Entry Channel Mode (Ecm) Switching; Applications Switching - Comtech EF Data Vipersat CDM-570 User Manual

E n t r y C h a n n e l M od e ( E C M ) S w i t c h i n g

Entry Channel Mode (ECM) Switching

STDMA entry channel mode provides a method for remotes requiring SCPC
access channels to enter/re-enter the network initially or after a power or other
site outage. The switch time will be variable based on the burst rate (bps) of the
STDMA group, the number of remotes with slots in the group, and where in the
burst cycle the remote is when it acknowledges receipt of the burst map.
Initial SCPC rates are settable for each remote in the STDMA group(s). Upon
detection of a burst map acknowledgement from a remote the STDMA burst
controller will send a switch request to the VMS with the operator specified
initial SCPC rate. Upon determining that there is an available demodulator and
pool bandwidth the VMS will send a multi-command to remove the remote
from the STDMA group, tune it and the switched demodulator to the specified
initial bit rate and selected pool frequency. The remote will stay at this initial
rate unless an application (such as VTC) or consistent load cause it to request
additional bandwidth from the VMS.
Entry channel mode is not driven by the presence or absence of customer traffic.
Once in ECM the switched initial data rate becomes the new temporary home
state. Temporary home state sets the low limit data load threshold, where the
remote will stop sending load switch request commands. Remotes no longer
require burst maps to maintain SCPC transmission.
After all remotes are processed into ECM, the Burst Controller drops into sanity
mode sending a keep alive map to service remotes which may have their SCPC
carrier inhibit flag set. The keep alive message is sent once every two seconds
until re-entry is invoked.

Applications Switching

Comtech Vipersat Networks describes the features of applications switching in
the VMS 3.x.x Users Guide. As it relates to this application, it is useful to
describe the fail-safe mechanism used for freeing pool bandwidth.
If the VMS loses communications with a switched remote for more than three
minutes, it will attempt to return the remote to home state. If the revert-to-home
state command succeeds (restoring communications) Entry Channel Mode will
cause the remote to switch to its initial SCPC bit rate.
If the revert-to-home state command fails, the VMS will send a command to
return the remote and the hub demodulator to the state where they were prior to
losing communications, but leave the remote enabled in the STDMA burst
controller. This provides the remote with 2 paths to rejoin the network:
V i p e r s a t C D M - 5 7 0 / 5 7 0 L U s e r G u i d e
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