Analysis of LAWN Traffic

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Analysis of LAWN Traffic Powered By Docstoc
					Analysis of LAWN Traffic

         Talal Jaafar
       Omid Momtahan
        Dheeraj Reddy
Outline
   Motivation
   Signal to Noise Ratio (SNR)
   SNR & BER (Bit Error Rate) Relation
   Why Monitoring SNR?
   Methodology
   Next Steps & Questions
Motivation
   Need for mobility
   Increasing number of wireless local-area
    networks among university and corporate
    campuses
   Clear understanding of usage patterns is
    helpful for design, deployment, and
    management of WLAN
Signal to Noise Ratio (SNR)
   SNR
       Is the ratio of the received signal strength
        (power) over the noise strength in the
        frequency range of the operation.
       Is an important parameter of the physical
        layer of a LAWN.
   Noise strength, in general, can include
    the noise in the environment and other
    unwanted signals (interference).
Bit Error Rate (BER) and SNR
   BER is inversely related to SNR
       SNR         BER

       SNR         BER

   High BER (low SNR)
       Increases packet loss
       Increases delay
       Decreases throughput
Monitoring the SNR in LAWN
   Radio channels in LAWN are not
    stationary with time (temporal fading).
   All the locations in the coverage area
    cannot be considered in the initial site
    survey.
   The exact relation between the SNR
    and the BER is not easy to determine in
    the multi channel environment.
    Nonstationary Channels
   Indoor channels
       Fast: Motion of
        people or other objects
       Slow: change of
        office decorations
    Nonstationary Channels
   Outdoor channels
       Slow: change in the botanical composition
BER as a function of SNR
   The actual channel changed the exact
    relation between BER and SNR.
Asymmetry
Transmission/Reception
   Different amount of noise received at each
    device (thus, SNR is different)
   Asymmetry in Signal Strength is due to:
    - temporal fading (multipath propagation)
    - frequency hopping between transmission
      and reception
   So, Signal Strength is also needed to be
    monitored to have a complete measure of the
    SNR in the network
Modalities
   Efficient traffic sniffing and capture
       NetBSD-current
       bpf interface extensions for wireless
       BSD Radiotap header (prepended)
       Modified libpcap and tcpdump
            Additional link-layer types (802.11 and
             802.11_RADIO)
            802.11 frame descriptors and decoders
Modalities
   Granular radio properties
       Signal,Noise
       Channel, Current data rate etc.
       One or more of the various radio
        properties (driver and radio dependent)
       We are using a Linksys WPC11 802.11b
        card.
Modalities
   Post processing and information
    extraction
   Use libpcap* to extract radio
    information as well as higher layer info
   Use radio info to study asymmetry and
    higher layer info to study ‘goodput’
Modalities
   Active monitoring
       Periodically get the bridge tables and the
        various 802.11 parameters
       Relevant MIBs are Bridge MIB and
        IEEE802dot11-MIB
       Workstation with standard SNMP tools
   ftp://ftp.cisco.com/pub/mibs/v1/BRIDGE-MIB.my
   ftp://ftp.cisco.com/pub/mibs/v2/IEEE802dot11-MIB.my
Questions?

				
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posted:11/4/2008
language:English
pages:15