NETWORK LAYER ANDDTRANSPORT LAYER�OF�OSI MODEL

INTRODUCTION TO OSI

• OSI is an OPEN SYSTEM INTERCONNECTION network.

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• It was introduced by ISO :INTERNATIONAL STANDARD ORGANISATION, in 1978’s.

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• It consists of seven different layers.

INTRODUCTION

• It is a standard network model.

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• A set of rules and conventions by which a network is built.

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• An open system consists following systems such as :

INTRODUCTION

• Application software
• Operating system
• System software.

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• It also includes the communication software to interact with other open systems.

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• Rules used by different layers are known as PROTOCOLS of the particular layer.

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Significance of OSI MODEL

• This model is used to create a NETWORK with different levels of abstraction.

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• Each layer os designed to perform WELL-DEFINED FUNCTION.

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• The number of layers should be optimized.

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Significance

• Each layer’s function is chosen with an eye towards international standrd Protocol.

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• Layer boundaries are designed to minimise the information flow across the interfaces.

Advantages and Disadvantages of OSI

ADVANTAGES :

• It is a layered model. Changes are one layer do not affect other layers, provided that the interfaces between the layers do not change drastically.

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• It is a generic model and acts as a guidance tool to develop any network model.

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ADVANTAGES OF OSI

• It distinctly separates services, interfaces, and protocols. Hence, it is flexible in nature. Protocols in each layer can be replaced very conveniently depending upon the nature of the network.

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• It supports both connection-oriented services and connectionless services.

DISADVANTAGES OF OSI

• The OSI model is very complex. The initial implementation was cumbersome, slow and costly.

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•  There are many layers, some of the layers like the session layer and presentation layer have very little functionality when practically deployed.

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DISADVANTAGES

• The standards of OSI model are theoretical and do not offer adequate solutions for practical network implementation.

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• The OSI model did not meet the practical needs as well as the TCP/IP model. So it was labeled as inferior quality

DIFFERENT LAYERS OF OSI MODEL

INTRODUCTION TO DIFFERENT LAYERS

• Physical layer - The physical layer (Layer 1) deals with transmission of individual bits from one node to another over a physical medium.

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• Data Link layer - The data link layer (Layer 2) converts the raw transmission facility provided by the physical layer to a reliable and error-free link.

Introduction to layers

• Network layer -The network layer (Layer 3) controls the source to destination delivery of data packets across multiple hops (nodes). It controls the operation of the subnet.

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• Transport layer - The transport layer (Layer 4) is responsible for delivery of an entire message from an application program on the source device to a similar application program on the destination device.

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Introduction to layers

• Session layer - The session layer (layer 5) is responsible for establishing, managing, synchronizing and terminating sessions between end-user application processes.

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• Presentation layer - The presentation layer (Layer 6) ensures that the message is presented to the upper layer in a standardized format. It deals with the syntax and the semantics of the messages.

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• Application layer - The application layer (Layer 7) is the topmost layer of the OSI model. It specifies the interfaces and supports services to the end users for network access.

INTRODUCTION TO NETWORK LAYER

• The network layer (Layer 3) controls the source to destination delivery of data packets across multiple hops (nodes). It controls the operation of the subnet.

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• The network layer works for the transmission of data from one host to the other located in different networks.

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•  The sender & receiver’s IP addresses are placed in the header by the network layer. 

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NETWORK LAYER

FUNCTIONS OF NETWORK LAYER

• Routing: The network layer protocols determine which route is suitable from source to destination. This function of the network layer is known as routing.

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• Logical Addressing: In order to identify each device on internetwork uniquely, the network layer defines an addressing scheme. The sender & receiver’s IP addresses are placed in the header by the network layer. 

Network layer

• Segment : Segment in Network layer is referred to as Packet. 

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• Routers : Network layer is implemented by networking devices such as routers. 

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INTRODUCTION TO TRANSPORT LAYER

• The transport layer provides services to the application layer and takes services from the network layer. 

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•  It is responsible for the End to End Delivery of the complete message.

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• The data in the transport layer is referred to as Segments. 

TRANSPORT LAYER

FUNCTIONS OF TRANSPORT LAYER

• Transport layer receives the formatted data from the Session layer performs Segmentation, and implements  Flow &Error control to ensure proper data transmission. It also adds Source and Destination port numbers in its header and forwards the segmented data to the Network Layer. 

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•  Transport Layer reads the port number from its header and forwards the Data which it has received to the respective application. It also performs sequencing and reassembling of the segmented data. 

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TRANSPORT LAYER

• Segmentation and Reassembly: This layer accepts the message from the (session) layer, and breaks the message into smaller units. 

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• Service Point Addressing: In order to deliver the message to the correct process, the transport layer header includes a type of address called service point address or port address. 

NOTE :The sender needs to know the port number associated with the receiver’s application. 

MAIN SERVICES OF TRANSPORT LAYER

•  Connection-Oriented Service: It is a three-phase process that includes 

– Connection Establishment �– Data Transfer �– Termination / disconnection 

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In this type of transmission, the receiving device sends an acknowledgement, back to the source after a packet or group of packets is received. This type of transmission is reliable and secure.

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SERVICES

• Connectionless service: It is a one-phase process and includes Data Transfer. In this type of transmission, the receiver does not acknowledge receipt of a packet. This approach allows for much faster communication between devices. Connection-oriented service is more reliable than connectionless Service.

DIFFERENCE BETWEEN LAYERS

NETWORK LAYER

TRANSPORT LAYER

• The network layer is the third layer of the OSI model.

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• The network layer provides communication between hosts of different networks.

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• The transport layer is the fourth layer of the OSI model.

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• The transport layer focuses on the process to process the delivery of data.

DIFFERENCE

NETWORK LAYER

TRANSPORT LAYER

• The network layer does not focus on maintaining the order of the data packets.

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• The various devices used in the network layer are Routers, Brouters, etc.

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• The network layer deals with host-to-host communication.�

• The transport layer maintains the order of data.

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• The various devices used in the transport are Segments, Load Balancers, etc.
• The transport layer deals with the port-to-port communication.

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CONCLUSION

• THUS TO CONCLUDE YOU CAN SAY THAT EACH LAYER OF OSI MODEL HAS ITS OWN IMPORTANT AND VARIOUS FUNCTIONS.

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• BOTH THE NETWORK LAYER IS USED TO CONNECT WITH INTERNETAND TRANSPORT LAYER IS CALLED THE HEART OF OSI MODEL.

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