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CDM-625 Advanced Satellite Modem
Quality of Service (QoS)
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
4
3
2
1
Total ►
*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
4
3
2
1
Total ►
L2 QoS
Input
QoS Output
Priority
Data Rate
Data Rate
4
500 Kbps
500 Kbps
3
800 Kbps
800 Kbps
2
2 Mbps
1700 Kbps
1
2 Mbps
5.3 Mbps
L2 QoS
Input
QoS Output
Priority
Data Rate
Data Rate
4
500 Kbps
500 Kbps
3
800 Kbps
800 Kbps
2
2 Mbps
2000 Kbps
1
2 Mbps
700 Kbps
5.3 Mbps
Remaining Data
Rate* (After Serving
the Priority Queue)
2500 Kbps
1700 Kbps
0 Kbps
0 Kbps
0 Kbps
3 Mbps
0 Kbps
Remaining Data Rate
(After Serving the
Priority Queue)
3500 Kbps
2700 Kbps
700 Kbps
0 Kbps
4 Mbps
0 Kbps
20–5
Revision 13
MN-CDM625
Output Data Rate
500 x (2.5/3) = 417 Kbps
800 x (2.5/3) = 667 Kbps
1700 x (2.5 /3) = 1416 Kbps
0 Kbps
2.5 Mbps
Output Data Rate
500 x (2.5/4)= 312.5 Kbps
800 x (2.5/4) = 500 Kbps
700 x (2.5 /4) = 1250
Kbps
700 x (2.5/4) = 432.5
Kbps
2.5 Mbps
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