Very Computer

I have access to a ppp server and modem.  Accessing the internet
directly from the ppp server usually gives 1.5mb/sec.  Accessing the ppp
server directly from the modem usually gives 24kb/sec.  When I try to
access the internet from the modem through the ppp server, the
connection speed is sporadic, usually slowing to less than 10kb/sec
especially when downloading large files.  Why does the speed decrease so
much when the two speeds are combined?

I have found it faster to download large files directly to the ppp
server.  Then, download them from the ppp server to the modem through
zmodem.  Is there any ppp server that downloads packets at 1.5mb/sec and
buffers them, while the modem downloads the buffered packets at a
constant 24kb/sec.

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Quote:>I have access to a ppp server and modem.  Accessing the internet
>directly from the ppp server usually gives 1.5mb/sec.

Quote:>Why does the speed decrease so much when the two speeds are combined?

Quote:>Is there any ppp server that downloads packets at 1.5mb/sec and
>buffers them, while the modem downloads the buffered packets at a
>constant 24kb/sec.

miguel

Quote:> >I have access to a ppp server and modem.  Accessing the internet
> >directly from the ppp server usually gives 1.5mb/sec.

> "Usually"? Or did you decide that must be the case since that's what a T1
> is? There aren't so many places on the internet you can get a sustained
> 1.5mbps from, even if you've got multiple T3s.

Quote:> >Why does the speed decrease so much when the two speeds are combined?

> One major reason is probably because the acknowledgement packets are
> generated on your modem-connected machine. So the remote server may send
> some data, then wait to hear that it went okay before sending the next
> chunk. Because of the higher latency of the two connections (your modem
> connection to the ppp server, and the "1.5mbps" connection from there to the
> rest of the net), this takes longer than you might like. In turn this
> results in a stopping-and-starting cadence which slows down the whole
> process.

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Quote:>The ppp server is on a university campus.  My previous experience with
>university connections is that they're extremely fast.  Byu.edu has a
>48mb/sec DS3 connection.  An ethernet connection on that campus
>routinely got 800mb/sec for me.

Quote:>Damn.  You can't beat the system.  Why can't the ppp server buffer the
>packets and send back acknowledgement packets itself?  Then a second
>process could send them to my modem and wait for its acknowledgement
>packets without stopping and starting the internet download.

A proxy server brings the file system into the equation, in effect using its
hard disk as a really large buffer (and often avoiding duplication of
identical data).

miguel

Excerpts from netnews.comp.os.linux.admin: 14-Oct-97 Re: How to buffer

Quote:> Damn.  You can't beat the system.  Why can't the ppp server buffer the
> packets and send back acknowledgement packets itself?  Then a second
> process could send them to my modem and wait for its acknowledgement
> packets without stopping and starting the internet download.