COMPUTER NETWORKS
(21UCA07)
LECTURE NOTES
UNIT - 1
B.C.A. II YEAR
IV SEMESTER
Ms.S.NANDHINI, Assistant Professor
DEPARTMENT OF COMPUTER APPLICATIONS
, K.S.R College of Arts and Science for Women,
Tiruchengode.
Unit - I
Introduction – Network Hardware - Software - Reference Models - OSI and TCP/IP
Models - Example Networks: Internet, ATM, Ethernet and Wireless LANs - Physical Layer
- Theoretical Basis for Data Communication - Guided Transmission Media.
1.1 Introduction
Development of the PC changes a lot in business, industry, science and education.Similar
revolution is occurring in data communication and networking Technologies advances are
making it possible for communications links to carry more and faster signal. Services are
evolving to allow the use of this expanded capacity
For example telephone services extended to have:
Conference calling
Call waiting
Voice mail
Caller ID
The effectiveness of a data communications system depends on Fourfundamental
characteristics: delivery, accuracy, timeliness, and jitter.
1. Delivery
• The system must deliver data to the correct destination. Data must be received by the
intended device or user and only by that device or user.
2. Accuracy
• The system must deliver the data accurately. Data that have been altered in transmission
and left uncorrected are unusable.
3. Timeliness
• The system must deliver data in a timely manner. Data delivered late are useless. In the
case of video and audio, timely delivery means delivering data as they are produced, in
the same order that they are produced, and without significant delay. This kind of
delivery is called real-time transmission.
4. Jitter
• Jitter refers to the variation in the packet arrival time. It is the uneven delay in the
delivery of audio or video packets. For example, let us assume that video packets are sent
every 30 ms. If some of the packets arrive with 30-ms delay and others with 40-ms delay,
an uneven quality in the video is the result.
1.1.1 Components of a data communication system
• The word data refers to information presented in whatever form is agreed upon by the
parties creating and using the data.
, • Data communications are the exchange of data between two devices via some form of
transmission medium such as a wire cable.
Figure 1 : Data Communication
1. Message:The message is the information (data) to be communicated. Popular forms of
information include text, numbers,pictures,audio,and video.
2.Sender:The sender is the device that sends the data message. It can be a computer,
workstation, telephone handset, video camera, and so on.
3.Receiver:Thereceiveristhedevicethatreceivesthemessage.Itcanbea computer, workstation,
telephonehandset, television, andso on.
4.Medium: The transmission medium is the physical path by which a message travels from
sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial
cable, fiber-optic cable, and radio waves.
5.Protocol:Aprotocolisasetofrulesthatgoverndatacommunications.Itrepresents
anagreementbetweenthe communicatingdevices.Withouta protocol,two
devicesmaybeconnectedbutnotcommunicating,justasapersonspeakingFrench cannot beunderstood
by aperson who speaksonly Japanese.
1.1.2 Data flow (simplex, half-duplex, and full-duplex)
Figure 2 : Data Flow
1.Simplex(onewaystreet)
• Thecommunication isunidirectional. Onlyonedeviceonalinkcantransmitandtheothercan
only receive.Thesimplexmodecanusetheentirecapacityofthechannel to send datain
onedirection.Example:Keyboards,Monitors
2.Half-Duplex(one-lanewithtwo-directionaltraffic)
• Eachstationcanbothtransmitandreceive,butnotatthesame time.
Whenonedeviceissending,theothercanonlyreceive,andvice versa.
Theentirecapacityofachannelistakenoverbythetransmitting device.Example: Walkie-
talkies
3.Full-Duplex(Duplex)(two-waystreet)
• In full-duplex, both stations can transmit and receive simultaneously. One common
example of full-duplex communication is the telephone network. When two people are
communicating by a telephone line, both can talk and listen at the same time. The full-
duplex mode is used when communication in both directions is required all the time.
Example: Telephone network
, 1.1.3 COMPUTER NETWORKS
•
Computernetworkconsistsoftwoormorecomputersthatarelinkedinordertoshareresources,exch
angedatafilesortoallow electronic communication.
•
Thecomputersonanetworkmaybelinkedthroughcables,telephonelines,radiowaves,satellitesor
infraredlightbeams.
• Therearetwoaspectsofcomputernetworks–hardwareand software.
• Hardwareincludesphysicalconnectionbetweentwomachinesby using adaptors, cables,routers,
bridgesetc.
• Softwareincludesasetofprotocols.Protocolsdefineaformal
languageamongvariouscomponents.Itmakeshardwareusablebyapplications.
1.1.4 Uses of Computer Networks
1. Business Applications
2. HomeApplications
3. Mobile Users
4. Social Issues
1. Business Applications
• A companymayhaveacomputerforeachworkeranduse them to designproducts,
writebrochures, anddo thepayroll. Resourcesharingistomakeallprograms,equipment,and
especiallydataavailabletoanyoneonthenetworkwithout regard to thephysical locationof
theuser.NetworkscalledVPNs(VirtualPrivateNetworks)maybe
usedtojointheindividualnetworksatdifferentsitesinto one extendednetworks.
Client –Server Model:It is widely used and forms the basis of much network usage.
Figure 3 :A network with two clients and one server
• Telephone calls between employees may be carried by the computer network instead of
by the phone company. This technology is called IP telephony or Voice over IP (VoIP)
Figure 4: The client-server model involves requests and replies
Many companies is doing business electronically, especially with customers and
suppliers is called e-commerce (electronic commerce).
