Iprelay can shape the tcp traffic forwarded through it to a specified bandwidth and allow this bandwidth to be changed on-the-fly. multiple data streams to different sockets may be shaped to the same total bandwidth, much like a traffic shaping router would. however, this application runs in user space, and works by acting as a tcp proxy.

here's what the author would like you to know: ip_relay sprang from the fact that i use a modem for home internet connectivity, and once a large download has started, other internet activities: telnet, surfing, voip, are largely useless. with ip_relay, you can suddenly decide to shape your downloads to 50% of your available bandwidth, and make use of the more interactive applications.

after using ip_relay for a while, it became obvious to me that it had another use: simulating bandwidth limits for other applications. most notably was testing vnc over an ethernet connection, but at modem speeds.

the original software is called ip_relay (http://www.stewart.com.au/ip_relay/) but its name has been changed according to debian policy.