Comtech EF Data RCS10 - Manual (Page 229)

RCS10 Redundant Communication System Principles of Operation
TM058 - Rev. 2.3 Page 5-13
5.9 Drop and Insert (D&I)
The Radyne ComStream DMD10 Drop & 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 n x 64 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 5-3 shows two modems looped together. This configuration could be simplified to just use
one modem, or extended to use more than two modems. Figure 5-4 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.
5.9.1 Drop Only
When Drop is enabled and Insert is disabled, the DMD10 performs a drop only function. Framed E1
or T1 data is input via the Send Data In port, the selected timeslots are dropped into the IBS frame
structure, and the unaltered terrestrial data is output via the Send Data Out port (See Figure 5-5).
5.9.2 Insert Only
When Insert is enabled and Drop is disabled, the DMD10 performs an insert-only function. If framed
terrestrial E1 or T1 data is available, it should be input via the Insert Data In port. The terrestrial
data is buffered inside the modem, the RX baseband processor inserts satellite data into the
selected timeslots in the G.704 frame, and the modified terrestrial data is then output via the
Receive Data Out port (See Figure 5-6).
If framed terrestrial data is not available, selection of the Internal T1/E1 frame source will cause the
modem to generate the required G.704 frame, the satellite data will be inserted into the selected
timeslots, and the resulting terrestrial data will be output via the Receive Data Out port. Any non-
inserted timelslots in the G.704 frame will be filled with the appropriate idle code (See Figure 5-7).