TCP/IP Model

By AJAL JOSEASSISTANT PROFESSORDEPT OF ECEMAIL: ec2reach@gmail.com

• Communication– Established standards– Standards are known as protocols

• Implementation– A framework is helpful in the design of

hardware and software for communication– ISO-OSI Model serves this purpose– ISO-OSI supersedes the TCP/IP model

INTRODUCTION

Introduced in 1978 and revised in 1984Formulates the communication process into structured layersThere are seven layers in the model, hence the name the 7-Layer modelThe model acts as a frame of reference in the design of communications and networking products

• ISO– International Standards Organization

• OSI– Open Systems Interconnect

ISO and OSI Defined

OSI & TCP/IP Models

TCP/IP Model

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

The Layered Approach to Communication

Upper Layers

Lower Layers

Middle Layer

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

Division of Layers

OSI: A Layered Network ModelThe process of breaking up the functions or tasks of networking into layers reduces complexity.Each layer provides a service to the layer above it in the protocol specification. Each layer communicates with the same layer’s software or hardware on other computers. The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network. The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications. Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

OSI Model

OSI Reference Model: 7 Layers

OSI Model

Physical Layer

Provides physical interface for transmission of information.

Defines rules by which bits are passed from one system to another on a physical communication medium.

Covers all - mechanical, electrical, functional and procedural - aspects for physical communication.

Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

OSI Model

= HARDWARE SPECIFICATIONS

Data Link Layer

OSI Model

• Purpose– Manages the flow of data over the physical

media

• Responsible for error-free transmission over the physical media

• Assures error-free data submission to the Network Layer

Network Layer

OSI Model

• Address messages• Address translation from logical to physical– Ex: DE PAUL INSTITUTE ----------> 102.13.345.25

• Routing of data– Based on priority– Best path at the time of transmission

• Congestion control

Transport Layer

OSI Model

• For sending data– Repackage the message to fit into packets

• Split long messages• Assemble small messages

• On receiving data– Perform the reverse– Send an acknowledgment to the sender

• Solve packet problems– During transmission and reception

Session LayerSession layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications.

This layer requests for a logical connection to be established on an end-user’s request.Any necessary log-on or password validation is also handled by this layer.Session layer is also responsible for terminating the connection.This layer provides services like dialogue discipline which can be full duplex or half duplex.Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint.

OSI Model

Presentation Layer

OSI Model

• Protocol conversion• Data translation• Encryption• Character set conversion• Expansion of graphics command

Application Layer

OSI Model

• Purpose– User application to network service interface

• Examples– File request from server– E-mail services– etc.

TCP/IP Model

Application LayerApplication programs using the network

Transport Layer (TCP/UDP)Management of end-to-end message transmission,

error detection and error correction

Network Layer (IP)Handling of datagrams : routing and congestion

Data Link LayerManagement of cost effective and reliable data delivery,

access to physical networks

Physical LayerPhysical Media