Mioelnir
Cataclysm Enterprises
Ev0ke
34
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Posted - 2011.12.16 04:21:00 -
[1] - Quote
Klandi wrote:Dust Fourtwenty wrote:bandwidth is not speed
ping is speed Just to be PERFECTLY correct: Speed of broadband is constant (speed of light) so ping and bandwidth incorrectly reference "speed" but it is the easiest to understand. Ping attempts to send a packet of information to gather statistics about its journey. How long it took to get there and return that information (if allowed) is returned and it does not reference speed.
Electric signals in copper wire propagate at roughly 2/3c, depending on how crappy your cabling is.
Optic signals in fibre cable propagate at speed s with s < c since while the carrier wave itself may travel at c, it does not travel down the fibre in a straight line, but gets constantly refracted at the outer edges of the fibre ("bounces between them"). So the distance inside the fibre is actually longer than the fibre itself resulting in signal propagation speeds below the speed of the carrier wave.
You are correct that "ping" does not measure speed but round-trip time. But, in the absence of anycast setups, usually time to a relatively fixed destination. If now the routing path stays the same you have time and a rough idea of the distance to the destination (if you actually know the destination's location; also distance here is not length of the traveled path), thus speed in a distance per unit of time sense. An information transmission speed though, not physical signal propagation speed.
In practice this is largely irrelevant though, since icmp echo is, due to small packet sizes and the protocol design, less affected by differences in the deployed switching technologies along its path, has no retransmission delays, congestion control algorithms, uneven endpoint support of things like selective acks, various fragment reassemblies along the path or window scaling problems on the endpoints.
There are myriads of possibilities why your echo RTT can be good, but the time it takes your application to successfully transmit a specific amount of information down what you perceive to be the same path via TCP very bad.
Game clients are much like interactive shells tough and not bulk transfers, so a bad baseline RTT which can be established via "pings" can dramatically increase the subjective unresponsiveness of the application. |