[e2e] Open the floodgate

[Michael Welzl]

>     >> we all have known for some time that i) TCP can't currently
>     >> distinguish between error loss and congestion loss, and ii) slowing
>     >> down for an error loss is a mistake.
>
>     > So why don't we have separate header/payload checksums in TCP yet
via a
>     > header option, as we now have in DCCP?
>
> The problem is that many routers (and low-level device drivers) simply
> discard packets which fail the link-level checksum, so many (most?) of
those
> error packets will simply never get to the host.

I thought that routers should only examine IP headers?
But maybe I'm being naive here ...

as for low-level device drivers - well, if you mean the link-level equipment
itself, there is a list at
http://www.icsi.berkeley.edu/~gurtov/corruption.html

We did some tests with 802.11 equipment, it's true that there seems to
be no chance to get erroneous data from this type of link layer. GPRS,
as an example, is different in this aspect, I've been told, and it's also on
this page.

I remember that "we don't need it, link layers won't give it to you anyway"
was one of the main reasons against UDP Lite. And, to me, one of the
most important reasons in favor of UDP Lite (which is now in the RFC
Editor Queue) was that the goal is to motivate link layer designers to
do so.

It's actually a chicken-egg type of problem:
Either we motivate link layer designers to hand over corrupt data
(without getting much immediate benefit), or they do it (without getting
much immediate benefit) and thereby motivate us to design protocols
that can use such data.

It's not so useless after all.

Cheers,
Michael