And its in your head.. In your overhead..

Posted by mkhairul - November 18, 2006 at 03:11:02 pm -

Categories: Tips, blog

While I was bored and waiting for FC6 (i386) download to finish… I found a site for bandwidth calculations. Lots of calculators. An interesting thing that I bumped into is the Overhead (I’ve heard of it before, cant remember).

I tried to calculate my download speed. In this case I used a file that I have downloaded.

2366 KB
Download time: 00:00:18
Actual Download Time: 1:54:41 -> 1:55:15 (34 seconds)
0.97379543533389687235841081994928

 

• File Size: 2366KB
• Ideal Download Time: 18 seconds
• Actual Download Time: 34 seconds
• Overhead = (18 / 34 ) * 100
• Overhead = 52%

From T1 Shopper’s Download Calculator:

"Actual transfer speeds will be slower than these times due to latency,
physical signaling overhead (i.e. the available transfer speed on a T1
is not 1536 Kbps since 192 Kbps is usually tied up in the T1 signaling
protocol), layer 4 transport and transmission protocol overhead (i.e. TCP
overhead, error checking, or protocol headers.  For example each IPv4
header is 160 bits, each UDP header is 64 bits, etc.  Add all this up
and you can loose over 10% of the total line capacity for just this one
step.), and handshaking negotiation procedures like "slow start" and others."

More Info:

• RFC 2001 - TCP Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery Algorithms

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