The Transport Layer

The transport Layer is the heart of the whole protocol hierarchy. Its task is to transport data from the source machine to destination machine, independently of the physical network. It should be reliable and cost effective.

Transport Service:

Goal:  The goal of this layer is to provide efficient, reliable and cost effective service to its users, normally processes in the application layer. To achieve this goal the transport layer makes use of the services provided by the network layer.

Transport entity:  The hardware and or software within transport layer that does work is called transport entity. This can be located in OS Kernel.

Types:  Two types of transport service are the connection oriented transport service

And connectionless   transport service. Connections have three phase: establishment, data transfer, release. The connection oriented transport service is similar to the connection oriented network service. Addressing and flow control are also similar in both layers. The transport code runs entirely on the users machine, but network layer runs mostly on routers operated by carrier. The users have no real control over network

Layer, so they cannot solve the problem. The only possibility is to put on top of the network layer another layer that improves quality of the service. The transport layer makes it possible for the transport service to be more reliable than the underlying network service. If there is any Lost packets it can be detected and compensated for

By the transport layer. Each transport service has its own interface.

Difference between network service and transport service:

• The connection oriented transport service is reliable. The purpose of the transport layer to provide a reliable service on top of unreliable network. Real networks can lose packets, so network layer is unreliable.
• The network service is used only by the transport entities. Transport service must be convenient and easy to use.

Summary:

• Transport layer is responsible for maintaining service for the user.
• It optimizes the resources that connect the two open system.
• It establishes transport connections between session entities.
• This layer segments data into smaller or larger packets, which levels the flow of data      between session entities.
• It provides communications flow control avoids congestion in network.