Editing Terminal adapter (section)

== ISDN ==
In [[ISDN]] terminology, the ''terminal adapter'' connects a ''terminal'' (computer) to the ISDN network. The TA therefore fulfills a similar function to the ones a [[modem]] has on the [[Plain old telephone service|POTS]] network, and is therefore sometimes called an '''ISDN modem'''.  The latter term, however, is partially misleading as there is no [[modulation]] or [[demodulation]] performed.

There are devices on the market that combine the functions of an ISDN TA with those of a classical modem (with an ISDN line interface).  These combined TA/modems permit connections from both ISDN and analog-line/modem counterparts.  In addition, a TA may contain an interface and [[codec]] for one or more analog telephone lines (aka ''a/b line''), allowing an existing POTS installation to be upgraded to ISDN without changing phones.<ref name=":0" />

Terminal adapters typically connect to a [[basic rate interface]] ([[S interface|S0]], sometimes also  [[U interface|U0]]).  On the ''terminal'' side, the most popular interfaces are [[RS-232]] serial and [[USB]]; others like V.35 or [[RS-449]] are only of historical interest.

Devices connecting ISDN to a network (e.g. [[Ethernet]]) commonly include [[router (computing)|routing]] functionality; while they technically include a TA function, they are referred to as (ISDN) [[router (computing)|router]]s.