Simulating Slow Internet Connection

Question

I know this is kind of an odd question  Since I usually develop applications based on the  assumption  that all users have a slow internet connection  But  does anybody think that there is a way to programmatically simulate a slow internet connection  so I can  see  how an application performs under various  connection speeds    I m not worried about which language is used  And I m not looking for code samples or anything  just interested in the logic behind it

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Also  for simulating a slow connection on some  nixes  you can try using ipfw  More information is provided by Ben Newman s answer on this Quora question

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Starting with Chrome 38 you can do this without any plugins  Just click inspect element  or F12 hotkey   then click on  toggle device mod  and you will see something like this     Among many other features it allows you to simulate specific internet connection  3G  GPRS   P S  for people who try to limit the upload speed  Sadly at the current time it is not possible   P S 2 now you do not need to toggle anything  Throttling panel is available right from the network panel    Note that while clicking on the No throttling you can create your custom throttling options

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Updating this  9 years after it was asked  as the answer I was looking for wasn t mentioned   Firefox also has presets for throttling connection speeds  Find them in the Network Monitor tab of the developer tools  Default is  No throttling     Slowest is GPRS  Download speed  50 Kbps  Upload speed  20 Kbps  Minimum latency  ms   500   ranging through  good  and  regular  2G  3G and 4G to DSL and WiFi  Download speed  30Mbps  Upload speed  15Mbps  Minimum latency  ms   2    More in the Dev Tools docs

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You can try Dummynet  it can simulates queue and bandwidth limitations  delays  packet losses  and multipath effects

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Google recommends    Network Link Conditioner on OSX Clumsy on Windows Dummynet on Linux

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You can use NetEm  Network Emulation  as a proxy server to emulate many network characteristics  speed  delay  packet loss  etc    It controls the networking using iproute2 package and it s enabled in the kernel of the most Linux distributions   It is controlled by the tc command-line application  from the iproute2 package   but there are also some web interface GUIs for NetEm  for example PHPnetemGUI2   The advantage is that  as I wrote  it can emulate not only different network speeds but also  for example  the packet loss  duplication and or corruption  random or defined delay  etc   so you can emulate various poorly performing networks   For your application it s absolutely transparent  you can configure the operating system to use the NetEm proxy server  so all connections from that machine will go trough NetEm  Or you can configure only your application to use it as a proxy   I have been using it to test the performance of an Android app on various emulated poor-performance networks

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There are TCP proxies out there  like iprelay and Sloppy  that do bandwidth shaping to simulate slow connections  You can also do bandwidth shaping and simulate packet loss using IP filtering tools like ipfw and iptables

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If you re running windows  fiddler is a great tool   It has a setting to simulate modem speed  and for someone who wants more control has a plugin to add latency to each request   I prefer using a tool like this to putting latency code in my application as it is a much more realistic simulation  as well as not making me design or code the actual bits   The best code is code I don t have to write   ADDED  This article at Pavel Donchev s blog on Software Technologies shows how to create custom simulated speeds  Limiting your Internet connection speed with Fiddler

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There is also another tool called WIPFW  - http   wipfw sourceforge net   It s a bit old school  but you can use it to simulate a slower connection  It s Windows based  and the tool allows the administrator to monitor how much traffic the router is getting from a certain machine  or how much WWW traffic it is forwarding  for example

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One common case of shaping a single TCP connection can actually be assembled from dual pairs of socat and cpipe in UNIX fashion like this   socat TCP-LISTEN 5555 reuseaddr reuseport fork SYSTEM  cpipe -ngr -b 1 -s 10   socat -  TCP localhost 5000    cpipe -ngr -b 1 -s 300   This simulates a connection with bandwidth of approximately 300kB s from your service at  5000 and to at approximately 10kB s and listens on  5555 for incoming connections  Caveat  Note that this per-connection  so each individual TCP connection gets this amount   Explanation   The outer  left  socat listens with the given options on  5555 as a forking server  The first cpipe command in the SYSTEM     option then throttles data that went into socket  5555  and comes out of the first  outer socat  to at most 10kByte s  That data is then forwarding using another socat which connects to localhost 5000  where the service you want to slow down should be listening   Data from localhost 5000 is then put into the right cpipe command  which  with the given values  throttles it to about 300kB s   The option -ngr to cpipe is important  It causes cpipe to read non-greedily from its input file-descriptor  Otherwise  you might get stuck with data in the buffers not being forwarded and waiting for a reply   Using the more common buffer tool instead of cpipe is likely possible as well    Credits  This is based on the  double-tee  recipe by Christophe Loor from the socat documentation

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Use a tool like TCPMon  It can fake a slow connection   Basically  you request it the exact same thing and it just forwards the exact same request to the real server  and then delays the response with only the set amount of bytes

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On Linux machines u can use wondershaper   apt-get install wondershaper    sudo wondershaper  interface   down   up    the  down  and  up  are bandwidth in kpbs  So for example if you want to limit the bandwidth of interface eth1 to 256kbps uplink and 128kbps downlink     sudo wondershaper eth1 256 128   To clear the limit     sudo wondershaper clear eth1

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Mac OSX since 10 10 has an app called Murus Firewall  which acts as a GUI to pf  the replacement for ipfw   It works very well for system-wide or domain-specific throttling  I was just able to use it to slide my download speed between 300Kbps and 30Mbps to test how a streaming video player adjusts

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I was using http   www netlimiter com  and it works very well  Not only limit speed for single processes but also shows actual transfer rates

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Use a web debugging proxy with throttling features  like Charles or Fiddler   You ll find them useful web development in general  The major difference is that Charles is shareware  whereas Fiddler is free

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For Linux  the following list of papers might be useful    A Comparative Study of Network Link Emulators  2009  KauNet  A Versatile and Flexible Emulation System  2009  Dummynet Revisited  2010  Measuring Accuracy and Performance of Network Emulators  2015    Personally  whilst Dummynet is good  I find NetEm to be the most versatile for my use-cases  I m usually interested in the effect of delays  rather than bandwidth  i e  WiFi connection issues   and it s super-easy to emulate random packet loss corruption  etc  It s also very accessible  and free  unlike the hardware-based Linktropy    On a side-note  for Windows  Clumsy is awesome  I would also like to add that  regarding websites  browser throttling is not an accurate method for emulating real-life network issues  I think  TKK  commented on a few of the reasons why above    Hope this helps someone

[performance] Simulating Slow Internet Connection

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