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DelayBox is an ns node that should be placed in between the source and destination nodes. With Delaybox, packets from a TCP flow can be delayed, dropped, and/or forced through a bottleneck link before being passed on to the next node. A distribution can be used to specify delay, loss, and/or bottleneck link speed for a source - destination pair. Each flow between that source - destination pair draws from the distribution to determine its characteristics. Delays in DelayBox are per-flow, rather than per-packet. Since DelayBox distinguishes between flows, the fid_ variable (flow identifier) should be set for each flow in the simulation. DelayBox can be used with both Tcp and FullTcp agents.