LinuxSA Mailing list archives

  From: Simon Hackett <simon@internode.com.au>
  To  : Evan Bourlotos <evan@cs.adelaide.edu.au>
        Andrew Reid <andrew.reid@plug.cx>
        Jason Tan <jason@rebel.rebel.net.au>
  Date: Fri, 11 May 2001 15:58:41 +0930

Re: CABLE net access in SA

At 10:51 AM +0900 11/5/01, Evan Bourlotos wrote:
>  >> We do a bit of gaming and seem to get pings as low as 30ms in some
>  >> servers such as the wireplay ones, and no noticable packet loss even while
>  >> someone was streaming video.

circa 20-22 ms to my home ADSL link from the office - but what's an 
extra 8 milliseconds between friends, eh? (answer: almost a third 
faster :) )


>  >
>  >For the time being :-)
>  >
>This problem will exist with ADSL as well I think ultimately the capacity
>of the network will be pushed with either. Underconfigured infrastructure,
>bad interconnects etc will cause this!

This is a bit deceptive.

There are common areas of -potential- bottleneck in both mechanisms - 
these include the amount of intra-exchange bandwidth, and the size of 
the 'feeder tail' into the exchange network from the ISP.

However, there is a one point of substantial difference between the 
two technologies, and that is the actual 'local loop' part of the 
network.

In ADSL, each 'last mile' really is a genuine private link - sharing 
your phone line. So on that 'last mile' you are the only person 
competing for the bandwidth.

On Cable, the 'last mile' is run on shared coax. Shared between you 
and a few hundred others in typical installations - up to a few 
thousand others if Telstra are doing things 'on the cheap' (and I 
don't know if they are or they aren't).

On that shared coax, your use of bandwidth directly impacts the 
remaining bandwidth for others. So your next door neighbour, when 
he's signed up, *will* affect your performance. And your other 400+ 
neighbours similarly.

Also, the back-channel on cable is a real bottleneck - the cable 
systems installed by Telstra and Optus are turned into 'cable modem' 
capable ones by installing transmission amplifiers in the return 
direction which 'hop' over each forward-direction amplifier and allow 
signals to pass back the other way. The bandwidth of this return 
channel is often in the hundreds of kilobits per second (only) range 
- half a meg to one meg being quite common in cable systems.

That's still shared between you and your several hundred neighbours.

This is why they don't want you to run servers. As soon as you start 
generating significant outbound data flow, you'll grind your entire 
neighbourhood to a halt.

This problem is so prevalent that in the USA, Pacific Bell are 
running a successful ad campaign for ADSL which uses exactly this 
problem as its selling proposition for ADSL.

Go to http://www.adcritic.com and type 'dsl' into their search box 
and hit return to see these adverts. I recommend it, they're very 
funny (of course, this might take a long time unless you have an ADSL 
connection - ahem)

All the other bottleneck potentials remain real (for ADSL as well as 
cable), but the core point here is that all the other bottlenecks 
-can be improved- if they become a factor, by adding more bandwidth 
at the bottlenecked point - which is easy to do, and viable (unless 
you are selling unlimited downloads - e.g. Telstra - in which case 
you won't do it because the limited bandwidth is a cost control 
mechanism).

But that issue of what happens when your next door neighbour goes 
wild on cable and screws you over - that's very real, and it'll hit 
alright. It always does, eventually.

All this means is this - enjoy it while it's fast, and understand 
that you have ADSL as an option to move to if it gets un-fast in the 
future.

Simon


---
Simon Hackett, Technical Director, Internode Systems Pty Ltd
31 York St [PO Box 284, Rundle Mall], Adelaide, SA 5000 Australia
Email: simon@internode.com.au  Web: http://www.on.net
Phone: +61-8-8223-2999          Fax: +61-8-8223-1777

-- 
LinuxSA WWW: http://www.linuxsa.org.au/  IRC: #linuxsa on irc.linux.org.au
To unsubscribe from the LinuxSA list:
  mail linuxsa-request@linuxsa.org.au with "unsubscribe" as the subject