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Appendix H. DROP AND INSERT
H.1
Drop and Insert (D&I)
The Drop and Insert (D&I) function provides an interface between a full T1 or E1 Trunk whose
framing is specified in CCITT G.704 and a fractional Nx64 Kbps Satellite Channel. The Drop
and Insert functionality conforms to IBS, small IDR, and Radyne Proprietary Efficient D&I
Framing Structures. For information pertaining to Radyne proprietary Efficient Drop and Insert
function, refer to Appendix I.
The Drop function allows the user to select the terrestrial T1 or E1 timeslots that are to be
dropped off for transmission over the link in the specified satellite channels. The Insert function
allows the user to select the T1 or E1 timeslots into which the received satellite channels are to be
inserted. The two functions are completely independent allowing maximum flexibility in
choosing configurations. The four-port G.703 Interface allows one or more modems to be looped
together using the same T1 or E1 trunk.
The Transmit Data Trunk is brought into the modem via the Send Data In (SDI) Port. From
there, the TX Baseband Processor extracts the selected timeslots from the G.704 Frame and
prepares them for transmission. The original trunk data is sent out of the modem unaltered via
the Send Data Out (SDO) Port. The Receive Data Trunk is brought into the modem via the Insert
Data In (IDI) Port. The data is buffered inside the modem and the RX Baseband Processor inserts
satellite data into the selected timeslots in the G.703 Frame. The modified terrestrial trunk is then
output via the Receive Data Out (RDO) Port.
Figure H-1 shows two modems looped together. This configuration could be simplified to just
use one modem, or extended to use more than two modems. Figure H-2 shows an alternative
method of looping where all of the drop (transmit) data is processed prior to performing any
insert (receive) processing. In both configurations, the terrestrial trunk is providing the timing for
the satellite transmission and for the terrestrial receive.
MN-DMD50 Revision 4
(D&I)
H–1
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