North American Network Operators Group
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Re: T3 Latency

  • From: dave o'leary
  • Date: Sat Feb 17 12:02:25 2001 
What is your confidence level that your test packets are taking
the path that you expect?

Are you multihomed?  Does your addressing and routing setup allow
for the return packets to be taking a different path other than the new DS3?
What address are your test pings being sourced with, and what is the
destination's return path to that address?

                                                dave

At 11:05 AM 2/17/01 -0500, Deepak Jain wrote:
Packet size of your pings may have something to do with it, but assuming
you are pinging with the same size packet across the board, the data
should be reliable. If you are using unix boxes your pings will have a
different level of resolution than say from a windows box. One test that
should be reasonably conclusive is the following.

The hop that is 22ms and 7 hops away from your upstream should ping you on
the other side of the new T3. If it approaches 42 ms, you have a 20ms
T3. Is it ATM? Your upstream could be running on a congested ATM cloud. If
the latency drops in the wee hours of the morning, even for a few minutes,
its congestion (which is obvious).

I have a 27 mile (measured by air or telco :) ) DS3 that even under 30mb/s
load pings minimum 1 ms average 1-2 ms. (cisco<->cisco). At 1400 bytes the
average goes to 3ms.

Your upstream may be putting you on a channelized interface on a router
that has a very busy VIP (if its a cisco). Or is running you through a lot
of electronics on the way.

The point here is that any kind of aggregation he is doing could eat up
10-20ms, by design or oversubscription. Bigger providers are more likely
to aggregate DS3s into bigger access methods whereas small providers
usually don't have the operational necessity.

Deepak Jain
AiNET

On Sat, 17 Feb 2001, Nipper, Arnold wrote:

>
> Chuck,
>
> should read 130mi/msec I guess. Which would end up with ~7msec per
> 1000miles.
>
>
> Arnold
>
> ----- Original Message -----
> From: "Charles Scott" <[email protected]>
> To: "Matthew F. Ringel" <[email protected]>
> Cc: <[email protected]>
> Sent: Saturday, February 17, 2001 3:33 PM
> Subject: Re: T3 Latency
>
>
> >
> >
> > Matthew:
> > Appears to be a typo in your final number of 130 mi/sec, but I get where
> > you're going with this. I'm just having a problem trying to figure out how
> > I end up with a couple thousand fiber miles from Northern Michigan to
> > Chicago. Should be interesting to sort this one out.
> >
> > Thanks,
> >
> > Chuck
> >
> >
> > On Sat, 17 Feb 2001, Matthew F. Ringel wrote:
> >
> > >
> > > The rule of thumb I use is that the speed of light in fiber-optic cable
> is
> > > roughly 2x10^8 m/sec.
> > >
> > > 2x10^8 m/sec = 200,000,000 m/sec = 200,000 km/sec = 200 km/msec =~ 130
> mi/sec
> > >
> > > I once worked with a customer whose first hop out was ~30ms, regardless
> of the
> > > load on the line (a t3, iirc). Sure enough, he was on a very large
> SONET ring
> > > that travelled the north-south length of the US roughly twice before his
> > > traffic went elsewhere.
> > >
> > > ......Matthew
> >
> >
> >
> >
>
>
>
>
>