ComTel Electronic Systems GmbH
- German manufacturer of ISDN routers.
- http://www.sonictelecom.de/index.php?parent=37&sub=yes&idcat=37&lang=2&namesub=Start

Dan Kegel's ISDN Page
- Dan Kegel's ISDN Page
- http://alumnus.caltech.edu/~dank/isdn/

Phil McKerracher's ISDN tutorial
- Designed to quickly bring a novice up to speed. Includes breakdown of ISDN functionality and networking.
- http://www.mckerracher.org/isdn

Controlware GmbH
- Offers ISDN backup solutions, video surveillance and fibre optic solutions, training, consultantancy, maintenance and support.
- http://www.controlware-products.com

ShareISDN
- Device to share the functions of an ISDN card with other users in a network.
- http://www.shareisdn.de/

CAPI 2.0 - the ISDN interface
- COMMON-ISDN-API: CAPI - the ISDN interface
- http://www.capi.org

Cause Codes
- Netopia ISDN router information, Cause Codes or ISDN errors.
- http://www.netopia.com/support/technotes/hardware/NIR_044.html

ISDN Tutorial
- A technical introduction to ISDN - history, terminology, protocol, references and ISDN book store.
- http://www.ralphb.net/ISDN

3Com
- Support tips for 3Com's ISDN products.
- http://infodeli.3com.com/infodeli/tools/isdn/spt-tips/index.htm

US West
- glossary of terms used by the telco in the ISDN arena
- http://www.uswest.com/products/data/isdn/isdn_glossary.html

Patapsco Communications
- Products include leased line backup, aggregation, protocol conversion and bandwidth on demand. Designed for commercial users, carriers and PTTs.
- http://www.patapsco.co.uk/

eyeSDN beäugt Ihren ISDN-Verkehr
- Schicht-1-Monitor am S0-Bus des ISDN
- http://www.mosesele.de/eyesdn/