1 Computer Fundamentals : Pradeep K. Sinha & Priti Sinha Computer Fundamentals : Pradeep K. Sinha & Priti Sinha Slide 1/78 Chapter 17: Data Communications & Computer Networks Chapter 17 Data Communications & Computer Networks Computer Fundamentals Pradeep K. Sinha Priti Sinha Computer Fundamentals : Pradeep K. Sinha & Priti Sinha Computer Fundamentals : Pradeep K. Sinha & Priti Sinha Slide 2/78 Chapter 17: Data Communications & Computer Networks In this chapter you will learn about: Basic elements of a communication system Techniques, channels, and devices used to transmit data between distant locations Types of computer networks Communication protocols and their use in computer networks Internetworking tools and their use in building large computer networks Wireless communications technologies and wireless networks Characteristics and advantages of distributed computing systems Learning Objectives Learning Objectives Computer Fundamentals : Pradeep K. Sinha & Priti Sinha Computer Fundamentals : Pradeep K. Sinha & Priti Sinha Slide 3/78 Chapter 17: Data Communications & Computer Networks Basic Concepts and Terminologies
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 1/78Chapter 17: Data Communications & Computer Networks
Chapter 17
Data Communications & Computer Networks
Computer Fundamentals
Pradeep K. Sinha
Priti Sinha
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 2/78Chapter 17: Data Communications & Computer Networks
In this chapter you will learn about:
� Basic elements of a communication system
� Techniques, channels, and devices used to transmit data
between distant locations
� Types of computer networks
� Communication protocols and their use in computernetworks
� Internetworking tools and their use in building large
computer networks
� Wireless communications technologies and wireless
networks
� Characteristics and advantages of distributed computing
systems
Learning ObjectivesLearning Objectives
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 3/78Chapter 17: Data Communications & Computer Networks
Basic Concepts and Terminologies
2
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 4/78Chapter 17: Data Communications & Computer Networks
Data Communications and Computer NetworksData Communications and Computer Networks
� A computer network is a network of computers
� It connects multiple computers in a manner to enablemeaningful transmission and exchange of data among them
Ref. Page 346
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 5/78Chapter 17: Data Communications & Computer Networks
Basic Elements of a Communication SystemBasic Elements of a Communication System
� Communication is the process of transferring a messagefrom one point to another
� Electronic systems that transfer data from one point toanother are called data communication systems
Sender
(source)
Medium
Creates and sends a
messageReceives the message
Carries the
message
Receiver
(sink)
Ref. Page 347
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 6/78Chapter 17: Data Communications & Computer Networks
Data Transmission ModesData Transmission Modes
(c) Full-duplex
Sender
Sender
(or Receiver)
Sender
(and Receiver)
Receiver
Receiver
(or Sender)
Receiver
(and Sender)
(a) Simplex
OR
AND
(b) Half-duplex
Ref. Page 347
3
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 7/78Chapter 17: Data Communications & Computer Networks
� Bandwidth: Range of frequencies available for datatransmission. It refers to data transmission rate. Higherthe bandwidth, the more data it can transmit
� Baud: Unit of measurement of data transfer rate.Measured in bits per second (bps)
Data Transmission SpeedData Transmission Speed
Ref. Page 348
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 8/78Chapter 17: Data Communications & Computer Networks
� Narrowband: Sub-voice grade channels in range from45 to 300 baud. Mainly used for telegraph lines andlow-speed terminals
� Voiceband: Voice grade channels with speed up to9600 baud. Mainly used for ordinary telephone voicecommunication and slow I/O devices
� Broadband: High speed channels with speed up to 1million baud or more. Mainly used for high-speedcomputer-to-computer communication or forsimultaneous transmission of data
Data Transmission Speed CategoryData Transmission Speed Category
Ref. Page 348
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 9/78Chapter 17: Data Communications & Computer Networks
Data Transmission Media
4
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 10/78Chapter 17: Data Communications & Computer Networks
The most commonly used ones are:
� Twisted-pair wire (UTP cable)
� Coaxial cable
� Microwave system
� Communications satellite
� Optical fibers
Data Transmission MediaData Transmission Media
Ref. Page 349
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 11/78Chapter 17: Data Communications & Computer Networks
