Transmit (Mil-188-114A, Rs-422); Interface Or Asymmetrical Data Rates; Receive; Drop And Insert (D&I) - Radyne DMD2050 Operation Manual

DMD2050 Universal Satellite Modem Theory of Operation

3.9.1 Transmit (MIL-188-114A, RS-422)

Set SCT Source to 'SCR'. The Tx Terminal Equipment must clock the TX Data with the SCT
Clock and return data and SCTE (Optional). If SCTE is returned to the modem from the terminal
equipment, set TX CLK SRC to SCTE. If SCTE is not returned to the modem, set TX CLK SRC
to SCT. The TX CLK POL should be set to AUTO.
3.9.2 G.703 Interface or Asymmetrical Data Rates
Loop timing with a G.703 Interface or Asymmetrical Data Rates requires external equipment at
the remote end that is capable of using the recovered RD Clock as source timing for (SCTE) SD.
The modem will not manipulate the clock frequency. Therefore, the transmit and receive clock
rates must be equal in order for the modem to perform loop timing.

3.9.3 Receive

Select the Buffer clock to RxSAT (SCR).
3.10 Drop and Insert (D&I)
The Radyne DMD2050 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 that conforms to the IBS and small IDR Framing Structures. For information pertaining
to Radyne's proprietary Drop & Insert, refer to Appendix E.
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.704 Frame. The modified terrestrial trunk is then
output via the Receive Data Out (RDO) Port.
Figure 3-10 shows two modems looped together. This configuration could be simplified to just
use one modem, or extended to use more than two modems. Figure 3-11 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.
TM110 – Rev. 1.3 3-13