Passage: The design of the network included the recognition that it should provide only the functions of efficiently transmitting and routing traffic between end nodes and that all other intelligence should be located at the edge of the network, in the end nodes. This design is known as the end-to-end principle. Using this design, it became possible to connect almost any network to the ARPANET, irrespective of the local characteristics, thereby solving Kahn's initial internetworking problem. One popular expression is that TCP/IP, the eventual product of Cerf and Kahn's work, can run over "two tin cans and a string." Years later, as a joke, the IP over Avian Carriers formal protocol specification was created and successfully tested.

Question: what is the popular expression?
hat TCP/IP, the eventual product of Cerf and Kahn's work, can run over "two tin cans and a string