ISDN on 2500's
I need to do ISDN on my 2500 routers, the question is what type of connections do I need to do this. Can I simply use a straight/crossover cable from one router BRI to another? I currently have a 2521 Router with a ISDN BRI Interface, I also have a 2525 which is a modular router with no modules. What type of equipment do I need to perform an ISDN lab between these two routes if possible?