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Packets Are Lost Due to an Incorrect WRR Weight

Publication Date:  2012-07-25 Views:  39 Downloads:  0
Issue Description
In project V of country S, a Hybrid radio link is comprised of the OptiX RTN 900 V100R002, where the AM function is enabled. When the local region is heavily rainy, if the AM function adjusts the modulation scheme to the lowest one, calls become difficult to get through.
Alarm Information

None.

Handling Process

1. Relevant personnel check the wireless base station and find that the base station works normally.

2. Relevant personnel query alarms on the OptiX RTN equipment and find that no bit error alarms or other alarms associated with the radio link are reported.

3. Relevant personnel query the IF performance of the OptiX RTN equipment and find no FEC performance count.

4. Relevant personnel query the radio link bandwidth and find that the radio link bandwidth is 20 Mbit/s and the voice service occupies a 10 Mbit/s bandwidth.

5. Relevant personnel query the QoS configuration and find that the PHB class of the voice service is AF4 and that WRR queue scheduling is performed based on the default WRR weight of 25%. When the AM function adjusts the modulation scheme to the lowest one, the available bandwidth is 20 Mbit/s. In this case, the bandwidth of the voice service is 5 Mbit/s (20 Mbit/s x 25%). That is, the voice service requests for a 10 Mbit/s bandwidth but occupies only a 5 Mbit/s bandwidth. Consequently, a large number of voice service packets are lost, and thus calls become difficult to get through.

To resolve this problem, the relevant personnel adjust the WRR weight to 50% so that the voice service can occupy 10 Mbit/s (20 Mbit/s x 50%) bandwidth in the case of the lowest modulation scheme.  
Root Cause

1. The wireless base station is faulty.

2. Bit errors occur on the radio link.

3. The data service bandwidth is insufficient.

 
Suggestions

1. It is recommended that you configure voice services with the PHB service class of EF and adopt the SP queue scheduling scheme.

2. If the WRR queue scheduling scheme must be adopted for voice services, it is recommended that you set an appropriate WRR weight for the voice services, according to the lowest modulation scheme supported by the radio link.  

END