Comtech EF Data SDM-300L3 - Manual (Page 269)

SDM-300L3 Satellite Modem Revision 1
Open Network Operations MN/SDM300L3.IOM
10–11
10.4.1 Description of D&I Operation
The main features of the D&I option are as follows:
• Data interface
• Transmit MUX
• Receive DEMUX
• ESC
• Backward Alarm
10.4.1.1 Data Interface
Data interface contains transformer - balanced data interfaces that support CCITT G.703
parameters and dejitter. This is compatible with AT&T Digital Speech Interpolation
(DSI) service. Data inputs and outputs named are listed below:
• Data Inputs Drop send data input A and B (DSD-A and DSD-B)
Insert send data input A and B (ISD-A and ISD-B)
• Data Outputs Drop receive data output A and B (DRD-A and DRD-B)
Insert receive data output A and B (IRD-A and IRD-B)
The system is frequently used with the drop receive data output signal (DRD - A, -B)
looped to feed the insert send data input signal (ISD-A, -B). This is accomplished at the
far end of any redundancy switching in order to allow transmit and receive chains to be
switched independently. The zero substitution codes (Alternate Mark Inversion [AMI],
B8ZS, and HDB3) are user
- selectable during configuration.
A data loopback function on the insert data is available in this section. This enables the
user to determine that the T1 or E1 data parameters correctly match those of this
interface. The drop data is always hard
- wired into loopback.
10.4.1.2 Transmit MUX
The data stream is TX MUX with a 1/15 overhead channel and the resultant information
rates are interfaced to the Mod/Demod/Coder sections of the modem. A phase-locked
loop generates the output clock (with overhead), using the input clock as a reference. The
input clock is normally the recovered clock from the data interface. If a valid input signal
is not present, the interface falls back to a 10
-5 accuracy reference clock generated in the
modem, and will transmit a valid IESS-308 framing pattern. If this occurs, the link will
remain open at the far end and a fault will be signaled.