Connecting with Computer Science, 2e Chapter 4 Networks.

Connecting with Computer Science, 2e

Chapter 4Networks

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: WirelessTechnologies (cont’d.)


Figure 4-2, Wireless technologies

Unguided Media: WirelessTechnologies (cont’d.)

Unguided Media: Wireless Technologies (cont’d.)

• 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”?

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 Chapter 4 Networks.

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