[46296] in North American Network Operators' Group
Re: Transatlantic response times.
daemon@ATHENA.MIT.EDU (Iljitsch van Beijnum)
Mon Mar 25 10:39:24 2002
Date: Mon, 25 Mar 2002 16:39:40 +0100 (CET)
From: Iljitsch van Beijnum <iljitsch@muada.com>
To: "Pistone, Mike" <Mike.Pistone@msfc.nasa.gov>
Cc: "'nanog@merit.edu'" <nanog@merit.edu>
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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.
