Determining Need-For-Change; Load Switch Example - Comtech EF Data Vipersat CDD-562L User Manual

L o a d S w i t c h i n g
• SCPC Step Down Threshold - Similar to STDMA Slot Capacity at Hub,
• SCPC Step Delay - Same as STDMA Switch Delay at Hub.
• SCPC Stepup Excess - Same as Percent Allocation at Hub. Note that the

Determining Need-for-Change

The following process is used to determine if bandwidth utilization warrants a
need-for-change.
The operator defines both a Step Up and Step Down threshold in terms of
percent utilization, a bandwidth margin value, and a latency or averaging
period. Once per second, the CDM router software determines the current
percent utilization by dividing the bits transmitted by the current transmit data
rate.
If the percent utilization exceeds the step up threshold or is less than the step
down threshold for the entire latency period, then an ASR (Automatic Switch
Request) is sent to the VMS. The bandwidth requirement for the ASR is
computed by taking the average percent utilization over the latency period and
multiplying that by the current data rate to determine the actual data rate used
over the measured interval. This number is multiplied by the margin value and
rounded up to the nearest 8 Kbps to determine the requested bandwidth.

Load Switch Example

An automatic load switching example, illustrated in the schematic diagram in
figure B-3, illustrates how a network can respond to changes in traffic volume
or load conditions. The network's capability and method of response to load
changes is determined by the setting and capability of each of the components in
the system, such as the transmitter power output, the antenna capabilities for
each of the sites in the network, and the policies set in VMS.
The elements for determining policies and their interactions are covered in this
section.
B-8
except Step Down is used to trigger a switch if the average load falls
below this value.
value applies to both Step Up and Step Down switches, and if computed
against the average traffic load at the time the switch is intiated.
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