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Port broadcast packet suppression of the NG-DWDM data board and CAR coupling

Publication Date:  2012-07-25 Views:  198 Downloads:  0

Issue Description

The TN11TBE board is configured with the 1Q bridge, with the configuration of the port stream. The port stream is bound with the CAR.
The settings of the CAR parameters: cir=100M, cbs=0, pir=100M, pbs=0.
The broadcast packet suppression is enabled. The suppression parameter is 3, that is, packets can broadcast through 300M (GE port). In the example, the CAR and broadcast packet suppression coupling are configured. When packets are sent in 1000 M, the 100 M broadcast packets can pass theoretically. The actual tests of the TN11TBE board are as follows:
? When the meter sends 100% broadcast packets, 30 M broadcast packets can pass.
? When the packet transmit rate decreases gradually, the passed broadcast packets increase gradually until 100 M.
? When the ratio of the non-broadcast packets to transmitted packets increases, the passed packets increase gradually. Up to 100 M packets can pass.
In the problem description, 100 M and 300 M are the assumed values. The symptom is the similar in the setting of other parameters. 

Alarm Information


Handling Process

In the case of the coupling test, engineers should not send 100% broadcast packets. Engineers should reduce the packet rate or increase the ratio of sending service packets. 

Root Cause

The problem is related to the BCM L2 chip broadcast packet suppression. The BCM chip broadcast packet suppression uses a counter to make statistic of the number of the passed packets. When the threshold is reached, the followed broadcast packets are lost. When 100% broadcast packets are sent, the 300 M broadcast packets are passed in 100% rate in the first part of each second. No packets are sent later. After the broadcast packet suppression, the rate of the service is uneven, that is, packets are sent in 100% rate (300 M) in the first 0.3 seconds in a second, and no packets are sent in the later 0.7 seconds.
When the packet stream passes the CAR, the CAR is valid for packets in 0.3 second. Hence, the actually passed packets are 30 M (300M*10%), because the CAR parameter is set to 100 M and 30 M packets are passed in 0.3 second (10 M packets are passed in 0.1 second).
When the transmit rate decreases, the packet rate passing the CAR is smaller. The packet rate is even; therefore, more broadcast packets are passed.
When the ratio of the service packets increases, service packets are not suppressed after the suppression of broadcast packets. More packets pass in the CAR.