EAP-TTLS platform

Goodmoorning to everybody: I want to mount a EAP-TTLS authentication platform, with a LDAP directory in the autentication&autorization server. I have read that having a LDAP directory for autenticating users could determine the autentication methods to use. So can't I use EAP-MD5 inside a EAP-TTLS tunnel ?? Only PAP, CHAP, MSCHAP methods should be used inside the tunnel?? Which are the differences between them?? I have beeing searching and I haven't found information. Could anyone give me some information about please?? Lots of thanks.