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From: Walter Roberson <roberson@hushmail.com>
Organization: Canada Eat The Cookie Foundation
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Subject: Re: Check internet connection status using Matlab
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Date: Sat, 18 Oct 2008 22:03:18 -0500
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Jan Simon wrote:
> Dear Walter Roberson!

>> Checking to see whether you are "connected to the 
>> internet" is, in practice, a singularly useless
>> thing to do.

> Perhaps it is enough for Jaime Zamora to check, if he is not disconnected. E.g. for
> a task like "start the mail program only, if it looks, like the machine has contact".

In Canada and the USA, it is standard practice for residential ISPs to block
outgoing access to all mail servers except the ISP's own mail server. This blocks
PCs infected with viruses or trojan horses from being able to run mass spam
or virus-sending attacks on systems in the rest of the world. You might be
"connected to the internet" and yet not be able to reach your mail server
of choice (and most of the ISPs did not bother to notify customers before
they started doing this kind of blocking.)

As I said before, checking whether you are "connected to the internet" is,
in practice, a singularly useless thing to do. If you have a specific
activity you want to undertake, then check to see whether you can do *that*,
not whether you are "connected to the internet". If you want to know
whether your PPPoE client is loaded and talking to your ADSL modem,
then check -that-.