Comtech EF Data MIDAS Version 4.X Basic Configuration User Manual
Page 47
MIDAS 4.2 Basic Configuration, Rev. 1
Setup and Operation 2–13
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This drop-down box allows the operator to select the Grade of Service for their
Video call. This will depend on the desired cost versus quality requirements.
The GOS choices for Video include:
• 128 1/2, 128 3/4
• 256 1/2, 256 3/4
• 384 1/2, 384 3/4
• 512 1/2, 512 3/4
• 768 1/2, 768 3/4
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This drop-down box allows the operator to select the amount of time, in
seconds, that the system will ring waiting for call setup before disconnecting.
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This is the maximum call length allowed, in seconds, and will only apply if the
Unlimited checkbox is not selected. This will vary according to the operator’s
discretion, and/or system bandwidth limitations.
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When selected, this checkbox allows calls of unlimited time duration. When it
is not selected, the amount of time specified in the Max Call Duration field will
apply.
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This allows the operator to enter the Doppler Buffer size, in bits, to
compensate for satellite movement.
• The depth of the receive buffer will depend upon four parameters:
• Doppler shift caused by satellite movement
• Stability of each clock (plesiochronous/Doppler operation only)
• Frame/Multiframe length of multiplexed data format
• Allowable time between clock slips
Doppler shift results from the movement of the satellite in space over a
period of one day in relation to the earth station. Doppler shift should not
result in a clock slip as the buffer will constantly fill and empty due to the
cyclic nature of the satellite motion.
Depending on the location of the earth station relative to the satellite, the
variation in propagation delay will typically be 1.15 ms (up to satellite and
back down). So, 2 ms will be sufficient for most commercial satellites.
Bits to Seconds: 1/DATA RATE * BITS = SECONDS
Seconds to Bits: DATA RATE * SECONDS = BITS