Connecting with Computer Science, 2e · Connecting with Computer Science, 2e 2 Objectives • In...

Connecting with Computer Science, 2e

Chapter 4 Networks

Connecting with Computer Science, 2e 2

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)

Objectives (cont’d.)

•  In this chapter you will (cont’d.): –  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


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


Connecting Computers

•  Linking computers through 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



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


Transmission Medium (cont’d.)

•  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


Figure 4-1, Coaxial, twisted pair, and fiber-optic cable are guided media

Transmission Medium (cont’d.)


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)


Table 4-1, EIA/TIA twisted pair cable categories

Copper Wire: Coaxial and Twisted Pair (cont’d.)

Copper Wire: Coaxial and Twisted Pair (cont’d.)

•  Twisted pair (cont’d.) –  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


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


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



Table 4-2, Wireless technologies

Unguided Media: Wireless Technologies (cont’d.)


Figure 4-2, Wireless technologies



•  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


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



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


Protocols (cont’d.)

•  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)


Table 4-4, Timing diagram for a communication protocol

Protocols (cont’d.)

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


ISO OSI Reference Model (cont’d.)

•  Conceptual model with seven discrete layers (cont’d.) –  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




•  Conceptual model with seven discrete layers (cont’d.) –  Presentation

•  Formats data for presentation to an application •  Performs character format translation: ASCII to

Unicode •  Syntax selection

–  Application •  Provides network access to applications


•  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



Figure 4-3, How the OSI model processes data



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


Network Types (cont’d.)

•  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


Figure 4-4, Example of a WAN configuration

Network Types (cont’d.)


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


Figure 4-5, LAN topologies

LAN Topologies (cont’d.)


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


LAN Communication Technologies (cont’d.)

•  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


Table 4-5, Bandwidths of LAN technologies

LAN Communication Technologies (cont’d.)

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


Network Communication Devices (cont’d.)

•  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



•  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)




•  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



•  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

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 3Kbps

•  Combined compression techniques and rearranged transitions are used to reach 56Kbps limit


Copy editor: “3Kbps”-should this be “30Kbps”?


Figure 4-6, Frequency modulation, amplitude modulation, and phase modulation

Switched Networks (cont’d.)



•  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


Table 4-6, High-speed WAN connections




•  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


Figure 4-7, FDM and TDM




•  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


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


Wireless Technologies

•  Offered by cell phone providers •  Technologies

–  EDGE, EVDO, and 3G –  May become the standard method of wireless

networking


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


One Last Thought

•  Networks are integral to computers and computing •  Computer scientists extensively interact with

networks •  Network concepts form a foundation for further study


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)


Summary (cont’d.)

•  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


Summary (cont’d.)

•  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

Connecting with Computer Science, 2e · Connecting with Computer Science, 2e 2 Objectives • In...

Documents

Transcript of Connecting with Computer Science, 2e · Connecting with Computer Science, 2e 2 Objectives • In...