LinuxSA Mailing list archives

  From: Mark Newton <newton@atdot.dotat.org>
  To  : Daryl Tester <dt@picknowl.com.au>
  Date: Sun, 26 Nov 2000 15:52:13 +1030

Re: ADSL Enabled Exchange Areas: Updated 20/11/2000

On Sun, Nov 26, 2000 at 02:16:44PM +1030, Daryl Tester wrote:

 > Mark Newton wrote:
 > 
 > > If you buy an ISDN card for your Linux box, you can place 64k calls through
 > > the NT1 interface which are tagged as "voice" calls (i.e.: 18c).  This
 > > effectively gives you a flat rate 36c 128kbps call to ISPs which support
 > > it.
 > 
 > I'm curious about this.  I was under the impression that the way
 > access servers differentiate between "data" and "voice" calls over
 > ISDN (and hence the decision to route to a modem or bypass the modem
 > straight to the PPP controller) was on the basis of that flag (bearer
 > capability?  Been a while since I mucked with ISDN too).  How does
 > this work then?  <Daryl prepares for his reality to be skewed yet
 > again>

The Bearer Capability flag is set by the end-user, not the network.
It's used to tell the network about the kind of bearer you want, 
rather than being used by the network to describe the bearer you have.

So, if you make a call with the bearer capability flag set to "Voice"
and then proceed to pump a 64k bitstream down it, that's perfectly fine.

Theoretically, BC=Voice means the network is free to do things like 
compression, which will fuck up data but preserve voice.  In practice,
there's so much backbone bandwidth in telco networks that they never
bother.

 > > Yup - You just need to fool Telstra into thinking you're making voice
 > > calls so they won't extort $1/hour out of you.
 > 
 > Rather ironic, as they're both 64K point to point connections (plus,
 > with a data call, you're not using codecs at the far end to attach
 > to the PSTN network - you'd think it'd be cheaper. :-).

Exactly what I've been saying for years.

   - mark

--------------------------------------------------------------------
I tried an internal modem,                    newton@atdot.dotat.org
     but it hurt when I walked.                          Mark Newton
----- Voice: +61-4-1620-2223 ------------- Fax: +61-8-82231777 -----

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