Connecting with Computer Science, 2e

1
Connecting with Computer Science, 2e

• Chapter 4
• Networks

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Objectives

• In this chapter you will
• Learn how computers are connected
• Become familiar with different types of
  transmission media
• Learn the differences between guided and unguided
  media
• Learn how protocols enable networking
• Learn about the ISO OSI reference model
• Understand the differences between network types
• Learn about local area networks (LANs)

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Objectives (contd.)

• In this chapter you will (contd.)
• Learn about wide area networks (WANs)
• Learn about wireless local area networks (WLANs)
• Learn about network communication devices
• Learn how WANs use switched networks to
  communicate
• Learn how devices can share a communication
  medium
• Learn about DSL, cable modems, and satellite
  communications

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Why You Need to Know About...Networks

• Networks
• Connect computers together
• Allows sharing of resources
• Used in government research centers,
  universities, large corporations, and home
  computing
• Integral part of computing for homes and
  enterprises
• Include the Internet
• Integrated into personal computers
• Computing professional
• Incorporates network technology into everything

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Connecting Computers

• Linking computers via a system bus is impractical
• PCI bus has 98 wires
• Requires a very thick cable
• Connection problem solved with technology
• Connecting requires a medium (e.g., wire)
• Carries electric signal and a communications
  protocol to manage processes

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Transmission Medium

• Transmission medium
• Material conducting electrical and / or
  electromagnetic signals
• Most popular copper
• Rating transmission media
• Bandwidth medium speed measured in bits / second
• Signal-to-noise ratio 10 log10 (signal/noise)
• Bit error rate ratio of incorrect bits to total
  number of bits in unit time
• Attenuation signal weakening over distance

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Transmission Medium (contd.)

• Two general transmission media types
• Guided
• Physical media
• Copper wire form of twisted pair or coaxial
  cable
• Fiber-optic uses glass and light to
  transmit data
• Unguided
• Air and space carry radio frequency ( RF ) or
  infrared ( IR ) light signals

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Transmission Medium (contd.)
Figure 4-1, Coaxial, twisted pair, and
fiber-optic cable are guided media
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Copper Wire Coaxial and Twisted Pair

• Two wires used to transmit data signal and
  ground
• Coaxial cable ( coax )
• Copper surrounded by metal shield to reduce noise
• Support bandwidths up to 600 MHz
• 10BaseT
• Twisted pair
• Replacing copper
• Twists dampens effects of inductance
• All copper wiring is subject to impedance
• Attenuation reduction in signal
• Two types shielded and unshielded ( UTP )

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Copper Wire Coaxial and Twisted Pair (contd.)
Table 4-1, EIA/TIA twisted pair cable categories
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Copper Wire Coaxial and Twisted Pair (contd.)

• Twisted pair ( contd. )
• Unshielded twisted pair ( UTP )
• More popular than shielded twisted pair ( STP )
• Category 5 ( Cat 5 )
• Most common twisted pair cable
• Maximum frequency 100 MHz
• Good for business and home use
• Computer industry has turned to optical media
• Provides faster data transmission

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Fiber-Optic Cable

• Glass fibers guide light pulses along a cable
• Thin strand of nearly pure glass
• Surrounded by reflective material and a tough
  outer coating
• Transmission speeds much higher than with copper
• Fiber-optic cables are much less susceptible to
  attenuation and inductance
• Principle of inductance does not apply
• Bandwidths hundreds of times faster than copper
• Economies of scale bringing price down

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Unguided Media Wireless Technologies

• Benefits of wireless technology
• Eliminates cables and cabling costs
• Provides device mobility
• Basis of wireless technology radio transmission
• Examples cell phones, microwave ovens, etc.
• Electronic signal is amplified
• Radiated from an antenna as electromagnetic waves
• Receiving antenna converts back to electronic
  signal
• Electromagnetic waves
• Transmitted at many different frequencies

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Unguided Media WirelessTechnologies (contd.)
Table 4-2, Wireless technologies
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Unguided Media WirelessTechnologies (contd.)
Figure 4-2, Wireless technologies
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Unguided Media Wireless Technologies (contd.)

• Difference between low-pitched sound and a
  high-pitched sound
• Frequency of the sound waves, or vibrations
• Uses same technology as car radio and cell phone
• Industry standards ( based on 2.4 GHz range )
• IEEE 802.11 series most common
• Bluetooth specification
• Short-range RF links between mobile computers,
  mobile phones, digital cameras, other portable
  devices
• Maximum distance between devices three inches to
  328 feet

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Light Transmission

• Infrared light used over short distances
• Uses transmission media of air
• Requires clear line of sight between devices
• Used in PDAs, cell phones, notebook computers,
  wireless keyboards, and mice
• Pulses of infrared light represent 1s and 0s of
  binary transmission
• Speeds up to 4 Mbps

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Protocols

• Set of rules facilitating communication
• Example classroom questioning
• Often represented with a timing diagram
• Transmission protocol
• Provides for an orderly flow of information
• HTTP, TCP / IP, FTP
• Transmission Control Protocol ( TCP )
• Allows two computers to establish a communication
  connection, transfer data, and terminate the
  connection

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Protocols (contd.)

