. Detecting and correcting a single bit error in the received data message 14

2-38. When you depress the TRANSMIT RESET switch on the TADIL A control panel, it causes the DTS to perform which of the following operations? 1 . 2 . 3 . 4. To immediately stop all transmissions To inhibit the generation of output data requests, generating a stop code and ending the current transmission To place the radio in radio silence To inhibit the generation of input data requests, generating a stop code and ending the current reception 2-39. The DTS is configured as a picket station in roll call mode. When you depress the TRANSMIT INITIATE switch on the TADIL A control panel, it will cause the DTS to perform which of the following operations, if any? 1. To immediately transmit the data 2. To allow the unit to enter the net 3. To assume control of the net as NCS 4. None 2-40. On the NCS platform, the MISS CALL indicator on the TADIL A panel will light when a picket fails to respond to two successive interrogations. 1 . True 2 . False 2-41. The address entered into the OWN STATION ADDRESS switches perform which of the following DTS functions? 1. Transmits the entered address to all other members of the net 2. Transmits the entered address to NCS only 3. Receives messages that match the entered address 4. Transmits tactical data when the interrogation message address matches the entered address 2-42. On the NCS platform operating in a Link-11 net where the units are approximately 100 miles apart, which of the following values should be entered into the RANGE IN MILES switches? 1 . 0 miles 2 . 25 miles 3 . 50 miles 4 . 100 miles 2-43. With a single address control indicator, an NCS platform can control what maximum number of participating units? 1. 5 2. 10 3. 15 4. 20 2-44. Data exchange between the Link-11 DTS and the CDS computer is controlled by the DTS using which of the 1 . 2 . 3 . 4. following control signal protocols? External interrupts External functions Input data requests Output data requests 15

2-45. During a receive data cycle, the DTS performs which of the following actions when frame two of the stop code is detected? 1 . 2 . 3 . 4. The frame is processed as a data frame and sent to the computer The DTS processes the stop code and resets itself only The DTS sends the end of receive external interrupt to the computer The computer processes the stop code and closes the input data buffer 2-46. Which of the following actions is performed by the DTS when a control station stop code is received? 1 . 2 . 3 . 4. The DTS compares the next two frames received with the own station address The DTS resets all I/O timing circuits The DTS sends the next two frames received to the CDS computer The DTS sends the prepare to transmit data interrupt to the computer 2-47. When the DTS recognizes own station address, it transmits which of the following signals first? 1 . 2 . 3 . 4 . Prepare to transmit interrupt The first frame of the preamble The phase reference frame Input data request 2-48. At the start of a transmit cycle, the output data request is first set active during which of the following frames? 1. The first frame of the preamble 2. The first frame of the start code 3. The phase-reference frame 4. The second frame of the start code 2-49. Which of the following events place when the CDS computer answer an ODR from the DTS the specified time limit? takes does not within 1 . The DTS generates the stop code 2 . The DTS hangs-up 3 . The computer generates an external function to clear the DTS 4 . The computer sends a stop code to the DTS 2-50. Which of the following events occur if an interrogated picket station does not answer an initial interrogations from the NCS within 15 frame intervals? 1. NCS interrogates the next station 2. NCS waits another 15 frame intervals 3. Link-11 network hangs up 4. NCS retransmits the interrogation to the unit that did not reply 2-51. A total of how many data tones are in the composite tone package developed by the DTS? 1 . 13 2 . 14 3 . 15 4 . 16 16

2-52. 2-53. 2-54. 2-55. The intelligence (data bits) in a data tone is stored by which of the following methods? 1 . Phase shifting the tone by a predetermined amount with respect to the following frame 2 . Phase shifting the tone by a predetermined amount with respect to zero degrees 3 . Phase shifting the tone by a predetermined amount with respect to the preceding frame 4. Increasing or decreasing the amplitude of the data tone with respect to the preceding frame During receive operations, exactly how many EDAC bits are extracted from the received data tones? 1. One 2. Two 3. Five 4. Six The EDAC bits enable the DTS to correct a total of how many received bit errors? 1. One 2. Two 3. Three 4. Four When operating the Link-11 with a UHF radio set, you should place the SIDEBAND SELECT switch in what position only? 1. LSB 2 . USB 3 . DIV 4 . AUTO 2-56. With Link-11 transmitting on the HF range and the sideband select switch set to the AUTO position, which of the following priorities are used by the DTS to find the data word with no errors to send to the computer? 1 . LSB, USB, DIV 2 . LSB, DIV, USB 3 . DIV, LSB, USB 4 . DIV, USB, LSB 2-57. The Link-11 radio set is in the transmit mode when the key line is clear. 1. True 2. False 2-58. Which of the following conditions would NOT be a valid reason for changing the unit functioning as NCS in a Link-11 net to improve net communications? 1 . The current NCS has one PU address entered wrong 2 . The current NCS has poor receiver sensitivity and is polling on top of PU responses 3 . Several PUS are in a propagation shadow 4 . Several PUs are out of range of the current NCS unit 2-59. Changing frequencies will always solve Link-11 problems. 1 . True 2 . False 17

