Appendix B - Automatic Switching B-7
Load Switching
Table B-3
Figure B-2
Autoswitching menu for a remote
•Auto Switching - Same as Hub
•Load Switching - Same as Hub
•SCPC Step Up Threshold - Same as STDMA Slot Capacity at hub.
•SCPC Step Down Threshold - Similar to STDMA Slot Capacity at hub
except Step Down is used to trigger a switch if the average load falls
below this value
•SCPC Step Delay - Same as STDMA Switch Delay at hub
•SCPC Stepup Excess - Same as Percent Allocation at hub. Note that the
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.
Determining Need-for-Change
The following process is used to determine if bandwidth utilization warrants a
need-for-change.
The user 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 8K to determine the requested bandwidth.