On 31 Aug 2004, at 12:39, John P. Looney wrote:
> On Tue, Aug 31, 2004 at 12:34:14PM +0100, Niall O Broin mentioned:
>> A standard PCI modem will not do what Asterisk does. Asterisk is
>> basically Linux based telephone exchange software, and to make a
>> telephone exchange from a PC requires software and line cards - a
>> modem
>> is NOT a telephone line card.
>> You being a ex-telecom engineer...what's the difference between a
> modem
> and a line card ?
>> They are both DSPs, I suppose...is it the ability to switch a circuit
> ?
> My brain hurts, just trying to think how analog signals are routed.
Well, a modem IS a line card, of a sort, but of a specialised sort
which enables you to extend a serial data channel over indefinite
distances over an analog phone line. A line card in Asterisk terms
connects to an analog or ISDN phone line, or various types of
telephone. I presume that these line cards are essentially D/A and A/D
converters for voice frequency signals - at least that is what they are
in grown up digital telephone exchanges.
Niall
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