What are the main responsibilities of the Transport Layer? What are the main services provided by the Transport Layer to the Application Layer? Solution Transport layer is the fourth layer in the OSI reference model. The main function of the transport layer is it acts as a bridge between two layers that is the third layer application layer which transport layer takes some packets from application layers and breaks it in to some sub parts and send those to the next one that is network layer. It maintaions the same sequence without any disturbance and mainly folows the order. The packets which are taken from the upper layer that is application layer in the form of segments. The application layer makes use of the transport layer because these are the host layers. Application layer defines TCP/IP application protocols and how host programs interface with Transport layer services to use the network..