© 1999, Cisco Systems, Inc.www.cisco.com
Networking ModelsOSI Model
Created by International Organization StandardizationPrepared by
Agha Mohammad HaidariNetwork Manager
ICT DirectorateMinistry of Communication & IT
Email : [email protected]#0700148122
Networking ModelsOSI Model
Created by International Organization StandardizationPrepared by
Agha Mohammad HaidariNetwork Manager
ICT DirectorateMinistry of Communication & IT
Email : [email protected]#0700148122
2-2CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
OSI ModelOSI Model
• The early development of networks was disorganized in many ways. Theearly 1980s saw tremendous increases in the number and size ofnetworks. As companies realized the advantages of using networkingtechnology, networks were added or expanded almost as rapidly as newnetwork technologies were introduced.
• By the mid-1980s, these companies began to experience problems fromthe rapid expansion. Just as people who do not speak the same languagehave difficulty communicating with each other, it was difficult for networksthat used different specifications and implementations to exchangeinformation. The same problem occurred with the companies thatdeveloped private or proprietary networking technologies. Proprietarymeans that one or a small group of companies controls all usage of thetechnology. Networking technologies strictly following proprietary rulescould not communicate with technologies that followed differentproprietary rules
2-3CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
OSI ModelOSI Model
• The Open System Interconnection (OSI) reference model released in1984 was the descriptive network model that the ISO created. Itprovided vendors with a set of standards that ensured greatercompatibility and interoperability among various network technologiesproduced by companies around the world.
2-4CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
OSI ModelOSI Model
Dividing the network into seven layers provides the following advantages:• It breaks network communication into smaller, more manageable parts.
• It standardizes network components to allow multiple vendor development and support.
• It allows different types of network hardware and software to communicate with each other.
• It prevents changes in one layer from affecting other layers.
• It divides network communication into smaller parts to make learning it easier to understand
2-5CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Seven Layers of theOSI Reference ModelSeven Layers of the
OSI Reference Model
• Layer 7: Application• Layer 6: Presentation• Layer 5: Session• Layer 4: Transport• Layer 3: Network• Layer 2: Data link• Layer 1: Physical
2-6CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Why a Layered Network Model?Why a Layered Network Model?
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
• Reduces complexity (one bigproblem to seven smallerones)
• Standardizes interfaces• Facilitates modular
engineering• Simplifies teaching and
learning
2-7CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Devices Function at LayersDevices Function at Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
NIC Card
Hub
2-8CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Host LayersHost Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host layers:Host layers: Provideaccurate data delivery betweencomputers}
2-9CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Media LayersMedia Layers
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host layers:Host layers: Provideaccurate data delivery betweencomputers
Media layers:Media layers: Controlphysical delivery of messagesover the network}
}
2-10CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions
Provides network services to applicationprocesses (such as electronic mail, filetransfer,
7 Application
2-11CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions
Network services to applicationsNetwork services to applications
• Ensures data is readable byreceiving system
• Format of data• Data structures• Negotiates data transfer
syntax for application layer
7 Application
6 Presentation Data representation
2-12CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions
Inter-host communication• Establishes, manages, and
terminates sessions betweenapplications
7 Application
6 Presentation
5 Session
Network services to applicationsNetwork services to applications
Data representationData representation
2-13CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions
7 Application
6 Presentation
5 Session
Transport4
InterInter--host communicationhost 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
2-14CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions
7 Application
6 Presentation
5 Session
Transport4
Network3
InterInter--host communicationhost communication
Network services to applicationsNetwork services to applications
Data representationData representation
EndEnd--toto--end connection reliabilityend connection reliability
Addresses and best path• Provides connectivity and path
selection between two endsystems
• Domain of routing
2-15CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions7 Application
6 Presentation
5 Session
Transport4
Network3
Data Link2
InterInter--host communicationhost communication
Network services to applicationsNetwork services to applications
Data representationData representation
EndEnd--toto--end connection reliabilityend 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, flowcontrol
2-16CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Layer FunctionsLayer Functions7 Application
6 Presentation
5 Session
Transport4
Network3
Data Link2
Physical1
InterInter--host communicationhost communication
Network services to applicationsNetwork services to applications
Data representationData representation
EndEnd--toto--end connection reliabilityend connection reliability
Addresses and best pathAddresses and best path
Access to mediaAccess to media
Binary transmission• Wires, connectors, voltages,
data rates
2-17CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Host A
Peer-to-Peer CommunicationsPeer-to-Peer Communications
Application
Presentation
Session
Transport
Network
Data Link
PhysicalBits
Frames
Packets
Segments
Host B
2-18CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Data EncapsulationData Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Host A Host B
Data} {
2-19CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Data EncapsulationData Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
Host A Host B
2-20CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Data EncapsulationData Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
FrameHeader
FrameTrailer
DataNetworkHeader
Host A Host B
2-21CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Data EncapsulationData Encapsulation
Application
Presentation
Session
Transport
Network
Physical
Data Link
Application
Presentation
Session
Transport
Network
Physical
Data Link
Data} {DataNetwork
Header
FrameHeader
FrameTrailer
DataNetworkHeader
0101101010110001
Host A Host B
2-22CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
The Application (Upper) LayersThe Application (Upper) Layers• Application
– User interface– Examples – Telnet, HTTP
• Presentation– How data is presented– Special processing, such as encryption– Examples – FTP enables you to choose binary or ASCII transfer.
