Simulating realistic latency to a WAN SQL server



  • Context: Our desktop application communicates with a SQL server, some clients use a WAN connection to reach this SQL server. When they complain something is very slow we ask a list of ping times to analyse the issue. After a developer fixed the issue, I want to verify that it indeed fixes the problem.

    With a reported average ping time of 150ms, I use TMNetSim to simulate this on my local machine with these settings: enter image description here This results in similar effects, but still the client is reporting a magnitude of extra seconds than my local test show. In an ideal world I would goto the client location, but since its on the other side of the world this is not really an option 🙂

    Question: What information and setup do I need to get a more realistic simulation?



  • This is a very common scenario. Sometimes there are ways to increase the speed of the requests by identifying problems with the route taken, but that requires traceroute and working with network admins and internet providers and is often a bit of a black hole. Often you can not fix the latency issues, so you need to fix your app to function as well as it can without timing out or breaking under those conditions.

    One cheap/easy suggestion: find a way to share desktop, or remote desktop to a server at the location that is having issues so you can troubleshoot more.

    To specifically answer your question, there is more than just latency to look at and those other things can often play a large role in overall performance in certain geographies, or with poor internet connections (Very common in parts of China and most of Europe):

    1. latency
    2. packet loss/packet corruption
    3. variation/jitter (just because average is 150, doesn't mean there aren't spikes)
    4. bandwidth

    There are a number of tools you can use to measure these things, here's an example of one free one: http://www.firewall.cx/networking-topics/general-networking/970-network-performance-testing.html

    Once you have that information, then to reproduce those conditions you can plug it in to a WAN simulator such as the one you're using, however keep in mind that they are not all created equal. The most accurate wan simulator I know of is a piece of hardware called a network nightmare: http://www.networknightmare.net/gigEnn/#Products


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