Department of Computer ScienceSouthern Illinois University Edwardsville

Dr. Hiroshi Fujinoki and Kiran GollamudiE-mail: {hfujino, kgollam}@siue.edu

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

The End

Thank you !!!

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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