Networksand

Communications

Telecommunications

Use of hardware and software to send and receive information over communications media.

Allows computer users throughout the world to communicate with one another.

Data TransmissionCharacteristics

Analog or Digital(Type of Signal)

Serial or Parallel (Order of Bits)

Analog/Digital Transmission

Analog signals take the form of continuous waves transmitted over a medium at a certain frequency range. Changes in the wave transmission reflect changes in voice and sound pitch.

Digital signals are sent as bits (0,1).

Digital Transmission

Computers use binary numbers (0,1) to transform data into digital signals.

Digital Signal

Modems

Converts digital signals into analog signals, so they can be sent over telephone lines.

“Modem” is derived from Modulate and Demodulate.

Modulation refers to the process of changing a digital signal into an analog signal.

Demodulation refers to the process of changing an analog signal into a digital signal.

Parallel Transmission

A group of 8 bits representing a single byte (plus 1 bit called a parity bit) are transmitted at the same time over 9 separate paths.

Computers are equipped with parallel and serial ports to connect modems, printers and mice.

Serial Transmission

All the bits (0s and 1s) that comprise the data are transmitted one bit after another in a continuous line.

Serial transmission is slower than parallel.

Communications Media

A physical link that allows computers to be connected to other computers in different locations.

Either wired or wireless

Point To Point

Twisted Pair Cable consists of two wires that are independent, insulated, and twisted around each other.

Coaxial cable consists of an insulated-center wire grounded by a shield of braided wire.

LAN Cabling

Fiber Optic Cable

Contains hundreds of clear fiberglass or plastic fibers (threads).

Communication Bandwidth

Rate of transmission over the medium. Measured in bits per second (bps).

Bandwidth

Broadband

Narrowband

Communications medium capable of carrying a large amount of data at faster speeds.

A communications medium carrying smaller amounts of data.

T- Carrier Lines

Extremely high speed dedicated connections between 2 points.

Provide for communication over the PSTN.

PSTN = Public Service Telephone Network

CSU/DSU = Channel Service Unit/ Digital Service Unit

ISDN Line

Special digital telephone line that transmits and receives information at very high speeds.

Wireless Communication

Wireless media transmit information as electromagnetic signals through the air.

Microwaves

Satellite Systems

Cellular Technology

Infrared Technology

Microwave Systems

Transmit data through the atmosphere from one microwave station to another.

Also transmit from a microwave station to a satellite and then back to earth to another microwave station.

Communications Satellite

Transponders receive signals from transmission devices on the ground called earth stations.

Solar powered device containing small, specialized radios called transponders.

Geosynchronous Orbits

In geosynchronous orbits, satellites circle the earth at the same speed as the earth’s rotation.

Allows people to communicate wirelessly to and from anywhere in the world.

Cellular Technology

Each area, called a cell, has its own antennae encompassing a circular space of 10-12 square miles in diameter.

Contact is maintained with cellular antennae.

Infrared Technology

Transmits data in the form of infrared light waves is transmitted from a special port in laptop to an infrared sensor on the printer.

Network Classifications

Network Architecture Refers to the way a network is designed or built.

Client/Server Architecture Information is sent from a client computer to a server. The server relays information back to the client or to other computers on the network.

Peer- to-Peer Each PC workstation has equivalent capabilities and responsibilities.Peer-to-Peer

Client/Server

Network Design

Network Topology (Layout) Refers to the way computers and peripherals are

configured to form networks.

Bus TopologyAll computers are linked by a single line of cable.

Star Topology

Multiple computers and peripheral devices are connected to a central computer or host.

Network Topology(Continued)

Each computer or workstation is

connected to two other computers with

the entire network forming a circle.

Combine different links.

Ring Topology

Hybrid Technologies

Wide Area Network (WAN)

A WAN spans a large geographical area and connects networks such as metropolitan area networks, public access networks, value added networks, and virtual private networks together.

Local Area Network (LAN)

A LAN is a private network that connects PCs or workstations located in close proximity.

Intranet

An intranet is accessible only by a business or organization, its members, employees or authorized users.

Access to an intranet Web site is restricted by a firewall.

Extranet

An extranet makes specific information available to users within the organization and other information available to outsiders.

Often companies share information with their business partners or customers using an extranet.

Networking CommunicationsHardware and Software

An electric device used in a LAN to link groups of computers.

Transmits data from only 1 device at a time over the channel.

Concentrator

Electric devices that receive signals and amplify and send them along the network.

Hub

Repeaters/Amplifiers

Electronic devices used to ensure messages are sent to their intended destination.

Routers

Internetworking Device

Consists of hardware and/or software that allows communication between two similar networks.

Electronic device that allows low speed devices to simultaneously share a single high speed communications media.

Electronic device that allows low speed devices to simultaneously share a single high speed communications media.

Multiplexer

Bridge

Connecting Networks Together

Consists of hardware and/or software that allows communication between two dissimilar networks.

Gateways

Connecting Dissimilar Networks

Communications Software

Allows computers to connect to access and use the network resources. E-mail software is used to send and receive electronic messages using the internet.

Allows groups of people on a network to share information and to collaborate on various projects.

Groupware

Allows users to access and view Web pages.

Web Browsers

Connecting Clientsto a Network

Communications Protocol

Protocol : A set of rules and procedures for exchanging information between network devices and computers.

Directional Protocols

Determine the directional flow of transmission among devices.

Directional Protocols

Direction method can be simplex, half-duplex, and full-duplex.

Asynchronous Transmission

Data sent by protocols are transmitted at irregular intervals using start and stop bits.

Synchronous Transmission

Blocks of bytes are wrapped in start and stop bytes called synch bits.

Governs how packets are constructed and sent to their destinations.

TCP/IP

Transmission Control Program/ Internet Protocol

The World Wide Web (WWW) is used to transfer Web pages to computers.

The World Wide Web (WWW) is used to transfer Web pages to computers.

(HTTP)Hypertext Transfer Protocol

Large files can be transmitted and received.

Large files can be transmitted and received.

File Transfer Protocol (FTP).

Allows recipient to retrieve messages.

Mail Transfer Protocols

Messages are transmitted using Simple Mail Transfer Protocol.

(SMTP) Simple Mail Transfer Protocol

(POP) Post Office Protocol

Enables wireless devices to access and use the internet using a client/server network.

Wireless ApplicationProtocol (WAP)

In 1997, the Institute of Electrical and Electronic Engineers (IEEE) approved a new protocol for wireless LAN technology called

802.11 (Wi-Fi).

On the Horizon

INCREASED BANDWIDTH AVAILABILITY• Free-space optics, a nascent technology that uses lasers to send optical

signals through the air• Dense wave division multiplexing (DWDM)

HIGHER-SPEED OPTICAL FIBERS• A single strand of fiber thinner than a human hair can carry every phone call and e-mail in the world• Hollow fiber—the next wave in fiber-optic cable

BEAMING DATA• Infrared transmission represents tremendous potential for the future.• Data traveling through space in the form of infrared light can move faster than radio waves, and with potentially less interruption.