Black Box Echo Series User Manual page 8

Echo 2 Mbps Multiplexer
It is also possible to connect two systems back to back directly in this manner, using an
appropriate cable. This configuration is described on page 25.
Where the Echo is to be used to provide unused PABX (or bridge) bandwidth to Nx64
X.21/V.11 ports, the optional Drop and Insert card is used as follows:
The Echo is set so that the slots used by the PABX are passed through to the main G.703 link
transparently. This is described on page 15. The remaining unused timeslots can now be
assigned as required to the channel ports.
The connection between the D&I port and the PABX will need to be crossed over using the
appropriate cable arrangement (same as the back to back Demo cable) shown on page 25.
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