Cables to Go CDM-570L manual Entry Channel Mode ECM Switching, Applications Switching

Entry Channel Mode (ECM) Switching

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:

B-14 Vipersat CDM-570/570L User Guide