I am downloading files from other sources, for testing purpose I am using netem to make delay while downloading the files. Its working fine, but I want to know on which factors of internet it(netem) effects. I mean it applies delay on Bandwidth or Download-Time or any connection related properties


When adding delay through NetEm, the packets' latency is increased. This comes to simulate slow/long network, e.g. long physical lines and/or a lot of switches in the way to the end point. Long latency might cause a slow down in bandwidth, especially for TCP traffic, since it increases the chance for retransmits due to timeouts. Since download time = file size / bandwidth, you can argue they are one and the same. If the added delay that causes long latency would also cause a degradation in average bandwidth, you'll experience longer download time. I suggest to first check the latency before and after applying the delay. You should expect an increase equals to the introduced delay (or 2 * delay for round-trip latency).

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