DMD20/20LBST Universal Satellite Modem
Theory of Operation
MN-DMD20-20LBST Revision 14
3–8
3.6
Loopback Features (Terrestrial & IF)
The modem provides for a number of different loopbacks. The Loopback supported are:
IF Loopback – Tx IF port is looped back to the Rx IF port
TX Terrestrial Loopback - Tx Data port is looped back to the Rx Data port after the
interface driver/receiver. (prior to the framing unit)
TX Baseband Loopback - Tx Data port is looped back to the Rx Data port after the
interface driver/receiver. (after the fraiming unit)
RX Terrestrial Loopback - Receive Data from the satellite is looped back for
retransmission to the satellite, providing a far end loopback. (prior to the framing unit)
RX Baseband Loopback - Receive Data from the satellite is looped back for
retransmission to the satellite, providing a far end loopback. (after to framing unit)
TX/RX Terrestrial Loopback - provides both Terrestrial loopbacks simultaneously
TX/RX Baseband Loopback - provides both Baseband loopbacks simultaneously
Usage of the modems loopback capabilities in conjunction with the Ethernet
data interface can produce undersirable network loops. In order to run any
type of data test with an Ethernet interface you must utilize two modems
connected back to back. Simply using one modem and a loopback will not
produce the desired results.
IMPORTANT