About the Redstone Speedtest
The Redstone Speed Test
application is used to give an indication of the available bandwidth on your
service. It does this by downloading a dynamically sized file via Flash from
your browser, it also uploads a standard size file
back to the web server to calculate upload speed.
The results are
calculated and displayed after the test completes, Redstone is also able to
view historical statistics of your Speed tests if you have any queries with
the results.
Interpret Your results
Bandwidth
Your
service from Redstone will have a specified bandwidth, given in bits/second.
This is referred to as Throughput and is the maximum available bit rate that
is physically transferred across the media.
Throughput/Goodput
With the Redstone
speedtest we are measuring Goodput, which is the number of useful
bit's per second received at the application level, which
excludes protocol overhead and retransmitted packets, this is why Goodput
is lower than throughput - the following explains the effect of protocol
overhead on available Goodput with a maximum throughput of 2Mbs/second.
Data is broken down
into packets to be transmitted over the network, the maximum packet size with
Ethernet is 1500 bytes of information, each packet has 20 bytes of IP header
information and 20 bytes of TCP header information which means that only 1460
bytes of bytes are available for the data or payload per packet, when this
packet is transmitted over Ethernet in a segment a 38 byte overhead is added
per packet.
With this in mind the
maximum Goodput is calculated as (1460/1538) x 2Mbit/s = 1.899Mbit/sec
Other factors affect
Goodput when calculating speed such as retransmission of lost or corrupt
packets and also collision detection in the Ethernet CSMA/CD protocol. The client used for the testing is also
adding to this with conditions such as local network performance (collision,
detection) Operating System efficiency and disk read/write performance.
Upload/Download testing
Because of the
mechanics of the Redstone Speedtest the upload file size is smaller than the
dynamically allocated download payload which means that the test result for
upload is not as accurate as download.
Further testing
To further test the
maximum throughput of your service Redstone has an FTP site available to test
data Goodput rates.
You can also manually
choose the file size to download and calculate the Goodput rate from
Redstone's manual speed testing site
