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How are Computers Connected?

How are Computers Connected?. Chapter 8. How do you connect computers?. Run wires between two computers Power Cord Plug into a power outlet Two wires needed to complete circuit Wires are securely covered in plastic insulation Ground wire – provides safety (third wire). Wires. Power Cord

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How are Computers Connected?

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  1. How are Computers Connected? Chapter 8

  2. How do you connect computers? • Run wires between two computers • Power Cord • Plug into a power outlet • Two wires needed to complete circuit • Wires are securely covered in plastic insulation • Ground wire – provides safety (third wire)

  3. Wires • Power Cord • Untwisted Pair • Wires lie next to each other • More interference • Twisted Pair • Used for telephone systems and network cabling • Coaxial Cable • Used for cable television wiring/video connections

  4. Connectors • FCC maintains registry of jacks (RJ) • RJ-11 • Telephones and computers • 4 or 6 wire • Usually only 2 wires used (red and green) – extra for future services • Labor is expensive

  5. Connectors • Point-to-point communications • Wires form direct connection from one computer to another • RJ-11 • Serial communication • Byte - 8 signals sent one after the other • Slow

  6. RJ-45 • Parallel communication • Twisted pairs • 8 wires send 4 signals at the same time • Interference is low • RJ-45 • Wider than RJ-11 • Category 5 (Cat 5)

  7. Standards for Cat 5 • 10BaseT • Slowest (1990) - only 4 wires used • One pair for sending; one pair for receiving • 10,000 bits of info per second • Base – baseband signaling • T – twisted pair

  8. Standards for Cat 5 • 100BaseT • 1995 • Uses 2 of 4 pairs • 100,000 bits of info per second • 1000BaseT • 1999 • 802.3ab • Uses all 4 pairs • 1 million bits of info per second

  9. New Standard • 10GBaseT • 802.3ae • 2002 • 10 million bits of info per second • Uses enhanced RJ-45 cable

  10. Network Connections • Star Network • Each computer connected to central machine • Telephone systems – small setup • Central machine is switch • Passes information • Telephone switching networks • Switch to switch

  11. Network Connections • Ethernet Networks • Single wire (or bus) runs to all machines • Any computer can send info to another computer • Header – intended recipient • All computers receive all communications, however only intended computer saves material

  12. Ethernet Networks • Rules or Protocols • One computer does not interfere with communications by another • Each computer ‘listens’ to the network as it transmits it message • If the message received is different, another computer sent message at same time • Wait random amount of time and resend • Maximum length for any message

  13. Token-Ring Network • Organizes computer logically into a circle or ring • Each computer – 2 connections • Communication is in single direction around circle • Messages have sender and addressee designator (in header) • Confirmation of receipt • Token – Authority to send message (one computer at a time) • Messages can be somewhat longer

  14. Expansion of networks • Variations in degree to which networks are used • To keep demand low on networks, many organizations maintain separate small networks and connect those networks • Ethernet networks • Cabling limited to 100 meters (328 feet) • Hubs - A common connection point • Repeaters – amplify electrical signals

  15. Network Expansion • Segment • A section of a network that is bound by bridges, routers or switches • Bridge • Keeps track of machines on one or both sides of a segment • Forwards messages when info must go from sender on one side to receiver on the other

  16. Wireless Technology • Wireless communications • Messages are divided into packets • Packet contains a header • IDs which machine is to receive the data • Infrared signals or radio waves • All wireless computers in an area share the airwaves, receive the same messages and determine if they are the recipient

  17. Wireless Technology • Access Point • Computer directly to the Internet (acts as intermediary) • Example: on a 2.4 GHz radio frequency band • Beacon • Repeating of identifying information by access point • Association – Portable wishes to make connection • Portable computers use radio waves or infrared signals to communicate with access point • As portable computers move, interact with new access point • If no computers have direct access to the Internet, portable computers still can interact with each other, but not with the Internet

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