Speed Tests

Speed Test App by Ookla

Speed Test 1 by DSL Reports

Speed Test 2 by SpeedTest.net


Tune Ups

TCP Tuning Parameters

RFC1323 High Performance TCP Options
FTP File Transfer Performance Analysis


Sniffer Intelligence Session Setup File for Measuring Throughput and TCP Performance:


Unzip the file and drop it into C:/Program Files/NetScout/Sniffer Analysis/Sniffer Intelligence/Sessions (Windows XP machines).


Bandwidth Latency Product

If it weren’t for Sliding Windows, all of our communication would be “stop and go”.
This would entail a lot of waiting on the part of the user.

The ideal TCP Window size is one that is larger than the bandwidth-delay product (BDP) to the resource.
If you are writing a file to a server, you want to still be sending a Window of data when the server’s first Acknowledgement arrives, so you effectively never stop

and wait for the Ack.  The same is true when reading or downloading a file.

What is the best Window size for me?

If the bandwidth is 10Mbps and each frame is 1518 bytes in length (or 12,304 bits after overhead), then it will take 1.23 milliseconds of bandwidth latency to put all the bits on the wire.
If the distance is 3,000 miles over UTP copper wire, then the distance latency is 27.27ms. Cumulatively, it will take 28.5ms of Network Delay before the first bit reaches the destination

Data sent in one direction, once it arrives, will require an acknowledgement in the reverse direction. Thus, the distance latency is multiplied by two.
(10,000,000bps x 0.02727s x 2) / 8 bits/Byte = 68,182B
If each TCP MSS is 1460B, then the closest larger TCP Window would be 70,080. The largest non-scaled TCP Window is 65,535.
You may need to enable TCP Window Scale if you and your server are cross-coastal.


The Details

At the beginning of the Ethernet frame is an 8-byte Preamble.

Between each frame output onto an Ethernet segment is a 12-byte time period of silence, known as the InterFrame Gap (IFG). This allows for the fair access principle.

The combination of the Preamble and IFG require an additional 20 bytes to be added to the largest Ethernet frame of 1518B for a total of 1538 bytes

1538B x 8 bits per byte = 12,304 bits

12,304bits / 10,000,000bps = 0.00123s or 1.23ms


Speed of light = c = 186,000 miles per second in a vacuum

Speed of light or electrical signal in UTP is .59c = 110,000 miles per second

3,000 miles / 110,000 mi/s = 0.02727s or 27.27ms

It will take 27.27ms for one bit to travel 3,000 miles over UTP copper


Network Delay is comprised of Bandwidth Latency and Distance Latency

ND = BL + DL ,        1.23ms + 27.27ms = 28.5ms

Round Trip Time (RTT) is from source to destination and back to source

RTT = ND x 2 or 57ms, in this case

Most ISPs will quote 65ms to 85ms of latency from coast to coast in America. This allows for the forwarding delay of repeaters, etc.

When computing the next largest window, it's best to use an even integer multiple of the MSS because of the Delayed Duplicates algorithm which

requires only every second data frame be Acked


More Bandwidth and Less Distance
What if you have 100Mbps connection to a server mid-way across the United States?
(100,000,000bps x ((1,500mi x 2) / 110,000mi/s)) / 8b/B = 341KB
Closest larger window is 341,460 using even integer multiples of the 1460B MSS.
Once you have chosen the ideal TCP Window for the worst case BDP, it can become the corporate standard for all new installations