2-60. When you keeping the radio set tuned to output maximum power, it causes which of the following problems? 1. 2. 3 . 4. Increases RFI/EMI on the transmitting unit only Increases receive data errors on receiving units by saturating the data terminal sets only Increases RFI/EMI on the transmitting unit and increases receive data errors by DTS saturation Decreases RFI/EMI on the receiving units 2-61. When the NCS enters dummy PUs, which of the following net conditions will exist, if any? 1. Net efficiency increases 2. Netcycle time decreases 3. Netcycle time increases 4. None, dummy PUs have no effect on the net 2-62. What following NCS action is the most effective net management technique when a PU is having trouble maintaining Link-11 communications? 1. 2 . 3 . 4. Continuing normal Link-11 operations while the trouble PU Directing the PU to go to radio silence so that the PU does not respond to interrogations Directing all units to change from a HF frequency to an UHF frequency Removing the troubled PU from the polling sequence until the problem is corrected and the troubled PU is ready to reenter the net 2-63. When you set up the DTS to run a single-station POFA, the DTS must be configured to operate in which of the following modes? 1. Simplex 2. Half duplex 3. Full duplex 4. POFA TEST mode 2-64. When you run a single-station POFA with the radio set which of the following equipments is/are NOT checked? 1. Security device I/O path 2. Antenna coupler 3. DTS-to-radio audio lines 4. Radio-to-DTS audio lines 2-65. Running a single-station POFA can assist the technician in isolating a problem in which of the following sections of the DTS? 1. Receive timing 2. Doppler correction 3. DTS to antenna interface 4. Transmit timing 2-66. A single-station POFA should print the interrupts in what sequence? 1. End of receive, prepare to transmit, prepare to receive 2. Prepare to receive, prepare to transmit, end of receive 3. Prepare to transmit, end of receive, prepare to receive 4. Prepare to transmit, prepare to receive, end of receive 18

2-67. A single-station POFA error printout that lists bit errors that are less than 10 percent of the total words transmitted is considered a successful POFA. 1. True 2 . False 2-68. A single broken line in the switchboard between the DTS and the crypto device could cause which of the following problems? 1. One bit always set to a logic “1” 2. One bit always set to a logic “0” 3. All bits randomly set to a logic “1” 4. All bits randomly set to a logic “1” or a logic “0” 2-69. The multi-station POFA is run in which of the following modes? 1. Net test 2 . Roll call 3 . Broadcast 4. Short broadcast 2-70. When a multi-station POFA is run, what total number of data words are in each block of data transmitted? 1 . 115 2 . 230 3 . 345 4. 460 2-71. When a multi-station POFA is run, all units participating in the test should be positioned within how many miles of each other? 2-72. A multi-station POFA should be run using which of the following frequencies? 1. Any HF frequency 2. Any UHF frequency 3. The current operational frequency only 4. The current secondary frequency only 2-73. The multi-station POFA should be run for what minimum amount of time? 1 . 5 minutes 2 . 7 minutes 3 . 10 minutes 4 . 15 minutes 2-74. At the completion of the multi-station POFA, the technician should record which of the following information on the error printout? 1. Distance and bearing of all PUS 2. Frequency used 3. Start and stop time of the POFA 4. All of the above 2-75. A multi-station POFA should be considered successful when the link quality factor is which of the following values? 1. Greater than 90 percent 2. Greater than 100 percent 3. Greater than 95 percent but less than 100 percent 4. It must equal 100 percent 1. 25 2 . 50 3 . 75 4. 100 19

ASSIGNMENT 3 Textbook Assignment: “Link-11 Fault Isolation,” chapter 3, page 3-7 through 3-22, “Link-4A,” chapter 4, page 4-1 through page 4-10. 3-1 . 3-2 . 3-3 . A multi-station POFA is considered successful when the computed receive error factor is less than what percentage? 1. 1 2. 5 3. 10 4. 15 Which of the following buffers is acceptable to be received from an unrecognized station (UNREC STA) when a multi-station POFA is running? 1. One buffer of 200 words 2. One buffer of 230 words 3. Two buffers of 200 words 4. Two buffers of 230 words The heading PARITY STATUS OF CORRECT WORDS lists which of the following error conditions? 1. 2 . 3 . 4. Words determined to be correct by the DTS parity check and found in error by the computer parity check Words determined to have an error and corrected by the DTS Words determined to be correct by both the DTS and the computer parity checks Words determined to be in error by the DTS parity check and found correct by the computer parity check 20 3-4 . 3-5 . 3-6 . 3-7 . The LMS-11 is designed to perform which of the following functions? 1 . 2 . 3 . 4 . Isolate problems to the component level in the Link-11 system Provide a history of Link-11 net performance Provide a real-time visual display of the Link-11 net operations Provide the technician with a visual display of the Link-11 operation of one unit The LMS-11 is a complex system designed to be permanently installed. 1. True 2. False The DPG and CDG equipment cases of the LMS-11 provide isolation from which of the following environmental forces? 1. 2 . 3 . 4 . Shock only Vibration only Shock and vibration Power surges The LMS-11 system printer is part of which of the following equipment groups? 1. Accessory 2. Control/display 3. Data processing 4. Support

