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.