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Re: Transatlantic response times.
On Mon, 25 Mar 2002, Pistone, Mike wrote: > I was curious if anybody would share what they consider to be average or > acceptable transatlantic ping response times over a T1. > I know there are tons of variables here, but I am looking for ballpark > figures. > Assume that utilization on the circuit is extremely low, and you are > measuring point to point across the line. You can also assume no other > bottlenecks effecting the response times (router performance, or what not). > Should you see a ~150ms trip? 250ms? 450ms??? Something like 70 - 100 ms with small packets. > Is there any equation to estimate response times? For example, if your > circuit from A to Z has a 500ms avg response, than that equates to a circuit > distance of aprox. 5000 miles or something? The three main components in the delay are: - serialization delay: it takes a certain amount of time to get a packet out of the interface. This is the size of the packet divided by the bandwidth of link. For instance: 1500 bytes = 12000 bits / 1536000 bps ~= 8 ms. (Double for RTT.) - speed of light: this depends on the medium. For fiber, it's about 200,000 km/s = 125,000 mi/s. So 5000 miles worth of fiber (which could be the atlantic, but your milage may vary) is 40 ms. (Double for RTT.) - queuing delays: this depends on how busy the circuit is and on the number of hops. You can remove the queuing factor by leaving your ping running for a fairly long time and then only look at the shortest RTT. If the shortest and the average RTTs are far apart, the circuit is very busy.