lab 13 Performance of anomaly in multi-rate wireless

Objective

• What is performance anomaly?
• How to deal with performance anomaly and enhance throughput
  

background

in 802.11b, node A and node B both want to send data to the server. Node A start to move away form the the server. The transfer rate of node A adjust from 11M to 1M. Node B will change the rate that affected by node A. It called " performance anomaly".


simulation steps

we observe the data collect from node C

generate 11m_sd and 1m_sd and 11m_rd and 1m_rd for node A and node B

11m_rd and 1m_rd are the record from node C, received form node B, A .




observe the throughput. 0~15 sec. node C recv. 2Mbps form node A and node C
when A's data rate decreased to 1Mbps, node B's throughput also deceased to 750kbps-->
performance anomaly. After 30 secs, node B's data rate is recovered.

• Method 1
  change frame size. if rate is 11Mbps, CBR packets size 1000bytes
  rate is 1Mbps, CBR packets size change into 256 bytes.
  

This method slow down the rapid decrease of node B.

• Method 2
  change the contention window
  data rate 11Mbps contention window set to 32
  data rate 1Mbps contention window set to 352
  all node packet size are the same which is 1000 bytes

The rapid decreasing of node A (red line)will not bother node B(blue line)

The performance anomaly can be solved.