[e2e] 10% packet loss stops TCP flow

[Reiner Ludwig]

At 15:32 03.03.05, Lloyd Wood wrote:
>> And, I think that all of this is well in line with the e2e argument:
>> "best effort" = "try until congestion forces you to drop".
>
>That's not an e2e argument. The end-to-end paper was first presented
>at a conference in 1981. Nagle's RFC896 advice on ameliorating
>congestion dates from 1984.
>
>The end-to-end paper is a comment on systems engineering. It is not a
>comment on congestion.

I was refering to the e2e argument paper by J.H. Saltzer, D.P. Reed and D.D. Clark from 1984. That paper is frequently referenced (and rightfully so) when argueing that "hop-by-hop functions can not replace an end-to-end function". There seems to be little doubt in the networking community about this e2e argument when discussing functions like 'reliablity'. After 1984, the e2e argument was then also used in the context of the function 'congestion control' (e.g., see discussions on IP vs. X.25).

However, the paper also discusses performance in a section called 'Performance aspects':
    "Clearly, some effort at the lower levels to improve network reliability can have
    a significant effect on application performance. But the key idea here is that 
    the lower levels need not provide "perfect" reliability.
    Thus the amount of effort to put into reliability measures within the data 
    communication system is seen to be an engineering tradeoff based on performance, 
    rather than a requirement for correctness."

In 1984, the paragraph above made a lot of sense, I think. But since 1988, when V. Jacobson had introduced 'e2e congestion control' and an 'adaptive e2e retransmission timer' that also adapts to RTT variations, I don't think that the paragraph's statement on "no need for perfect reliability" holds any longer; at least not in general and not for the case of 'L2 ARQ'.

But you're right, the e2e argument paper does not define the term 'best-effort'. Has it ever been defined?

///Reiner