• Session– Keeping different applications’ data separate
– defines how to start, control, and end conversations (calledsessions).
– Examples – Operating system/application access scheduling
2-23CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
The Data-Flow (Lower) LayersThe Data-Flow (Lower) Layers
• Transport– Focuses on issues related to data delivery– Reliable or unreliable delivery– Segmentation of large application data– Error correction before transmit– Examples: TCP, UDP,
• Network– This layer defines end-to-end delivery of packets.– Provide logical addressing which routers use for path determination– Examples: IP,
2-24CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
The Lower Layers (cont.)The Lower Layers (cont.)
• Data link– These protocols are necessarily concerned with the type of media– Combines bits into bytes and bytes into frames– Access to media using MAC address– Error detection not correction
• Physical– Moves bits between devices– Specifies voltage, wire speed, and pinout cable .
2-25CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
The Data-Flow (Lower) LayersThe Data-Flow (Lower) Layers
• Transport– Focuses on issues related to data delivery– Reliable or unreliable delivery– Segmentation of large application data– Error correction before transmi
• Network– This layer defines end-to-end delivery of packets.– Provide logical addressing which routers use for path determination
2-26CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Network Layer: Path DeterminationNetwork Layer: Path Determination
Which Path?Which Path?
• Layer 3 functions to find the bestpath through the internetwork
2-27CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Network Layer: Communicate PathNetwork Layer: Communicate Path
1
2
3
4
5
6
7
89
10 11
• Addresses represent the path of mediaconnections
• Routing helps contain broadcasts
2-28CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Transport LayerTransport Layer
• Segments upper-layer applications• Establishes an end-to-end connection• Sends segments from one end host to another• Optionally, ensures data reliability
2-29CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Presentation LayerPresentation Layer
ASCIIEBCDICEncrypted
• Text• Data
login:
PICTTIFFJPEGGIF
• Graphics• Visual images
• Sound
• VideoMPEGQuickTime
MIDI
• Provides code formatting andconversion for applications
2-30CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Application LayerApplication Layer
Word ProcessorPresentation GraphicsSpreadsheetDatabaseDesign/ManufacturingProject PlanningOthers
COMPUTERAPPLICATIONS
Electronic MailFile TransferRemote AccessClient-Server ProcessInformation LocationNetwork ManagementOthers
NETWORKAPPLICATIONS
2-31CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
The OSI ModelThe OSI Model
• Application – Think of browsers.• Presentation – Think of common data format.• Session – Think of dialogs and conversations.• Transport – Think of flow control and reliability.• Network – Think of path selection, routing, and logical addressing.• Data Link – Think of frames and media access control.• Physical – Think of signals and media.
2-32CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
History and Future of TCP/IPHistory and Future of TCP/IP
• The U.S. Department of Defense(DoD) created the TCP/IPreference model because itwanted a network that couldsurvive any conditions.
• Some of the layers in the TCP/IPmodel have the same name aslayers in the OSI model.
2-33CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
TCP/IP modelTCP/IP model
• Application layer
• Transport layer
• Internet layer
• Network access layer
The TCP/IP model has the following four layers
2-34CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Similarities of the OSI and TCP/IPmodels
Similarities of the OSI and TCP/IPmodels
• Both have layers.
• Both have application layers, though they include very differentservices.
• Both have comparable transport and network layers.
• Networking professionals need to know both models.
2-35CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
Differences of the OSI and TCP/IPmodels
Differences of the OSI and TCP/IPmodels
• TCP/IP combines the presentation and session layer into its application layer.• TCP/IP combines the OSI data link and physical layers into one layer.• IP is called a network layer, or Layer 3, protocol. Similarly,• the TCP/IP transport layer defines many functions, including error recovery, as does the OSI• transport layer—so TCP is called a transport layer, or Layer 4, protocol.
2-36CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com
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