&gt; The demarcation is generally clearly marked (plastic box often called a &#x27;network interface device&#x27;) and is almost never located at the modem itself.<p>Yes, but if cable companies always provided and required you use their cable modems, then there would be a clear demarcation point, the cable modem.  Whether it&#x27;s usually inside or outside is irrelevant (and &quot;usually&quot; in this case is debatable.  I&#x27;ve worked at multiple business locations where it&#x27;s inside, because there is a location dedicated for it).  Of course there <i>isn&#x27;t</i> a clear demarcation at the cable modem, as many cable companies allow you to use your own cable modem instead of theirs, which is why I said the issue is &quot;muddied&quot;.