Comtech EF Data CDM-625 - Manual (Page 435)

CDM-625 Advanced Satellite Modem Revision 15
Quality of Service (QoS) MN-CDM625
20–3
QoS Example 1
QUESTION: If the modem Tx data rate is set to 180 Kbps, then what is the QoS Tx data rate?
ANSWER “A” – For HW version 2.1 or newer:
The QoS Tx data rate can be set from 64 Kbps to 1 Mbps, in 64 Kbps steps. If the 180 Kbps
modem Tx data rate is not in 64 Kbps step size, then the QoS Tx data rate will be the next 64
Kbps, which is 196 Kbps.
ANSWER “B” – For HW version 1.1 or older:
If the Modem Tx Data rate of 180 Kbps is greater than 128 Kbps but less than 256 Kbps, then the
modem Tx data rate will be set to 256 Kbps.
20.2.2 Flow Control
In Layer 2 QoS mode, the CDM-625 supports Ethernet-based pause frame control (IEEE 802.3).
Flow control can be enabled or disabled independently in any of the LAN ports. Flow Control
requires WAN Buffer Length to be large enough so that
Data Rate in kbps
x buffer length / 4096 ≥ 24 .
20.2.3 Port-based Layer 2 QoS
When selecting Port-based Layer 2 QoS, each port’s priority is configurable to a QoS queue
priority of 1 (lowest) to 4 (highest). In this mode, irrespective of traffic type, all traffic ingress on
a particular port is treated with the priority assigned to that port.
In the event any port is overdriven with ingress traffic, if there is insufficient queue memory to
store the packet, then the packet will be dropped and drop stats will be incremented against
that port.
QoS Example 2
• 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 1 Mbps.
• The ingress traffic on each port is set to 250 Kbps.