DOI: 10.21227/3tcj-w318
title: CRAWDAD pdx/vwave (2007-08-29)

description: date/time of measurement start: 2006-06-12date/time of measurement end: 2006-07-24collection environment: Analysis of the MAC-level behavior of WLANs is required in order to better deploy and design future systems. To this end, collection and analysis of traffic traces is an important task. We collected six traffic traces around Portland, Oregon using a commercial sniffer VWave which has a nano-second time resolution, and conduct an analysis of fine time scale (second or fraction of a second) packet, flow, and error characteristics of these networks.network configuration: We collected data at six different locations of which three (first three below) were located on-campus and three off-campus: - PSU (Portland State University) CS Department Near Faculty Offices in Networking Closet - PSU Library, 3rd Floor - PSU Cafeteria - Office overlooking ``Pioneer Square'' from the second floor - Urban Grind Coffee - Worldcup Coffee at Powell's Booksdata collection methodology: These traces were collected using a VeriWave WT20 Appliance which was kindly loaned to us by the folks at VeriWave http://www.veriwave.com. The WT20 hardware consists of two 802.11 reference radios, real-time linux, and two processors. The WT20 provides nanosecond resolution timestamps and it logs the time when it began seeing a frame and the time when the frame finished arriving.limitation: We face two challenges in data collection: The first is placement of the VWave sniffer. Because it has a lower effective receiver sensitivity than most access points today (-75dBm versus -90dBm), we must prevent a large possible packet loss with careful antenna choice and placement. The second problem is practical -- we had to obtain permission from the three merchants and further needed to ensure that our equipment was as unobtrusive as possible so as not to affect the ``normal'' behavior of the users.revision summary: A new traceset (pdx/vwave/wlan_nano) has been added.Tracesetpdx/vwave/wlan_pcapTraceset of six wireless LAN traffic traces around Portland, Oregon, collected using a commercial sniffer VWave which has a nano-second time resolution.methodology: The WT20 hardware consists of two 802.11 reference radios, real-time linux, and two processors. The WT20 provides nanosecond resolution timestamps and it logs the time when it began seeing a frame and the time when the frame finished arriving. We are using Veriwave WT20 in a somewhat novel way. It listens with two radios simultaneously on the same channel, recording frames to a per-radio, 256 MB, ring-buffer. The WT20's firmware will discard any frames received with a signal less than -75 dBm, but the rest (Data and Management, but not Control) are logged without any scrubbing. A tclsh script, running on a laptop connected to the WT20 (via ethernet), grabs the contents of this ring-buffer from each radio in-turn, every 10 seconds. This data is dumped as a VWR file, a proprietary Veriwave file format, and then converted to a libpcap file on the fly. At the end of a 4 hour capture we have 1440 files which are stitched together using a program we have developed for this purpose (after finding that existing tools like mergecap and tcpslice either contained bugs or didn't work with 802.11 traces).format: tcpdump (pcap) formatpdx/vwave/wlan_pcap Tracespdx/vwave/wlan_pcap/psu-cs: Wireless LAN traffic trace collected from PSU (Portland State University) CS Department.file: 2006_06_12_psu_cs.cap.gzconfiguration: Where: PSU (Portland State University) CS Department Near Faculty Offices in Networking Closet Duration: 1 Hour (1500 - 1600), Monday Description: The capture antennas were placed at the same level and immediately in front of the access-point antennas. The closest clients are at least one wall away. We used this site for prototyping our capture methodologies.pdx/vwave/wlan_pcap/library: Wireless LAN traffic trace collected from PSU (Portland State University) Library.file: 2006_07_10_library.cap.gzconfiguration: Where: PSU (Portland State University) Library, 3rd Floor Duration: 4 Hours (1400 - 1800), Monday Description: Each library floor is covered by at least three access-points. We positioned our capture antenna on a table, about 4 feet away from the access-point antenna (ceiling mounted) and with roughly the same vantage.pdx/vwave/wlan_pcap/cafeteria: Wireless LAN traffic trace collected from PSU (Portland State University) Cafeteria.file: 2006_07_10_cafe.cap.gzconfiguration: Where: PSU (Portland State University) Cafeteria Duration: 4 Hours (0930 - 1330), Monday Description: For this capture we placed our capture antenna directly under a sector antenna which serves the cafeteria. The room is mostly free of impediments, providing line-of-sight to nearly all users.pdx/vwave/wlan_pcap/pioneer-sq: Wireless LAN traffic trace collected from a large outdoor area in downtown Portland.file: 2006_06_26_pioneer.cap.gzconfiguration: Where: Office overlooking ``Pioneer Square'' from the second floor Duration: 4 Hours (1130 - 1530), Monday Description: This location serves Pioneer Square, a large common outdoor area in downtown Portland, and surrounding coffee-shops and businesses. We setup the VeriWave WT20's antenna to the side of the access-point antenna, in a neighboring room. One wall and about 5 feet separated the capture antenna from the access-point antenna.pdx/vwave/wlan_pcap/urban-grind: Wireless LAN traffic trace collected from a coffee shop in Portland.file: 2006_07_20_ug.cap.gzconfiguration: Where: Urban Grind Coffee Duration: 2 Hours (1300 - 1500), Thursday Description: The Urban Grind is a popular coffee-shop in Portland for laptop-users, and gets as much or more laptop-traffic then any other coffee-shop in Portland. This space, like the cafeteria, has very few impediments - both the access-point and the capture antenna have line of sight to nearly every client device. The capture antenna was placed approximately 10 feet from the ceiling-mounted access point.pdx/vwave/wlan_pcap/powells: Wireless LAN traffic trace collected from a coffee shop at a bookstore in Portland.file: 2006_07_24_powells.cap.gzconfiguration: Where: Worldcup Coffee at Powell's Books Duration: 4 Hours (1030 - 1430), Monday Description: The coffee shop at Powells sees a typical, slow but steady stream of laptop users. Aside from a couple of book-cases, it is a mostly open space. We positioned our capture antenna on a bookshelf approximately 8 feet above the ground to have good line-of-site to the access-point and the laptop-using patrons.