[ih] Fwd: Packet Radio Info (lossiness of Ethernet)

[Craig Partridge]

My favorite Ethernet coax disaster was a friend who managed a network, I
believe at Northeastern, where they had much higher packet loss.  After a
few days they discovered a section of coax (with unrepaired tap holes) had
been reused to extend the coax through a janitor's closet -- and the
cleaning product fumes had caused wonderful copper+[something] crystals to
form in the coax.

Craig

On Sat, Apr 18, 2026 at 4:49 PM John Gilmore via Internet-history <
internet-history at elists.isoc.org> wrote:

> vinton cerf via Internet-history <internet-history at elists.isoc.org> wrote:
> > The lossiness of packet radio, packet satellite and ethernet all drove
> TCP reliability...
>
> I recall when we wired up Sun Building 1 in Mountain View in the early
> 1980s, using the original 10 megabit thick Ethernet using "vampire
> taps".  Every employee's office had a computer, and they were all on the
> Ethernet -- one big long yellow Ethernet cable for the whole building.
>
> We were shocked that when we measured, we were getting about 1%
> undetected packet loss.  On Ethernet!  We had thought that Ethernet
> was supposed to just work.
>
> Some of it probably related to back-to-back Ethernet frames that
> newer Ethernet chips with DMA that could send continuous packets
> (particularly after their driver was tuned up).  Older Ethernet boards
> didn't have enough buffer space or tuning to capture more than one,
> two, or three packets in a row.  New machines could send a 4k memory
> page as a single fragmented UDP packet, using four back-to-back
> Ethernet frames.  If one of them was dropped, a timeout ensued and
> the whole thing had to be re-sent.
>
> That long Ethernet was also getting huge numbers of broadcast packets,
> each of which woke up the CPU on every workstation in the building.
> Most were ARP.  ARPs for machines that were powered off, or offline,
> or nonexistent, tended to be retried, too.  Sometimes forever, if
> a machine's config file had a typo in an address.
>
>         John
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