Determining Buffer Size - Paradise Datacom P300 Series Installation & Operating Handbook

Clock from the interface / terrestrial network
If the modem has a station clock (which also drives the network which the Rx output feeds), then
select Rx Clock =
clock comes from the network, is presumably derived from the same master clock which clocks the
network). Set the Tx Clock =
Other clock modes
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
and Rc is the remote clock accuracy (e.g. ±1 x 10
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).
P300H P300 Series Modem Installation and Operating Handbook
. If there is no station clock then set Rx Clock =
.
-9
),
-11
)
(which as the Tx
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