"The Hourglass model is essentially the idea of funnelling all communications through some common, ubiquitous communications protocol. Prominent examples of this common protocol are Internet Protocol (IP) and Asynchronous Transfer Model (ATM) "
The data that is created by an application needs to pass through the layer of the TCP/IP reference model to reach the destination. For Example, The application layer protocol used might be HTTP, FTP or TFTP. Every Application layer protocol is associated with a transport layer protocol depending on wheather it is connection-oriented or connection-less. The transport layer protocol in turn interacts with IP for routing the data packets. It is very important to understand that irrespective of the application layer protocol and the transport layer protocol the only protocol that is used for routing the data packets is IP. When the data transmission through the four layers is visualized it takes the shape of an hourglass and thus the model is called the IP Hourglass Model.
See Figure, When Source-A and Source-B interacts with HTTP so the request is forward to IP and Source-C interacts with IP using UDP and then IP forward or send the data to Network Interfaces say Ethernet or X.25 (creates on the basis of technology used) and then request is recieved by Destination-A, Destination-B and so on.
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