department of computer science southern illinois university edwardsville dr. hiroshi fujinoki and...
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Department of Computer ScienceSouthern Illinois University Edwardsville
Dr. Hiroshi Fujinoki and Kiran GollamudiE-mail: {hfujino, kgollam}@siue.edu
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Response Time
Problem Definition
Problem
The elapsed time between the end of an inquiry on a computer system and the beginning of a response
• Long response time
• Operating system overhead
Due to high web traffic load
FAT look-up, following a sector-chain,multiple clients etc
• Transmission time
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Delay Causes
We have 3 different causes of delay
RECEIVER
Network Protocol Processing Overhead
Operating system overhead
Internet
Request
ResponseRequest (1)
Response with tag (2)
Request (3)
Response (4)
Internet
Request
Response
SENDER
Routing Overhead + Error/Flow control Overhead
Internet
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HTTP Client/Server model
HTTP Client HTTP Server
TCP SyncTCP Sync ACK
HTTP Get
Transmitting-requested file
Requested filestarts arriving.
Time
• Response time
• Transmission time
Terms Defined
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Existing work for Client/Server model
Existing Methods
Caching Server Clustering Mirroring
The following are the existing techniques to reduce response time and transmission delay
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Object Packaging
Objective
• Reduced network protocol overhead during the transmission at routers
• Reduced number of packets by minimizing fragmentation
To improve response time and transmission time by :
• Single request for the multiple files
• Reduced OS overhead at a web server
Reduced FAT lookups
CRC calculation overhead
Memory copies
Flow control and error control
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Concept Of Object Packaging
• Is a collection of web files in a web site
• Files are sequentially packed without compression
Object Packaging:
Object Package
Number of objects
Object Offset Fields
File #1 File #n
Pointer
File header
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Packaging Format Of Object Packaging
Object Information Field
File name sub File size sub File attribute sub
Number of objects (files) sub
Object Information FieldObject Information Field
File name subfield File size subfield File attribute subfield
Number of objects (files) subfield
• Object Information Field: Contains the information of the packed files
• Data Field: Contains the contents of the requested files
• Number of objects: Tells how many packed files are there
Sub field
•A collection of the names of the contained files •A collection of the sizes of the contained files • File Attribute Subfield: Each file is a binary, text, or executable
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Experiment Modeling
• Client Machine: The host that requests the server for the data
• Hub : Broadcasts every packet to every port
• Traffic Monitor: Monitors the all the traffic (packets) that are passing
Test-Bed
Requests
Requested Files
Web Server Client
Traffic Monitor
Hub
Local Disk
Requests
Requested Files
Requests
Requested Files
Web Server Client
Traffic Monitor
Hub
Local Disk
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Experiment Design
• Files with 1K, 4K and 10K bytes are placed in the server machine
• Factors measured for both the existing method and object Packaging
2. Average bytes transferred
3. Number of Transferred packets
1. Average response time
Experimental Setup
4. Transmission time
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Experimental Output• The figures represent all factors measured with different file sizes.
Existing Method
Object Packaging
File 4K
0%
20%
40%
60%
80%
100%
Avg. Time No.Of Pkts Bytes transferred
Time
Per
cent
age
File 10K
Per
cen
tag
e
Existing Method
Object Packaging
0%
20%
40%
60%
80%
100%
Avg. Time No.Of Pkts Bytes transferred
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Experimental Output
•0%
•20%
•40%
•60%
•80%
•100%
•1K •4K •10K
•Average file size (in bytes)
• Per
cent
age
to th
e ex
istin
g m
etho
d
•Transferred bytes
•Response time
•Transferred packets
•0%
•20%
•40%
•60%
•80%
•100%
•1K •4K •10K
•Average file size (in bytes)
• Per
cent
age
to th
e ex
istin
g m
etho
d
•Transferred bytes
•Response time
•Transferred packets
0%
20%
40%
60%
80%
100%
0 25 50 75 100
Per
cent
age
to th
e ex
isti
ng m
etho
d
Number of transferred files
File size = 10K
File size = 4K
File size = 1K
0%
20%
40%
60%
80%
100%
0 25 50 75 100
Per
cent
age
to th
e ex
isti
ng m
etho
d
Number of transferred files
File size = 10K
File size = 4K
File size = 1K
Number of transferredpackets relative to theexisting method
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Summary
• No modification of an operating system at the server side nor transmission protocol at routers required
• Multiple file transmissions by object packaging proposed
• Object packaging is efficient in reducing response time and transmission load and time
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Future work
1. Perform the experiments using a Gigabit Ethernet cable
2. To observe the scalability
There are two on-going activities and future works
1. Measuring the CPU load, response time and propagation delay on the server
2. Measuring all the above but for multiple clients
Future Works
On Going Activities
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References1. M. Arlitt and C. Williamson, “Web Server Workload Characterization: The Search for Invariants,” Proceedings of the 1996 ACM SIGMETRICS Conference on the Measurement and Modeling of Computer Systems,” May 1996, pp. 126-137
2. GVU’s WWW User Surveys, Georgia Institute of Technology URL: http://www.gvu.gatech.edu/user_surveys
3. J. Ousterhout, “Why Aren't Operating Systems Getting Faster As Hardware?,” Proceedings of Summer 1990 USENIX Conference, June 1990, pp. 247-256
4. P. Druschel, “Operating System Support for High-Speed Networking,” Communications of the ACM, vol. 39, no. 2, September 1996, pp. 41-51
5. P. Markatos, “Speeding-up TCP/IP: Faster Processors Are not Enough,” Proceedings of the 21st IEEE International Performance, Computing, and Communications Conference, April 2002, pp. 341-345
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References6. M. Busari and C. Williamson, “On the Sensitivity of Web Proxy Cache Performance to Workload Characteristics,” Proceedings of IEEE INFOCOM,April 2001, pp. 1225-1234
7. J. Dilley, “The Effect of Consistency on Cache Response Time,” IEEE Network, vol. 14, no. 3, May/June 2000, pp. 24-28
8. S. Glassman, “A caching relay for the Worldwide Web,” Computer - Networks and ISDN Systems, vol. 27, no. 2, October 1994, pp. 165-173
9. D. Lee, “Pre Fetch Document Caching to Improve Worldwide Web User Response Time,” Master's Thesis. Virginia Polytechnic Institute and State University, March 1996
10. J. Mogul, “Squeezing More Bits Out of HTTP Caches,” IEEE Network, vol. 14, no.3, May/June 2000, pp. 6-14
11. Figures of Red hat and Windows from the internet sites.
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The End
Thank you !!!
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Client Side Caching
• Reduced latency
• Effective only when same files are repeatedly requested
• Reduced server load
• Reduced bandwidth consumption in a network
• Additional hardware or expertise is required
• No benefit if object is not cached
• May be unable to cache multimedia content
• Unable to cache dynamically generated content
Advantages
Disadvantages
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Mirroring Technique
• Improves throughput
• Low capacity
• Complete redundancy of data
• Fast recovery from a disk failure
• Expensive
• No improvement in data access speed
Advantages
Disadvantages
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Server Clustering
• Load balancing
• Fail over
• Fault resilience
• Scalability
• Requires investment for hardware
• Request dispatcher may be a bottleneck
Disadvantages
Advantages
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