Chapter 8: Communications and Networks
Transfer Rate
the speed with which modems transmit data varies.
Gbps
Billion bits per second
Five Topologies are:
Bus Network Ring Network Star Network Tree Network Mesh Network
How do wireless connections happen?
By using radio waves to communicate. Example: smartphones and many other Internet-enabled devices use radio waves to place telephone calls and to connect to the Internet. Primary technologies used for wireless connections are Bluetooth, Wi-Fi, microwave, WiMax, cellular, and satellite connections.
Videoconferencing
provides a very-low-cost alternative to long-distance telephone calls using electronic voice and video delivery.
Three commonly used type of modems:
DSL (digital subscriber line) Cable Modem Wireless Modem
Applications that depend on communication systems:
Email, Texting, Videoconferencing, Electronic Commerce.
Coaxial cable
High-frequency transmission cable, replaces the multiple wires of telephone lines with a single solid-copper core. It is used to deliver television signals as well as to connect computers in a network. In terms of the number of telephone connections, a _____________ cable has over 80 times the transmission capacity of twisted pair.
Texting
provides very efficient direct text communication between individuals using short electronic messages.
Packetization
Information sent or transmitted across the Internet usually travels through numerous interconnected networks. Before the message is sent, it is reformatted or broken down into small parts called packets. Each packet is then sent separately over the Internet, possibly traveling different routes to one common destination. At the receiving end, the packets are reassembled into the correct order.
Network Operating Systems (NOS)
Interactive software between applications and computers coordinating and directing activities between computers on a network. These activities include electronic communication and the sharing of information and resources.
Modem (modulator-demodulator)
It is a communication device that translates the electronic signals from a computer into electronic signals that can travel over telephone lines.
Mbps
Million bits per second
Local Area Networks (LANs)
Networks with nodes that are in close physical proximity—within the same building, for instance. Typically, LANs span distances less than a mile and are owned and operated by individual organizations.
Terms of Computer Networks:
Node Client SErver Directory Server Host Router Switch Network interface cards (NIC) Network Operating Systems (NOS) Network Administrator
Protocols
Rules for exchanging data between computers. The protocol http:// is the most common.
Four basic elements of the Communication Systems:
Sending and receiving devices Connection devices Data transmission specifications Communication channel
Communication Systems
electronic systems that transmit data from one location to another.
Communication channels
The actual connecting medium that carries the message between sending and receiving devices. The medium can be a physical wire, cable., or wireless connection.
Topology
The configuration of a network.
The modem enables:
The modem enables digital personal computers to communicate across different media, including telephone wires, cable lines, and radio waves.
Sending and receiving devices
These are often a computer or specialized communication device. They originate (send) as well as accept (receive) messages in the form of data, information, and/or instructions.
Data transmission specifications
These are rules and procedures that coordinate the sending and receiving devices by precisely defining how the message will be sent across the communication channel.
Digital Signals
These represent the presence or absence of an electronic pulse—the on/off binary signals. Computers can only understand digital signals. Before processing can occur within the system unit, a conversion must occur from what we understand (analog) to what the system unit can electronically process (digital).
Communication channel
This is the actual connecting or transmission medium that carries the message. This medium can be a physical wire or cable, or it can be wireless.
Tbps
Trillion bits per second
Four categories of bandwidth:
Voiceband/low-bandwidth Medium band Broadband Baseband
provides a fast, efficient alternative to traditional mail by sending and receiving electronic documents.
WiMax (Worldwide Interoperability for Microwave Access)
a new standard that extends the range of Wi-Fi networks using microwave connections. WiMax is commonly used by universities and others to extend the capability of existing Wi-Fi networks.
Wireless Connections do not use:
a solid substance to connect sending and receiving devices. Rather, they move data through the air.
Network interface cards (NIC)
aka network adapter card. Used to connect a computer to one or more computers forming a communication network whereby users can share data, programs, and hardware.
Node
any device connected to a network. Example: It could be a computer, printer, or data storage device.
Electronic Commerce
buying and selling goods electronically.
twisted-pair cable
cable consisting of pairs of copper wire that are twisted together. Both standard telephone lines and Ethernet cables use twisted pair.
Computer Network
communication system that connects two or more computers so that they can exchange information and share resources. Networks can be set up in different arrangements to suit users' needs.
Microwave
communication that uses high-frequency radio waves. It is sometimes referred to as line-of-sight communication because microwaves can only travel in a straight line. Because the waves cannot bend with the curvature of the earth, they can be transmitted only over relatively short distances. Thus, microwave is a good medium for sending data between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of microwave stations with microwave dishes or antennas.
Cellular
communication uses multiple antennae (cell towers) to send and receive data within relatively small geographic regions (cells). Most cell phones and mobile devices use cellular networks.
