Networks and 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 Transmission Characteristics Analog or Digital (Type of Signal) Serial or Parallel (Order of Bits)

Analog/Digital Transmission Digital signals are sent as bits (0,1). 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 Transmission Digital Signal Computers use binary numbers (0,1) to transform data into digital signals.

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 Serial transmission is slower than parallel. All the bits (0s and 1s) that comprise the data are transmitted one bit after another in a continuous line.

Communications Media Point To Point A physical link that allows computers to be connected to other computers in different locations. Either wired or wireless

LAN Cabling 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.

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). Broadband Communications medium capable of carrying a large amount of data at faster speeds. Narrowband A communications medium carrying smaller amounts of data.

T- Carrier Lines Extremely high speed dedicated connections between 2 points. PSTN = Public Service Telephone Network CSU/DSU = Channel Service Unit/ Digital Service Unit Provide for communication over the PSTN.

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 Infrared Technology Cellular Technology Satellite Systems

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 Solar powered device containing small, specialized radios called transponders. Transponders receive signals from transmission devices on the ground called earth stations.

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

Cellular Technology Allows people to communicate wirelessly to and from anywhere in the world. Contact is maintained with cellular antennae. Each area, called a cell, has its own antennae encompassing a circular space of 10-12 square miles in diameter.

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. Client/Server Peer-to-Peer

Network Design Network Topology (Layout) Refers to the way computers and peripherals are configured to form networks. Bus Topology All 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) Ring Topology Each computer or workstation is connected to two other computers with the entire network forming a circle. Hybrid Technologies Combine different links.

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 Access to an intranet Web site is restricted by a firewall. An intranet is accessible only by a business or organization, its members, employees or authorized users.

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 Communications Hardware and Software Hub An electric device used in a LAN to link groups of computers. Repeaters/Amplifiers Electric devices that receive signals and amplify and send them along the network. Concentrator Transmits data from only 1 device at a time over the channel.

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

Connecting Networks Together Bridge Consists of hardware and/or software that allows communication between two similar networks. Multiplexer Electronic device that allows low speed devices to simultaneously share a single high speed communications media.

Connecting Dissimilar Networks Gateways Consists of hardware and/or software that allows communication between two 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.

Connecting Clients to a Network Web Browsers Allows users to access and view Web pages. Groupware Allows groups of people on a network to share information and to collaborate on various projects.

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.

TCP/IP Transmission Control Program/ Internet Protocol (HTTP) Governs how packets are constructed and sent to their destinations. (HTTP) Hypertext Transfer Protocol File Transfer Protocol (FTP). The World Wide Web (WWW) is used to transfer Web pages to computers. Large files can be transmitted and received.

Mail Transfer Protocols (POP) Post Office Protocol Allows recipient to retrieve messages. (SMTP) Simple Mail Transfer Protocol Messages are transmitted using Simple Mail Transfer Protocol.

Wireless Application Protocol (WAP) In 1997, the Institute of Electrical and Electronic Engineers (IEEE) approved a new protocol for wireless LAN technology called 802.11 (Wi-Fi). Enables wireless devices to access and use the internet using a client/server network.

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.