chap. 2 network models

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Chap. 2Chap. 2Network ModelsNetwork Models

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2.1 Layered Tasks2.1 Layered Tasks

Sender, Receiver and Carrier

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Layered TasksLayered Tasks

Hierarchy

Higher Layer

Middle Layer

Lower Layer

Services

The Each layer uses the services of the layer immediately below it.

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2.2 Internet Model2.2 Internet Model

Five Layer Internet Model

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Internet ModelInternet Model

Peer-to-peer Processes

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Peer-to-peer ProcessesPeer-to-peer Processes

Interfaces between Layers

Each interface defines what information and services a layer must provide for the layer above it.

Well defined interfaces and layer functions provide modularity to a network

Organizations of the layers

Network support layers : Layers 1, 2, 3

User support layer : Layer 5

It allows interoperability among unrelated software systems

Transport layer (Layer 4) : linking two subgroups

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Peer-to-peer ProcessesPeer-to-peer Processes

An exchange using the Internet model

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Physical LayerPhysical Layer

coordinates the functions required to transmit a bit

stream over a physical medium.

(deal with the mechanical and electrical specification of

the primary connections: cable, connector)

- Physical characteristics of interfaces and media

- Representation of bits

- Data rate : transmission rate

- Synchronization of bits

is responsible for transmitting individual bits from one

node to the next node

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Physical LayerPhysical Layer

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Data Link LayerData Link Layer

The data link layer is responsible for transmitting frames

from one node to the next.

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Data Link LayerData Link Layer

Major duties

Framing

Physical addressing

Flow control

Error control

Access control

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Data Link LayerData Link Layer

Hop-to-hop (node-to-node) delivery

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Data Link LayerData Link Layer

In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection

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Network LayerNetwork Layer

The network layer is responsible for the delivery of

packets from the original source to the final destination.

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Network LayerNetwork Layer

Logical addressing

Routing

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Network LayerNetwork Layer

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Transport LayerTransport Layer

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Transport LayerTransport Layer

The transport layer is responsible for delivery of a message from

one process to another.

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Transport LayerTransport Layer

Port addressing

Segmentation and ressemblt

Connection control

Flow control

Error control

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Transport LayerTransport Layer

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Application LayerApplication Layer

The application layer is responsible for providing

services to the user.

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Application LayerApplication Layer

The major duties of the application

Mail services

File transfer and access

Remote log-in

Accessing the World Wide Web

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Summary of LayersSummary of Layers

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2.3 OSI Model2.3 OSI Model

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OSI Reference ModelOSI Reference Model

OSI : Open System Interconnection by ISO

Basic Reference Model : ISO-7498

Purpose of OSI Model

~ is to open communication between different systems without requiring changes to the logic of the underlying hardware and software.

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The ModelThe Model

OSI Model

~ is layered framework for the design of network systems that allows for communication across all types of computer systems

Layered Architecture

~ shows the layers involved when a message is sent from device A to device B

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Model (cont’d)Model (cont’d)

The OSI Model

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OSI LayersOSI Layers

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Model (cont’d)Model (cont’d)

Peer-to-peer process

~ process on each machine that communicate at a

given layer

Interfaces between Layers

~ defines what information and services a layer must

provide for the layer above it

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Applications for All Layers Applications for All Layers