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P300H P300 Series Modem Installation and Operating Handbook Page 142
These require careful consideration based on the exact situation. If you have questions relating to this
subject, and are willing to at least draw a diagram of the system you are implementing then you are
welcome to contact us by fax for advice for your exact application.
8.2.3 Determining Buffer Size
Use the following calculation to determine the buffer size required for any application:
If Lc is the local clock accuracy (e.g. ±1 x 10 ),
-9
and Rc is the remote clock accuracy (e.g. ±1 x 10 )
-11
and Ms is the Minimum slip period in days (e.g. 40 days)
then the required Plesiochronous Buffer size (middle to end) in seconds is:
Bs = Ms x 24 x 60 x 60 x (Lc + Rc).
Simplifying, allowing a factor of two (end to end buffer, not middle to end) and allowing 2mS for the Doppler
shift gives:
Bs = .002 + 172800 x Ms x (Lc + Rc) Seconds.
So using the example figures above gives 0.00898 seconds, so 9ms is required to absorb the
plesiochronous effects. To this you must add any Doppler requirement (ie 2ms for each satellite hop).