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 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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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