In my CCNA training in 2007ish we actually got to use an ISDN simulator of some sort. It was a large physical box. I think you can buy them on eBay still. Pr

In my CCNA training in 2007ish we actually got to use an ISDN simulator of some sort. It was a large physical box. I think you can buy them on eBay still. Pretty sure this is no longer on the CCNA unfortunately. Maybe just a small mention.