chp8

• Connectivity


  Using computer networks to link people and resources
• Communications


  The process of sharing data, programs, and information between two or more computers
• Applications that depend on communication systems

  • E-mail
  • Texting
  • Video Conferencing
  • Electronic commerce
• Communication systems


  • They are electronic systems that transmit data from one location to another
  • They can be wired or wireless
• Basic elements of a communication system

  • Sending and receiving devices
  • Connection devices
  • Data transmission specifications
  • Communication channel
• Physical connections


  • Twisted pair cable
  • Coaxial cable
  • Fiber-optic cable
• Wireless connections


  They do not use a solid substance to connect, they use the air itself and most use radio waves to communicate
• Primary wireless technologies


  • Bluetooth
  • Wi-Fi
  • Microwave
  • WiMax
  • Cellular
  • Satellite
  • Infrared
  • GPS
• Bluetooth


  Radio communication standard that transmits data over short distances of up to approximately 33 feet
• Wi-Fi


  Uses high-frequency radio signals to transmit data, send and receive data at different speeds
• Microwave


  Uses high-frequency radio waves, referred to as line-of-sight as they can only travel in a straight line, good for short distances
• WiMax


  Extends the range of wi-fi networks using microwave connections, commonly used by universities and others to extend the capability of existing Wi-Fi networks
• Cellular


  Uses multiple antennae (cell towers) to send and receive data within relatively small geographic regions (cells)
• Satellite


  Uses satellites as microwave relay stations, uplink is sending data to a satellite, downlink is receiving data from a satellite
• GPS (Global Positioning system)


  Uses satellites to determine geographic location of devices
• Infrared


  Uses infrared light waves to communicate over short distances, requires line-of-sight between sending and receiving devices
• Analog signals


  Telephone signals, continuous electronic wave
• Digital signals


  Computer signals, presence or absence of an electronic pulse, on/off
• Transfer rates


  Mbps - million bits per second<|>Gbps - billion bits per second<|>Tbps - trillion bits per second
• Modem


  Modulator-demodulator, modulation is the process of converting from digital to analog, demodulation is the process of converting from analog to digital
• Types of modems


  • DSL
  • Cable
  • Wireless
• Connection services for corporations

  • Leased lines
  • T1/T3/DS3
  • OC lines
• Connection services for individuals

  • DSL
  • Cable
  • Satellite
  • Cellular
  • Fiber Optic
  • Dial-up
• Bandwidth


  How much information can move across the communication channel in a given amount of time
• Types of bandwidth


  • Voiceband
  • Medium band
  • Broadband
  • Baseband
• Protocols


  Communication rules for exchanging data between computers
• HTTPS


  Hypertext Transfer Protocol Secure, widely used to protect the transfer of sensitive data
• TCP/IP


  Transmission control protocol/Internet protocol
• Features of TCP/IP


  • Identification
  • Domain Name Server (DNS)
  • Packetization
• TCP/IP


  • Identification - Identifying sending and receiving devices, every computer on the Internet has a unique numeric address called an IP Address
  • Domain Name Server (DNS) - Converts text-based addresses to IP addresses
  • Packetization - Allows message to be broken into small parts called packets, allows message to be reassembled at destination
• Specialized Terms in a Network

  • Nodes - Any device connected to a network
  • Client - A node that requests and uses resources from other nodes
  • Server - A node that shares resources with other nodes
  • Directory Server - Specialized server that managers resources
  • Host - Computer system that can be accessed over a network
  • Router - Node that forwards or routes data packets
  • Switch - Central node that coordinates the flow of data
  • Network Interface Cards (NIC) - Expansion card that connects a computer to a network
  • Network Operating System - Control activities of all computers on the network
  • Network Administrator - Computer specialists responsible for network operations
• Network Types


  • Local Area Networks (LANs) - Computers and devices linked in distances of less than a mile, linked by cable
  • Home Networks - LANs used by individuals in home/apartments, can be connected by various means including a wireless LAN (WLAN)
  • Wireless LAN (WLAN) - All communications pass through the network's centrally located wireless access point or base station, hotspot is a wireless access point that is open to the public
  • Personal Area Networks (PANs) - Works within a very small area, connects cell phones to headsets, PDAs to other PDAs, keyboards to cell phones, etc.
  • Metropolitan Area Network (MANs) - Span distances up to 100 miles, network linking nodes and resources within the geographical bounds of a city
  • Wide Area Networks (WANs) - Countrywide and worldwide networks, use microwave relays and satellites to reach users, Internet is the widest WAN
• Network Architecture


  • Network Topology - Physical arrangement of the network
  • Network Strategy - How the information and resources are shared
• Ring Network


  • Topology where each device is connected to two other devices forming a ring, when a message is sent it passes through each device until it reaches its destination
  • Disadvantage - If a computer or device on a ring network fails, the entire network potentially could stop functioning
  • Advantage - Can span a larger distance than a bus network, but is more difficult to install
• Star Network


  • Topology where each device connected directly to a central network switch, all communications pass through the switch, each connecting device is asked ("polled") whether it has a message to send and then each device is in turn allowed to send its message, the switch sends the message to the intended recipient
  • Advantage - On a star network, if one node fails, only that node is affected, the other nodes continue to operate normally
  • Disadvantage - If the hub or switch fails, the entire network is inoperable until the device is repaired
• Bus Network


  • Consists of a single central cable, to which all computers and other devices connect, the bus is the physical cable that connects the computers and other devices, the bus in a bus network transmits data, instructions, and information in both directions
  • Advantage - Computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network, failure of one device usually does not affect the rest of the bus network
  • Disadvantage - The bus itself might become inoperable, if that happens, the network remains inoperative until the bus is back in working order
• Tree Network


  • Topology where each device connected to a central node either directly or through subordinate nodes, also called hierarchical, the central node is connected to two or more subordinate nodes that in turn are connected to other subordinate nodes, useful in centralized organization
• Mesh Network


  • Topology that does not use a specific physical layout, but requires that each node have more than one connection to other nodes, if a path between two nodes is disrupted, data can be rerouted around the failure using another path, wireless technologies are frequently used to build mesh networks
• Network Strategies


  • Peer-to-Peer (P2P) Network - All nodes have equal authority, can act as both client and server, BitTorrent - file sharing software, lack of security
  • Client/Server Network - Central computers coordinate and supply services to other nodes on the network, server provides access, advantages - handle large networks efficiently, availability of powerful network management software to monitor and control network activities, disadvantages - cost of installation and maintenance, commonly used server operating systems - Windows Server, Mac OS X Server, Linux, Solaris
• Intranet


  Private network within an organization, works like the Internet