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Web Performance Tuning by Patrick Killelea

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How Much Bandwidth Do You Need?

Server bandwidth is the single most important factor in the performance of your web site. The math to determine what bandwidth you need is, in essence, very simple:

hits/second * average size of a hit in bits = bits/second

That is, you need some estimate of the number of hits per second you want to be able to serve. Then you need to know the average size of one of these hits. From this, you know what sort of network bandwidth you need.

Thinking About Bandwidth

You can get some perspective when thinking about bandwidth from the following chart. Note that Table 2.1 uses the decimal million (1000000) and not “mega” which is 220 = 1048576.

Table 2-1. Bandwidth Comparison

Mode of data transfer

Million bits/second

Comments

Fast typist

0.000035

70 words/min × 5 chars/word × 6 bits/char × M/106 × min/60 seconds.

4800bps modem

0.004800

4800 bits/sec × M/106

This is also about maximum human reading speed.

POTS sampling rate

0.064000

Voice over plain old telephone service is sampled at 64kbps.

ISDN, two channels bonded

0.128000

 

One million 10000-byte web hits in one day, evenly distributed

0.925925

106 hits/day × 80Kbits/hit × day/86400 seconds × M/106.

Audio CD

1.280000

40000 samples/second × 16 bits/sample × 2 (stereo) × M/106.

T-1 (DS-1 or primary ISDN)

1.544000

Carries 24 POTS channels with 8kbps overhead.

Ethernet

10.00000

 

Token Ring

16.00000

 

IDE Hard disk

16.00000

Sustained throughput.

T-3 (DS-3)

44.60000

672 DS-0’s, 28 ...

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