Comtech EF Data CDM-570/570L Vipersat - Manual (Page 127)

Appendix B - Automatic Switching B-9
Load Switching
If the average bandwidth used exceeds the threshold percentage of available
bandwidth, then a flag is set indicating a switch is pending. At this point, the
statistics are reset and the traffic load is then computed for the time period spec-
ified by the switch delay. At the end of this delay, if the threshold is still
exceeded, a switch is initiated. The data rate specified for the switch is deter-
mined by taking the current load, as indicated by the bytes queued during the
delay period, multiplying it by the percent allocation and rounding up to the
next 8 kbps.
A key point is that in most of the STDMA modes, the bandwidth allocated to
each Remote is constantly being adjusted to the needs of the network. As long
as the network is running below capacity, most Remotes will get the bandwidth
they need and a switch will not be required. Only when a Remote requires more
bandwidth than is available in STDMA will a switch occur.
In Dynamic Cycle mode, each Remote will always appear to be running at near
100% capacity, even when there is actually excess bandwidth available. This is
because in this mode, the Remotes are almost never given more bandwidth than
they need. As a result, the algorithm for this mode uses a maximum allowed slot
size rather than the actual allocated slot size to calculate the effective data rate.
This results in a more accurate estimate of the available STDMA bandwidth.
Load Switching—Remote
Once a Remote has been switched from STDMA mode to SCPC mode, it
checks its bandwidth requirements to see if a change is needed. A running aver-
age of the data traffic passing over the WAN is maintained as a percentage of
the current data rate for the Remote. This average is accumulated for at least the
specified delay (Step Up/Step Down) period. Then, once per second, the current
utilization is checked against the Step Up and Step Down Thresholds. If the
utilization is outside the up/down range, a request is generated to switch to the
calculated rate. After the request is granted, the running average is reset and the
cycle is repeated.
Remote Switching Parameters
The parameters for controlling the Step Up/Step Down switching process for a
CDM-570/570L Remote are set in the page shown in figure B-3. An example of
this page for an SLM-5650A Remote is shown in figure B-4.