Comtech EF Data CDM-425, Installation And Operation Manual

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CDM-425 Advanced Satellite Modem
Revision 0
Appendix M M–4 MN-CDM-425
QoS Example 3
SETUP:
•
Port-based Layer 2 QoS mode is selected.
•
Port Layer 2 QoS Priorities are set as follows:
o
Port 1 priority is set to 1
o
Port 2 priority is set to 2
o
Port 3 priority is set to 3
o
Port 4 priority is set to 4
•
The modem data rate is set to 2500 Kbps.
•
The ingress traffic on Ports 1 and 2 are set to 2 Mbps.
•
The ingress traffic on Port 3 is set to 800 Kbps.
•
The ingress traffic on Port 4 is set to 500 Kbps.
QUESTION:
What is the total output data rate and what are the individual port output data rates?
ANSWER:
•
Based on Table M-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
Remaining Data
Rate* (After Serving
the Priority Queue)
Output Data Rate
2 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
Total ► 5.3 Mbps 3 Mbps 0 Kbps 2.5 Mbps
*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.