IMHO ping isn't even meant to be used for bandwidth testing as it only shows roundtrip times which have nothing to do with bandwidth but with latency.
Indeed. Most people seem to completely confuse bandwidth (speed) with latency (lag). Ping measures *only* latency.
I like to use these two datacomm scenarios to highlight the difference between latency and bandwidth:
1. Telegraph (as popular in the 19th century): The time to send a keypress from one town to another is almost instantaneous (limited primarily by the speed of light as the voltage pulse travels the wire and by the speed with which the solenoid can respond to the pulse). But each letter takes more than one keypress (packet) providing only slightly faster than 1 baud even with a skilled operator. This is a very low bandwidth (slow speed: bad) with very low latency (less lag: good). Using this for an Internet connection would result in good ping times (unless the operator was behind in sending or receiving) but horrid speed.
2. Truck load of tape: Fill a truck (packet) with tapes full of data and drive it from one site to another. The packet size is huge. The latency may be minutes, hours or days depending on how far the truck has to go. But when the packet arrives the number of bytes transferred per second can be phenomenal. For example, moving 600 SDLT600 tapes holding 600GB each across town in an hour would be 360,000GB/hour or 100GB/second, but the latency would be an hour.
Back in reality, a compromise giving reasonably low latency and reasonably high bandwidth is what everyone wants. Personally, I'm trying to get my latency below 100ms so that my reflex response time in CounterStrike is fast enough to see the guy that killed me. My IDSL bandwidth of only 144Kbps is irrelevant (except when I'm downloading service packs or "multimedia" ;).
--
Jeff Woods <kazrak+kernel@xxxxxxxxxxx>
"Never underestimate the bandwidth of a C5A full of tape libraries!"
- : send the line "unsubscribe linux-admin" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
