Inter-Tel AXXESS Manual page 130

Specifications
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INTER-TEL AXXESS
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Page 2-62
MANUAL VERSION 11.0 – May 2008
U Interface (User Interface): A connection coming into the system from an external
transmission system (ISDN provider), which is typically a Central Office [local
exchange]. (BRI U interface is a two-wire connection and PRI U interface is a four-wire
connection.) All BRI ISDN devices with a U interface normally have an NT1 built-in to
interface directly to the Network (ISDN provider or Central Office/Local Exchange).
T Interface (Trunk Interface): A four-wire connection between the NT1 that termi-
nates the transmission coming from the Central Office [local exchange] and the NT2
that connects to the user's TE. This interface is located at the customer site.
S Interface (Station Interface): A four-wire connection between the NT2 and the
user's TE. This interface is located at the customer site.
S/T Interface (Station/Trunk Interface): Because the BRI Station card (BRS) can be
programmed for either a station port (S) or a trunk port (T) the interface, LIT is referred
to as the S/T Interface.
Basic Rate Interface Terminology