CRAWDAD pdx/vwave (2007-08-29)

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.

测量开始日期/时间：2006-06-12；测量结束日期/时间：2006-07-24
采集背景：为更好地部署与设计下一代无线局域网（Wireless Local Area Network, WLAN）系统，需对其媒体访问控制层（Media Access Control layer, MAC层）行为开展分析。为此，流量轨迹的采集与分析是一项核心任务。本数据集使用搭载纳秒级时间分辨率的商用嗅探器VWave，在俄勒冈州波特兰市周边采集了6组流量轨迹，并对这些网络的细时间尺度（秒级或亚秒级）数据包、流以及错误特征展开分析。

网络配置：本次数据采集覆盖6个不同地点，其中3处位于校园内（前3处），另外3处位于校园外：
- 波特兰州立大学（Portland State University, PSU）计算机科学系网络机柜附近的教师办公室区域
- 波特兰州立大学图书馆三楼
- 波特兰州立大学食堂
- 俯瞰「先锋广场（Pioneer Square）」的二楼办公室
- Urban Grind咖啡店
- 鲍威尔书店内的Worldcup咖啡店

数据采集方法：本数据集的流量轨迹由VeriWave WT20采集设备完成，该设备由VeriWave团队慷慨出借（官网：http://www.veriwave.com）。WT20硬件包含两块802.11标准参考无线电模块、实时Linux操作系统以及双处理器，可提供纳秒级分辨率的时间戳，记录设备首次检测到帧的时刻与帧完全接收的时刻。

数据局限：本次采集面临两项挑战：其一为嗅探器部署问题。相较于当前多数接入点（-90dBm），VWave嗅探器的有效接收灵敏度更低（-75dBm），因此需谨慎选择天线类型与部署位置，避免出现大量数据包丢失。其二为实操限制：需获得3家商户的许可，并确保采集设备尽可能隐蔽，以免干扰用户的正常网络行为。

修订说明：已新增轨迹集pdx/vwave/wlan_nano。
轨迹集pdx/vwave/wlan_pcap：在俄勒冈州波特兰市周边采集的6组无线局域网流量轨迹，采集工具为搭载纳秒级时间分辨率的商用嗅探器VWave。

采集流程：WT20硬件包含两块802.11标准参考无线电模块、实时Linux操作系统以及双处理器，可提供纳秒级分辨率的时间戳，记录设备首次检测到帧的时刻与帧完全接收的时刻。本次采集以较为新颖的方式使用VeriWave WT20设备：其两块无线电模块可同时监听同一信道，将捕获的帧存储至每块无线电专属的256MB环形缓冲区中。WT20固件会丢弃信号强度低于-75dBm的帧，但其余帧（数据帧与管理帧，不包含控制帧）会被无过滤地记录。通过以太网连接至WT20的笔记本电脑上运行的tclsh脚本，每10秒依次从每块无线电的环形缓冲区中提取数据，以专有Veriwave文件格式VWR导出，随后实时转换为libpcap格式文件。在一次4小时的采集任务结束后，将生成1440个文件，通过自研程序完成拼接（此前测试发现mergecap、tcpslice等现有工具存在漏洞，或无法兼容802.11流量轨迹）。

格式：tcpdump（pcap）格式

pdx/vwave/wlan_pcap 轨迹集

pdx/vwave/wlan_pcap/psu-cs：从波特兰州立大学计算机科学系采集的无线局域网流量轨迹
文件名：2006_06_12_psu_cs.cap.gz
配置信息：
采集地点：波特兰州立大学计算机科学系网络机柜附近的教师办公室区域
采集时长：1小时（1500 - 1600），周一
采集说明：采集天线与接入点天线处于同一高度且紧邻前方，最近的客户端至少隔着一堵墙。本次采集用于验证采集方法的可行性。

pdx/vwave/wlan_pcap/library：从波特兰州立大学图书馆采集的无线局域网流量轨迹
文件名：2006_07_10_library.cap.gz
配置信息：
采集地点：波特兰州立大学图书馆三楼
采集时长：4小时（1400 - 1800），周一
采集说明：图书馆每层至少部署3台接入点。采集天线放置在距离天花板安装的接入点天线约4英尺的桌面上，二者视野高度相近。

pdx/vwave/wlan_pcap/cafeteria：从波特兰州立大学食堂采集的无线局域网流量轨迹
文件名：2006_07_10_cafe.cap.gz
配置信息：
采集地点：波特兰州立大学食堂
采集时长：4小时（0930 - 1330），周一
采集说明：本次采集将天线直接部署在服务食堂的扇形天线下方。食堂空间几乎无遮挡，几乎所有用户都能与天线实现视距传输。

pdx/vwave/wlan_pcap/pioneer-sq：从波特兰市中心大型户外区域采集的无线局域网流量轨迹
文件名：2006_06_26_pioneer.cap.gz
配置信息：
采集地点：俯瞰「先锋广场」的二楼办公室
采集时长：4小时（1130 - 1530），周一
采集说明：该地点服务于先锋广场——波特兰市中心的大型公共户外区域，以及周边的咖啡店与商户。我们将VeriWave WT20的天线部署在相邻房间内，与接入点天线间隔一堵墙和约5英尺距离。

pdx/vwave/wlan_pcap/urban-grind：从波特兰市内一家咖啡店采集的无线局域网流量轨迹
文件名：2006_07_20_ug.cap.gz
配置信息：
采集地点：Urban Grind咖啡店
采集时长：2小时（1300 - 1500），周四
采集说明：Urban Grind是波特兰颇受欢迎的笔记本用户聚集地，其笔记本流量规模不低于波特兰其他任何咖啡店。与食堂类似，该空间几乎无遮挡，接入点与采集天线几乎能与所有客户端设备实现视距传输。采集天线放置在距离天花板安装的接入点约10英尺的位置。

pdx/vwave/wlan_pcap/powells：从波特兰一家书店内的咖啡店采集的无线局域网流量轨迹
文件名：2006_07_24_powells.cap.gz
配置信息：
采集地点：鲍威尔书店内的Worldcup咖啡店
采集时长：4小时（1030 - 1430），周一
采集说明：鲍威尔书店内的咖啡店客流稳定，以笔记本用户为主，整体节奏平缓。除少量书架外，空间基本开放。我们将采集天线部署在距地面约8英尺的书架上，以获得与接入点及使用笔记本的顾客良好的视距传输条件。