[[FileImage:IP stack connections.drawio.pngsvg|thumb|414x414px350px|Conceptual data flow in a simple network topology of two hosts (''A'' and ''B'') connected by a link between their respective routers. The application on each host executes read and write operations as if the processes were directly connected to each other by some kind of data pipe. After establishment of this pipe, most details of the communication are hidden from each process, as the underlying principles of communication are implemented in the lower protocol layers. In a common application analogy, Host A's web browser appears directly connected to Host B's web server via an [[HTTP#HTTP application session|Application Layer HTTP session]] identified by an address like a cookie. Atat the transport layer the communication appears as processhost-to-process communication,<ref name=":0" /> each process addressed by a port numberhost, without knowledge of the application data structures and the connecting routers., Finally,while at the internetworking layer using the Internet Protocol (IP), packets of bytes traverse individual network boundaries asare traversed at each router forwards a packet towards its destination IP address.]]
[[Image:UDP encapsulation.svg|thumb|350px|Encapsulation of application data descending through the layers described in RFC 1122]]
