Dial-up is an analog signal, and is limited to 53 Kb/s. Some users only get around 45-50 Kb/s, most are in the 24-40 range depending on the distance between the modem and the local telephone central office.
ISDN is a fully digital signal with a bit rate of 64 Kb/s per channel. Two B (Bearer) channels will give 128 Kb/s. It'll be more stable than dial-up as it's an always on signal. But it takes an ISDN modem which is more expensive than a dial-up modem. And the service is more expensive.
In the long run, ISDN is faster than dial-up.
But cable tops them all. My Comcast gives me a 4 Mb/s connection, faster than a T-1.
Good luck,
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What advantage does ISDN have over Dial up (normal telephone line)

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