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?