a bane of my existence. moving on....

ISDN Protocols
E - Applies to ISDN on an existing phone network.
I - Concepts, terminology, and services
Q - Switching and signaling

ISDN Function Groups
TE1 - Terminal Endpoint Device type 1. A BRI that understands ISDN standards.
TE2 - Predates ISDN standards. You have to use a TA (terminal adaptor) to generate BRI signals for a Cisco interface.

ISDN Reference Points
There are four different reference points to define logical interfaces between functional groupings such as TAs and NT1s.
R defines the reference point between non-ISDN equipment and a TA.
S defines the reference point between user terminals and an NT2.
T defines the reference point between the NT1 and line-termination equipment in a carrier network. This is only used in North America where the NT1 function isn't provided by the carrier network.

god, that's enough. I don't want to think about it....