[ILUG] ISDN adaptors

[Brady, Padraig]

Theoretically I suppose the same thing could
be done with ISDN TAs as for winmodems. I.E.
take some of the logic out to be implemented
by code running under the hostOS. For the winmodem
(which is little more than a mono sound card with 
a phone jack) the signal is sent to the windows
driver to process. The reason there are no Linux
drivers is that it would be impractical to create
one without releasing the source code and for this
setup the driver really is the modem, the details
of which the manafacturers obviously want kept secret.

Anyway the same principle could be applied to the TA I 
suppose where the digital bitstream is passed up to the driver 
to process (L1, L2 and L3), hence removing the need for a
CPU on the PCI card. The (small) disadvantages I can see to 
doing this are:
	1. There are different flavours of ISDN everywhere
	   (so much for standards!), and you would need 
	   configurable parameters for the ISDN TA driver,
	   rather than making TAs hardcoded for particular markets.
	2. Since windoze\Linux are not realtime OS' there
	   could be loads of reliability issues, as the data
	   rate for ISDN is up to 192Kbps?

So it comes down to interfaces, whether they're documented
or not. In the winmodem case no, for ISDN cards ?
OK looking around on the net to see if anyone has done
cheapo cards, and if so are there documented interfaces to them?...... 
Hmm found this:
http://www.isdn4linux.de/faq/i4lfaq-5.html
Interesting! The summary is the cheapo cards without CPU are 
known as passive, and the full cards are known as active.
It's actually the opposite to the winmodem situation! The
more sophisticated cards (active) CAN have non-standard
interfaces, whereas the passive cards USUALLY use common 
chipsets which can be driven with a generic driver.

So in summary, YES you can have ISDN cards that just work
with a specific OS. Very few passive cards have undocumented
interfaces and so this doesn't apply, but more, active cards
have undocumented interfaces and so there is more of a problem
here.

Padraig.

-----Original Message-----
From: Donncha O Caoimh [mailto:donncha.ocaoimh at tradesignals.com]
Sent: 07 April 2000 14:20
To: ilug at linux.ie
Subject: [ILUG] ISDN adaptors


Please excuse my complete ignorance in this area, I've a small question
about ISDN cards.

Can any parallels be drawn between PCI modems and PCI ISDN adaptors? ie.
PCI modems are generally winmodems, same with PCI ISDN adaptors? (I
doubt it but I'm just wondering..)

Donncha.

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