U interface: For basic-rate
access in an Integrated Services
Digital Network (
ISDN) environment, a
user-to-
network interface reference point[?] that is characterized by the use of a 2-wire-
loop transmission system that (a) conveys
information between the 4-wire user-to-network interface,
i.e., the S/
T reference point[?], and the
local exchange[?], (b) is located in the servicing
central office, and (c) is not as distance sensitive as a service using a T interface.
Source: from Federal Standard 1037C