North American Network Operators Group

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Re: Question about propagation and queuing delays

  • From: David Hagel
  • Date: Sun Aug 21 21:39:41 2005
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Richard,

Thanks for the highly informative answer.

Would there be any data out there on what fraction from this 60ms to
80ms RTT is raw propagation delay and what fraction is typical packet
queuing delay at intermediate switches? Does queuing delay play much
of a role at all these days? Or is it all just propagation delay?

Thanks,
- Dave

On 8/21/05, Richard A Steenbergen <[email protected]> wrote:
> On Sun, Aug 21, 2005 at 07:13:39PM -0400, David Hagel wrote:
> >
> > I was wondering what are the typical coast-to-coast propagation and
> > queuing delays observed by today's backbone networks in North America.
> > Is there any data/study which provides a breakdown of different
> > components of such end-to-end delays in today's backbone networks?
> 
> Well that all depends on the routes in question doesn't it. Propagation is
> the key factor on longhaul networks, but there are many economic and
> technological decisions that tend to work against laying fiber in straight
> lines, such as the need to hit as many large cities along the way, those
> pesky right-of-ways, and the cost of optimized routes with lower capacity
> vs less optimized routes with most capacity.
> 
> Lets take one major example, the "cross country" path between the two most
> important Internet locations in the US, the San Jose area in California,
> and the northern Virginia area near Washington DC.
> 
> The best path out there seems to be a nearly direct route from Sprint,
> coming in at around 61-62ms rtt. This is a relatively rare route however,
> not taken by most networks. The "much more common" optimized version is
> around 67-68ms, which tends to route via paths like DC or Philadelphia,
> via Cleveland, Chicago, (St. Louis or the northern loop through
> Minneapolis), Kansas City, Denver, Sacramento, San Francisco...
> 
> The path gets worse when there is no direct route between the mid-atlantic
> and Chicago, usually resulting in DC, New York, Boston, Buffalo,
> Cleveland... This tends to kick it up to around 72ms on the good side,
> 75ms on the bad side. It can also get worse when the direct path between
> Denver and California (Sacramento often) does not exist, resulting in
> paths via Los Angeles or Seattle, and around 78ms-80ms rtt.
> 
> Above 80ms it stops becoming acceptable, and is only doable by a network
> which is missing some key route that most people seem to have. Of course
> is is also possible to come in with a better southern crosscountry path,
> via something like DC, Atlanta, (New Orleans and Houston, or paths via
> Arkansas), Phoenix, and Los Angeles. A reasonably optimized version of
> this route tends to weigh in at around 61-62ms, plus another 9-10ms from
> Los Angeles to San Jose.
> 
> If you take a detailed look at fiber routes from the big 3 (Level 3, WCG,
> and the GX/Qwest builds) you can get a pretty good idea of what paths are
> out there, and the differences between them. Of course if someone were to
> come along and combine optimal segments from all of them you would end up
> with a network far superior to anything currently available, but the
> practical cost under current economical conditions would just be absurd.
> Ironically, the cost of linking the different carriers who are in
> different buildings within the same metro area in all the cities necessary
> is probably right up there with the cost of the longhaul itself. :)
> 
> Bottom line about latency, gamers don't pay the bills.
> 
> --
> Richard A Steenbergen <[email protected]>       http://www.e-gerbil.net/ras
> GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)
>