Single-Ended Operation - US Robotics USR3520 User Manual

then send call-progress messages to the legacy application software that mimic those of a dial-up
modem. If the answering Modemulator is configured to auto-answer or if the application software
issues an answer command, the connection will complete, which emulates the behavior of dial-up
modems.
 If the answering Modemulator does not auto-answer or manually answer, the connection will
time-out, which emulates the behavior of dial-up modems.
 If the answering Modemulator has a cellular connection already in-progress with another
Modemulator, the current connection will not be interrupted and the originating Modemulator will
report NO DIALTONE or BUSY or NO CARRIER.
The following diagram illustrates a simplified peer-to-peer legacy system using two Modemulators and
peer-to-peer cellular service.

Single-Ended Operation

First, follow the Getting Started
System Architecture
A legacy M2M host site (Headquarters, Operations Center, Transaction Processor) is the destination of
data being transferred from all of the remote sites. This host site has application hardware and software
that interfaces with the Internet to accept an IP connection and transfer the data.
The legacy M2M remote sites are the sources of data being transferred to the host site. Each remote
site has application hardware and software that normally interfaces with a serial dial-up modem used to
transfer the data.
Modemulators can replace the dial-up modems at all or some of the remote sites. The Terminal port of
the Modemulator at each remote site connects to a serial port of the remote application hardware that
would normally connect to a serial dial-up modem.
Modemulator User Guide
chapter in this guide to verify that one Modemulator is operating properly.
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