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Network Measurements of a Wireless Classroom Network
Carey Williamson Nuha Kamaluddeen
Department of Computer ScienceUniversity 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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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 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
IEEE 802.11b wireless LAN Ad hoc mode Web server (Apache) 13 students, sharing
6 laptops and 2 PDAs Wireless network analyzer
Web Server Sniffer
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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 (Feb’03)
Aggregate Packets Transmitted on WLAN
0
100
200
300
400
500
600
700
800
Time in Seconds
Pa
cke
ts p
er
1 se
c In
terv
al
0 1400
Packets Transmitted by Client IP 200
0
100
200
300
400
500
600
700
Time in Seconds
Pa
cke
ts p
er
1 s
ec I
nte
rva
l
Packets Transmitted by Client IP 204
0
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200
300
400
500
600
700
Time in Seconds
Pa
cke
ts p
er
1 s
ec I
nte
rva
l
Packets Transmitted by Client IP 207
0
100
200
300
400
500
600
700
Time in Seconds
Pa
cke
ts p
er
1 s
ec I
nte
rva
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Packets Transmitted by Client IP 212
0
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400
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600
700
Time in Seconds
Pa
cke
ts p
er
1 s
ec I
nte
rva
l
Packets Transmitted by Client IP 220
0
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700
Time in Seconds
Pa
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ts p
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1 s
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Packets Transmitted by Client IP 208
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700
Time in Seconds
Pa
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ts p
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1 s
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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
SYN
SYN/ACK
ACKGET URL
YOUR DATA HERE
FINFIN/ACK
ACK
Web Client Web Server
Example Web Page
Harry Potter Movies
As you all know,the new HP moviecame out in Juneand then there willbe a new bookshortly after that…
“Harry Potter andthe Bathtub Ring”
page.html
hpface.jpg
castle.gif
Client Server
The “classic” approachin HTTP/1.0 is to use oneHTTP request per TCPconnection, serially.
TCP SYN
TCP FIN
page.htmlGet
TCP SYN
TCP FIN
hpface.jpgGet
TCP SYN
TCP FIN
castle.gifGet
Client Server
The “persistent HTTP”approach can re-use thesame TCP connection forMultiple HTTP transfers,one after another, serially.Amortizes TCP overhead,but maintains TCP statelonger at server.
TCP FIN
Timeout
TCP SYN
page.html
Get
hpface.jpg
Get
castle.gif
Get
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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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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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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
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