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 12/78Chapter 17: Data Communications & Computer Networks
Coaxial CableCoaxial Cable
Outer PVC shield
Copper mesh
PVC insulation
Central copper
wire
Ref. Page 349
5
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 13/78Chapter 17: Data Communications & Computer Networks
Microwave Communication SystemMicrowave Communication System
Transmitting station
In between
repeaters
Transmitting antennas Receiving antennas
Line of sight Line of sight Line of sight
Ref. Page 349
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 14/78Chapter 17: Data Communications & Computer Networks
Satellite Communication SystemSatellite Communication System
Transmitting
station on earth
6 GHz 4 GHz
Uplink Downlink
Receiving
station on earth
Satellite in space
Ref. Page 350
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 15/78Chapter 17: Data Communications & Computer Networks
Optical Fiber Communication SystemOptical Fiber Communication System
Electrical signal
Optical fiber
Amplifier
Electrical signalLight-to-electrical-
wave converterElectrical-to-light-wave converter
Light waves
Sender Receiver
Ref. Page 352
6
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 16/78Chapter 17: Data Communications & Computer Networks
Digital and Analog Data Transmission
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 17/78Chapter 17: Data Communications & Computer Networks
Digital and Analog Data TransmissionDigital and Analog Data Transmission
� Analog signal: Transmitted power varies over acontinuous range. Example: sound, light, and radiowaves
� Digital signal: Sequence of voltage pulses representedin binary form
� Computer generated data signal is digital, whereastelephone lines carry analog signals
(Continued on next slide)
Ref. Page 353
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 18/78Chapter 17: Data Communications & Computer Networks
� When digital data is to be sent over an analog facility, digital signals must be converted to analog form
� Conversion of digital signal to analog form is known as modulation
� Conversion of analog signal to digital form is known as demodulation
� Digital transmission of data is preferred over analog transmission of data due to lower cost, higher transmission speeds, and lower error rate
Digital and Analog Data TransmissionDigital and Analog Data Transmission
Ref. Page 353
7
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 19/78Chapter 17: Data Communications & Computer Networks
Analog and Digital SignalsAnalog and Digital Signals
+v
-v
0 1/f 2/ft
(a) Analog signal
Voltage
t
v
0 0
1 1
0 0
1 1
(b) Digital signal
Ref. Page 354
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 20/78Chapter 17: Data Communications & Computer Networks
Modulation TechniquesModulation Techniques
� Amplitude Modulation (AM): Two binary values (0 and1) of digital data are represented by two differentamplitudes of the carrier signal, keeping frequency andphase constant
� Frequency Modulation (FM): Two binary values ofdigital data are represented by two different frequencies,while amplitude and phase are kept constant
� Phase Modulation (PM): Two binary values of digitaldata are represented by shift in phase of carrier signal
Ref. Page 354
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 21/78Chapter 17: Data Communications & Computer Networks
ModemsModems
� Modem is short for MOdulator/DEModulator
� Special device used for conversion of digital data toanalog form (modulation) and vice-versa (demodulation)
� Essential piece of hardware where two digital devices(say two computers) want to communicate over ananalog transmission channel (say a telephone line)
Ref. Page 354
8
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 22/78Chapter 17: Data Communications & Computer Networks
Use of Modems in Data CommunicationsUse of Modems in Data Communications
Sender computer
Receiver computer
1 1
0 0
0 0
0 1
1 1
0 0
0 0
0 1
Digital signalsDigital signals
Analog signals on telephone line
Demodulator
Modulator
Modulator
Demodulator
A modem at sender computer
end
A modem at receiver computer end
Ref. Page 355
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 23/78Chapter 17: Data Communications & Computer Networks
Factors for Modem SelectionFactors for Modem Selection
� Transmission speed
� Internal versus external
� Facsimile facility
� Error correction
� Data compression
Ref. Page 355
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 24/78Chapter 17: Data Communications & Computer Networks
Data Transmission Services
9
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 25/78Chapter 17: Data Communications & Computer Networks
Data Transmission ServicesData Transmission Services
� Data transmission service providers are popularlyknown as common carriers
