As a simple example showing how bandwidth is shared among the
logical interfaces, assume that all traffic is sent on queue 0. Assume
also that there is a 40-Mbps load on all of the logical interfaces.
Configuration details are shown in Table 65.
Table 65: Sharing Bandwidth
Among Logical Interfaces
Logical Interface (Unit)
Traffic Control Profile
WRR Percentages
Weights
Unit 1
PIR 100 Mbps
95, 0, 0, 5
10, 1, 1, 1
Unit 2
CIR 20 Mbps
25, 25, 25, 25
64, 64, 64, 64
Unit 3
PIR 40 Mbps, CIR 20 Mbps
50, 30, 15, 5
128, 76, 38, 13
Unit 4
Unshaped
95, 0, 0, 5
10, 1, 1, 1
When the port is shaped at 40 Mbps, because units 2 and
3 have a guaranteed rate (CIR) configured, both units 2 and 3 get
20 Mbps of shared bandwidth.
When the port is shaped at 100 Mbps, because unit 2 and
3 have a guaranteed rate (CIR) configured, each of them can transmit
20 Mbps. On units 1, 2, 3, and 4, the 60 Mbps of excess bandwidth
is shaped according to the values shown in Table 66.
Table 66: First Example
of Bandwidth Sharing
Logical Interface (Unit)
Calculation
Bandwidth
Unit 1
10 / (10+64+128+10) x 60 Mbps
2.83 Mbps
Unit 2
64 / (10+64+128+10) x 60 Mbps
18.11 Mbps
Unit 3
128 / (10+64+128+10) x 60 Mbps
36.22 Mbps
Unit 4
10 (10+64+128+10) x 60 Mbps
2.83 Mbps
However, unit 3 only has 20 Mbps extra (PIR and CIR) configured.
This means that the leftover bandwidth of 16.22 Mbps (36.22 Mbps –
20 Mbps) is shared among units 1, 2, and 4. This is shown in Table 67.
Table 67: Second Example
of Bandwidth Sharing
Logical Interface (Unit)
Calculation
Bandwidth
Unit 1
10 / (10+64+128+10) x 16.22 Mbps
1.93 Mbps
Unit 2
64 / (10+64+128+10) x 16.22 Mbps
12.36 Mbps
Unit 4
10 (10+64+128+10) x 16.22 Mbps
1.93 Mbps
Finally, Table 68 shows the
resulting allocation of bandwidth among the logical interfaces when
the port is configured with a 100-Mbps shaping rate.
