Comtech EF Data CTOG-250 - Manual (Page 225)

CTOG-250 Comtech Traffic Optimization Gateway Revision 1
Appendix E MN-CTOG250
E–3
E.2 Advanced VSAT Outbound ACM Scheme
The description of Outbound ACM operation serves as the prelude to configuring Advanced VSAT
for ACM operation. These key discussion points are:
• Target Es/No Margin;
• Es/No Reporting Mechanization and Timing;
• Monotonic Operation;
• ModCod Selection.
E.2.1 Target Es/No Margin
Links normally include margin to meet performance criteria for SLA adherence. The Target
Es/No Margin is added to the published guaranteed Es/No specification per ModCod for ACM
operation. When ACM is enabled, in order for each remote site to switch to the next ModCod
in a way that maintains a level of performance – generally near the QEF (Quasi Error Free) PER
(Packet Error Rate) point of 10 -7 – Target Es/No Margin serves to add margin to the guaranteed
Es/No specification. The value of Target Es/No ranges from 0 to 4.5 dB
For example, an Es/No Margin of 1.0 dB would mean that the minimum Es/No required to run
at ModCod (5) QPSK 3/5 would be the guaranteed Es/No (2.7 dB) plus the Target Margin
(1.0 dB) = 3.7 dB.
The Target Es/No Margin can and should also be used as a way to dial in a maximum fade
slope (rate of change). ACM messages sent from the remote demodulators to the Hub side
ACM Controller contain the Es/No estimate that the demodulator was seeing at that particular
time.
If it takes ~260 ms to get the Es/No message to the CTOG-250 and another ~260 ms for the
new ModCod to be received at the remote, the additional Target Margin above the QEF
threshold will allow the system ~520 ms of fading before packets are dropped.
E.2.2 Es/No Reporting Mechanization and Timing
The Advanced VSAT Outbound ACM mechanization is formed on proprietary IP packets
generated at each remote CDM-840 transmitted in band back to the ACM Controller (CTOG-
250 or CDM-800) via the established link with the corresponding CDD-880 Multi Receiver
Router demodulator device. These proprietary messages are transmitted on the Hub-side
Management LAN to the ACM controller to ensure proper prioritization
To ensure proper operation, care must be taken to review and adhere to the LAN
cabling requirements defined in the CTOG-250 Comtech Traffic Optimization
Gateway Installation and Operation Manual.