1 Packet Switching, Layer Models and Protocol Suites.

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Packet Switching, Layer Packet Switching, Layer Models and Protocol Suites Models and Protocol Suites

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OutlineOutline Packet vs. circuit switchingPacket vs. circuit switching Layered tasksLayered tasks Internet protocol suitesInternet protocol suites ISO's OSI modelISO's OSI model

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Layered TasksLayered Tasks Computer networks are complex Computer networks are complex

systemssystems Tasks involve varieties of hardware and Tasks involve varieties of hardware and

software components, and protocolssoftware components, and protocols

Networking task is divided into Networking task is divided into several subtasks, or layersseveral subtasks, or layers

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Real World ExampleReal World Example Communication between managers Communication between managers

of two companiesof two companies

Communicate

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What Actually HappensWhat Actually Happens Communication takes place thru many Communication takes place thru many

layerslayersLogical communication

Secretary:types a letter

Delivery boy:drops the letter

Secretary:reads and reportsthe message

Delivery boy:takes the letter

Post office:Processes and routes the letter

Postal truck

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OSI ModelOSI Model OSI – OSI – OOpen pen SSystems ystems IInterconnectionnterconnection

Developed by the Developed by the IInternational nternational SStandards tandards OOrganizations rganizations (ISO)(ISO)

Two additional layersTwo additional layers Presentation layerPresentation layer Session layerSession layer

7.Application Layer7.Application Layer

6.Presentation 6.Presentation LayerLayer

5.Session Layer5.Session Layer

4.Transport Layer4.Transport Layer

3.Network Layer3.Network Layer

2.Data Link Layer2.Data Link Layer

1.Physical Layer1.Physical Layer

User

TransmissionMedium

Hardware

Software

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Application LayerApplication Layer

The only layer to interact with userThe only layer to interact with user

Responsible for providing services to the userResponsible for providing services to the user

SMTP HTTP FTP SMTP HTTP FTP

Data

Data H5

ApplicationLayer

to Transport from Transport

Data H5

DataLogical communication

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Presentation LayerPresentation Layer

Duties/servicesDuties/services Data translationData translation EncryptionEncryption DecryptionDecryption CompressionCompression

Responsible for handling differences indata representation to applications

Responsible for handling differences indata representation to applications

1111

Session LayerSession Layer

Duties/servicesDuties/services Interaction managementInteraction management

Simplex, half-duplex, full-duplexSimplex, half-duplex, full-duplex Session recoverySession recovery

Responsible for establishing, managing and terminating connections between applications

Responsible for establishing, managing and terminating connections between applications

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Transport LayerTransport Layer

Duties/servicesDuties/services Port addressingPort addressing Segmentation and reassemblySegmentation and reassembly Connection controlConnection control Flow control (end-to-end)Flow control (end-to-end) Error control (end-to-end)Error control (end-to-end)

Responsible for delivery of a messagefrom one process to another

Responsible for delivery of a messagefrom one process to another

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Transport LayerTransport Layer

TransportLayer

Data

from Application

Data1 Data2 Data3H4 H4 H4

to Network

Data

to Application

Data1 Data2 Data3H4 H4 H4

from Network

(segments)

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Network LayerNetwork Layer

Duties/servicesDuties/services Logical addressingLogical addressing RoutingRouting

Responsible for the delivery of packetsfrom the original source to the destination

Responsible for the delivery of packetsfrom the original source to the destination

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NetworkLayer

Data

from Transport

to Data Link

Data

to Transport

from Data Link

Data H3 Data H3

(packet)

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Network 1

Network 6

Network 5

1.1 1.2

6.6

6.1

6.3

5.7

5.2

Network 33.8

3.3Router

Data 1.15.7

1.1, 1.2, 6.1, 5.7, ... are logical addresses1.1, 1.2, 6.1, 5.7, ... are logical addresses

R1

R3R2

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Data Link LayerData Link Layer

Duties/servicesDuties/services FramingFraming Physical addressingPhysical addressing Flow control (hop-to-hop)Flow control (hop-to-hop) Error control (hop-to-hop)Error control (hop-to-hop) Access controlAccess control

Responsible for transmitting framesfrom one node to the next

Responsible for transmitting framesfrom one node to the next

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Data LinkLayer

Data

from Network

to Physical

Data

to Network

from Physical

Data H2 Data H2

(frame)

T2 T2

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3B

A3, 3B, 82, 9F, ... are physical addressesA3, 3B, 82, 9F, ... are physical addresses

9F 82 A3

Data 9FT2 A3

Data

H2

2020


Network 1

Network 6

Network 5

1.1 1.2

6.6

B1

6.3

5.7

5.2

Network 33.8

3.3

Data 1.15.7

97 32

25

79

62

54

74

12

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Data 1.15.7 2597

Data 1.15.7 6279

Data 1.15.7 7454

R1

R3R2

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Physical LayerPhysical Layer

Duties/servicesDuties/services Physical characteristics of Physical characteristics of

interfaces and mediainterfaces and media Representation of bitsRepresentation of bits Data rate (transmission rate)Data rate (transmission rate) Synchronization of bitsSynchronization of bits

Responsible for transmitting individual bitsfrom one node to the next

Responsible for transmitting individual bitsfrom one node to the next

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Physical LayerPhysical Layer

PhysicalLayer

Data

from Data Link to Data Link

Data

01001011 01001011

Transmission medium

(bits)

2323

The Big PictureThe Big Picture

L5 data H5

L4 data H4

L3 data H3

L2 dataT2 H2

0111011010101001010101001

L5 data H5

L4 data H4

L3 data H3

L2 dataT2 H2

0111010101010010101010101

5

4

3

2

1

5

4

3

2

1

Transmission medium

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Internet ModelInternet Model

ApplicatiApplicationon

TransportTransport

NetworkNetwork

Data LinkData Link

PhysicalPhysical

NetworkNetwork

Data LinkData Link

PhysicalPhysical

NetworkNetwork

Data LinkData Link

PhysicalPhysical

ApplicatiApplicationon

TransportTransport

NetworkNetwork

Data LinkData Link

PhysicalPhysical

Transmission medium

senderrouter

routerreceiver

OSI v TCP/IPOSI v TCP/IP

1 Packet Switching, Layer Models and Protocol Suites.

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