Maxwell, the intelligent network emulator, rate limitation mechanism.

The rate limiter slows down transmission of packets so that they exit the opposite interface at a user specified effective bit rate. While no one packet is actually transmitted at the requested rate, the packets are spaced so that the time span encompassing two or more packets equals the requested bit rate.

The rate parameters control the transmission so that, on average, no more than the given rate in bits/second is transmitted out the opposite interface (note that a rate of zero disables rate impairment). When an Ethernet frame is received, only the bits in its data section are included in the rate computation – the frame preamble, header, FCS, and so on, are ignored. To accurately compute the packet delays, the number of overhead bits in the emulated outgoing link layer needs to be included in the rate computation. To calculate the number of such overhead bits, the following aspects of the emulated link layer must be provided: the minimum and maximum payload bit size and the average number of bits in the emulated link layer's headers and tails, if any. To emulate discards properly a value for the maximum emulated transmission queue length (in bits, not bytes) must be provided. Lastly, for highest fidelity the actual measured transmission rate between Maxwell and the final endpoint is entered in bits/second and actual measured transit delay is entered. Note that setting the actual rate to zero excludes both the actual rate and actual transit duration from the rate computations.

Note that actual rates are likely to be 10M, 100M, and 1000M bits/second. Typical actual transit delay through Maxwell for a packet is typically under 20 microseconds, though it can vary depending on any processing delay due to a loaded plugin. As an example, on a 100M Ethernet link the actual rate you would enter into the actual rate field is 100,000,000 and 0.00002 in the GUI (or 20 when using the Remote API) for actual delay.