Asynchronous Transfer Mode (
ATM) is, according to the
ATM Forum, "a
telecommunications concept defined by
ANSI and
ITU (formerly CCITT) standards for carriage of a complete range of user traffic, including
voice,
data, and
video signals". ATM was developed to meet the needs of the
Broadband Integrated Services Digital Network, as defined in the late 1980s, and designed to unify telecommunication and
computer networks. It was designed for a network that must handle both traditional high-throughput data traffic (e.g., file transfers), and
real-time,
low-latency content such as voice and video. The reference model for ATM approximately maps to the three lowest layers of the
ISO-
OSI reference model:
network layer,
data link layer, and
physical layer. ATM is a core protocol used over the
SONET/SDH backbone of the
public switched telephone network (PSTN) and
Integrated Services Digital Network (ISDN), but its use is declining in favour of
all IP.