This page modified on 04/25/04.
| Answer | Correct Statement |
| 1. T | Communications describes a process in which two or more computers or devices transfer data, instructions, and information. |
| 2. T | E-mail is the transmission of messages and files via a computer network. |
| 3. T | Groupware is a software application that helps groups of people work together on projects and share information over a network. |
| 4. T | A network is a collection of computers and devices connected together via communications devices and transmission media. |
| 5. F | A
Wide Area Network (WAN) is a network that coves a large geographic area
using communications channel that combines many types of media such as
telephone lines, cables, and radio waves.
A Metropolitan Area Network (MAN) is a high-speed network that connects the local area networks in a metropolitan area such as a city or town and handles the bulk of communications activity across that region. |
| 6. F | On
a star network, all of the computers and devices on the network connect to
a central device.
On a ring network, a cable forms a closed loop (ring) with all computers and devices arranged along the ring. |
| 7. F | An
intranet is an internal network that uses Internet technologies.
An extranet allows customers or suppliers to access part of its intranet. |
| 8. T | A dial-up line is a temporary connection that uses one or more analog telephone lines for communications. |
| 9. T | A cable modem is a digital modem that sends and receives digital data over the cable television network. |
| 10. F | The core of a fiber optic cable consists of done, dozens, or hundreds of thin strands of glass or plastic optic fiber that use light to transmit signals. |
| 11. T | Microwaves
are radio waves that provide high speed signal transmission.
What makes a wave a microwave is that it has a carrier with a wavelength in the range of 30 cm down to 1 mm. This corresponds to a frequency in the range of 1 GHz - 300 GHz. |
1a. What is global positioning system (GPS)?
A global positioning system (GPS) is a navigation system that consists of a receiver that accepts and analyzes signals sent by 3 or more of the 24 GPS satellites in order to determine the receiver's geographic location. For a great tutorial, go to http://www.trimble.com/gps/index.html
1b. What is Digital AngelTM?
Digital Angel Corporation makes an RFID chip called VeriChip that can be implanted under the skin. It can transmit an identification code in response to an interrogation signal from a nearby RF scanner. Some versions can also measure and transmit body temperature and pulse.
2a. How are a local area network (LAN), a metropolitan area network (MAN), and a wide area network (WAN) different?
A local area network (LAN) is a network that connects computers and devices in a limited geographical area.
A metropolitan area network (MAN) is a high-speed network that connects local area networks in a metropolitan area.
A wide area network (WAN) is a network that covers a large geographic area.
2b. What is a wireless LAN?
A wireless LAN is a LAN that uses no physical wires.
3a. What is a dedicated server?
A dedicated server performs a specific task.
3b. How are a file server, a print server, a database server, and a network server different?
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File server: Stores and manages files. |
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Print server: Manages printers and print jobs. |
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Database server: Stores and provides access to a database. |
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Network server: Manages network traffic (activity). |
4a. What is a network topology?
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Network topology is the arrangement of nodes and paths in a communications
network.
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Network physical topology is the arrangement of cables and physical connections between devices in a communications network. | ||||
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Network logical topology describes the arrangement of which other processors each processor on a network shares information with for the purpose of processing. |
4b. How are a bus network, a ring network, and a star network different?
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A bus network consists of a single central cable to which all computers and other devices are connected. Ethernet networks are based on a bus topology. This is the cheapest and simplest system to construct, and it requires no system administrator. | ||||||
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A ring network connects nodes together in a continuous loop or ring.
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A star network connects all nodes to a central node or computer, called a
hub.
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A mesh network is a network of arbitrarily connected nodes. A simple mesh network consists of interconnected rings. This is the most important model, and is similar to the Internet. | ||||||
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A sneaker net is a network connected by people carrying messages on removable media between computers (running in sneakers or athletic shoes). |
..........
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It is not uncommon for a logical ring network or logical bus network to be implemented with a physical star network. |
5a. What are bandwidth and latency?
Amplitude Modulation Basics tutorial, Agilent
FM Fundamentals tutorial, Agilent
Wireless (RF) Fundamentals, Agilent
|
Bandwidth is the information carrying capability of a communications channel. It is the width in frequency of a communications channel due either to the physical properties of the channel, or the allocated frequency band of the channel. Frequency bandwidth δf is measured in Hertz (Hz). It is also measured in bits per second (bps). The number of bits per second you can place in a channel of a given bandwidth in Hertz depends, in part, on the communication signal design. The baseline comparison is to take the reciprocal of frequency bandwidth, 1/δf. This does not tell the whole story. For example, in telephone communications, a multibit modulation scheme using a combination of amplitude levels and phases is used to achieve rates at 8 bits per Hz of the carrier frequency. |
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Latency is the time it takes a signal to travel from one location to another on a network. |
5b. How do bandwidth and latency affect the performance of a communications channel?
Increasing the bandwidth increases the communication channel physical capacity. When the network nodes do not significantly delay a message, an increase in channel bandwidth decreases latency.
1a. What is noise?
Electrical noise is the random component of voltage and current. Other nonrandom components that are undesired signals are called interfering signals, or interference. Both degrade the ability to receive the desired signal. The text calls noise an electrical disturbance that can degrade communications.
1b. Why do most of today's networks not use coaxial cable?
Other transmission media, such as fiber-optic cable, transmit signals at faster rates.
2a. How are analog signals different from (binary) digital signals?
