Some more numbers and some technical details ;)

As far as I know the cap ceiling is imposed on the modem itself. This does not imply that hooking up more computers on a router/switch/hub will allow you to download/upload more because of the data transfer has a bottleneck at the cable modem.

Comcast caps @375kBytes/sec

30days = 2592000sec

Therefore in a month the maximum transfer u can do over a cable modem is:

375kBytes/sec X 2592000sec = 972 GigaBytes

Before we start going into more details and get too technical about how cable modem works, please note that upload and download caps are different. For a cable modem, imagine just a single pipe that can carry water in two directions from point A to B. More water is going down from point A to the other end at point B. And less water is going from point B to point A. When this imaginary water is flowing from point B to point A the water going from point A to point B (in the opposite direction) will slow down because of the "forces" in the opposite directions that the water is flowing. Whenever water in is flowing at its maximum speed in one direction (say point B to point A), this "phenomenon" is called saturation. All this applies to the data flowing in a single coaxial cable as well (I don't want to get into extra details about this).

To simplify a lengthy explanation, a cable modem's upload saturates when it is uploading data therefore this clogs the download. To cable modem users note that whenever you are trying to send homemade movies to your relatives overseas, websites that you are browsing will load slower than usual. You could experiment with it by downloading some large file and uploading at the same time.

Are you ppl still awake? :)

If you are, let me continue,

Now, considering that 0.972 TeraBytes is the maximum you could transfer in a month (30 days) hypothetically. Recall that the upload cap Comcast HSI advertised is 256kbits/sec(also 32kBytes/sec. And also recall that the download is clogged when the upload saturates. Therefore you can never download 0.97 TeraBytes a month because it is only a hypothetical value. You could never see those webpages if your total upload is zero Byte. Furthermore, the bandwidth is shared so during peak hours your download never reaches the maximum ~1TB per month.

Conclusion: The anonymous network engineer at comcast is giving false information or exaggerating on subscribers that is downloading more than 1 terabyte per month since in a single month nobody could download more than 0.97 terabytes (unless comcast at his area sets the download cap at a higher limit) even when he is using multiple computers to download at the same time.

But as he said the limit that triggers subscribers to get those abuse letters were 100GB per month. Therefore, it is not impossible to get an abuse letter if u leave your computer on 24/7 downloading.

Be warned.

[ reply ]

Link to this comment: http://www.securityfocus.com/comments/articles/7940/24697#24697