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Differences Between Gigabit Ethernet IQ and Gigabit Ethernet IQ2 PICs

The following CoS differences arise because Gigabit Ethernet IQ PICs and Gigabit Ethernet IQ2 PICs use different hardware:

Gigabit Ethernet IQ2 PICs support a transmission rate within a queue, but do not support an exact rate within a queue. You can apply a weight to a queue, but you cannot put an upper limit on the queue transmission rate that is less than the logical interface can support. Consequently, the exact statement at the [edit class-of-service schedulers scheduler-name transmit-rate (rate | percent)] hierarchy level is not supported for Gigabit Ethernet IQ2 interfaces.
Gigabit Ethernet IQ2 PICs support only one queue in the scheduler map with medium-high, high, or strict-high priority. If more than one queue is configured with high or strict-high priority, the one that appears first in the configuration is implemented as strict-high priority. This queue receives unlimited transmission bandwidth. The remaining queues are implemented as low priority, which means they might be starved.
To ensure that protocol control traffic (such as OSPF, BGP, and RIP) are not dropped at the oversubscribed ingress direction, the software puts control protocol packets into a separate control scheduler. There is one control scheduler per port. These control schedulers are implemented as strict-high priority, so they transmit traffic until they are empty.
On Gigabit Ethernet IQ2 PICs, you can configure a single traffic-control profile to contain both a PIR (the shaping-rate statement) and a CIR (the guaranteed-rate statement). On Gigabit Ethernet IQ PICs, these statements are mutually exclusive.
Gigabit Ethernet IQ2 PICs support only two fill levels in the RED drop profile. The recommended definition of the RED drop profile is as follows:class-of-service { drop-profiles { drop-iq2-example1 { fill-level 20 drop-probability 0; fill-level 100 drop-probability 80; } } }

This configuration defines a drop profile with a linear drop probability curve when the fill level is between 20 and 100 percent, and a maximum drop probability of 80 percent.

You can configure more than two fill levels in the drop profile, but the software only uses the points (min_fill_level, 0) and (max_fill_level, max_probability) and ignores other fill levels. The drop probability at the minimum fill level is set to 0 percent even if you configure a non-zero drop probability value at the minimum fill level. The following example shows a sample configuration and the software implementation:

Configuration



class-of-service {


drop-profiles {


drop-iq2-example2 {
fill-level 30 drop-probability 10;
fill-level 40 drop-probability 20;
fill-level 100 drop-probability 80;
}


}


}

Implementation



class-of-service {


drop-profiles {


drop-iq2-example2-implementation {
fill-level 30 drop-probability 0;
fill-level 100 drop-probability 80;
}


}


}

If you configure more than two fill levels, a system log message warns you that the software supports only two fill levels and displays the drop profile that is implemented.

Though the interpolate statement is supported in the definition of a RED drop profile, we do not recommend using it. The following example shows a sample configuration and the software implementation:

Configuration



class-of-service {


drop-profiles {


drop-iq2-example3 {


interpolate {
fill-level [ 30 50 80 ];
drop-probability [ 10 20 40 ];
}


}


}


}

When you use the interpolate statement and the maximum fill level is not 100 percent, the software adds the point (100, 100). Therefore, the drop-iq2-example3 drop profile is implemented as:

Implementation



class-of-service {


drop-profiles {


drop-iq2-example3-implementation {
fill-level 2 drop-probability 0;
fill-level 100 drop-probability 100;
}


}


}

The implemented minimum fill level is not 30 percent as configured, but 2 percent because of the 64-point interpolation.

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