[rescue] Creating/Simulating/Emulating an old 1970s Bell Telephone Network

abuse at cabal.org.uk abuse at cabal.org.uk
Tue Aug 16 10:16:17 CDT 2005

Geoffrey S. Mendelson <gsm at mendelson.com> wrote:
> You might want to look at ASTERISK, an open source (linux based)
> PBX. You can get the cards relatively cheaply, two 4 port FXS
> (telephone), eBay clones, cards, two PIII or better X86 PCs

You don't even need that fancy a PC. I've got it running in production
on a 400MHz PII that also hosts mooli.org.uk shell accounts and the
Bastard Mailserver as well as some other stuff.

To drag it slightly back on topic, Asterisk should also run nicely on
a reasonable spec SPARC box, say a U5 or U30. I've not tried to
compile it on Solaris, but it's a slam-dunk on Linux. (If Debian,
aptitude install asterisk should just work, whatever the

> If you wanted to add an outgoing line, a 4 port FXO (exchange) card
> is also realtivly cheap, but a $20 (or less) Intel chipset soft
> voicemodem will give a single line at the expense of a PCI slot and
> CPU cycles.

*Certain* winmodems are driver-compatible with the Digium X100P, but
they're pretty crap. You can only have one X100P (or clone) per system
as a combination of bad design on both it and the x86 interrupt model.
(Each X100P generates 8,000 interrupts per second.)

The X100P doesn't work properly on anything other than US-style
telephone systems. You get lots of near-end echo in the UK, and this
sounds worse than you'd expect due to added VoIP latencies.

You're better off getting something like the Sipura SPA-3000 if you
want to connect to the phone system. It's a SIP device (so it's
effectively an extension on the Asterisk box) that has one socket to
plug a phone into, and another to plug into the PSTN. I've got a
SPA-2000 which gives me two phone sockets. (SPA units are about #100
each, so I guess about $150 in leftpondia.)

As a bonus, if you use an ATA instead of a Digium card, you're not
locked into using Linux like you would be with the X100P.

The SPA also has programmable impedance (plain resistive, or UK-style
complex impedance), so you can demonstrate the effects of mismatching
telco kit from different countries.

PGP key ID E85DC776 - finger abuse at mooli.org.uk for full key

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