� Various types of services offered by common carriersare:
� Dial-up line: Operates in a manner similar to atelephone line
� Leased line: Special conditioned telephone linethat directly and permanently connects twocomputers
� Integrated Services Digital Network (ISDN):Telephone system that provides digital (not analog)telephone and data services
(Continued on next slide)
Ref. Page 356
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 26/78Chapter 17: Data Communications & Computer Networks
� Value Added Network (VAN): Provides value-addeddata transmission service. Value added over and abovethe standard services of common carriers may includee-mail, data encryption/decryption, access tocommercial databases, and code conversion forcommunication between computers
Data Transmission ServicesData Transmission Services
Ref. Page 356
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 27/78Chapter 17: Data Communications & Computer Networks
Multiplexing Techniques
10
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 28/78Chapter 17: Data Communications & Computer Networks
MultiplexingMultiplexing
� Method of dividing physical channel into many logicalchannels so that a number of independent signals maybe simultaneously transmitted
� Electronic device that performs multiplexing is knownas a multiplexer
� Multiplexing enables a single transmission medium toconcurrently transmit data between severaltransmitters and receivers
Ref. Page 357
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 29/78Chapter 17: Data Communications & Computer Networks
A Multiplexed SystemA Multiplexed System
T1 T2 T3 T4
Multiplexer
Modem
Modem
Multiplexer
Computer
Ref. Page 357
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 30/78Chapter 17: Data Communications & Computer Networks
Two Basic Methods of MultiplexingTwo Basic Methods of Multiplexing
� Frequency-Division Multiplexing (FDM): Availablebandwidth of a physical medium is divided into severalsmaller, disjoint logical bandwidths. Each componentbandwidth is used as a separate communication line
� Time-Division Multiplexing (TDM): Total timeavailable in a channel is divided among several users,and each user of the channel is allotted a time sliceduring which he/she may transmit a message
Ref. Page 358
11
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 31/78Chapter 17: Data Communications & Computer Networks
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 37/78Chapter 17: Data Communications & Computer Networks
Synchronous TransmissionSynchronous Transmission
Char Char Char Char Char Char
Indefinite time interval
between two blocks of data
A block of characters may consist
of hundreds of characters
Trailer containing
end of block indicationHeader containing
synchronizing and other
information
Ref. Page 359
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 38/78Chapter 17: Data Communications & Computer Networks
Switching & Routing Techniques
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 39/78Chapter 17: Data Communications & Computer Networks
Switching TechniquesSwitching Techniques
� Data is often transmitted from source to destinationthrough a network of intermediate nodes
� Switching techniques deal with the methods ofestablishing communication links between the senderand receiver in a communication network
� Three commonly used switching techniques are:
� Circuit switching: Dedicated physical path isestablished between sending and receiving stationsthrough nodes of the network for the duration ofcommunication
(Continued on next slide)
Ref. Page 360
14
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 40/78Chapter 17: Data Communications & Computer Networks
� Message switching: Sender appends receiver’sdestination address to the message and it istransmitted from source to destination either bystore-and-forward method or broadcast method
� Packet switching: Message is split up into fixed sizepackets and each packet is transmitted independentlyfrom source to destination node. Either store-and-forward or broadcast method is used for transmittingthe packets. All the packets of a message are re-assembled into original message at the destinationnode
Switching TechniquesSwitching Techniques
Ref. Page 360
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 41/78Chapter 17: Data Communications & Computer Networks
Circuit Switching MethodCircuit Switching Method
Source node Destination
node
Dotted lines and shaded
balls indicate the circuit
established
Switching nodes
Ref. Page 361
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 42/78Chapter 17: Data Communications & Computer Networks
Store-and-Forward Method of Message SwitchingStore-and-Forward Method of Message Switching
Either path 1-2-3-4 or 1-5-4 may be used totransmit a message from A to B.
