MIS Chapter 6-1

modems

Analog signals: continuous Digital signals: discrete pulses Modulation: translating digital data to analog Demodulation: translating analog data to digital Modems modulate & demodulate data

infrared transmission

Infrared transmission can be used to send data short distances, for example, from a handheld computer to a desktop or a printer. Infrared transmission can also be used to connect peripherals, such as a mouse, to a computer

data transmission speeds

Measured in bits per second (bps) Kilobits per second (kbps) Megabits per second (Mbps) Gigabits per second (Gbps)

telecommunications applications

Voice & electronic mail Electronic software & document distribution Telecommuting Videoconferencing Distance learning Public Network Services (AOL)

microwave

Whereas broadcast media, such as microwave, don't require the purchase of physical media, the hardware required is more expensive. Microwave is a high frequency radio signal. In terrestrial microwave, a signal travels directly between microwave transmission towers

hybrid network

a combination of the various topologies

t1 carrier

a digital carrier for data and image; dedicated and costly very fast, typically used by corporations and universities

open systems interconnection model

a standard framework for designing network architectures. The OSI model divides the data communications process into 7 layers. Different protocols handle functions at different layers. Layers allow protocols from different levels to be mixed and matched. The top layer of the OSI model, the Application Layer, defines standards for how the application running on a computer interacts with other applications on the network. The third OSI layer, the Network layer, defines how messages are routed through interconnected networks, such as the Internet. The bottom layer, the physical layer, defines electrical and interface standards that transmit bits over the media. Communicating devices must use the same standards at corresponding levels

centralized processing

all processing is done in one location; easiest strategy

coaxial cable

also made from copper. However, because of extra shielding and insulation, coax has less interference, and therefore a higher capacity, or bandwidth, than does twisted pair TV cable in your home

value-added carriers

beyond long distance companies that sell services over their telecommunications systems to subscribers special purpose carriers and additional services

private branch exchange (PBX)

can manage voice and data within a building. Not only does the PBX internally route calls, but it can be used to connect a few external phone lines to numerous internal lines

signal

carries a message sender to signal to receiver air, wire

distributed processing

computers at different locations are connected by a communications network data and processing are located where it is most efficient and effective

front end processors

computers that manage communications to and from a computer system; relieves the main computer of work so that it can be free to process other tasks; usually mainframe or midrange computers

wide area network

connect devices over large geographic distances using common carrier facilities AT&T

ring network

connected in a ring and messages are routed around the ring from one device to the next no central coordinating computer

bridge

connects two local area networks that use the same protocol at the second layer of the OSI model, the data link layer

bus network

contains devices connected directly in a straight line no central coordinating computer

network topology

describes how a network is logically organized

multiplexers

devices that combine signals from several computers to allow them to be sent over a single transmission line

decentralized processing

different locations have their own processing devices; devices at different locations aren't connected together

how a modem works

digital signals are modulated into analog signals, which can be carried over existing phone lines. the analog signals are then demodulated back into digital signals by the receiving modem

telecommunications

electronic communication of signals, such as telephone or radio

communications software

error checking message formatting security network operating system (performs the same functions for a network that an operating system does for a computer) network management software(includes programs that allow a network manager to monitor activity and status of network devices from a single computer)

international networks

global transborder data flows infrastructure differences

telecommunications devices

hardware that makes an electronic transmission occur or make it more efficient modems, multiplexers, and front-end processors

star network

has a central, coordinating device; each computer on the network is directly attached only to the central device

satellite transmission

involves sending a signal from a microwave tower to the satellite, which is basically a microwave station, then back to another microwave tower delays to upload and download the signal often make this impractical for short distances

local area network

limited geographical area any topology possible network interface card peer to peer or client to server

network types

local area, wide area, international, home & small business

common carriers

long distance telephone companies

twisted pair cabling

made of pairs of copper wires twisted together. Twisted pair is used for the phone connection to your house. In networking it is common to see cable consisting of 4 pairs of wires. Each pair is twisted together to reduce electrical interference between neighboring pairs, or crosstalk. The more twists there are per foot, the less interference there will be

fiber optic cable

made of thin filaments of glass or plastic, not of copper wire. Whereas a data signal travels over twisted pair or cable as electricity, signals are transmitted as light pulses over fiber. Lasers or LCDs produce the light. A thin coating, called cladding, prevents the light from leaving the strand

routers

more complex than bridges, and connect networks that use different data link layer protocols. A router looks at the address on the message and determines which network to send it over. Many different networks can be connected to a router. Routers are the main device connecting the many networks making up the Internet.

gateways

operate at OSI layers above the network layer and connect networks that are very dissimilar connects networks that use different protocols in the top layers of the OSI stack

telecommunications carriers

provide the technological infrastructure, such as lines and satellites, that enable data to be sent from one place to another

switches

replacing bridges and gateways; can examine the address of a message and route it, but are more efficient and adaptable than older devices

protocols

rules or standards that all devices on a network must follow in order to communicate successfully; allow interoperability of technology from different manufacturers

file server connection

sends the user the entire file that contains the data requested. the downloaded data can then be analyzed, manipulated, formatted, and displayed by a program that runs on the user's personal computer

cellular transmission

service area is divided into cells; cellular signals are integrated into the regular telephone network

client/server connection

some computers are designated as servers for specific tasks, such as printing, database management, printing, program execution, or communications. Network computers request services from the servers. Processing occurs on both the clients and the servers, so clients receive exactly the data or services needed

hierarchical netwrok

structured as an upside down tree messages are passed to computers along the branches

data communications

subset of telecommunications referring to the electronic collection, processing, and distribution of data

line types

switched-- available from common carriers; connect the sender's and receiver's phones dedicated-- or leased, lines continuously connect two devices at fixed points; no dialing required

computer networks

telecommunications media, telecommunications devices, software, hardware devices consists of at least two computers or other devices connected by above

electronic data interchange (EDI)

the computer-to-computer exchange of data between companies or trading partners

asynchronous communication

the receiver gets the message at a later time; sending a letter

synchronous communication

the receiver gets the message immediately

communications

the transmission of a signal over a medium from a sender to a receiver

wide-area telecommunication service (WATS)

the use of toll-free numbers. The company pays a fee to the phone company, depending on the volume of incoming or outgoing calls. WATS is very cost-effective for organizations that frequently make long distance calls

types of media

twisted pair coaxial cable fiber-optic cable microwave transmission The first 3 types of media - twisted pair, coaxial cable, and fiber optic cable - are usually referred to as guided or conducted media. That is, a signal is conducted over a physical medium. Microwave and other forms of wireless transmission are called broadcast media. Generally speaking, there are fewer errors in guided than in broadcast media.

terminal to host connection

users have dumb terminals connected to a host computer; all file access and processing is done on the host

integrated services digital network

uses existing common carrier lines to digitally send data, video, image, or voice at speeds over 64 kilobits per second fast for video and other applications

digital subscriber lines (DSL)

uses existing phone wires for fast connections for home and business. This means that users can download from the Internet at speeds over 500 kbps; upstream transmission (from the home or business out) may be slower. DSL is not universally available, although usage is growing fast fast, comes over standard phone lines