a/b interface
The a/b interface is a two- wire copper interface of the analog telephone network for operating analog telephones or other terminal equipment such as modems, fax or Btx devices that are operated on the analog telephone network. The designation "a" and "b" comes from the consecutive designation of the two wires of the copper twisted pair.
a/b interfaces can also be used in the ISDN network, via a TA a/b terminal adapter. Unfortunately, not all ISDN features can be implemented by such a terminal adapter. However, you can connect all terminals that have an a/b interface directly via the terminal adapter. Group 2 and 3 fax machines, modems and telephones.
When transmitting via ISDN systems, the respective terminal device must be marked. For this purpose, a terminal selection digit is set in the terminal adapter. The combination between terminal selection digit and service identifier only allows connections between compatible terminals.