Analysis of LAWN Traffic

1
Analysis of LAWN Traffic

• Talal Jaafar
• Omid Momtahan
• Dheeraj Reddy

2
Outline

• Motivation
• Signal to Noise Ratio (SNR)
• SNR BER (Bit Error Rate) Relation
• Why Monitoring SNR?
• Methodology
• Next Steps Questions

3
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

4
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).

5
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

6
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.

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Nonstationary Channels

• Indoor channels
• Fast Motion of people or other objects
• Slow change of office decorations

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Nonstationary Channels

• Outdoor channels
• Slow change in the botanical composition

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BER as a function of SNR

• The actual channel changed the exact relation
  between BER and SNR.

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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

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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

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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.

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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

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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.m
  y

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Questions?