Preamble Time; Guard Band; Slot Data Length; Figure 3-18 Slot Preamble Time Display - Comtech EF Data Vipersat SLM-5650A User Manual

V i p e r s a t C o n f i g u r a t io n

Preamble Time

This parameter, which appears in all Hub configurations, displays the current
Slot Preamble size in milliseconds for the Remotes in the group. The Preamble
is the period between when the Remote begins to transmit (sends an ACK) to
the Hub and when the first data packet is sent. This allows time for signal lock
to occur before data is sent, thus preventing data loss.
The Preamble Time is automatically set based on internal calculations that
correlate transmit burst acquisition preamble times to STDMA transmit data
rates and Acquisition Mode selection. Standard Acquisition Mode uses an
uncoded signature. Long Acquisition Mode uses both uncoded and coded
portions of the preamble, as is shown for the example in figure 3-18. The sum
of these two values equals the total Preamble Time; in this case, 40 ms.
Figure 3-18
Slot Preamble Time display

Guard Band

This parameter, which appears for all Hub configurations, displays the current
length of the Slot Guardband in milliseconds for the Remotes in the group. The
Slot Guardband is the amount of time between the point when one Remote
completes transmitting data and the point when the next Remote in the cycle
begins transmitting. This prevents the Remote from overrunning the next termi-
nal in the cycle. The setting for this parameter should be obtained using the
Vipersat STDMA Calculator. Typically, a value of 30 ms is sufficient.
Tip: Contact a Comtech Vipersat Networks representative for a copy of the
latest Viper Calculator.
To modify this parameter on a Hub unit, enter a value from 0–250 in the Guard
Band field, then click the Submit button. The value represents time in millisec-
onds.
Figure 3-19
Slot Guardband field

Slot Data Length

This menu item displays the Slot Data Length in milliseconds as well as in
bytes, and represents the amount of data that can be transmitted or received in
C h a p t e r 3 - U s i n g t h e W e b S e r ve r I n t e r f a c e ( W S I ) 3-19