Latency vs speed

[#1]

Hi,

I have a question for you guys.

We have a custom application here that runs on our LAN. So, server and clients are local. This application runs on TCP and do a LOT of requests in a small time.

Now we have a data center in another city. We want to move the server to this DC and keep users here locally via WAN link. When we try this, all our tests takes about 4 times the time vs LAN.

Our LAN has <1 ms of latency. Our WAN link (which is brand new, no one use it except our tests for the moment) is a steady 4ms latency link. So, about 4 times more....as our tests results.

In LAN, our links are 1gb between server and clients. Same thing for our WAN link.   For the test, we did a LAN extension. So there is no firewall or router. Only L2 because we wanted to test without other equipment in the loop.

So, if all links are the same speed (1gb), but the wan links have 4 times the latency, can we conclude that it's normal that our all tests are four times longer ?

Remember there is no router/firewall, QoS or other traffic running. Only a pure L2 link with just us doing the traffic.

Thank you

[Aaron Harrison]

Yes. Latency is a measure of time; if you multiply time by 4 it takes 4 times as much time.

Sounds like the app (if truly custom) is within your control and you can perhaps have your devs optimise it to make fewer, larger calls.

Aaron

[Richard Bradfield]

A couple of things,

the wan link does have  service provider equipment it passes through, so minor delay there,

But the main thing is just physics and the speed of light! I don't know how far away your other location is but obviously going to take longer to go there than just in a local LAN.

HTH

Richard

[Joseph W. Doherty]

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Posting

No you cannot assume 4 times the latency will slow an application by 4 times.  It depends much on how the application interacts with the network.

An an example, you mention your LAN latency is less than a ms.  It might be much less.  Suppose it was .25 ms.  In that case, your WAN latency would be 16 times slower.  Or suppose it's .1 ms, then your WAN latency is 40 times slower.

That said, increased latency will slow almost any application.

[Vinny]

thank you all

I'll explain that to people here that need explainations :)