3-8 . 3-9 . 3-10. 3-11. Which of the following components is NOT part of the LMS-11 data processing group? 1. Control processing unit 2. Dual 5.25-inch disk drive unit 3. Audio interface unit 4. Power control unit The HP9920U computer of the LMS-11 contains what additional amount of random access memory (RAM)? 1. 2 MB 2. 4 MB 3. 8 MB 4. 12 MB The data communications interface of the LMS-11 provides which of the following functions? 1. Parallel synchronous interface with the Link-11 data terminal 2. Parallel asynchronous interface with the printer 3. Serial synchronous interface with the Link-11 data terminal 4. Serial asynchronous interface with the printer The audio interface unit of the LMS-11 connects which of the following signals? 1. USB from HF radios only 2. LSB from HF radios only 3. USB from UHF radios only 4. USB and LSB from HF radios and USB from UHF radios 3-12. To determine the phase shift of the Link-11 audio tones the LMS-11 uses which of the following methods? 1. Fast Fourier Transform formula 2. Comparison of the raw analog signal with the preceding frame 3. Phase shift signal from the DTS 4. Digital data from the crypto device 3-13. 3-14. 3-15. 3-16. The control/display group consists of which of the following units? 1. Composite video and color output circuit card assemblies 2. Data communications interface and HP interface bus 3. Color monitor and keyboard 4. Color printer and interconnecting cables The color display monitor of the LMS-11 uses composite video when it performs which of the following operations? 1. Normal LMS-11 operations 2. Start-up operations only 3. Testing operations only 4. Both start-up and testing operations The functional keys on the LMS-11 keyboard are color-coded to facilitate operator selections and entries. 1. True 2. False During initialization of the LMS-11, which of the following operator entries is NOT a required entry? 1. Date and time 2. Own-ship PU number 3. Net mode 4. Data rate 21

3-17. 3-18. 3-19. 3-20. When initializing the LMS-11, the operator enters 127 frames as the CALL-TIMEOUT value. What type of link-11 operation is indicated by this entry? 1. NET TEST 2. Normal roll call mode 3. Satellite link operation 4. NET SYNC The link monitor mode of the LMS-11 displays what information? 1. Quantitative information concerning the operation of a maximum of 21 PUs 2. Detailed characteristics of the received signal from a specified PU 3. Real-time link activity 4. A graphic representation of the power levels of the received Link-11 tones from a single PU Which of the following function keys on the LMS-11 keyboard would the operator depress to select the link monitor mode? 1. LM 2. NET 3. SPECT 4. PU A PU address of 77 is used by the LMS-11 to indicate which of the following units, if any? 1. PU 77 2. NCS 3. Task force flagship 4. None, 77 is an illegal address IN ANSWERING QUESTIONS 3-21 THROUGH 3-25, REFER TO FIGURE 3-7 IN THE TEXT. 3-21. Which of the following colors indicates the preamble on the link monitor screen of the LMS-11? 1. Yellow 2. Red 3. Cyan 4. Green 3-22. A small cyan line in the middle of the data field indicates the LMS-11 has detected which of the following signals? 1. Start code 2. Stop code 3. Phase-reference frame 4. Noise 3-23. Which of the following displays is used to indicate the LMS-11 is listening? 1. A thick blue line 2. A thin blue line 3. A thick red line 4. A thin red line 3-24. The phase-reference frame is displayed on the link monitor display in what manner? 1 . 2 . 3 . 4. As a small green line between the start code and the data As a small red line between the start code and the data As a small green line between the preamble and the start code As a small red line between the preamble and the start code 3-25. Data frames are represented on the link monitor display by which of the following colors? 1. Yellow 2. Red 3. Cyan 4. Green 22

