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Re: [PLUG] [OT] Fiber in PA
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There are a few conditions that make asymmetric linespeeds not only
feasible, but appropriate.
First, traffic patterns from home users typically include far more
downstream than upstream traffic. Upstream traffic is usually just their PC
sending web requests and the like. However, people do download lots of
stuff, so the higher downstream speed is desirable.
Second, there are equipment limitations that get in the way of high-speed
upstream. At the DSLAM, you have a situation where there is a controlled
environment. Therefore, your equipment can burn more power and still
survive. At home, you have a little plastic box with no fans, so you are
severely limited in the amount of power you can dissipate in there. This
means that the DSLAM is capable of higher transmit power than the DSL Modem
and can therefore transmit a higher datarate while still maintaining signal
integrity at the receiver. The modem, with a lower transmitter power, has to
transmit data slower in order to maintain a S/N ratio sufficient to avoid
Inter-Symbol Interference.
The problem that is growing with DSL is that people are uploading more and
more - sending music files, home movies, and pictures to family, and all
kinda other stuff that requires more upstream. Verizon, I believe, is
offering a cheap fiber access solution that has 15Mbps downstream and 2Mbps
upstream, basically tripling peoples' upstream rates. I just wish I could
get it where I am! :)
E
----- Original Message -----
From: "William H. Magill" <magill@mcgillsociety.org>
To: <plug@lists.phillylinux.org>
Sent: Thursday, December 09, 2004 9:27 AM
Subject: Re: [PLUG] [OT] Fiber in PA
>
> On 07 Dec, 2004, at 19:55, Kevin Brosius wrote:
>
> > That sounds strangely like the upper end of DSL (over copper, I'd
> > guess.) Low cost, and 768k up is the speed cap I've heard for every
> > DSL
> > line I've tried to quote around here.
>
> The 768K up link speed max is either a modem design problem or network
> design issue.
>
> It is not an inherent limitation of ADSL.
>
> The reason that virtually every ADSL network offers much higher
> download speeds than upload is because the amount of traffic involved
> is actually smaller!!!
>
> Yes smaller. The game that is played here is the "caching server" game.
> The probably is that "download" materials will be found on the cachinge
> server, and therefore NOT have to traffic the network backbone to the
> Internet. Whereas ALL upload traffic will have to traffic the network
> backbone out to the Internet. ... at least, that is the theory.
>
> Are there really twice as many hits on the caching server and therefore
> that much less of a load on the backbone between downloads and uploads?
> I don't believe that anyone has actually examined that part of the
> theory. I've never seen any published results.
>
> The upload/download tradeoff was also viewed from the "consumer" point
> of view -- very few consumers are interested in uploading anything more
> than an occasional email message... while they want to download LOTS of
> stuff all the time.
>
>
>
> T.T.F.N.
> William H. Magill
> # Beige G3 - Rev A motherboard - 768 Meg
> # Flat-panel iMac (2.1) 800MHz - Super Drive - 768 Meg
> # PWS433a [Alpha 21164 Rev 7.2 (EV56)- 64 Meg]- Tru64 5.1a
> # XP1000 [Alpha EV6]
> magill@mcgillsociety.org
> magill@acm.org
> magill@mac.com
> whmagill@gmail.com
>
>
>
___________________________________________________________________________
> Philadelphia Linux Users Group --
http://www.phillylinux.org
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>
___________________________________________________________________________
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Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
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