Modem Stacking Installation - L3 Communications MPM-1000A Operator's Manual

MPM-1000A Operator Manual 1000-7075 Rev E

14.2 Modem Stacking Installation

The design of the Modem allows multiple Modems to be tied together as a single virtual
Modem. The minimum number of Modems is two (2) and the maximum number of
modems is six (6). When six (6) modems are configured as a single virtual Modem, it
supports up to 12 transmit carriers and 24 receive carriers. Figure 14-2 shows how to
connect six modems together for Modem stacking operation.
IF Combiner, IF splitter, Ethernet Switch, control computer, WAN router and
interconnecting cables are customer furnished equipment. The Electromagnetic
Interference/Electromagnetic Compatibility (EMI/EMC) and signal characteristics of
these CFE should be chosen not to affect the performance of the Modems.
Modems in the stack are identical in hardware configuration with upgraded dual-core
processor. The CDU Ethernet port of each Modem is connected to an external Ethernet
Switch for inter-Modem communication. This external Ethernet Switch is also connected
to an external control PC for the HCI. The Data Ethernet port of the Master Modem is
the single data interface for the entire stack of modems.
If available, connect an accurate station frequency reference signal, 5MHz or 10 MHz,
to the Reference input of the Master Modem. Reference output from the Master
Ruggedized Modem is connected to the Reference input of the 1st Slave Ruggedized
Modem, and so forth as shown in the diagram. The overall length of the frame strobe
cable should not exceed four (4) foot long. Because the Frame Strobe signal is a
balanced electrical interface, pin 30 wire and pin 31 wire should be twisted
approximately 1-turn per inch from Modem to Modem and the twisted pair should be
shielded by the ground signal at pin 29.
14-2