3-26. An NCS report can be easily identified on the link monitor display by which of the following features? 1. A two digit address at the end of a report only 2. No call-up message between the end of the preceding report and the NCS report only 3. Both a two digit address at the end of the report and no call up message between the preceding report and the NCS report 4. A call message to the NCS address 3-27. An address shown in red on the XMT-ADDRS line of the status display indicates which of the following conditions? 1. The addressed unit is being interrogated 2. The addressed unit failed to answer two interrogations 3. The addressed unit has replied to an interrogation 4. The unit indicated is the next address in the polling sequence 3-28. When the LMS-11 is operating in the link monitor mode and a phase reference frame is detected which, of the following status indicators is active? 1. CC1 2. PHA 3. PRE 4. EOT 3-29. When the LMS-11 is operating in the link monitor mode and the first frame of a picket stop code is detected, which of the following status indicators is active? 1. CC1 2. PHA 3. PRE 4. EOT 3-30. 3-31. 3-32. 3-33. In the status box, the number in the %DATA indicates which of the following quantities? 1 . 2 . 3 . 4 . The total percentage of data in the last message received The percentage of data that is error free in the last message received The total percentage of data received during the most recent net cycle The percentage of data that is error free received during the most recent net cycle The net cycle time that is displayed in the LMS-11 status box indicates which of the following time cycles? 1. Start code to start code of NCS only 2. Control stop to control stop of NCS only 3. Control stop to control stop of an operator selected PU only 4. Control stop to control stop from either NCS (default) or an operator selected PU The Net Display mode of the LMS-11 is capable of displaying two separate types of information. 1. True 2. False In the summarize mode of the net display, a summary of quantitative information is displayed for a maximum of how many PUs? 1. 10 2. 11 3. 20 4. 21 23

3-34. 3-35. 3-36. 3-37. The net display mode can only be displayed when Link-11 is operating in which of the following modes? 1. Net test 2. Net sync 3. Roll call 4. Short broadcast The PU field in the header of the Net Display screen of the LMS-11 is used to define which of the following units, if any, while in the summarize mode? 1. NCS 2. Own station PU number 3. The PU whose recurring transmission is used to define a cycle 4. None, the PU field is only used during the History mode To change the Net Display screen from the summarize mode to the PU history mode, the operator would take which of the following actions? 1. Depress the history mode key on the keyboard 2. Enter a zero into the SUMMARIZE field of the Net Display header 3. Enter the PU number of the unit to be monitored in the PU field 4. Both 2 and 3 above On the Net Display screen, which of the following values indicates an unacceptable SNR? 1. 5 dB 2. 15 dB 3. 25 dB 3-38. When the LMS-11 is in the Net Display (summarize) mode, which of the following conditions will cause the FRAME CNT value of a picket to be displayed in yellow and followed by a “?”? 1. The average number of frames per transmission exceeds seven 2. The average number of frames per transmission is six or less 3. The average signal to noise level per transmission exceeds 20 dB 4. The average signal to noise level per transmission is less than 20 dB 3-39. The %THRU column of the Net Display screen displays which of the following values? 1. The percentage of data received by the listed PU that is error-free 2. The percentage of message data frames received by the LMS-11 that contain errors 3. The percentage of message data frames received by the LMS-11 that are error-free 4. The percentage of control code frames received 3-40. Which of the following power levels listed in the REL 605 column of the Net Display screen indicates normal operation of the link? 1. -3 dB 2. –6 dB 3. +3 dB 4. +6 dB 4. 34 dB 24

3-41. 3-42. Using TADIL A specifications, what is the maximum allowable variation of power in the Link-11 data tones? 1. 1.0 dB 2. 1.5 dB 3. 3.0 dB 4. 4.0 dB The PU display of the LMS-11 presents a graphic representation of the relative power and phase error of the Link-11 signal received from a specified unit. 1. True 2. False 3-43. 3-44. What information is displayed on the relative power bar graph of the PU display? 1. 2. 3. 4. The power of the 605 Hz tone only The relative power of the data tones with respect to the 605 Hz tone The relative power of each data tone with respect to the average power of all the data tones The relative power of each data tone with respect to an internal standard When the relative power bar graph is read, a data tone that is +2 dB greater than the average will be displayed in which of the following colors? 1. Cyan 2. Green 3. Yellow 3-45. The phase error bar graph of the LMS-11 display what information about the Link-11 signal? 1. Relative power 2. Mean deviation of the phase error only 3. Standard deviation of the phase error only 4. Both the mean and standard deviations of the phase error 3-46. A standard phase deviation of 15 degrees for a data tone will be represented on the bar graph in which of the following colors? 1. Cyan 2. Green 3. Yellow 4. Red 3-47. The LMS-11 will indicate that the data received is bad if the standard deviation falls in which of the following ranges? 1. A positive value less than 45 degrees 2. A positive value greater than 45 degrees 3. A negative value less than 45 degrees 4. Both 2 and 3 above 3-48. The incidence of bit errors will increase as the signal-to-noise ratio increases. 1. True 2. False 4. Red 25

