User guide

Appendix F - Automatic Switching F-5
Load switching
needed. Note that the GIR allocations are restricted so that the assigned
GIR totals cannot exceed available bandwidth. If this restriction is
somehow violated, then it will not be possible to properly allocate
bandwidth when the network is overloaded.)
• Entry Channel Mode - This is the same as Dynamic Cycle, except that as
soon as the Hub receives an STDMA ACK, it initiates a switch to SCPC
mode based on the policy set for that remote.
The important thing to understand about “Bytes in Queue” is that any data that
is not transmitted (i.e. does not fit) in the next slot will be reported again in the
next STDMA ACK. Thus the “Bytes in Queue” is not necessarily an accurate
measure of the actual traffic being passed through the remote.
The “Queued Bytes” on the other hand, reflects only the data that was received
in the last cycle and thus is never duplicated (not including TCP retransmis-
sions). This is the metric that is used for computing average load and initiating a
load switch as needed.
Before discussing how load switching is determined, it is necessary to explain
the user parameters that control the switch. The menu shown in figure F-1 and
figure F-2 shows the entries in the automatic switching menu at the hub that are
used to control load switching.
Figure F-1 Hub switching menu, CDM-570/570L