Glauser, Fred, and Eric Quinn. CCNP BCRAN Exam Cram 2 , 2003, Que, ISBN: 0-7897-3020-0.
Flanagan, William A. ISDN: A Practical Guide To Getting Up And Running , 2000, CMP Books, ISBN: 1578200482.
ISDN Tutorial: http://www.ralphb.net/ISDN/
Glauser, Fred, and Eric Quinn. 
ISDN Tutorial: http://www.ralphb.net/ISDN/ 