Network Measurements of a Wireless Classroom Network

1
Network Measurements of a Wireless Classroom
Network

• Carey Williamson
• Nuha Kamaluddeen
• Department of Computer Science
• University of Calgary

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Introduction

• Wireless technologies are prevalent today
  continued growth in popularity
• Example IEEE 802.11b 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

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

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

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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...

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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)

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Experimental Setup
Web Server
Sniffer

• IEEE 802.11b wireless LAN
• Ad hoc mode
• Web server (Apache)
• 13 students, sharing 6 laptops and 2
  PDAs
• Wireless network analyzer

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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

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Aggregate Traffic Profile (Feb03)
0
1400
13
Per-Client Traffic Profiles
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TCP-level Analysis

• Trace file
• Info about each TCP/IP packet exchanged
• 1400 seconds ( 23 minutes)
• 262 TCP connections observed

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Tutorial HTTP and TCP

• TCP is a connection-oriented protocol

YOUR DATA HERE
Web Client
Web Server
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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
hpface.jpg
page.html
castle.gif
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Server
Client
The classic approach in HTTP/1.0 is to use
one HTTP request per TCP connection, serially.
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Server
Client
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.
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TCP Connection Duration

• 56 lasted lt 10 seconds
• Some lasted gt 3 minutes

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TCP Number of Packets
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TCP Number of Bytes

• 92 transferred less than 2 MB
• One connection transferred 50 MB
• Contributed 20 of total traffic!
• Heavy-tailed behaviour

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TCP Connection Throughput
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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

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HTTP Number of Packets
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HTTP Number of Bytes

• Up to 24 MB
• Majority transferred lt 2 KB

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HTTP Transfer Throughput

• Higher average than TCP connection throughput

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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