3-49. Which of the following tones are graphically displayed by the LMS-11 Spectrum Display? 1. 30 tones that are the odd harmonics of 55 Hz 2. 30 tones that are the even harmonics of 55 Hz 3. The 605 Hz tone and the noise tone only 4. The 15 data tones only 3-50. Under ideal conditions, at what level should the data tones be displayed on the bar graph of the spectrum display? 1. 0 dB 2 . +6 dB 3 . -6 dB 4. +4 dB 3-51. 3-52. When the operator enters PU 00 into the PU address field of the spectrum display what effect, if any, will it have on the operation of the LMS-11? 1. 00 is an illegal address; therefore, no data will be displayed 2. The LMS-11 will continuously update the display for each unit in the net 3. The LMS-11 will update the display for NCS only 4. No effect, the LMS-11 will continue to update the last legal address entered Carrier suppression can only be tested when the Link-11 system is operating in which of the following modes? 1. Net Test 2. Net Sync 3. Roll call 4. Broadcast 26 3-53. When reading the LMS-11 spectrum 3-54. 3-55. 3-56. display, the technician notices that only the 605 Hz tone and the 2195 Hz tones are displayed. Which of the following setup entries would cause this display? 1. The RESTRICT field set to preamble only 2. The RESTRICT field set to data only 3. The PU field is set to a unit not in the net 4. The SIDEBAND SELECT is set to USB only Link-4A is what type of tactical digital information link? 1. Ship-to-aircraft 2. Ship-to-submarine 3. Ship-to-shore 4. Ship-to-ship Link-4A is used to transmit which of the following types of information? 1. High-speed computer-to-computer tactical information 2. Tactical information from a CDS ship to a non-CDS ship 3. Aircraft control and target information 4. All of the above Link-4A data is transmitted by using which of the following methods? 1. Frequency-shift keying 2. Phase-shift keying 3. Audio frequency tone shift 4. Quadrature differential phase-shift keying

3-57. What is the maximum number of aircraft that can be controlled by s single Link-4A controlling station? 1. 25 2 . 50 3 . 75 4. 100 3-58. Aircraft control messages from the Link-4A controlling station are developed by the CDS computer using which of the following types of information? 1. Radar-derived target data 2. Reply data from aircraft 3. Other sources of tactical information 4. All of the above 3-59. Link-4A uses which of the following frequency bands for data exchange? 1. HF only 2. UHF only 3. VHF only 4. Both UHF and VHF 3-60. In which of the following Link-4A modes of operation is an aircraft directed to a specific location to be at an optimum position for an attack? 1. Precision course direction 2. Automatic carrier landing 3. Air traffic control 4. Intercept vectoring system 3-61. In which of the following Link-4A modes of operation is used to maintain safe flight patterns and assigns priority for landing approach? 1. Precision course direction 2. Automatic carrier landing system 3. Air traffic control 4. Intercept vectoring 3-62. Which of the following Link-4A modes of operation is used for the remote guidance of bombers, reconnaissance aircraft, and drones? 1. Precision course direction 2. Automatic carrier landing system 3. Air traffic control 4. Intercept vectoring 3-63. In which of the following Link-4A modes of operation is used to land an aircraft on the flight deck of a carrier? 1. Precision course direction 2. Automatic carrier landing system 3. Air traffic control 4. Intercept vectoring 3-64. The CAINS aircraft alignment data loaded into the navigation computer of the aircraft consists of which of the following types of data? 1. The latitude and longitude of the ship only 2. The ship’s velocity only 3. The latitude, longitude, and ship’s velocity 4. The waypoint data 3-65. The CAINS alignment and waypoint data is initially loaded into the aircraft using which of the following methods? 1. Hard-wired deck edge outlet boxes only 2. UHF RF transmission only 3. Either hard-wired deck edge outlet boxes or UHF RF transmission 4. HF transmission only 27

3-66. The standard CDS control message is (a) milliseconds in duration, while the reply message is (b) milliseconds in duration. 1. (a) 2 (b) 14 2. (a) 2 (b) 18 3. (a) 14 (b) 14 4. (a) 14 (b) 18 3-67. The CAINS receive cycle duration is equal to what total number of milliseconds? 1. 2 2 . 4 3 . 14 4. 18 3-68. The transmit frame is divided into what total number of 200 µsec time slots? 1. 13 2. 56 3. 70 4. 200 3-69. What total number of time slots make up the sync preamble of each transmit frame? 1. 13 2. 42 3. 56 4. 70 3-70. What total number of transmit frame time slots contain message data bits? 1. 8 2 . 13 3 56 4. 70 28 3-71. 3-72. 3-73. 3-74. 3-75. Which of the following transit frame signals causes the transmitter to turn off and starts the receive cycle? 1. Stop pulse 2. Sync burst 3. Guard interval 4. Transmitter un-key The reply message contains what total number of data time slots? 1. 13 2. 42 3. 56 4. 70 Which of the following Link-4A test messages is used to provide aircraft with the means to verify proper operation of Link-4A? 1. The monitor reply message 2. The monitor control message 3. The universal test message 4. All of the above Which of the following Link-4A test messages causes internal testing of the data terminal set? 1. The monitor reply message 2. The monitor control message 3. The universal message 4. All of the above Which of the following AN/SSW-1() subassemblies provides system timing for Link-4A operations? 1. Digital-to-digital converter 2. Monitor test panel 3. Coordinate data transfer control 4. Pulse amplifiers

