Tx Baseband Processing; Rx Baseband Processing; Monitor & Control (M&C) Subsystem - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem

3.2.3 Tx Baseband Processing

The Tx Data and Clock enters the Baseband Processor, passes through a Rate Adapting FIFO and
enters the Framer/Drop Processor. In IDR, IBS, and D&I Modes, the framer adds the appropriate
framing and ESC as defined in IESS-308 and 309. In D&I Mode, the framer acquires the
terrestrial framing structure, E1 or T1, and synchronizes the Drop Processor. The Drop Processor
extracts the desired time slots from the terrestrial data stream and feeds these channels back to the
framer. The framer then places the 'dropped' terrestrial time slots into the desired satellite
channel slots. The data is then sent to the Reed-Solomon Encoder.
When enabled, the Reed-Solomon Encoder, encodes the data into Reed-Solomon Blocks. The
blocks are then interleaved and synchronized to the frame pattern as defined by the selected
specification (IESS-308, IESS-309, DVB, etc.). After Reed-Solomon Encoding, the composite
data and clock are applied to the BB Loopback Circuit.

3.2.4 Rx Baseband Processing

The Receive Processor performs the inverse function of the Tx Processor. Data received from the
satellite passes through the BB Loopback Circuit to the Reed-Solomon Decoder to the Deframer.
The Deframer acquires the IBS/IDR/DVB frame, synchronizes the Reed-Solomon Decoder and
extracts the received data and overhead from the frame structure, placing the data into the PD
Buffer, sending the overhead data to the UIM. The data is extracted from the buffer and is sent to
the UIM. Backward Alarm indications are sent to the M&C Subsystem. In Drop and Insert
Mode, the Insert Processor synchronizes to the incoming terrestrial T1/E1 Data Stream, extracts
satellite channels from the PD Buffer, and then inserts them into the desired terrestrial time slots
in the T1/E1 Data Stream.
3.3 Monitor & Control (M&C) Subsystem
The modems M&C system is connected to most of the circuitry on any board contained in the
modem. These connections provide status on the working condition of the circuitry as well as
providing the data required for the various measurements the modem provides. The M&C
processes this information and generates status indications as well as alarms when necessary.
Detailed status information is available via the modems various user interfaces including the
remote and terminal ports. An external summary fault is available on the RS422 Data interface
The M&C contains a high-performance microprocessor and is responsible for overall command
and control of modem functions. The M&C is constantly monitoring all subsystems of the
modem by performing a periodic poll routine and configures the modem by responding to
commands input to the system. During each poll cycle, the status of each of the subsystems is
collected and reported to each of the external ports. Performance statistics such as Eb/No, buffer
fill %, etc. are compiled. If faults are detected, the M&C will take appropriate actions to
minimize the effect of such faults on the system (refer to the Fault Matrices in Chapter 6).
The modem supports the following M&C protocols:

Terminal Interface (Section 3.2.1)

Remote Port Interface (Section 3.2.2)

Ethernet M&C, Web Browser & SNMP (Section 3.2.3)

Modem Status, Alarms & Contact Closures (Section 3.2.4)
MN-DMD50– Revision 3
Theory of Operation
3–5