AT&T's ISDN Point-To-Multipoint Implementation

CCITT specifies that more than one ISDN user terminal may be equipped on a Basic Rate Interface. This configuration is commonly known as a point-to-multipoint configuration, or as a Passive Bus. Until recently, no specification existed that allowed messages to address specific terminals on a Passive Bus. Another important factor is optimizing the use of the two B-channels when there are more than two terminals equipped on the Passive Bus.