ASSIGNMENT 4 Textbook Assignment: “New Technology in Data Communications,” chapter 5, pages 5-1 through 5-17; “Local-Area Networks,” chapter 6, pages 6-1 through 6-18. 4-1 . 4-2 . 4-3 . 4-4 . Which of the following pieces of 4-5 . equipment is replacing older Link-11 data terminal sets? 1. AN/USQ-36 Data Terminal Set 2. C2P 3. AN/USQ-125 Data Terminal Set 4. Link-16 The CP-2205(P)(V)/USQ-125 processor 4-6 . board performs which of the following functions? 1. Modulation/demodulation 2. Error detection and correction 3. Radio set interface 4. All of the above Which of the following CP-2205(P)(V)/USQ-125 components 4-7 . provides for communications with the CDS computer? 1. Processor board 2. Interface board 3. Power supply 4. Modulator The CP-2205(P)(V)/USQ-125 is capable of data encryption. 4-8 . 1. True 2. False The single-tone waveform link capability of the CP-2205(P)(V)/USQ-125 provides which of the following functions? 1. Interface with a satellite modem 2. Increases UHF transmission range 3. Increases HF transmission range 4. Reduces HF propagation anomalies Which of the following options of the CP-2205(P)(V)/USQ-125 incorporates a routine to calculate the optimum frequency? 1. Enhanced link quality analysis 2. Maximum useable frequency 3. Single-tone waveform link 4. Multi-frequency link Which of the following options of the CP-2205(P)(V)/USQ-125 transmits Link-11 data through a standard wire-line modem? 1. Enhanced link quality analysis 2. Maximum useable frequency 3. Single-tone waveform link 4. Multi-frequency link Which of the following options of the CP-2205(P)(V)/USQ-125 incorporates most of the functions of the LMS-11? 1 . 2 . 3 . 4. Enhanced link quality analysis Maximum useable frequency Single-tone waveform link Multi-frequency link 29

4-9 . Which of the following options of the CP-2205(P)(V)/USQ-125 improves Link-11 operations by using four frequencies simultaneously? 1. Enhanced link quality analysis 2. Maximum useable frequency 3. Single-tone waveform link 4. Multi-frequency link 4-10. The normal configuration of the multi-frequency link options uses (a) HF frequencies and (b) UHF frequencies. 1. (a) 2 (b) 1 2. (a) 3 (b) 1 3. (a) 2 (b) 2 4. (a) 3 (b) 2 IN ANSWERING QUESTIONS 4-11 THROUGH 4-15, SELECT FROM THE FOLLOWING LIST THE SYSTEM TEST OPTIONS OF THE CP-2205(P)(V)/USQ-125 DATA TERMINAL SET DESCRIBED IN THE QUESTION. NOT ALL ITEMS IN THE LIST ARE USED. A. Radio echo test B. Loopback test 1 C. Loopback test 2 D. Loopback test 3 E. Loopback test 4 F. DTS fault isolation test 4-11. This option is selected when a single station POFA is running without the radio. 1. A 2. B 3. C 4. D 4-12. 4-13. 4-14. 4-15. 4-16. 30 When this test is run, the computer interface is disabled and a test message is repeatedly sent to the radio set. 1. A 2. B 3. C 4. D This test is used to verify the operation of the computer interface, crypto device and the data terminal interface circuits. 1. C 2. D 3. E 4. F This test places the DTS in full-duplex mode to run a single station POFA with the radio. 1. A 2. B 3. C 4. D This option performs an internal self-test of the DTS audio circuits. 1. A 2. B 3. C 4. D The data terminal can be controlled from a remote location by use of which of the following pieces of equipment? 1 . 2 . 3 . 4 . A 286 personal computer only A 386 or better personal computer only The C-12428/USQ-125 Control Unit only Either a 386 or better personal computer, or the C-12428/USQ-125 Control Unit

4-17. 4-18. 4-19. 4-20. 4-21. Link-16 uses which of the following communications protocols? 1. Netted or roll call 2. Time division, command and response 3. Time division multiple access 4. Frequency-division multiplexing Each unit participating in a Link-16 net is identified by assigning it what type of designator? 1. A PU number 2. A JU number 3. A link identifier 4. A hull number What is the duration a Link-16 message? 1. 7.8125 msec 2. 7.8125 µsec 3. 7.8125 seconds of each time slot in 4. It varies, according data transmitted to the amount of During the transmission of data, exactly how often does Link-16 change frequency? 1. Every 13 µsec 2. Every 13 msec 3. Daily 4. When the frequency is excessively noisy Link-16 is configured for a stacked net. At any one time, what number of nets can a single terminal transmit and receive data? 1. One 2. Two 3. Three 4. Four 4-22, 4-23. 4-24. 4-25. 4-26. A Link-16 data word is comprised of what number of data bits? 1. 50 2. 60 3. 70 4. 80 A Link-16 fixed format message is which of the following message types? 1. V-series 2. R-series 3. M-series 4. J-series Which of the following message types are used for Link-16 voice communications? 1. Fixed format 2. Free text 3. Variable format 4. Unformatted Which of the following message types are used to exchange tactical data? 1. Fixed format 2. Free text 3. Variable format 4. Unformatted Compared to Link-11, Link-16 is nodeless for which of the following reasons? 1 . 2 . 3 . 4. Once the net is established, all units must participate Only one unit controls the net Once the net is established, operations can continue regardless of the participation of any particular unit A computer is not required to participate in the net 31

