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 1999 802.3ab Uses all 4 pairs 1 million bits of info per second

New Standard

10GBaseT 802.3ae 2002 10 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