4–8 • Transparent Module
TES9 Software User Manual (Iss. 04)
Data Throughput Calculations
When encoding a transparent stream using data supplied through the LAN, the throughput is
completely defined by the Data Count specified for the stream, assuming that the transmit
computer and LAN can supply data as needed. This is defined by the following equation:
T = FV x DC bytes/second
Where:
•
FV
is the field rate for interlaced formats, or the frame rate for progressive formats.
•
DC
is the Data Count set for the Transparent module in TES9Set.
When encoding a transparent stream using data supplied through a serial port, the throughput
depends on the Data Count and also on the serial port baud rate. The maximum throughput is the
lesser of the baud rate and the data rate value resulting from the following equation:
DR = FV x 10 x DC bits/second
Where:
•
FV
is the field rate for interlaced formats, or the frame rate for progressive formats.
•
DC
is the Data Count set for the Transparent module in TES9Set.
• The factor 10 in the equation reflects the fact that each 8-bit value is carried on the serial
link with one start and one stop bit.
This is expressed in bits/second to allow comparison with the serial port baud rate.
For example, if FV = 59.94 and DC = 100, DR = 59,940 bits/second.
If the serial port speed is set to 57,600 bits/sec, the TES9 cannot fully use the capacity that has
been reserved for this stream, and the throughput will be 57,600 bits/sec. If the port speed is
115,200 bits/sec, the TES9 will use flow control to maintain an average rate of 59,940 bits/sec
However, if the transmit computer does not respect flow control, data will be lost.
This points out the importance of flow control. If you are not certain that the program you are
using to send data to the TES9 responds properly to XON/XOFF flow control, it is advisable to
select a Data Count value for the transparent stream which is large enough to ensure that flow
control is never needed. For example, with FV= 59.94, a DC value of 193 or greater can transport
a 115,200 bits/sec stream without flow control.
Similarly, when decoding a transparent stream, care must be taken to set the serial port baud rate
high enough for the throughput of the stream. In the above example with DC=100, the serial port
for the decode stream would need to be set to 115,200 bits/sec, since 57,600 bits/sec is
insufficient to sustain the throughput of 59,940 bits/sec.
