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