Effects of a Bad Channel on the overall WLAN Performance.
CS577 Advanced Networking Spring 05
Ashish Samant, Jon Gretarsson, Feng Li{Asamant, jontg, lif}@cs.wpi.edu
Computer Science DepartmentWorcester Polytechnic Institute
Worcester, MA, 01609 USA
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Outline
• Introduction
• Experimental Methods– Tools and Setup– Experimental Design
• Preliminary Results and Analysis
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Motivation
• Increasingly, deployment of streaming multimedia over wireless LANs– Hardware price decreasing. –Wireless link capacity increasing:
11Mbps(802.11b), 54Mbps(802.11g).– Streaming techniques becoming
mature.
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Related Work
• SWAN-PAM (Streaming over Wireless LAN) (PAM and NOSSDAV)– Disadvantage: Only study the video
performance without competing traffic.
• Mobility on Wireless Streaming Performance (Williamson paper).– Disadvantage: • Fake AP , IEEE 802.11b.• Need a further analysis for competing
traffic.
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Williamson’s conclusion
In Infrastructure wireless network• “I Jumped, do you Jump? “– Poor Channel condition for one client
will degrade the performance of the client at good channel condition.
• Access Point (AP) may be the Bottle neck. – The Queue in AP may be fill up by the
packets when the wireless channel is poor.
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Objectives
• Correlate performance for Competing Traffic (streaming traffic and TCP Bulk Downloading).– Wireless Link Layer– Network Layer – Application Layer
• Focus on – the effects on performance from the competing
traffic streaming traffic at bad location (verifying Williamson’s paper)
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Outline
• Introduction
• Experimental Methods– Tools and Setup– Experimental Design
• Preliminary Results and Analysis
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Wireless Layer
• WRAPI– Signal Strength– Uplink fail/retry fraction– Downlink dup fraction
• Typeperf.exe–WLAN capacity– CPU usage– Receiving bandwidth
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Network Layer
• UDP Ping– RTT– Packet loss rate
• Wget.exe– TCP throughput– Throughput capacity
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Application Layer
• Media Tracker– Frame Rate– Loss Rate– Scaling Level
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Experimental Setup
• Three runs• Two laptops– Laptop A remains fixed in ‘Good’
Location– Laptop B is in ‘Good’ Location for one
set of experiments, and is then moved to a ‘Bad’ Location
• Media Server on 100 Mbps WLAN• Access Point serving 802.11g
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Experimental Setup
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
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Experimental Setup
• Experiments were conducted during off-hours in the Fuller Sub-Basement
• AP bottleneck ensured with preliminary tests
• WRAPI used to ensure that ping-pong never occurs
• Good Locations were within A21• Bad Location was at the end of
hallway, near service entrance
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Experimental Design
• Laptop A– Good Location– Light UDP Traffic– TCP Bulk
Download
• Laptop B– Good, Bad
Location– Light UDP Traffic– TCP Bulk
Download– UDP Stream– TCP Stream
