CONCLUSIONS
End-to-end arguments are a kind of "Occam's razor" when it comes to choosing the functions to be provided in a communication subsystem. Because the com- munication subsystem is frequently specified before applications that use the subsystem are known, the designer may be tempted to "help" the users by taking on more function than necessary. Awareness of end-to-end arguments can help to reduce such temptations. It is fashionable these days to talk about layered communication protocols, but without clearly defined criteria for assigning functions to layers. Such layerings are desirable to enhance modularity. End-to-end arguments may be viewed as part of a set of rational principles for organizing such layered systems. We hope that our discussion will help to add substance to arguments about the "proper" layering.