Rogers explains ???shaping' policy

[James Knott]

Lennart Sorensen wrote:
> On Thu, Jun 12, 2008 at 06:00:18PM -0400, James Knott wrote:
>> There are also technical reasons why asymmetrical service is easier to 
>> provide.  One is the amount of bandwidth allocated to upload, bearing in 
>> mind this technology was developed long before cable internet access.  
>> Another issue is resolving contention between users.  When downloading, 
>> the data is simply sent out on the wire as quickly as possible.  On the 
>> upload side, there has to be some method of ensuring all users properly 
>> share the available bandwidth.
> 
> Yeah certainly cable modems have a large pipe for downloads shared
> between all users on a segment, while uploads are in multiple smaller
> channels.  Given not everyone is going to be downloading at the same
> time, it does mean you get more download than upload speed.
> 
> For ADSL I am not sure.  I don't believe there is any real difference in
> line quality required for say 5MBit/800kbit ADSL versus 2.2Mbit SDSL,
> but maybe that isn't true.  Of course many people would probably pick
> the ADSL 5Mbit over the SDSL 2.2Mbit given the choice, while a few would
> want the SDSL instead.
> 

ADSL splits the spectrum used into upload and download directions 
(similar to what cable modems do), whereas SHDSL uses echo cancellation 
so that both directions use the same spectrum.  However, that method is 
also more expensive than the simple filters used within the ADSL modem, 
which are not the same filters as used to separate regular phone service 
from ADSL.  The available bandwidth for either is dependent on cable 
distance and quality.  You can also get SHDSL sets that support multiple 
pairs, for increased bandwidth adn reliability.  I've never seen that 
with ADSL, though technically, it's certainly possible.


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