CDM-625 Advanced Satellite Modem Revision 13
Quality of Service (QoS) MN-CDM625
20–5
QUESTION: What is the total output data rate and what are the individual port output data
rates?
ANSWER “A” – For HW Ver. Rev 2.1 and newer:
• Based on Table 20-1 for a modem Tx bandwidth of 2.5 Mbps, the QoS output bandwidth is
set to 3 Mbps.
• Since the modem Tx bandwidth and QoS output data rates are not the same, after Layer 2
QoS prioritization the modem will further limit the output data rate to the Tx bandwidth of
the mode. The individual port data rates will henceforth be trimmed (normalized) to the
data rate of the modem Tx bandwidth without considering the priorities.
Port
L2 QoS
Priority
Input
Data Rate
QoS Output
Data Rate
Rate* (After Serving
Output Data Rate
4 4 500 Kbps 500 Kbps 2500 Kbps 500 x (2.5/3) = 417 Kbps
3 3 800 Kbps 800 Kbps 1700 Kbps 800 x (2.5/3) = 667 Kbps
2 2 2 Mbps 1700 Kbps 0 Kbps 1700 x (2.5 /3) = 1416 Kbps
1 1 2 Mbps 0 Kbps 0 Kbps 0 Kbps
*After Priority 4, even though the actual modem TX data rate is 2500 kbps, the QoS
leftover data rate is still 2500 kbps since QoS bandwidth is 3000 kbps.
ANSWER “B” – For HW Ver. Rev 1.1 and older:
• Based on Table 20-1 for a modem Tx bandwidth of 2.5 Mbps, the QoS output bandwidth is
set to 4 Mbps.
• Since the modem Tx bandwidth and QoS output data rates are not the same, after Layer 2
QoS prioritization the modem will further limit the output data rate to the Tx bandwidth of
the modem. The individual port data rates will henceforth be trimmed (normalized) to the
data rate of the modem Tx bandwidth without considering the priorities.
Port
L2 QoS
Priority
Input
Data Rate
QoS Output
Data Rate
(After Serving the
Output Data Rate
4 4 500 Kbps 500 Kbps 3500 Kbps 500 x (2.5/4)= 312.5 Kbps
3 3 800 Kbps 800 Kbps 2700 Kbps 800 x (2.5/4) = 500 Kbps
2 2 2 Mbps 2000 Kbps 700 Kbps
Kbps
1 1 2 Mbps 700 Kbps 0 Kbps
700 x (2.5/4) = 432.5
Kbps
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