• Must have provisions to check for errors and
  retransmit
• International Organization for Standardization (
  ISO )
• Coordinates worldwide standards development
• Comité Consultatif International Téléphonique et
  Télégraphique ( International Telegraph and
  Telephone Consultative Committee, CCITT )
• Formulated the ISO Open Systems Interconnect
  reference model ( ISO OSI reference model )

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Protocols (contd.)
Table 4-4, Timing diagram for a communication
protocol
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ISO OSI Reference Model

• Composed of seven distinct layers
• Physical
• Data Link
• Network
• Transport
• Session
• Presentation
• Application
• Real world applications many times do not divide
  it into these separate layers
• But it is useful to think about it in this manner

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ISO OSI Reference Model

• Conceptual model with seven discrete layers
• Physical
• Defines electrical, mechanical, procedural, and
  functional specifications for activating and
  maintaining the physical link between end systems
• Data Link
• Provides reliable data transit, physical
  addressing, data error notification, ordered
  delivery of frames, and flow control
• Network
• Provides connectivity and path selection, and
  assigns addresses to messages

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ISO OSI Reference Model (contd.)

• Conceptual model with seven discrete layers
  (contd.)
• Transport
• Guarantees delivery of datagrams
• Provides fault detection, error recovery, and
  flow control
• Manages virtual circuits
• Session
• Establishes, maintains, and terminates
  communication session between applications

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ISO OSI Reference Model (contd.)

• Conceptual model with seven discrete layers
  (contd.)
• Presentation
• Formats data for presentation to an application
• Performs character format translation ASCII to
  Unicode
• Syntax selection
• Application
• Provides network access to applications

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ISO OSI Reference Model (contd.)

• Layers are defined by two components
• Header
• Layer and message information
• Sending side of the communication creates the
  header
• Corresponding layer on the receiving side uses
  the header
• Protocol Data Unit ( PDU )
• Communicates information about the message to the
  next layer on the same side

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ISO OSI Reference Model (contd.)
Figure 4-3, How the OSI model processes data
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Network Types

• May be classified according to size and proximity
• Local area network ( LAN )
• Small number of computers connected in close
  proximity
• Usually confined to building or complex
• Uses copper wire
• Wide area network ( WAN )
• Many computers spread over large geographical
  area
• Typically spans cities, states, or continents

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Network Types (contd.)

• MAN ( metropolitan area network )
• Spans a city or metropolitan area
• Distinction between WAN and MAN
• No standardized definition
• LAN is confined to a single building
• Internet is classified as largest WAN
• WLAN ( wireless local area network )
• LAN using wireless transmission medium
• IEEE 802.11 protocol family often used

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Network Types (contd.)
Figure 4-4, Example of a WAN configuration
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LAN Topologies

• Network configurations
• Node computer attached to a network
• Addressable device
• Three basic LAN topologies
• Ring connects computers in a loop with cable
• Star computers connected to hub (central point)
• Bus configured like a system bus on a
  computer (most popular)
• Internet and home networking
• Increasing star topology popularity

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LAN Topologies (contd.)
Figure 4-5, LAN topologies
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LAN Communication Technologies

• Ethernet
• Widely used technology
• Industry standard
• Based on a bus topology
• Can be wired in a star pattern (star/bus)
  topology
• Original Ethernet transferred data at 10 Mbps
• Fast Ethernet transfers data at 100 Mbps
• Gigabit Ethernet transfers data from 1 to 10 Gbps

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LAN Communication Technologies (contd.)

• Token ring
• Second most popular LAN technology
• Uses a ring topology
• Controls access to the network by passing token
• Capable of data transfer of 4 or 16 Mbps
• FDDI and ATM
• Generally faster and more expensive

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LAN Communication Technologies (contd.)
Table 4-5, Bandwidths of LAN technologies
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Network Communication Devices

• LANs, WANs, and WLANs can be connected to form
  larger, more complex WANs
• Devices used to created connectivity
• Network interface cards
• Repeaters, hubs, and switches
• Bridges
• Gateways
• Routers and firewalls

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Network Communication Devices (contd.)

