Rogers explains ???shaping' policy
James Knott
james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org
Thu Jun 12 23:18:49 UTC 2008
Lennart Sorensen wrote:
> On Thu, Jun 12, 2008 at 12:38:13PM -0400, CLIFFORD ILKAY wrote:
>
>> What is so special about uploaded vs. downloaded packets? Are uploaded
>> packets "heavier"? Bandwidth is bandwidth. I should be able to specify
>> the QoS so that I can dynamically allocate the proportion of up/down
>> rates as my needs change. All Rogers has to tell me is that I can burst
>> up to some transfer rate. I'll take care of the rest.
>>
>
> Actually DOCSIS was just misdesigned. The amount of bandwidth allocated
> for uploads from customers is much much lower than the bandwidth
> allocated for downloads. It is I believe much more asymetric than ADSL.
>
That's due to the way cable bandwidth was set up, long before there were
cable modems. Way back in the B.C (before cable modems) cable TV carried
just that TV and did so (with minor variations) using the same spectrum
as broadcast TV. That spectrum starts at 54 MHz and goes up from there.
Later, when cable companies started getting interested in offering
other, interactive, services, they were placed at frequencies below 54
MHz and used filters to separate the two directions. So, anything
upstream has to fit in that space below 54 MHz, while downstream can use
any part of the spectrum above 54 MHz up to a few hundred MHz. While
some of the details have changed since then, the same situation applies,
when you try to fit TV and upload data on the same piece of coaxial
cable. There isn't much DOCSIS can do about that. This problem does not
exist on the fibre part of the network.
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