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Digital signals are intended to represent discrete-valued signals consisting of only ones and zeros. |
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Analog signals are intended to represent a continuous range of values. |
Digital signals do not need to be grouped into bytes in order to be digital signals. All that is required is that a digital signal represent two states, 0 and 1. Digital message formats exist for which no byte boundaries are used. Digital signals are used to represent more than just text information. High speed special purpose networks often have message formats that are designed for minimum size to hold the required information.
Note (for budding electrical engineers): All digital signals are represented using analog signals. Good engineering is required to keep the digital content recoverable from the analog signal. There are several schemes for encoding digital signals, not just a high voltage and a low voltage. The application will determine the design approach taken. In general, it is not as hard to represent, transmit, and recover digital content from an analog signal as it is to represent, transmit, and recover an intended analog signal which can vary continuously. Digital communications has limitations. Extremely high frequency signals are difficult to process digitally. There is a significantly important niche which only analog can satisfy.
2b. Why must both the sending and receiving ends of some communications channels have a modem for data transmission to occur?
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The transmitting end must modulate the original (digital) signal onto the carrier wave for transmission. |
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The receiving end must demodulate the signal from the carrier wave after transmission to recover the original (digital) representation. |
3a. What is a network operating system (NOS)?
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A network operating system organizes and coordinates the activities on a local area network. |
3b. What tasks does a network operating system perform?
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Administration: Includes adding, deleting, and organizing users and performing maintenance tasks such as backup. |
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File management: Locates and transfers files. |
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Printer management: Involves prioritizing print jobs and reports sent to specific printers on the network. |
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Security: Consists of monitoring and, when necessary, restricting access to network resources. |
4a. How is a peer-to-peer network different from a client/server network?
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Each computer on a peer-to-peer network can share the hardware, data, or
information located on any other computer in the network. Each
computer, or peer, stores files on its own storage devices.
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A client / server network has one or more computers that act as a server;
the other computers on the network can request services from the
server.
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Note: A server is a piece of software which resides on a host machine. It is common to have more than one server on a single host. For example, a single machine may have a mail server, a file server, and a world wide web server hosted on the same machine. It is often desirable to select a fast computer with lots of memory and hard disk space as a host.
4b. What is the role of a network administrator?
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A network administrator is the operations person in charge of the network. |
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This person has the responsibility of keeping a network operating smoothly according to access and service policies of the organization. |
1a. What is packet switching?
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Packet switching is the technique of breaking a message into individual packets, sending the packets along the best route available, and then reassembling the data. |
1b. How do routers and communications protocols enable packet switching?
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A router chooses the path to forward a message from one network node to another network node. If the most direct route to the destination is congested or not working, the router sends the packet along an alternate route. |
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A communications protocol specifies the rules that define how devices connect to each other and transmit data over a network. The protocol used to define packet switching on the Internet is TCP/IP. |
The essence of a router is that it chooses routes. It is a message switching computer.
1b. Why are shielded twisted-pair (STP) cables used instead of unshielded twisted-pair (UTP) cables in environments susceptible to noise?
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Electrical shielding is a conductor that surrounds the signal-bearing cable. It reduces the effect of electrical noise and interference that originates externally from the cable being protected by providing a path of least resistance for induced current. Shielding also helps provide mechanical protection to the cable. |
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Magnetic Shielding. Some shielding is made with a material with high magnetic permeability, such as soft iron or steel. This is used to reroute magnetic flux in the vicinity of the cable away from the conductor in the center of the cable. |
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Insulation is a dielectric material that has a very large resistance per unit length. It is a non-conductive material. It does not shield against magnetic fields. Insulation is used to prevent electrical grounding, shorting between conductors, and to increase electrical safety. |
Twisting a pair of signal conductors together is done to reduce effects of cross-talk and cable-borne noise by cancellation. In cables with multiple pairs (common in local area networks), each signal pair is separately twisted with a different number of twists per unit length.
Shielded twisted pair (STP) is better than unshielded twisted pair (UTP) in environments of high electomagnetic fields, such as in an industrial environment. Unshielded twisted pair cable does not protect the signal from noise arriving external from the cable.
Sources of electromagnetic noise:
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Industrial environment: electric generators, transformers (including equipment using transformers), electric motors, solenoids (used in cutters, stampers, extrusion, weaving machines), arc welding equipment, other electrical equipment |
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Office environment: fluorescent lighting, other office equipment (electric typewriters, composers, fax, electric staplers, electric hole punches, etc), mobile communications station (for emergency service dispatchers) |
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Home environment: kitchen appliances (can opener, microwave oven), electric motors (vacuum cleaner, fan, air conditioner compressor motor, refrigerator compressor motor, other appliances), CRT (idiot box [TV], computer monitor), HAM radio |
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Automobile: spark plugs, spark plug coil, alternator, electrical coolant fan motors, windshield wiper motors. |
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Earth: sun spots, lightning, aurora borealis. |
Other cable and transmission line components.
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Cables may also have a strength member for handling tension without straining the signal carrying medium, whether wire or optical fiber. |
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When mechanical protection is a major issue, separate armor is used around the cable. Armor can be braided wire or a pipe. |
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Environmental Barrier. The external covering of a cable provides a barrier against moisture and corrosion, and may be designed to protect against specific chemicals. |
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Temperature Control. Temperature control is important in specialized applications, including superconducting applications involving power and signal processing. This may include use of fluids (gas or liquid) that do not conduct electricity well. |
