Bandwidth throttling and traffic shaping happens when a network attempts to limit the amount of bandwidth that a given service or user may use. Many ISPs terms and conditions specify a maximum data download per month allowed but they are not too keen to tell you about it when you sign up with them.
Citing bandwidth abuse from a few users some ISPs will sneakily throttle the Internet speed for users they claim to be downloading too much data, this bandwidth throttling is mostly used against P2P software protocols as P2P software is notorious for its bandwidth usage, technically bandwidth limits could be imposed to any application and it is often used for people on mobile Internet tariffs.
If you observe your Internet speed has ups and downs frequently or peer to peer applications do not reach the same Internet speed that your browser does, chances are that your ISP could be rate limiting your traffic for certain bandwidth intensive operations or at peak time.
How to test if your ISP is limiting Internet bandwidth
Nealyzr: Online test that analyses your overall Internet connection, it can detect an ISP slow DNS server, blocked TCP and ports, IMAP, SSL diagnosis and much more. You will have to allow Java to run in your computer, which could be a security risk if you don’t know the source. The project is backed up by the University of Berkeley which is a trust worthy entity.
Switzerland Network Testing Tool: This open source tool has been developed by the Electronic Frontier Foundation and it will test the integrity of data communications over networks, ISPs and firewalls. This traffic shaping test will spot IP packets which are forged or modified between clients, inform you, and give you copies of the modified packets.
NOTE: The Switzerland Network Testing Tool only works from command line, to be used by advanced computer users.
Glasnost test: To perform this Internet traffic shaping test you will need Java installed. The Glasnost test can detect bandwidth throttling in P2P software, Email, video streaming and even Usenet traffic shaping.
This traffic shaping test uses a Java applet to compare your regular download speed against the speed at which Flash videos get streamed to your system. It can also compare the download speed for email attachments (via POP and IMAP), normal HTTP based file transfers, torrents and binary downloads from Usenet servers.
The Glasnost test will create a fake data stream between your computer and their servers and then monitor the data packets flow.
Measurement Lab: M-Lab is a multi-functional internet performance measurement tool supported by Google that includes numerous online tests to check your Internet connection reach, ideal to troubleshoot Internet network problems.
Neubot: A research project that checks network neutrality is being enforced. You have to download their open source client for Windows, Mac or Linux and run it in your computer, the program will perform a series of tests in the background using the distributed Measurement Lab platform to find out if any kind of throttling is taking place. Data is collected by the University of Torino to carry out an study on Internet providers that throttle bandwidth.
How to run a traffic shaping test
Some Internet Service Providers only limit Internet speed at peak times, if you suspect your ISP is limiting your bandwidth consider carrying out various tests at different times and make sure that there are no other processes running in the background before performing the ISP throttling test.