Subject: Ftp throuput rates for dial-up PPP modems.

From: [email-masked] (Nelson C. L. Pedrozo)
Date: Mon, 1 Jul 1996 17:03:56 -0300

Hello WU list,

  I'm part of an ISP and am currently facing the following problem:
My clients, using dial-up PPP, can't seem to get more than 1/4's worth
of their total modem throughput (14400, for example), when transferring
via ftp. Any special reason why? I suspect the ftp protocol itself, but
can't be sure.
  Let me illustrate:

	14400 modem = 1.8 kbytes/sec --> user gets roughly 0.4 kbytes/sec.
	28800 modem = 3.6 kbytes/sec --> user gets roughly 1.0 kbytes/sec.

  What's odd about all this is that if you use windows 95, and bring up the
modem monitor, it *shows* throughput that nears the modem's full throughput.
It's just the ftp-data part that is much less. 

  Any clues, lights, insights, hints?

   Thanks,

			Nelson C. L. Pedrozo

---

From: "W. James Showalter" <[email-masked]>
Date: Tue, 2 Jul 1996 09:09:33 -0400 (EDT)

For SLIP/PPP connections using TCP things like the MTU size and the TCP 
window size are important.  Also, depending on the usage and transfers it 
is possible to get significantly better thruput in one direction vice the 
other.  For our Communication Servers and our Winsock clients we use an 
MTU of 600 and a TCP window of 4095.  Some experimentation may be in 
order to determine the best settings.

Also keep in mind that some of the bandwidth is gobbled up by protocol 
headers.  And the fact that the modem appears to max its transfer rate is 
that you could be doing lots of TCP retransmits which would reduce your 
effective thruput at the application level.

Good luck!
Jim