Download - Day 1.3 osi reference
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OSI Reference Model
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All - Application
People - Presentation
Seems - Session
To - Transport
Need of - Network
Data - Data Link
Processing - Physical
How to Remember
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Why a Layered Network Model?
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
• Reduces complexity (one big problem to seven smaller ones)
• Standardizes interfaces
• Simplifies teaching and learning
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Devices Function at Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
NIC Card
Hub
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Host Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host layers: Host layers: Provide accurate data delivery between computers}
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Media Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host layers:Host layers: Provide accurate data delivery between computers
Media layers:Media layers: Controlphysical delivery of messages over the network}}
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Application Layer
Provides network services to application processes (such as electronic mail, file transfer, and terminal emulation)
7 Application
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Presentation Layer
Network services to applicationsNetwork services to applications
• Ensures data is readable by receiving system
• Format of data• Negotiates data transfer
syntax for application layer
7 Application
6 Presentation Data representation
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Session Layer
Inter-host communication• Establishes, manages, and
terminates sessions between applications
7 Application
6 Presentation
5 Session
Network services to applicationsNetwork services to applications
Data representationData representation
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Transport Layer
7 Application
6 Presentation
5 Session
Transport4
Inter-host communicationInter-host communication
Network services to applicationsNetwork services to applications
Data representationData representation
End-to-end connection reliability• Concerned with data transport
issues between hosts• Data transport reliability• Establishes, maintains, and
terminates virtual circuits• Fault detection and recovery• Information flow control
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Network Layer
7 Application
6 Presentation
5 Session
Transport4
Network3
Inter-host communicationInter-host communication
Network services to applicationsNetwork services to applications
Data representationData representation
End-to-end connection reliabilityEnd-to-end connection reliability
Addresses and best path• Provides connectivity and path
selection between two end systems
• Domain of routing
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Data Link Layer
7 Application
6 Presentation
5 Session
Transport4
Network3
Data Link2
Inter-host communicationInter-host communication
Network services to applicationsNetwork services to applications
Data representationData representation
End-to-end connection reliabilityEnd-to-end connection reliability
Addresses and best pathAddresses and best path
Access to media• Provides reliable transfer of data
across media• Physical addressing, network
topology, error notification, flow control
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Physical Layer
7 Application
6 Presentation
5 Session
Transport4
Network3
Data Link2
Physical1
Inter-host communicationInter-host communication
Network services to applicationsNetwork services to applications
Data representationData representation
End-to-end connection reliabilityEnd-to-end connection reliability
Addresses and best pathAddresses and best path
Access to mediaAccess to media
Binary transmission• Wires, connectors, data rates
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7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host A
Communications
Application
Presentation
Session
Transport
Network
Data Link
PhysicalBits
Frames
Packets
Segments
Host B
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Data EncapsulationApplication
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Host A Host B
Data} {
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Data EncapsulationApplication
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
Host A Host B
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Data EncapsulationApplication
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
Frame
HeaderFrame
TrailerDataNetwork
Header
Host A Host B
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Data EncapsulationApplication
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
Frame
HeaderFrame
TrailerDataNetwork
Header
0101101010110001
Host A Host B
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Layers 1 & 2: Physical & Data Link
Layers
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MAC Address24 bits
ROMRAM
24 bits
0000.0c12. 3456Serial NumberVendor Code
• MAC address is burned into ROM on a network interface card
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Layer 3: Network Layer
© 1999, Cisco Systems, Inc. www.cisco.com
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Network Layer: Path Determination
Which Path?Which Path?
• Layer 3 functions to find the best path through the internetwork
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Layers 4–7: Transport, Session,
Presentation, and Application Layers
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• Segments upper-layer applications• Establishes an end-to-end connection• Sends segments from one end host to another• Optionally, ensures data reliability
Transport Layer
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Transport Layer— Establishes Connection
Synchronize
Synchronize
Acknowledge
Negotiate Connection
Receiver
Data Transfer
Connection Established
(Send Segments)
Sender
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Transport Layer— Sends Segments with Flow Control
Transmit
Buffer FullNot Ready
StopProcessSegments
Buffer OKReadyGo
Resume Transmission
ReceiverSender
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Transport Layer— Reliability with Windowing
•Window Size = 1
Sender
Send 1 Receive 1
Receiver
Ack 2
Send 2 Receive 2Ack 3
Sender
Send 1Send 2
Receive 1Receive 2
Receiver
•Window Size = 3
Send 3 Receive 3Ack 4
Send 4
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Transport Layer— An Acknowledgement Technique
Sender Receiver
Send 2Send 1
Send 3Ack 4
Send 5Send 4
Send 6Ack 5
Send 5Ack 7
1 2 3 4 5 6 7 1 2 3 4 5 6 7
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Transport to Network Layer
End-to-End SegmentsEnd-to-End Segments
Routed PacketsRouted Packets
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• Coordinates applications as they interact on different hosts
Session Layer
• Network File System (NFS)• Structured Query Language (SQL)• Remote-Procedure Call (RPC)• AppleTalk Session Protocol (ASP)• DEC Session Control Protocol (SCP)
Service Request
Service Reply
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• Provides code formatting and conversion for applications
Presentation Layer
ASCIIEBCDICEncrypted
• Text• Data
login:
PICTTIFFJPEGGIF
• Graphics• Visual images
• Sound
• VideoMPEGQuickTime
MIDI
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• User Interaction
Application Layer
Word Processor
Presentation Graphics
Spreadsheet
Database
Design/Manufacturing
Project Planning
Others
COMPUTERAPPLICATIONS
Electronic Mail
File Transfer
Remote Access
Client-Server Process
Information Location
Network Management
Others
NETWORKAPPLICATIONS INTERNETWORK
APPLICATIONS
Electronic Data Interchange
World Wide Web
E-Mail Gateways
Special-Interest Bulletin Boards
Financial Transaction Services
Internet Navigation Utilities
Conferencing (Voice, Video, Data)
Others
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• OSI reference model describes building blocks of functions for program-to-program communications between similar or dissimilar hosts
• Layers 4–7 (host layers) provide accurate data delivery between computers
• Layers 1–3 (media layers) control physical delivery of data over the network
Summary