North American Network Operators Group

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Re: Transatlantic response times.

  • From: Iljitsch van Beijnum
  • Date: Mon Mar 25 10:41:10 2002

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.