2. Home Applications
(21UCA07)
LECTURE NOTES
UNIT - 1
B.C.A. II YEAR
IV SEMESTER
Ms.S.NANDHINI, Assistant Professor
DEPARTMENT OF COMPUTER APPLICATIONS
, K.S.R College of Arts and Science for Women,
Tiruchengode.
Unit - I
Introduction – Network Hardware - Software - Reference Models - OSI and TCP/IP
Models - Example Networks: Internet, ATM, Ethernet and Wireless LANs - Physical Layer
- Theoretical Basis for Data Communication - Guided Transmission Media.
1.1 Introduction
Development of the PC changes a lot in business, industry, science and education.Similar
revolution is occurring in data communication and networking Technologies advances are
making it possible for communications links to carry more and faster signal. Services are
evolving to allow the use of this expanded capacity
For example telephone services extended to have:
Conference calling
Call waiting
Voice mail
Caller ID
The effectiveness of a data communications system depends on Fourfundamental
characteristics: delivery, accuracy, timeliness, and jitter.
1. Delivery
• The system must deliver data to the correct destination. Data must be received by the
intended device or user and only by that device or user.
2. Accuracy
• The system must deliver the data accurately. Data that have been altered in transmission
and left uncorrected are unusable.
3. Timeliness
• The system must deliver data in a timely manner. Data delivered late are useless. In the
case of video and audio, timely delivery means delivering data as they are produced, in
the same order that they are produced, and without significant delay. This kind of
delivery is called real-time transmission.
4. Jitter
• Jitter refers to the variation in the packet arrival time. It is the uneven delay in the
delivery of audio or video packets. For example, let us assume that video packets are sent
every 30 ms. If some of the packets arrive with 30-ms delay and others with 40-ms delay,
an uneven quality in the video is the result.
1.1.1 Components of a data communication system
• The word data refers to information presented in whatever form is agreed upon by the
parties creating and using the data.
, • Data communications are the exchange of data between two devices via some form of
transmission medium such as a wire cable.
Figure 1 : Data Communication
1. Message:The message is the information (data) to be communicated. Popular forms of
information include text, numbers,pictures,audio,and video.
2.Sender:The sender is the device that sends the data message. It can be a computer,
workstation, telephone handset, video camera, and so on.
3.Receiver:Thereceiveristhedevicethatreceivesthemessage.Itcanbea computer, workstation,
telephonehandset, television, andso on.
4.Medium: The transmission medium is the physical path by which a message travels from
sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial
cable, fiber-optic cable, and radio waves.
5.Protocol:Aprotocolisasetofrulesthatgoverndatacommunications.Itrepresents
anagreementbetweenthe communicatingdevices.Withouta protocol,two
devicesmaybeconnectedbutnotcommunicating,justasapersonspeakingFrench cannot beunderstood
by aperson who speaksonly Japanese.
1.1.2 Data flow (simplex, half-duplex, and full-duplex)
Figure 2 : Data Flow
1.Simplex(onewaystreet)
• Thecommunication isunidirectional. Onlyonedeviceonalinkcantransmitandtheothercan
only receive.Thesimplexmodecanusetheentirecapacityofthechannel to send datain
onedirection.Example:Keyboards,Monitors
2.Half-Duplex(one-lanewithtwo-directionaltraffic)
• Eachstationcanbothtransmitandreceive,butnotatthesame time.
Whenonedeviceissending,theothercanonlyreceive,andvice versa.
Theentirecapacityofachannelistakenoverbythetransmitting device.Example: Walkie-
talkies
3.Full-Duplex(Duplex)(two-waystreet)
• In full-duplex, both stations can transmit and receive simultaneously. One common
example of full-duplex communication is the telephone network. When two people are
communicating by a telephone line, both can talk and listen at the same time. The full-
duplex mode is used when communication in both directions is required all the time.
Example: Telephone network
, 1.1.3 COMPUTER NETWORKS
•
Computernetworkconsistsoftwoormorecomputersthatarelinkedinordertoshareresources,exch
angedatafilesortoallow electronic communication.
•
Thecomputersonanetworkmaybelinkedthroughcables,telephonelines,radiowaves,satellitesor
infraredlightbeams.
• Therearetwoaspectsofcomputernetworks–hardwareand software.
• Hardwareincludesphysicalconnectionbetweentwomachinesby using adaptors, cables,routers,
bridgesetc.
• Softwareincludesasetofprotocols.Protocolsdefineaformal
languageamongvariouscomponents.Itmakeshardwareusablebyapplications.
1.1.4 Uses of Computer Networks
1. Business Applications
2. HomeApplications
3. Mobile Users
4. Social Issues
1. Business Applications
• A companymayhaveacomputerforeachworkeranduse them to designproducts,
writebrochures, anddo thepayroll. Resourcesharingistomakeallprograms,equipment,and
especiallydataavailabletoanyoneonthenetworkwithout regard to thephysical locationof
theuser.NetworkscalledVPNs(VirtualPrivateNetworks)maybe
usedtojointheindividualnetworksatdifferentsitesinto one extendednetworks.
Client –Server Model:It is widely used and forms the basis of much network usage.
Figure 3 :A network with two clients and one server
• Telephone calls between employees may be carried by the computer network instead of
by the phone company. This technology is called IP telephony or Voice over IP (VoIP)
Figure 4: The client-server model involves requests and replies
Many companies is doing business electronically, especially with customers and
suppliers is called e-commerce (electronic commerce).
2. Home Applications
