dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
1
share rss forum feed

bernardc

join:2009-12-13
Berkeley, CA
reply to bobjohnson

Good info

Thank you, Bob. Now we're getting somewhere. I'll be interested to find out what specifically those reasons are for it always being lopsided.

You're right that the low frequencies upstream, being around 5% of the downstream, is an important limitation. The theoretical limit, called the Nyquist rate, is a bitrate of twice the frequency.


bobjohnson
Premium
join:2007-02-03
Orlando, FL
Reviews:
·AT&T U-Verse
·T-Mobile US
said by bernardc:

Thank you, Bob. Now we're getting somewhere. I'll be interested to find out what specifically those reasons are for it always being lopsided.

I'm just sharing the IM messages instead of passing it on in my own words.
Me (8/26):
so why would you guys not be able to get the upload symmetrical?
Phil (8/26):
It's not that we won't be able to, tech speaking. Docsis will get there if they want it to but the plant will not be able to. The system is shared with so many different things and rr is a small part. We already have symm fiber to business, whatever they want basically. Even when we go sdv and get rid of analog there will still be a lower usable amount of bandwidth for return bc of interference and other variables that are not in the labs but are in real life where they r deployed.
Phil (8/26):The system and specs were designed to send data to the sub and that's the way it will always be. We're basically retroing a 1 way design so eventually we won't be able to go any further. Sorry for writing a book. Have a good night
--


bernardc

join:2009-12-13
Berkeley, CA
Thank you again Bob for further good info.

(RR,
Do they still run the Fort Bragg steam train? Back in '89 it had the best whistle operator I'd ever heard.)


JigglyWiggly

join:2009-07-12
Pleasanton, CA
i thought it was just because there is less frequency devoted to the upstream?

harald

join:2010-10-22
Columbus, OH
kudos:2
reply to bernardc
An administrative decision in 1948 set the low end of the TV spectrum at 54 MHz. When 2-way cable systems were developed, that left only the frequencies below 54 MHz for the upstream and a guard band.

On the downstream side, the bandwidth is allocated between cable TV channels and Internet

On the upstream side the frequencies are allocated to cable modem upstreams (set-top box control data, FM radio, and cable telephone don't take up much bandwidth).

So the limitation is the amount of bandwidth available. The amount allocated for both up and downstream is decided by the cable companies.

Since the cable plant is strictly an analog system, changing the frequency break becomes very difficult.


RR Conductor
NWP RR Inc.,serving NW CA
Premium
join:2002-04-02
Redwood Valley, CA
kudos:1
reply to bernardc
said by bernardc:

Thank you again Bob for further good info.

(RR,
Do they still run the Fort Bragg steam train? Back in '89 it had the best whistle operator I'd ever heard.)

They sure do, and it's better than ever! I'll IM you all the goodies lol