• NIC
• Required for physical device connected to network
• Usually in motherboard expansion slot or card
  slot in notebook
• Includes external port
• Has unique 48-bit address (physical or MAC
  address)
• Repeater
• Alleviates attenuation problem
• Amplifies signal along cable between nodes
• Does not alter data content

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Network Communication Devices (contd.)

• Hub
• Special repeater with multiple inputs and outputs
• Allows multiple nodes to share same repeater
• Switch
• Repeater with many input and output ports
• Inputs and outputs are not connected
• Examines header and makes point-to-point
  connection to output addressed by packet
• Assumes Data Link duties (OSI Layer 2)

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Network Communication Devices (contd.)

• Bridge
• Similar to a switch
• Divides network into segments to reduce traffic
• Gateway
• Similar to a bridge
• Can interpret and translate different network
  protocols
• Can connect networks of different types

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Network Communication Devices (contd.)

• Router
• Like bridges and gateways
• Function at higher OSI Layer 3
• Directs network traffic based on logical address
• Firewall
• Protects network
• Filters potentially harmful incoming and outgoing
  traffic
• May be router based
• Examines/restricts inbound and outbound traffic
• Implemented in hardware or software

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Switched Networks

• Telephone network adapted to carry digital data
• Modems convert binary signals into audio signals
• Telephone companies split a copper conductor
  bandwidth into multiple ranges or bands
• Frequency modulation ( FM )
• Amplitude modulation ( AM )
• Phase modulation ( PM ) boost speed to 30Kbps
• Combined compression techniques and rearranged
  transitions are used to reach 56Kbps limit

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Switched Networks (contd.)
Figure 4-6, Frequency modulation, amplitude
modulation, and phase modulation
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Switched Networks (contd.)

• High-speed WANs
• Demand for higher access speeds
• Extend system bus
• Copper capable of speeds up to 1.5 Mbps
• Leasing all wire bandwidth ( 24 channels )
  results in faster connection
• Very expensive
• Dedicated line called T1
• T3 line consists of 28 T1 lines
• Fiber-optic cables
• Optical carrier ( OC ) lines faster than T3

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Switched Networks (contd.)
Table 4-6, High-speed WAN connections
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Switched Networks (contd.)

• Multiple access
• FDM ( frequency-division multiplexing)
• Divides bandwidth among subscribers
• Channel is sustained for duration of session
• Wasteful use of resources
• TDM ( time-division multiplexing )
• Divides bandwidth based on time
• Achieves effect speeds greater than FDM

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Switched Networks (contd.)
Figure 4-7, FDM and TDM
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Switched Networks (contd.)

• Digital subscriber line ( DSL )
• Combines FDM and TDM
• Divides bandwidth into 247 channels
• Allocates 4 KHz for voice, remainder for data
• Modem used to place voice communication into the
  correct frequency band
• Speeds range from 256 Kbps to 1.5 Mbps
• Download speeds differ from upload speeds
• Subscriber located less than 18,000 feet from
  station

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Cable Modems

• CATV coax cable carries hundreds of channels
• Channels allocated 6 MHz bandwidth
• Transmit speeds up to 42 Mbps
• Connects Ethernet cable to modem
• Uses TDM technology to vary upload and download
  speeds

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Wireless Technologies

• Offered by cell phone providers
• Technologies
• EDGE, EVDO, and 3G
• May become the standard method of wireless
  networking

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Satellite Technologies

• Long distance wireless technology
• Provides high-speed access to users in remote
  locations
• Dish is used to receive television signals
  adapted for data transmission
• Becoming an affordable alternative

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One Last Thought

• Networks are integral to computers and computing
• Computer scientists extensively interact with
  networks
• Network concepts form a foundation for further
  study

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Summary

• Networks link computers around the world
• Networks are extensions of system bus
• Transmission media, set of protocols, and network
  devices create connectivity
• Metrics for rating media bandwidth,
  signal-to-noise ratio, bit error rate, and
  attenuation
• Transmission media may be guided or unguided
• Guided media copper wire ( coax and twisted pair
  ) and fiber-optic cables
• Unguided media air or space ( wireless )

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Summary (contd.)

• Protocols set of rules for communication
• Standards TCP/IP and seven-layered OSI model
• Network types LANs, WLANs, WANs, MANs
• LAN topologies ring, star, bus
• LAN technologies Ethernet, token ring, FDDI, ATM
• Network devices NIC, repeater, hub, switch,
  bridge, gateway, router, firewall
• Switched networks convert analog to digital
  using FM, AM, PM, compression, rearranged
  transitions

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Summary (contd.)

• DSL combines FDM and TDM to boost copper wire
  signals to 1.5 Mbps
• Cable modems coax cables transmit at 1.5 to 42
  Mbps
• Satellite technologies long distance wireless