Why Do Broadband Speed Tests Give Different Results? Speed Test
Average Why Do Broadband Speed Tests Give Different Results? Internet Speed
Broadband speed tests can give different results depending on how far away you are from the nearest test server, or how much traffic there is on the network at the time.
The first point refers to what is known as 'distance-vector routing'. Network routers communicate with each other about where they have knowledge of networks and subnetworks. Traffic will randomly arrive at one of these routers and will be forwarded to another router that is closer to the destination. This other router will then forward the traffic towards its destination.
Since the speed test software sends a stream of data (i.e., a series of packets) to the nearest server, this data may get dropped because it hasn't been 'routed' to a closer router first. This is especially likely between hops along the path (for example, if the data travels from London to Frankfurt and then Tel Aviv, it will be dropped several times or corrupted).
The second point is more fundamental: Internet traffic is routed via multiple paths of connections between routers. Sometimes there are many more paths between two machines that may meet the eye. This is because the routers attempt to store as much information about their neighbors and traffic levels between different networks as they can, including estimates of how busy each path is likely to be at a particular time. Some of this data is then integrated into routing algorithms that make decisions about what route to use for sending different types of traffic.
Of course, this is all done automatically and rapidly by the routers themselves, so any discrepancies are unlikely to be noticed by users until something goes wrong—for example, a software update breaks router algorithms, or there are physical outages which remove some set of paths from use for an extended period of time.
The third point is the main suspect for why speed tests can give different results. Your test server isn't necessarily your nearest server, especially if you are using a software package that only has servers in a few locations (for example, broadband choices doesn't have any servers in Asia or South America).
Its Easy To Fix
Get another speed test that has servers in the places you want to see. In reality, it's rather more tricky: if you are connected via a router that is implementing complex routing algorithms, then this becomes much harder because there may be no single best answer for where a particular packet should or will go (for example, two different paths might perform equally well).