D
AB
C
1
3
2
4
5
Ref. Page 362
15
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 43/78Chapter 17: Data Communications & Computer Networks
Broadcast Method of Message SwitchingBroadcast Method of Message Switching
Nodes 1 2 3
Message
Broadcast channel
n
Ref. Page 362
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 44/78Chapter 17: Data Communications & Computer Networks
Routing TechniquesRouting Techniques
� In a WAN, when multiple paths exist between the sourceand destination nodes of a packet, any one of the pathsmay be used to transfer the packet
� Selection of path to be used for transmitting a packet isdetermined by the routing technique used
(Continued on next slide)
Ref. Page 363
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 45/78Chapter 17: Data Communications & Computer Networks
Routing TechniquesRouting Techniques
� Three popularly used routing algorithms are:
� Source routing: Source node selects the entire pathbefore sending the packet
� Hop-by-hop routing: Each node along the pathdecides only the next node for the path
� Hybrid routing: Source node specifies only a fewmajor intermediate nodes of the complete path, andhop-by-hop routing method is used to decide thesubpaths between any two of the specified nodes.
Ref. Page 363
16
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 46/78Chapter 17: Data Communications & Computer Networks
Network Topologies and Types
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 47/78Chapter 17: Data Communications & Computer Networks
Network TopologyNetwork Topology
� A network’s topology refers to the way in which the networklinks its nodes
� It determines the various data paths available between anypair of nodes in the network
� Choice of a topology depends on a combination of factorssuch as:
� Desired performance
� Desired reliability
� Size of the system
� Expandability
� Cost of components and services
� Availability of communication lines
� Acceptable delays in routing
Ref. Page 364
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 48/78Chapter 17: Data Communications & Computer Networks
Network TopologiesNetwork Topologies
� Although number network topologies are possible, fourmajor ones are:
� Star network
� Ring network
� Completely connected network
� Multi-access bus network
Ref. Page 364
17
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 49/78Chapter 17: Data Communications & Computer Networks
Star Network Star Network
Host node
Ref. Page 364
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 50/78Chapter 17: Data Communications & Computer Networks
Ring Network Ring Network
Ref. Page 365
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 51/78Chapter 17: Data Communications & Computer Networks
� Network Interface Card (NIC or network card) is a hardwaredevice that connects a computer to a network, bothfunctionally and physically
� It is an add-on card that is connected directly to a computer’sI/O bus
� NIC’s ROM has the network’s physical-layer communicationprotocol
Ref. Page 369
21
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 61/78Chapter 17: Data Communications & Computer Networks
The OSI ModelThe OSI Model
� The Open System Interconnection (OSI) model isframework for defining standards for linkingheterogeneous computers in a packet switched network
� Standardized OSI protocol makes it possible for any twoheterogeneous computer systems, located anywhere inthe world, to easily communicate with each other
� Separate set of protocols is defined for each layer in itsseven-layer architecture. Each layer has an independentfunction
Ref. Page 369
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 62/78Chapter 17: Data Communications & Computer Networks
Layers, Interfaces, and Protocols in the OSI ModelLayers, Interfaces, and Protocols in the OSI Model
Node 1
Layer 7 (application)
Layer 6 (presentation)
Layer 5 (session)
Layer 4 (transport)
Layer 3 (network)
Layer 2 (data link)
Layer 1 (physical)
Application protocol
Presentation protocol
Session protocol
Transport protocol
Network protocol
Data-link protocol
Physical protocol
Layer 7 (application)
Layer 6 (presentation)
Layer 5 (session)
Layer 4 (transport)
Layer 3 (network)
Layer 2 (data link)
Layer 1 (physical)
Process A Process B
Node 2
Network
Interface
Interface
Interface
Interface
Interface
Interface Interface
Interface
Interface
Interface
Interface
Interface
Ref. Page 370
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 63/78Chapter 17: Data Communications & Computer Networks
An example illustrating transfer of message M from sending node to the receiving node in the OSI model: Hn, header added by layer n:Tn, trailer
added by layer n.
