1 Network Measurements of a Wireless Classroom Network Carey Williamson Nuha Kamaluddeen Department of Computer Science University of Calgary

2 Introduction Wireless technologies are prevalent today; continued growth in popularity Example: IEEE b WLAN (“WiFi”) Economical, convenient, flexible solution for tetherless network access (11 Mbps) Enabler for mobile computing Two possible modes of usage: Infrastructure mode Ad hoc mode

3 Infrastructure Mode Carey Internet Access Point (AP) cnn.com

4 Motivation Observation: The same wireless technology that allows clients to be mobile also allows servers to be mobile Hybrid networking paradigm, combining client-server and ad hoc networking, without general Internet infrastructure Portable, short-lived, ad hoc networks “Portable networks” Is this useful? How well does it work?

5 Portable Network (1 of 2) Carey Access Point (AP) mystuff.com

6 Portable Network (2 of 2) Carey mystuff.com

7 Portable Networks Concept Set up when needed, tear down after Typically needed for minutes or hours When and where not known a priori No existing network infrastructure General Internet access not available, but not required either Pre-defined content; target audience Modest number of users; mobile too

8 Example Usage Scenarios Classroom area network (e.g. “legacy classroom”) Press conferences, media events Conventions and trade shows Disaster recovery sites Recruiting events Schools Voting...

9 Classroom Experiment Winter 2003 CPSC 641 graduate course at U of C ( Performance Issues in High Speed Networks ) Course content available online Mirrored copy of Web site provided in classroom using wireless Web server Students download desired content Review lecture notes Begin work on assignment (large trace file)

10 Experimental Setup IEEE b wireless LAN Ad hoc mode Web server (Apache) 13 students, sharing 6 laptops and 2 PDAs Wireless network analyzer Web Server Sniffer

11 Results Analysis Overview Aggregate traffic profile Per-client traffic profile TCP-level analysis TCP connection-level statistics Throughput analysis HTTP-level analysis Web user behaviour Persistent HTTP connections

12 Aggregate Traffic Profile (Feb’03) 01400

Per-Client Traffic Profiles

14 TCP-level Analysis Trace file Info about each TCP/IP packet exchanged 1400 seconds (~ 23 minutes) 262 TCP connections observed

15 Tutorial: HTTP and TCP TCP is a connection-oriented protocol SYN SYN/ACK ACK GET URL YOUR DATA HERE FIN FIN/ACK ACK Web ClientWeb Server

Example Web Page Harry Potter Movies As you all know, the new HP movie came out in June and then there will be a new book shortly after that… “Harry Potter and the Bathtub Ring” page.html hpface.jpg castle.gif

Client Server The “classic” approach in HTTP/1.0 is to use one HTTP request per TCP connection, serially. TCP SYN TCP FIN page.html Get TCP SYN TCP FIN hpface.jpg Get TCP SYN TCP FIN castle.gif Get

Client Server The “persistent HTTP” approach can re-use the same TCP connection for Multiple HTTP transfers, one after another, serially. Amortizes TCP overhead, but maintains TCP state longer at server. TCP FIN Timeout TCP SYN page.html Get hpface.jpg Get castle.gif Get

19 TCP – Connection Duration 56% lasted < 10 seconds Some lasted > 3 minutes

20 TCP – Number of Packets

21 TCP – Number of Bytes 92% transferred less than 2 MB One connection transferred 50 MB Contributed 20% of total traffic! Heavy-tailed behaviour

22 TCP – Connection Throughput

23 HTTP Requests per TCP Conn. Persistent connection Download multiple HTTP objects in one TCP connection Most TCP connections are non-persistent, but most HTTP transfers are on persistent connections Heavy-tailed or power-law behaviours

24 HTTP – Number of Packets

25 HTTP – Number of Bytes Up to 24 MB Majority transferred < 2 KB

26 HTTP Transfer Throughput Higher average than TCP connection throughput

27 Summary and Conclusions Portable networks: a novel paradigm for the use of wireless ad hoc networks Adequate performance for small WLAN classroom area network environment Works well even for wireless media streaming of audio and video with up to 8 clients (French 217, March 2004) Future work: exploring other scenarios using this networking paradigm