User manual
MultiModem ISI Hybrid Series, ISIHI-2S 9
Chapter 1– Introduction
• Flash PROM for easy firmware upgrades
• Automatic detection of the data protocol for answering incoming data calls
• Embedded protocol analyzer for troubleshooting the connection to the ISDN network
The ISDN TAs provide data communication using Basic Rate Interface (BRI). They
provide two 64 Kbps
bearer
channels for voice or data and one 16 Kbps D
channel for
signaling information (2B+D) and are compatible with V.120, PPP, and X.75.
The TAs provides dial-up asynchronous communication capability with other personal
computers, terminals, on-line computer services, or other types of computer systems.
What is a S/T-Interface? An ISDN Basic Rate (BRI) U-Loop consists of 2 conductors
from the CO (telephone company central office) to the customer premises. Equipment on
both sides of the U-loop is carefully designed to deal with the long length of the U-loop
and the noisy environment it operates in. At the customer premises, the U-loop is
terminated by an NT1 (network termination 1) device. An NT1 (network terminator 1) is a
device that provides an interface between the two-wire twisted-pairs used by telephone
companies in their ISDN BRI network and an end-user’s four wire terminal equipment.
The NT1 drives an S/T-bus that usually is 4 wires but in some cases may be 6 or 8 wires.
The name of the S/T bus comes from the letters used in the ISDN specifications to refer
to two reference points, S and T. Point T refers to the connection between the NT1
device and customer supplied equipment. Terminals can connect directly to NT1 at point
T, or there may be a PBX (private branch exchange, e.g., a customer-owned telephone
exchange). When a PBX is present, point S refers to the connection between the PBX
and the terminal.
Note that in ISDN terminology,
terminal
can mean any sort of end-user ISDN device,
such as data terminals, telephones, FAX machines, etc. The following diagram reflects
interface points in a typical ISDN network.
Terminal
Terminal
NT2
(PBX)
NT2
Telco Company
Interface
Terminal
Point S
Point S
48 wires
Point S
Point T
48 wires
Point U
48 wires