Comtech EF Data RCS10 - Manual (Page 219)

RCS10 Redundant Communication System Principles of Operation
TM058 - Rev. 2.3 Page 5-3
The Reed-Solomon encoder, if engaged, is designed as an installable option which encodes the
data into Reed-Solomon blocks. The blocks are interleaved and synchronized to the frame pattern
as defined in IESS-308 and IESS-309. After RS encoding, the composite data and clock are applied
to the BB loopback circuit.
5.5.3 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 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 module. In closed-net mode, the data is extracted from the buffer and
is sent to the UIM module. Backward alarm indications are sent to the M&C subsystem. If 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.
5.5.4 Clock Selection
Both the Tx Clock and the Buffer Clock source may be independently locked to one of the following:
SCT (Internal Oscillator), SCTE (External Tx Terrestrial Clock), EXC clock (External Clock Source),
or Rx Satellite Clock (Loop Timing). Additionally, for loop timing applications, the SCT clock source
can be selected to be Rx Satellite Clock.
5.5.5 Baseband Framing/Multiplexing
The framing/multiplexer is capable of multiplexing a relatively low-speed overhead channel onto the
terrestrial data stream resulting in a slightly higher combined or aggregate data rate through the
modem. The overhead channel is recovered at the far end. The type of data carried in this overhead
channel depends upon the type of framing selected for the Modulator and Demodulator. Framing
type 1_15 is specified by the IESS-309 standard and is commonly known as IBS overhead. Framing
type 96K is specified by the IESS-308 standard and is commonly known as IDR overhead.
The basic frame structure used by the multiplexer is that specified in the IESS-309 standard, Page
60, Figure 10, resulting in a 16/15 aggregate to through data ratio. Most of the IESS Framing
Structure diagram is shown below.
Two software controlled modes are designed into the card to best utilize the available bits; “Normal”
and “Enhanced”. The characteristics of the channel interface is also determined by the normal or
enhanced mode.
The ES to ES Data Channel can be set under software-control to either RS-232 or RS-485 mode.
The connector at the rear of the UIO module labeled “Async” or “ES-ES” carries this data. Refer to
section 2 for the pin assignments.
In the Enhanced mode, a 2-wire receive operating mode can be selected for the receive data into the
ES-ES channel. In this mode the receive input is muted while the transmit data output is active. In
4-wire mode the receive is always enabled. In the normal IBS mode only the 4-wire mode is
available. Note that the transmit and receive pairs are physically separate wires and must be
connected together if true RS-485 2-wire connectivity is desired.