I'm trying to learn more about how a network (both LAN and Internet) handles traffic, and one part of this is the question of parallelism.
In the documentation for Speedtest.net, in describing how exactly the test works, it mentions that "up to 4 threads" can be used, without describing what those threads actually consist of.
My question is, what determines the degree of parallelism that can occur across a network? I know once a signal reaches the destination server, it's all up to that server's resources and the receiving program. But how does parallelism work across the network?
For example, does the network interface card take the request and split it up for quicker transfer across cable? Or does it just package up everything into larger chunks and let a router/switch do that?
Specifically, I'm trying to understand this from a business > business network sense, so I'm not worried about things like a local cable modem or local DSL adapter.