On Thu, Apr 27, 2000 at 05:58:33PM -0400, Bruce E. Harris wrote:
-> Thanks for the advice, Linux is back, firewall is working, life if good.
->
-> I did get an email from my ISP telling me I am running at the max home user DSL
-> speed the offer. Still, why would a 300K file take 30 sec to d/l if my speed is
-> suppose to be running at over 400kps?
There are a number of possible reasons.
First, speed rate is usually expressed in bits per second. A 300k file is
some 2,400K bits.
Second, that's the raw data rate, including overhead such as PPP and IP
frame headers. The transfer protocol has its own overhead, such as ACKs
and NAKs for file chunks received or not received. Data may be mangled en
route (e.g. a collision on an Ethernet leg), requiring a
retransmission. There may also be time lags between the time a NAK is
transmitted and the time the replacement packet is sent. Etc. Your payload
rate will be noticeably less than the data rate.
Third, there may be some other thing between your computer and the source
host which is the real bottleneck, say an overloaded hub or switch
somewhere in the net.
When I worked at HP, we set up two PA-RISC workstations with a 100BT card
each, and a hub. We then tuned the IP stack for the job at hand, which was
to see how fast we could push data through the 100BT network. Using UDP,
which has a lot less overhead than HTTP or FTP, we saw throughputs of
60-80% of the rated speed of 100Gb.
So while I'm not wild about the speed you are reporting, I suspect you
don't have a serious problem.
--
-- C^2
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