[svlug] Reprise: Adjusting retransmission parameters

[Eric Nickell]

Karen Shaeffer wrote:
> 
> On Mon, Feb 19, 2001 at 07:17:27AM -0800, Eric Nickell wrote:
> >
> > Is there no way to recharacterize the retransmission parameters?
> >
> > > The main problem is that I'm using Sprint Wireless. (No DSL, no cable
> > > modems available in my area.) The medium is very bursty. High
> > > throughput, long latency, and dropped packets ranging from 1-2% to more
> > > than 50%, depending on time of day.
> > >
> > > I suspect (but don't know for sure) that the dropped packets are being
> > > lost from my house to their antenna, not the other way around.
> > > Moreover, I suspect that I could improve the situation (not fix, just
> > > improve) by adjusting the time my linux box waits before retransmitting
> > > a packet.  I have looked through the documetation for the /proc
> > > variables, but if there's something relevant there, I didn't recognize
> > > it.
> > >
> > > My setup is a fairly vanilla install of RH7.0, sitting behind a Ravelin
> > > VPN box.
> 
> Hi Eric,
> 
> Did you look here?

Karen,

Thank you for the reply.  Yes, I had already looked there. (Well,
actually, I had been examining a copy on the web.)  I have just reviewed
/usr/src/linux-2.2.16/Documentation/networking/ip-sysctl.txt since I'm
writing this from work.  (I am running a 2.4 kernel at home where I have
the problem.)

I've looked at each of the variables and had the guy here at my office
who is the Sun networking guru scan it as well.  I am, unfortunately,
ignorant of the most basic understanding of tcp/ip.  In any case,
looking through the documentation variable by variable, I did not see
anything that looked like the obvious thing to try.  A howto on the net
also suggested that it was a bit dangerous to go poking values
indiscriminately into the networking stuff. (Dangerous in the sense of
leaving your machine in an unbootable state.)


> /usr/src/linux-2.4.0/Documentation/networking/ip-sysctl.tx
> 
> It defines all your /proc options in there. You probably want to use a
> 2.4.x kernel--preferrably 2.4.1 or newer. After you look around in
> there, come back and ask additional questions with a bit more specificity.

I'm afraid that I cannot produce questions with more specificity.
Possibly, is there further documentation on any of these variables, esp
those marked "undocumented" in the group that includes tcp_retries1,
tcp_retries2, tcp_max_delay_acks, tcp_fin_timeout, tcp_max_ka_probes,
tcp_hoe_retransmits, which are listed as "Undocumented for now"?

It's looking bleaker and bleaker...

Eric Nickell