Can you pass if you know very little regarding ISDN?

in CCNA & CCENT
I know very little about ISDN, and usually just do really bad on the ISDN section of my transcenders. Is there a significant amount of ISDN material on the test? (enough to make you fail if you suck at it?)
Thanks
Thanks
Comments
With that being said, you can study only key terms for ISDN and still pass the CCNA but you will be selling yourself short for companies that rely on ISDN.
Is there anyway I can simulate an ISDN connection in my lab so I can really practice it? How much do ISDN connections cost? I suppose I could get one setup at the house for a month or so just for practice purposes?
Thanks again