How to buffer packets between a 1.5mb/sec and 24kb/sec connection

How to buffer packets between a 1.5mb/sec and 24kb/sec connection

Post by Miles Ogde » Wed, 15 Oct 1997 04:00:00



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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How to buffer packets between a 1.5mb/sec and 24kb/sec connection

Post by Miguel Cr » Wed, 15 Oct 1997 04:00:00



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.

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.

You may want to look into ftp proxy servers. If the difference in speeds
between the two links is great, though, nothing will beat skipping PPP
altogether and just zmodeming the file from your local server.

miguel

 
 
 

How to buffer packets between a 1.5mb/sec and 24kb/sec connection

Post by Adam William » Wed, 15 Oct 1997 04:00:00


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.

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.  Yes, the portion of the ppp server
bandwidth I get now is a mere slice of the ethernet connection, but it's
still considerably faster than the modem.

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.

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.

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How to buffer packets between a 1.5mb/sec and 24kb/sec connection

Post by Miguel Cr » Thu, 16 Oct 1997 04:00:00



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.

And the University of Michigan, where I spent my halcyon undergrad days, has
a bundle of T3s you could sweep out a barn with. None of that did anything
about the congestion elsewhere in the Internet, or the various chokepoints
between me and a given interesting site. About the only places I could get
truly serious speed to were other Big 10 schools. No big deal, I just
thought the original poster was escalating assumptions into observations
with his claim of "usually" seeing 1.5Mbps. If you "usually" see 1.5Mbps to
anywhere farther away than you could bike without stopping for a drink, then
the internet has come a long way since this morning.

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.

You're talking about a lot of buffering there, sir. Not too many users have
to be downloading multi-megabyte files before you've eaten through several
pounds of SIMMs. Your average terminal server is just not up to the task.

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

 
 
 

How to buffer packets between a 1.5mb/sec and 24kb/sec connection

Post by James P Blandin » Thu, 16 Oct 1997 04:00:00


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.

well, if you had 48 (an average amount) users logged in and the NAS had
to buffer every packet coming in at (hypothetically) 1.5mb/s for each of
them that would present quite a memory problem...most NAS's only come
standard with 4 megs of ram...
 
 
 

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