End-to-end principle

Intermediary nodes (such as gateways and routers) that exist to establish the network may still implement these features to improve efficiency but do not guarantee end-to-end functionality.

[3] A basic premise of the principle is that the payoffs from adding certain features required by the end application to the communication subsystem quickly diminish.

[c] Put differently, it is far easier to obtain reliability beyond a certain margin by mechanisms in the end hosts of a network rather than in the intermediary nodes,[d] especially when the latter are beyond the control of, and not accountable to, the former.

[e] Positive end-to-end acknowledgments with infinite retries can obtain arbitrarily high reliability from any network with a higher than zero probability of successfully transmitting data from one end to another.

"[10]: 2.3 The ARPANET was the first large-scale general-purpose packet switching network – implementing several of the concepts previously articulated by Baran and Davies.

End-to-end acknowledgment and retransmission is the responsibility of the connection-oriented Transmission Control Protocol (TCP) which sits on top of IP.

The functional split between IP and TCP exemplifies the proper application of the end-to-end principle to transport protocol design.

[3] The most important limitation of the end-to-end principle is that its basic premise, placing functions in the application endpoints rather than in the intermediary nodes, is not trivial to implement.

This leads to the idea of modeling each application via its own application-specific protocol that supports the desired coordination between its endpoints while assuming only a simple lower-layer communication service.