Transport Layer

Introduction

                       In the previous blog on Network layer, we discussed how it is necessary to convert frames into packets and route them to various destinations. Now, advancing a bit we try to understand the Transport layer which is also the 4th layer in the OSI Model. 

What is Transport Layer?

                              The Transport Layer is one of the seven OSI model layers, which manages end-to-end communication in computer networks. It sits above the network layer and below the session layer and manages end-to-end communication between devices in a network. It's primary function is to manage end-to-end data transmission, offering services such as segmentation, error checking, flow control and multiplexing to enable secure and efficient data transfer. '

How Transport Layer Works?

The transport layer acts as an intermediary, receiving services from the Application layer while providing services to the Network layer. 

=> On the Sender side, the transport layer takes data (messages) from the Application layer and proceeds to segment it. It breaks down the original message into smaller segments, incorporates the source and destination port numbers into the segment's header, and dispatches the segmented data to the Network layer. 

=> On the receiver side, this layer receives the data from the Network layer, reconstructs the segmented information, and then routes the message to the proper port within the Application Layer. 

Services of Transport Layer

Transport layer protocol offer services that can be categorized into five distinct groups. They are as follows: -

End-to-End delivery

In computer networking, just as the Data Link layer relies on MAC addresses to ensure precise frame delivery and the Network Layer uses IP addresses for effective packet routing, the Transport Layer also depends on port numbers. Port numbers are essential for accurately directing data segments to the appropriate process among several concurrently running on a single host. 

Addressing

Addressing involves the capability to establish communication with the precise application running on a computer. This addressing procedure commonly employs network ports to allocate distinct port numbers to both the sending and receiving applications residing on a machine. The combination of the IP address utilized in the network layer and the port number within the transport layer results in a unique address for each application, ensuring precise identification and communication. 

Reliable delivery

Reliability in the context of network data transmission refers to the system's capability to address potential errors that may occur during data transfer. If data undergoes unintended alterations during transit, error correction mechanisms and checksums are in place to identify and rectify these issues. If a data packet is lost during transmission, it is recognized, and the system initiates a retransmission process. 

Flow control

Flow control within the transport layer refers to its capability to prevent the transmission of data beyond what the network can reliably handle. This involves buffering both outgoing and incoming data until sufficient network capacity is available for smooth transmission. In cases where the receiver's buffer reaches its capacity, the sending rate is adjusted downward to avoid overwhelming the recipient. 

Multiplexing

Multiplexing, often described as a many to one process, involves consolidating data from multiple sender processes into a single packet, which includes appropriate headers. This consolidated packet is then transmitted as a unified entity. Multiplexing enables the concurrent utilization of various processes on a host within a network environment , with each process being distinguished by its unique port number. 

Transport Layer Protocols

TCP - Transmission Control Protocol

UDP - User Datagram Protocol

TLS - Transport Layer Security

RSVP - Resource Reservation Protocol

RPL - Routing Protocol

Conclusion

# The Transport layer is one of the seven OSI mode layers, which manages end-to-end communication in      computer networks

# The Transport layer sits above the network layer and below the session layer and manages end-to-end          communication between devices in a network. 

# UDP and TCP are the two most widely used transport layer protocols. 

         I hope this blog makes you understand some basics about Transport Layer. Remember, there is much more to know and learn about the processes and working of this layer.

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