The Transport Layer

   End-to-End Communication

The Transport Layer is the lowest "end-to-end" layer of the OSI model, that is, the lowest layer in which peer software processes at either end of a connection carry on a conversation. Processes in the Transport Layer act as if their nodes are adjacent. They rely on lower layers to handle the details of passing data through intermediate nodes and transmitting it across the network, as shown on the Messages and Transport Layer Diagram.

The Transport Layer has been termed a "keystone" in the layer hierarchy, because it frequently resides at the border between the delivery mechanism, such as a public IP network, and the upper software layers of the enterprise network.