Date post: | 19-Jun-2015 |
Category: |
Technology |
Upload: | wathsala-vithanage |
View: | 1,582 times |
Download: | 7 times |
Bassa: A Time Shifted Web Caching System for
Developing Regions
Wathsala W. Vithanage | Ajanth S. Atukorale
June 29, 2011
Introduction
Web caches in developing regions have varying hit rates. (10% -25% in India according to J. Chen et al. [1] and 50% in Cambodiaaccording to Bowei et al. [2])
Even with web caching page load times are quite high indeveloping regions due to congestion on low bandwidth networks
Large file downloads can be time shifted by a web proxy. Whennetworks are highly congested web proxies can perform time shiftedcaching by queuing the request in order to fetch the file later.
Observations
Networks in most developing countries are highly congestedduring the day time and underutilized during the night.
This has been observed in an analysis of WWW traffic inGuana and Cambodia [2].
This has been observed in Sri Lankan universities as well [3].
Bandwidth Utilization
Figure: Bandwidth utilization before time shifted caching.
Time Shifting the Caching Process
Based on content1 It might be possible to time shift caching of certain content
types. (Ex: Video, Application, etc)
Based on size1 It might be possible to time shift caching of content based on
an object size threshold. (Ex: Objects larger than 20MB)
Time Shifting the Caching Process
1
10
100
1000
10000
1 10 100 1000 10000 100000 1e+06
Fre
quen
cy
Object Size
Video Content
(a) Video Content
1
10
100
1000
10000
100000
1e+06
1 10 100 1000 10000 100000 1e+06 1e+07
Fre
quen
cy
Object Size
Application Content
(b) Application Content
1
10
100
1000
10000
100000
1e+06
1e+07
1 10 100 1000 10000 100000 1e+06 1e+07
Fre
quen
cy
Object Size
Peak HoursOff Peak Hours
(c) Split by Time
1
10
100
1000
10000
100000
1e+06
1e+07
1 10 100 1000 10000 100000 1e+06 1e+07
Fre
quen
cy
Object Size
All Object for 24 Hours
(d) All Objects
Figure: Logarithmic plot of object size (in 8KB bins) distribution.
Time Shifting based on Object Size
Deciding the appropriate object size threshold for time shifting.
Figure: Object size threshold vs bandwidth usage with the fitted curve ofthe form
√
a/x + b where a = 2.075 and b = 0.059.
Abstract Time Shifted Caching System
Figure: Proxy server with time shifted caching capability.
Time Shifting Results
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20
Am
ount
of D
ata
Time of the Day
TotalLarger than 70MB
Figure: Object size threshold vs bandwidth usage
Time Shifting Results
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 50 100 150 200 250 300
Use
d ba
ndw
idth
/Tot
al B
andw
idth
Object Size Threshold
Data for 24 Hours
Data for Peak Hours
(a) Bandwidth Utilization After (b) Bandwidth Utilization Before
Figure: Bandwidth Utilization vs Size Threshold
Time Shifting Results
The 23% of the bandwidth saved by time shifting of caching hasincreased the number of data volume and number of requests.
Table: Details on Deployment Environment.
Number of Requests Data Volume in GB
Before 7,909,912 760After 9,967,372 1030
Time Shifting Results
Table: Summary percentages.
Content Type Before As a
Percentage
of 760GB
After As a
Percentage
of 1030GB
Change
in Data
Volume
Video 40.38% 47.42% +59.15%Application 33.06% 33.03% +35.40%
Audio 0.29% 0.59% +175.72%Image 13.74% 8.95% -11.52%Text 12.04% 5.99% -32.57%Other 0.49% 4.02% +1011.86%
Time Shifting Results
7% of the total bandwidth was used during the night fordownloading video content.
4% of the total bandwidth was used for downloading binary,octet-stream types (ISO disk images and Executables).
Bandwidth consumed for text and images were reduced by-32.5% and -11.5% respectively.
35% increase in the data volume after time shifted cachingwas introduced.
Even though 23% of the bandwidth was freed during thedaytime only 21.7% of this amount was utilized.
1 This implies that our network was not saturated afterdeploying Bassa.
2 This also tells us that it is possible to increase the object sizethreshold to a larger value.
100% increase in large file downloads.
Conclusion
Bassa has reduced the network congestion during the day.Increased video content is an evidence.
Bassa has utilized the network that idles throughout night.
Bassa has encouraged users to download large files such asISO disk images and Videos. 100% increase in large filedownloads.
Some users got annoyed as 8% of the downloads failed due tosession timeouts.
Bassa Architecture
Figure: Bassa Components and Messages.
User Interface
Figure: Bassa Main User Interface.
User Interface
Figure: Bassa Personal User Interface.
Questions and Comments
References
Jay Chen, Saleema Amershi, Aditya Dhananjay, and LakshmiSubramanian.Comparing web interaction models in developing regions.In Proceedings of the First ACM Symposium on Computing
for Development, ACM DEV ’10, pages 6:1–6:9, New York,NY, USA, 2010. ACM.
Bowei Du, Michael Demmer, and Eric Brewer.Analysis of www traffic in cambodia and ghana.In Proceedings of the 15th international conference on World
Wide Web, WWW ’06, pages 771–780, New York, NY, USA,2006. ACM.
W V Wathsala, B Siddhisena, and A S Atukorale.Next generation proxy servers.In Proceedings of 10th International Conference on Advanced
Communication Technology, volume 3 of ICACT ’08, pages2183–2187, 2008.