About PSTN-ISDN remote access

Hello...
I have an exercise in the University and i have some questions about remote access using dial in.
Can the site with remote server provide both pstn and isdn access? I read some articles and i conclude that the site must have ISDN PRI lines and digital modems. I've also read that if the remote user wants to have 56kbps speed the server needs to be conected with the CO with a V90 Digital switch (and of course the clients must have V90 modems). Is these true? The remote users will be assigned IPs by the DHCP?
Thanks

I can answer some of that. Firstly, the maximum you can get using analogue modem-to-modem links is 48k. To get the full 56k you are correct that the central end of the link needs to be digital. Also there is no reason why a dial-in server cannot support several access technologies, for example you could have ISDN and ADSL or ISDN and analogue dial-up. You just need the approporiate hardware and comms provision