About the Redcentric Speedtest
The Redcentric 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, Redcentric is also able to view historical statistics of your Speed tests if you have any queries with the results.
Interpret Your results
Your service from Redcentric 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.
With the Redcentric 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.
Because of the mechanics of the Redcentric 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.
To further test the maximum throughput of your service Redcentric 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 Redcentrics manual speed testing site
Other internet speed testing sites are available and the more popular use the same technology as Redcentrics, though results from these are typically unreliable as they reside outside of Redcentrics ISP network and are therefore affected by third party network conditions, also, the load on these sites from other users and the bandwidth available to the company hosting the sites needs to be taken into account during testing.