Satellite
communication uses satellites orbiting about 22,000 miles above the earth as microwave relay stations. Many of these are offered by Intelsat, the International Telecommunications Satellite Consortium, which is owned by 114 governments and forms a worldwide communication system. Satellites orbit at a precise point and speed above the earth.
Connectivity
concept related to using computer networks to link people and resources.
Network Architecture
describes how a network is arranged and how resources are coordinated and shared. It encompasses a variety of different network specifics, including network topologies and strategies.
Bandwidth
determines how much information can be transmitted at one time. It is a measurement of the communication channel's capacity. There are three bandwidths: voice band, medium band, and broadband. A measurement of the width or capacity of the communication channel. Effectively, it means how much information can move across the communication channel in a given amount of time. Example: o transmit text documents, a slow bandwidth would be acceptable. However, to effectively transmit video and audio, a wider bandwidth is required. There are four categories of bandwidth:
Global positioning system (GPS)
devices use that information to uniquely determine the geographic location of the device. Available in many automobiles to provide navigational support, these systems are often mounted into the dash with a monitor to display maps and speakers to provide spoken directions. Most of today's smartphones and tablets use GPS technology for handheld navigation.
Star Network
each device is connected directly to a central network switch. Whenever a node sends a message, it is routed to the switch, which then passes the message along to the intended recipient. The star network is the most widely used network topology today. It is applied to a broad range of applications from small networks in the home to very large networks in major corporations.
Tree Network
each device is connected to a central node, either directly or through one or more other devices. The central node is connected to two or more subordinate nodes that in turn are connected to other subordinate nodes, and so forth, forming a treelike structure. (See Figure 8-19.) This network, also known as a hierarchical network, is often used to share corporate wide data.
Bus Network
each device is connected to a common cable called a bus or backbone, and all communications travel along this bus.
Demodulation
he process of converting from analog to digital.
DSL (digital subscriber line)
modem uses standard phone lines to create a high-speed connection directly to your phone company's offices. These devices are usually external and connect to the system unit using either a USB or an Ethernet port. Provides high-speed connection using existing telephone lines.
Ring Network
network in which each device is connected to two other devices, forming a ring. There is no host computer, and messages are passed around the ring until they reach the correct destination.
Modulation
process of of converting from digital to analog
Bluetooth
short-range radio communication standard that transmits data over short distances of up to approximately 33 feet. Bluetooth is widely used for wireless headsets, printer connections, and handheld devices.
fiber-optic cable
special transmission cable made of glass tubes that are immune to electronic interference. Data is transmitted through fiber-optic cables in the form of pulses of light. Data transmission speeds of fiber-optic cables are incredible; recently speeds of 1 petabit per second were measured (a petabit is 1 million gigabits). Compared to coaxial cable, it is lighter, faster, and more reliable at transmitting data. Fiber-optic cable is rapidly replacing twisted-pair cable telephone lines.
Computer Communications
the process of sharing data, programs, and information between two or more computers.
Connection devices
these devices act as an interface between the sending and receiving devices and the communication channel. They convert outgoing messages into packets that can travel across the communication channel. They also reverse the process for incoming messages.
Mesh Network
this topology is the newest type and does not use a specific physical layout (such as a star or a tree). Rather, the mesh network requires that each node have more than one connection to the other nodes. (See Figure 8-20.) The resulting pattern forms the appearance of a mesh. If a path between two nodes is somehow disrupted, data can be automatically rerouted around the failure using another path. Wireless technologies are frequently used to build mesh networks.
Cable Modem
type of modem that uses coaxial cable to create high-speed computer connections. uses the same coaxial cable as your television. Like a DSL modem, a cable modem creates high-speed connections using the system unit's USB or Ethernet port.
Wireless Modem
typically a small plug-in USB or ExpressCard device that provides very portable high-speed connectivity from virtually anywhere. Almost all computers today have built-in wireless modems. For those that do not, wireless adapter cards are available that plug into USB or special card ports.
Voiceband (low bandwidth)
used for standard telephone communication. Personal computers with telephone modems and dial-up service use this bandwidth. Although effective for transmitting text documents, it is too slow for many types of transmission, including high-quality audio and video.
Medium band
used in special leased lines to connect midrange computers and mainframes, as well as to transmit data over long distances. This bandwidth is capable of very-high-speed data transfer.
Wi-Fi (wireless fidelity)
uses high-frequency radio signals to transmit data. A number of standards for Wi-Fi exist, and each can send and receive data at a different speed.
strategy
way of coordinating the sharing of information and resources.
Broadband
widely used for DSL, cable, and satellite connections to the Internet. Several users can simultaneously use a single broadband connection for high-speed data transfer. Ex: includes microwave, satellite, coaxial cable, and fiber-optic channels. It is used for very-high speed computers.
Baseband
widely used to connect individual computers that are located close to one another. Like broadband, it is able to support high-speed transmission. Unlike broadband, however, baseband can only carry a single signal at a time.
