I'm using a PPP connection to the external world and I'm having problems
with TPC throughput, for example an ftp download.
The symptoms are the following. I monitor both the modem lights and the
hash mark progress.
Initially everything goes fine -- the receive light is on constantly and
the hash advances about 4K/sec, which is what the 56K modem gives.
At some point the hash marks stop advancing, and shortly after the receive
light stops. At this point I can check with ifconfig that there has been
one packet error on the interface.
After a while there is some sporadic activity on the lights, a whole slew
of hash marks appears at once, and the transmission resumes normally.
This process is repeated at regular intervals, so the effective throughput
is much less than the peak -- about 2.6 K/s.
What I believe is happening is that the dropped packet is not ACK-ed at
the TCP level, and the remote host stop sending further packets until this
one is retransmitted.
What is the relevant parameter to tweak, so that the error is encountered
and the packet -- retransmitted _before_ the other packets stop flowing?
Also, what could cause the fairly regular dropping of the packets?