End-to-End Arguments in System Design; Saltzer, Reed, & Clark

The authors describe the "end-to-end" principle in this paper as it relates to deciding on the specific functionality built into a communication system: that some functions require some information or help from the application regardless, so building that functionality into the communication system itself is not necessarily beneficial, and indeed can even cause harm at times. Leaving out extra functionality from the low-level system can be preferable because applications that don't need the functions still have to deal with the performance hit in the underlying system and also because some applications will implement the function better or in more detail than the communcation system.

They provide a few examples to further their argument. The reliable file transfer example provides a more concrete notion to this principle, stressing that even if the underlying communication system has some fancy built-in guarantees, the application itself still has to check (and possibly handle) a small variety of errors, so complicating the communication system is not particularly helpful.

The "MIT checksum incident" example almost seems to argue that low-level function implementation is a harmful thing; if the networks hadn't used a packet checksum, perhaps the application programmers would have built in their own verification method and caught packet corruption earlier. I was skeptical of this notion that the communication system should be completely stripped off all duty to ensure correct data transmission, but luckily the authors countered this idea immediately, insisting that proper design involves a tradeoff between complexity costs of the communication system and the performance hits from an application having to deal with many errors in a simple communication system.

I like the notion of the end-to-end principle being the equivalent of RISC, in that both advocate paring down the underlying tools (communication system and instruction set, respectively) to the core building blocks necessary for everything else to get built on top of. The notion of layers in a network stems from this idea, with the underlying IP being simple and higher-level TCP/UDP/etc. layers actually offering the performance guarantees. This paper is important because it is likely one of the initial bases for the layers of the Internet Protocol Suite.