1. Bassa: A Time Shifted Web Caching System for
Developing Regions
Wathsala W. Vithanage | Ajanth S. Atukorale
June 29, 2011

2. Introduction
Web caches in developing regions have varying hit rates. (10% -
25% in India according to J. Chen et al. [1] and 50% in Cambodia
according to Bowei et al. [2])
Even with web caching page load times are quite high in
developing regions due to congestion on low bandwidth networks
Large file downloads can be time shifted by a web proxy. When
networks are highly congested web proxies can perform time shifted
caching by queuing the request in order to fetch the file later.

3. Observations
Networks in most developing countries are highly congested
during the day time and underutilized during the night.
This has been observed in an analysis of WWW traffic in
Guana and Cambodia [2].
This has been observed in Sri Lankan universities as well [3].

4. Bandwidth Utilization
Figure: Bandwidth utilization before time shifted caching.

5. Time Shifting the Caching Process
Based on content
1 It might be possible to time shift caching of certain content
types. (Ex: Video, Application, etc)
Based on size
1 It might be possible to time shift caching of content based on
an object size threshold. (Ex: Objects larger than 20MB)

6. Time Shifting the Caching Process
10000 1e+06
Video Content Application Content
100000
1000
Frequency
Frequency
10000
100 1000
100
10
10
1 1
1 10 100 1000 10000 100000 1e+06 1 10 100 1000 10000 100000 1e+06 1e+07
Object Size Object Size
(a) Video Content (b) Application Content
1e+07 1e+07
Peak Hours All Object for 24 Hours
1e+06 Off Peak Hours 1e+06
100000 100000
Frequency
Frequency
10000 10000
1000 1000
100 100
10 10
1 1
1 10 100 1000 10000 100000 1e+06 1e+07 1 10 100 1000 10000 100000 1e+06 1e+07
Object Size Object Size
(c) Split by Time (d) All Objects

7. 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 of
the form a/x + b where a = 2.075 and b = 0.059.

8. Abstract Time Shifted Caching System
Figure: Proxy server with time shifted caching capability.

9. Time Shifting Results
1
Total
Larger than 70MB
0.8
Amount of Data
0.6
0.4
0.2
0
0 5 10 15 20
Time of the Day
Figure: Object size threshold vs bandwidth usage

10. Time Shifting Results
0.8
Data for 24 Hours
Used bandwidth/Total Bandwidth
0.7 Data for Peak Hours
0.6
0.5
0.4
0.3
0.2
0.1
0
0 50 100 150 200 250 300
Object Size Threshold
(a) Bandwidth Utilization After (b) Bandwidth Utilization Before
Figure: Bandwidth Utilization vs Size Threshold

11. Time Shifting Results
The 23% of the bandwidth saved by time shifting of caching has
increased the number of data volume and number of requests.
Table: Details on Deployment Environment.
Number of Requests Data Volume in GB
Before 7,909,912 760
After 9,967,372 1030

12. Time Shifting Results
Table: Summary percentages.
Content Type Before As a After As a Change
Percentage Percentage in Data
of 760GB of 1030GB 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%

13. Time Shifting Results
7% of the total bandwidth was used during the night for
downloading 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 caching
was introduced.
Even though 23% of the bandwidth was freed during the
daytime only 21.7% of this amount was utilized.
1 This implies that our network was not saturated after
deploying Bassa.
2 This also tells us that it is possible to increase the object size
threshold to a larger value.
100% increase in large file downloads.

14. 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 as
ISO disk images and Videos. 100% increase in large file
downloads.
Some users got annoyed as 8% of the downloads failed due to
session timeouts.

15. Bassa Architecture
Figure: Bassa Components and Messages.

16. User Interface
Figure: Bassa Main User Interface.

17. User Interface
Figure: Bassa Personal User Interface.

18. Questions and Comments

19. References
Jay Chen, Saleema Amershi, Aditya Dhananjay, and Lakshmi
Subramanian.
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, pages