Sharing Bandwidth Among Logical Interfaces

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 233.

Table 233: Sharing Bandwidth Among Logical Interfaces

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.
2. When the port is shaped at 100 Mbps, because units 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 234.

   Table 234: First Example of Bandwidth Sharing

   Logical Interface (Unit)	Calculation	Bandwidth
   1	10 / (10+64+128+10) x 60 Mbps	2.83 Mbps
   2	64 / (10+64+128+10) x 60 Mbps	18.11 Mbps
   3	128 / (10+64+128+10) x 60 Mbps	36.22 Mbps
   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, and 2, and 4. This is shown in Table 235.

Table 235: Second Example of Bandwidth Sharing

Finally, Table 236 shows the resulting allocation of bandwidth among the logical interfaces when the port is configured with a 100-Mbps shaping rate.

Table 236: Final Example of Bandwidth Sharing

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