1. Getting Started
1.1 Introduction
The AI-5120 Telephone Line Monitor is a compact device designed to detect and analyze
various telephony related signals. By sensing the voltage present on the telephone line it
determines the line state (on hook, or off-hook) in addition to detecting common signals
such as DTMF, FSK, and DC line voltage. Working in conjunction with the TRsSim
software on a PC, the AI-5120 becomes a valuable tool in analyzing and debugging
Caller ID and SMS (Short Message Service) data transmissions. Like an oscilloscope,
the AI-5120 can capture and display waveforms showing the various signals present on
the telephone line. However, unlike an oscilloscope, it can also automatically trigger on
events specific to telephony.
Some of the common events that the AI-5120 detects and analyzes are:
•
DTMF Dialing
•
FSK Caller ID and ETSI SMS Data
•
Pulse Dialing
•
Ringing
•
CAS/DTAS Tones
•
On/Off hook, Line Reversals, Open Switching Intervals (OSI)
As a line monitor, the AI-5120 does not go off-hook (seize the line), or generate tones. It
only listens. The impedance presented by the AI-5120 to the telephone line is over 10
Mohm. As such it has little to no effect on any signals present on the telephone line.
The supplied TRsSim PC software provides a high level graphical user interface for
controlling the AI-5120. As events are detected, the software displays timing and
measurement information. In addition, waveforms for each event may be recorded for
display and further analysis. Waveforms can be played back to the AI-5120's BNC
monitor or speaker out, or exported as wave files for analysis using various software
packages. The TRsSim software automatically decodes FSK based Caller ID conforming
to the Telecordia, ETSI, and Japanese NTT standards. It displays the message contents at
either a high level showing the parameter values, or at a low level showing each byte
detected. Additionally, Short Message Service (SMS) following the ETSI ES 201 912
standard is supported. Details of each SMS FSK message can be displayed along with
various signal measurements.
Any signals present on the telephone line may be routed to the AI-5120's rear panel BNC
output connector or speaker/headphone connector. This provides a simple means to pass
signals to external equipment requiring an unbalanced input. A wide range of
programmable filters can be inserted in the signal path helping to reject unwanted signals
AI-5120 User Guide
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