Iso Osi Referene model Model

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Microcomputer Networking II

St. Cloud State Un iversi ty

MCS 426, Fall 1999 Instructor: Adomas Svir skas

The ISO/OSI Reference Model

The Model

Functionality of Layers Example Networks


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The OSI Model

Basic principles of layered architecture:

Each layer means different layer of abstraction

Each layer should perform a well defined function The functions of layer should promote standardization

The information flow across the interfaces should be

minimized

The number of layers should be large enough to

separate functionality and small enough to keep the

architecture under control


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The OSI Model

Introduced in 1983

The OSI model has seven layers

The OSI model is not a network architecture

It does not specify the exact services ant protocols

It specifies what kind of functions each layer should

perform

ISO has produced standards for each layer as separate

documents Good model to study networking concepts


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Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum




The OSI reference model


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The Physical Layer

Transmission of raw bitsover communication

channel

Transmission media, its physical properties

Magnetic media Twisted pair

Coaxial cable

Fiber optics

Wireless transmission

Data rate of communication channel


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The Data Link Layer

Providing error-free transmission line for upper

layers between two adjacent nodes

Breaking information into framesand using

services of physical layer Error-detecting codes

Error-correcting codes

Ensuring uniqueness and correctness of frames

Flow control between sender and receiver

Access to shared communication channel


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The Network Layer

Routing of data packetsfrom source host to

destination host

Controlling network congestion

Accounting of network traffic Internetworking - interconnection of multiple

heterogeneous networks

Addressing issues

Packet sizes

Protocol differences


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The Transport Layer

Transmission of data between software entities on

end-point hosts

Providing channel for each application, mapping

channels to Network Layer connection Ensuring uniqueness and correctness transmitted

of data units

Quality of Service (QoS) management

Connection management, naming

Flow control and buffering


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The Session Layer

Establishment of sessions between applications

Enhancing Transport Layer services

Dialogue control: directions, etc.

Token management

Synchronization: checkpoints


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The Presentation Layer

Providing general solutions to syntax and

semantics transmitted data

Encoding of data on the wire into intermediateformat

Compression of data

Encryption of data


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The Application Layer

All the network application software

Network virtual terminals

File transmission

Electronic mail File servers

Database servers

Application servers

Object servers Transaction servers


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Data Transmission in OSI model


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The TCP/IP Reference Model


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Initial TCP/IP protocols

Iso Osi Referene model Model

Documents