Transmit (Rs-422 Or V.35 Interface); Interface Or Asymmetrical Data Rates; Receive; Drop And Insert (D&I) - Radyne DMD20 Installation And Operation Manual

DMD20 Universal Satellite Modem Theory of Operation

3.9.1 Transmit (RS-422 or V.35 Interface)

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 to SCTE. If SCTE is not returned to the modem, set TX CLK to SCT.
The TX CLK PHASE 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 DMD20 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. 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.
TM103 – Rev. 1.1 3-13