User guide

Vipersat Configuration
3-18 Vipersat CDM-570/570L User Guide
Slot Preamble Length
This menu item, which appears in all Hub and Remote configurations, displays
the current Slot Preamble size in milliseconds and bytes for the remotes in the
group. The Slot 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. Higher data rates allow for a shorter preamble, since it is easier to achieve
signal lock. The setting for this parameter should be obtained using the Vipersat
STDMA Calculator.
Note: When either the BFAT feature is enabled or the Hub type is ECMv2, the
preamble length is set automatically for the unit.
On a Hub unit, entering P at the command prompt allows changing the pream-
ble duration in milliseconds.
Figure 3-17 Slot Preamble Length prompt
On Remote units, this menu item is an information-only display.
Slot Data Length
This menu item displays the Slot Data Length in milli-seconds and bytes for the
remotes in the group, and represents the amount of data that can be transmitted
or received in one spin of the STDMA cycle by each of the Remotes belonging
to that group. This is the amount of time that the remote is provided to send data
in the cycle.
Depending on the Hub type that is defined for the modem, the appearance of
this parameter will vary:
• Fixed – Slot Data Length
• Dynamic Slot – Nominal Data Length, Minimum Data Length
• Dynamic Cycle – Maximum Data Length, Minimum Data Length
• GIR – Minimum Data Length
• Entry Channel – Data Length, Minimum Data Length
NOTE