An example illustrating transfer of message M from sending node to the receiving node in the OSI model: Hn, header added by layer n:Tn, trailer
added by layer n.
Sender node
H7 M
Process A
H2 H3 H4 H5 H6 H7 M1 T2
H3 H4 H5 H6 H7 M1
H4 H5 H6 H7 M1
H6 H7 M
H4 H5 H6 H7 M2
H3 H4 H5 H6 H7 M2
H2 H3 H4 H5 H6 H7 M2 T2
H5 H6 H7 M
Receiver node
H7 M
Process B
H2 H3 H4 H5 H6 H7 M1 T2
H3 H4 H5 H6 H7 M1
H4 H5 H6 H7 M1
H6 H7 M
H4 H5 H6 H7 M2
H3 H4 H5 H6 H7 M2
H2 H3 H4 H5 H6 H7 M2 T2
H5 H6 H7 M
Ref. Page 373
22
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 64/78Chapter 17: Data Communications & Computer Networks
Internetworking Tools
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 65/78Chapter 17: Data Communications & Computer Networks
Internetworking Internetworking
� Interconnecting two or more networks to form a singlenetwork is called internetworking, and the resultingnetwork is called an internetwork
� Goal of internetworking is to hide details of differentphysical networks, so that resulting internetworkfunctions as a single coordinated unit
� Tools such as bridges, routers, brouters, and gatewaysare used for internetworking
� The Internet is the best example of an internetwork
Ref. Page 373
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 66/78Chapter 17: Data Communications & Computer Networks
Bridges Bridges
� Operate at bottom two layers of the OSI model
� Connect networks that use the same communicationprotocols above data-link layer but may use differentprotocols at physical and data-link layers
Ref. Page 373
23
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 67/78Chapter 17: Data Communications & Computer Networks
RoutersRouters
� Operates at network layer of the OSI model
� Used to interconnect those networks that use the samehigh-level protocols above network layer
� Smarter than bridges as they not only copy data fromone network segment to another, but also choose thebest route for the data by using routing table
Ref. Page 374
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 68/78Chapter 17: Data Communications & Computer Networks
GatewaysGateways
� Operates at the top three layers of the OSI model(session, presentation and application)
� Used for interconnecting dissimilar networks that usedifferent communication protocols
� Since gateways interconnect dissimilar networks,protocol conversion is the major job performed bythem
Ref. Page 374
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 69/78Chapter 17: Data Communications & Computer Networks
Wireless Networks
24
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 70/78Chapter 17: Data Communications & Computer Networks
Wireless Computing SystemsWireless Computing Systems
� A wireless computing system uses wirelesscommunication technologies for interconnecting computersystems
� It enhances functionality of computing equipment byfreeing communication from location constraints of wiredcomputing systems
� Wireless computing systems are of two types:
� Fixed wireless systems: Support little or nomobility of the computing equipment associated withthe wireless network
� Mobile wireless systems: Support mobility of thecomputing equipment to access resources associatedwith the wireless network
Ref. Page 374
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 71/78Chapter 17: Data Communications & Computer Networks
Issues in Wireless Computing SystemsIssues in Wireless Computing Systems
� Lower bandwidth
� Variable bandwidth
� Higher error rate
� Increased security concern
� Dynamically changing network
� Lost or degraded connection
� Support for routing and location management functions
� Limited power
Ref. Page 374
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 72/78Chapter 17: Data Communications & Computer Networks
Wireless ApplicationsWireless Applications
� Interesting and important applications include:
� Mobile e-commerce applications (m-commerce)
� Web surfing
� Access to corporate data by employees while they aretraveling
� Mobile video-on-demand
� Location-sensitive services such as finding nearby movietheaters or restaurants
Ref. Page 375
25
Computer Fundamentals : Pradeep K. Sinha & Priti SinhaComputer Fundamentals : Pradeep K. Sinha & Priti Sinha
Slide 73/78Chapter 17: Data Communications & Computer Networks