Comtech EF Data SLM-5650A Vipersat - Manual (Page 119)

Appendix B - Automatic Switching B-21
Entry Channel Mode (ECM) Switching
Burst Map causing it to rejoin the network through ECM. The VMS will
park the demodulator previously in use and free the bandwidth slot.
2. If the outage was due to an extended rain fade or other communications
blockage with no loss of power, the Remote will rejoin the network via the
previously assigned SCPC channel. When the VMS receives a PLDM it will
send a Revert-to-Home State command and free the bandwidth slot and burst
demodulator. The Remote will then rejoin the network through ECM.
Since it is not possible to know which of the above scenarios caused the
communications outage, the VMS will not free the bandwidth slot except
through operator intervention.
Figure B-10 and figure B-11 diagram the time state differences and the process
of recovery. Note that the times referenced in the diagrams are approximate.
Figure B-10 ECM Switch Recovery: < 3 minutes
Unit Reboot 0
Burst
Demod
Switched
Demod
VMS Remote
State
Connected
0
Home State - STDMA
Wait for TX Grant
30
Satellite Delay
250 ms + 30ms E-E
State
Disconnected
180
State Unknown Force
Registration
Set ID
180.28
Switch
Acknowledgment &
PLDM
191.35
Process Switch
Command
189.305
Switch Command
ECM
Switch
Acknowledgment
Force Connected
Registration
Acknowledgment
Failure
189
Revert Switch
Command
189.025
STDMA TX Grant
Burst ACK
190.31
189.6
No Switch wait ACK
191.59
192.18
State
Connected
Switch Command
ECM
Switch
Acknowledgment
Process Switch
Command
191.895
Switch
Acknowledgment &
PLDM
191.9
191.615
ECM Switch Recovery < 3min.
3/7/05