4-27. 4-28. 4-29. 4-30. 4-31 . Which of the following JTIDS security features is designed to prevent jamming? 1. Data encryption 2. Waveform encryption 3. Introduction of jitter and noise 4. Frequency hopping Which of the following network participation groups is normally excluded from Navy command and control units? 1. Weapons coordination 2. Air control 3. Fight-to-fighter 4. Secure voice JU numbers 00001 through 00177 are normally assigned to which of the following units? 1. Link-4A and Link-16 capable units 2. Command and Control units 3. Link-16 capable aircraft 4. Link-11 and Link-16 capable units Which of the following Link-16 track numbers would designate the same Link- 11 track? 1. 00000 through 07777 2. 01000 through 77777 3. 00200 through 07777 4. 00500 through 77777 A Link-16 track that has a reported track quality of 15 indicates the track is within exactly how many feet of the reported position? 1. 10 2. 25 3. 50 4. 75 4-32. 4-33. 4-34. 4-35. 4-36. 32 Which of the following track identifications has been added for use with the Link-16 system? 1. Neutral 2. Hostile 3. Assumed hostile 4. Unknown The identifier “Unknown assumed enemy” has been changed in the Link-16 system to what identifier? 1. Neutral 2. Suspect 3. Unknown assumed hostile 4. Hostile Link-16 has added which of the following data fields to friendly aircraft status reports? 1. Ordnance inventory 2. Equipment Status 3. Fuel available for transfer 4. All of the above The Relative Navigation function of the Link-16 system is required for which of the following functions? 1 . 2 . 3 . 4 . Maintain synchronization Maintain position Detect course errors Correct the navigation plot Which of the following equipment configurations fully implements the capabilities of the Link-16 system? 1. Model-3 2. Model-4 3. Model-5 4. Model-6

4-37. 4-38. Using the Link-16 Model-5 system, link data generated by the ACDS computer is normalized to be independent of any particular system. 1. True 2. False Using the Link-16 Model-5 system, what component formats link data for transmission over any one of the three data links? 1 . 2 . 3 . 4 . ACDS C2P Link-16 data terminal TDS computer IN ANSWERING QUESTIONS 4-39 THROUGH 4-42, SELECT FROM THE FOLLOWING LIST THE EQUIPMENT COMPONENT GROUPS OF THE JTIDS TERMINAL THAT PERFORMS THE FUNCTION OR OPERATION DESCRIBED IN THE QUESTION. NOT ALL ITEMS IN THE LIST A. B. C. D. E. ARE USED. Digital data processor group Receiver/transmitter group High power amplifier group Power interface unit Secure data unit 4-39, 4-40. A removable assembly that stores cryptovariables. 1. B 2. C 3. D 4. E Generates a 75 MHz intermediate frequency for internal communications. 1. A 2. B 3. C 4. D 4-41. 4-42. 4-43. 4-44. 4-45. Provides the interface with the antenna. 1. A 2. B 3. C 4. D Performs digital-to-analog and analog-to-digital conversion of voice signals. 1. A 2. B 3. C 4. D The Command and Control (C2P) system controls and manages the interface of which of the following data links? 1. Link-4A only 2. Link-11 only 3. Link-16 only 4. All tactical data links Messages received by the C2P over the Link-11 net cannot be retransmitted over the Link-16 net. 1. True 2. False A local area network (LAN) performs which of the following functions? 1. Enables users to share data 2. Enables users to share peripheral devices 3. Allows users to send and receive messages via computer 4. All of the above 33

