Changes between Version 47 and Version 48 of 802.11/wlan_exp/app_notes/dcf_with_multiple_flows


Ignore:
Timestamp:
Apr 22, 2014, 9:50:16 AM (10 years ago)
Author:
chunter
Comment:

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  • 802.11/wlan_exp/app_notes/dcf_with_multiple_flows

    v47 v48  
    3838These statistics are sufficient to calculate total throughput, packet delivery ratio (PDR) and average number of re-transmissions per packet.
    3939
    40 '''TODO: NEEDS DATA'''
    41 
    4240||    ||||=  Flow 1  =||||=  Flow 2  =||||=  Flow 3  =||||=  Flow 4  =||
    4341|| Carrier Sensing || On || Off || On || Off || On || Off || On || Off ||
    44 || Tx Pkts || 1a || 1b || 2a || 2b || 3a || 3b || 4a || 4b ||
    45 || Rx Pkts || 1a || 1b || 2a || 2b || 3a || 3b || 4a || 4b ||
     42|| # MPDU Tx || 51808 || 1b || 51792 || 2b || 114116 || 3b || 121787 || 4b ||
     43|| # PHY Tx || 65535 || 1b || 66211 || 2b || 140036 || 3b || 147488 || 4b ||
     44|| # PHY Re-Tx || 13727 || 1b || 14419 || 2b || 25920 || 3b || 25701 || 4b ||
     45|| # MPDU Rx || 51806 || 1b || 51792 || 2b || 114115 || 3b || 121788 || 4b ||
     46|| Throughput (Mbps) || 1.97 || 1b || 1.97 || 2b || 4.33 || 3b || 4.62 || 4b ||
    4647
    4748It is clear that without carrier sensing all flows suffer...
    … …  
    9495||||=  '''Contention Windows at Each Node vs. Time'''  =||
    9596||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_cw_vs_time.png, width=500)]]  ||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_cw_vs_time.png, width=500)]]  ||
    96 ||  '''Carrier Sensing Enabled'''  ||  '''Carrier Sensing Disabled'''  ||
     97||  '''Physical Carrier Sensing Enabled'''  ||  '''Physical Carrier Sensing Disabled'''  ||
    9798
    9899These plots show the actual contention window value of every node at the time of every PHY transmission. The contention window is only updated following PHY transmissions, so these plots capture the complete history of contention window values at every node. The impact of carrier sensing on contention window is dramatic. Disabling carrier sensing increases the probability of collisions. As explained above, more collisions leads to more transmission failures, leading to higher expected contention window values. This is exactly what the results show.