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North American Network Operators Group

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Re: T3 Latency

  • From: Charles Scott
  • Date: Sat Feb 17 11:58:18 2001

On Sat, 17 Feb 2001, 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).

  Have been testing from our 7204 router and from various linux boxes. No
matter how small the packet size, we always see the 20 ms. 
  Yes, the total ping time to that other system is a minumum of 42 ms. Not
running ATM and have not seen any times when the latency drops below 20ms.
> 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.

  This may be the key. More of an effect of the way they're bringing me
in. I guess I need to ask them some specific questions.


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