4-46. Which of the following items is a node in a LAN system? 1. Twisted pair cable 2. Communications media 3. Fiber-optic cable 4. Large capacity hard drive 4-47. Twisted pair cable used in a LAN has which of the following advantages? 1. High data transmission speeds 2. Low costs and easy to install 3. Shielded from electrical interference 4. Secure data transmission 4-48. In designing a LAN system that requires the transmission of digital data, audio, and video simultaneously, which of the following cables would be best suited to the system? 1. Twisted pair 2. Shielded twisted pair 3. Broadband coaxial 4. Baseband coaxial 4-49. Which of the following types of cable is immune to interference from electrical and electronic devices? 1. Fiber optic 2. Baseband coaxial 3. Shielded twisted pair 4. Telephone cable 4-50. Which of the following devices provides the interface between the LAN and a personal computer? 1. Network server 2. NIC 3. Disk server 4. Cables 4-51. Which of the following devices is used to 4-52. 4-53. 4-54. 4-55. manage the shared resources of the LAN? 1. Network server 2. NIC 3. Disk server 4. Network monitor Early disk servers suffered from which of the following problems? 1. Lack of security 2. No data organization 3. No disk management 4. All of the above Ensuring data integrity by preventing multiple users access to the same record at the same time is known as what process? 1. File locking 2. Field locking 3. Record locking 4. Disk lockout Which of the following servers was developed to provide reliable disk management in a LAN? 1. Disk server 2. Print server 3. File server 4. Network server Which of the following functions is NOT performed by the file server? 1. Routing files to a central printer for printing 2. Processing of the network control software 3. Converting high-level disks calls from a workstation to low-level disk commands 4. Maintaining the list of user privileges and authorizations 34

4-56. 4-57. 4-58. 4-59. 4-60. When designing and building a LAN system, all workstations must be from the same manufacturer. 1. True 2. False The OSI reference model is used to define which of the following communications standards? 1. Interconnection of communications facilities 2. Software 3. Hardware 4. Protocol What layer of the OSI reference model describes the electrical, the mechanical, and the functional interface of the communications channel? 1. Physical layer 2. Data link layer 3. Network layer 4. Transport layer What layer of the OSI reference model establishes and deletes host-to-host connections across the network? 1. Data link layer 2. Network layer 3. Transport layer 4. Session layer As a translator for the network, what layer of the OSI reference model provides a common representation for data which can be used between the application processes? 1 . 2 . 3 . 4. Network layer Transport layer Session layer Presentation level/layer 4-61. Which of the following layers of the OSI reference model provides error-free transmission of information over the physical medium? 1. Physical 2. Data link 3. Network 4. Transport 4-62. Communications between users on two different machines are established by what layer of the OSI reference model? 1. Data link 2. Network 3. Transport 4. Session 4-63. Based on network conditions and priority of service, what layer of the OSI reference model decides which physical pathway the data should take? 1. Physical 2. Data link 3. Network 4. Transport 4-64. The application level/layer of the OSI reference model provides the protocols for which of the following user items? 1. Media interface 2. Electronic mail 3. Routing of messages between networks 4. Data compression 4-65. Which of the following is NOT a LAN topology? 1. Linear 2. Ring 3. Star 4. EtherNet 35

4-66. 4-67. 4-68. 4-69. Which of the following features of a linear bus topology should be considered an advantage? 1 . 2 . 3 . 4. Signal interference when nodes are too close to each other System remains operable even when one or more nodes fail Very secure system Very easy to run system diagnostics from the LAN administrator In which of the following network topologies, if any, is each node individually connected to the network server? 1. Linear bus 2. Star 3. Ring 4. None of the above Which of the following network access methods requires each node to wait for permission to transmit data? 1. CSMA 2. CSMA/CD 3. Token passing 4. Contention On a network that uses the CSMA/CD access method, which of the following actions, if any, will be taken when a data collision is detected? 1 . 2 . 3 . 4. The workstation will cease transmission and wait until the line is clear The workstation will continue to transmit data The network server will assign the next open time to the workstation that suffered the collision No action is taken; the data is lost 4-70. In a LAN using a token ring topology, the interface and protocols are defined by which of the following IEEE standards? 1. IEEE 802 2. IEEE 802.3 3. IEEE 802.4 4. IEEE 802.5 4-71. Which of the following LAN systems uses a token ring topology and has a data throughput of 4 Mbits and 16 Mbits per second? 1. EtherNet 2. STARLAN 3. ARCnet 4. IBM Token Ring IN ANSWERING QUESTIONS 4-72 THROUGH 4-74, SELECT FROM THE FOLLOWING LIST THE NETWORK OPERATING SYSTEM COMPONENT THAT PERFORMS THE FUNCTION DESCRIBED IN THE QUESTION. NOT ALL ITEMS IN THE LIST ARE USED. A. Control kernel B. Network interfaces C. File systems D. File extensions 4-72. Provides low-level subnet protocols and translation for bridging hardware drivers with the network operating system. 1. A. 2. B. 3. C. 4. D. 4-73. Controls data organization, storage, and retrieval on the various storage systems available to the network. 1. A. 2. B. 3. C. 4. D. 36

4-74. The main subsystem of the network operating software. 1. A. 2. B. 3. C. 4. D. 4-75. Which of the following network operating systems, if any, is designed for very few users and light usage? 1. Full featured 2. Low cost 3. Zero slot 4. None of the above 37

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