TROLL(1) Revised April 19, 1993 TROLL(1)NAMEtroll ! network simulator / datagram forwarderSYNOPSIStroll -h desthost -i destport [options] portDESCRIPTIONTr oll is an application designed to simulate the various quirks and vagaries of a network environment. Thetroll forwards UDP datagrams between processes, possibly dropping, delaying, garbling, and/or duplicatingthose datagrams.COMMAND LINE ARGUMENTSport The UDP port number on which the troll will listen for incoming datagrams. This argument ismandatory, and must be an integer between 1024 and 65535.The following options override various default parameters. They can also be set by interactive commands,as described below. Options specied as percent must be an integer in the range from 0 through 100.!hdesthostThe destination host iwhere to send troll datagrams after applying delays, reordering, etc.(REQUIRED)!idestport The destination port for outgoing datagrams. (REQUIRED)!f le The distribution of datagram delays is to be taken from the named le rather than computedfrom the delay parameter. See the description of the delay le interactive command below.!cnumber The capacity of the simulated network, in datagrams (default is 16). If this capacity isexceeded, newly arriving datagrams will be discarded immediately.!g percent The percentage of datagrams that should be garbled (default is 0%).!lnumber The maximum datagram lifetime, in milliseconds. If this value is specied as zero (the default),no maximum is enforced. Otherwise, datagrams are discarded on output from the troll if theyhave been delayed too long.!m percentThe percentage of datagrams that should be duplicated (sent multiple times; default is 0%).!r Prevent reordering. With this option, delays are all interpreted as relative: Datagrams arequeued rst-in-rst out, with delays between datagrams calculated according to the delayparameter (see !s, !se, and !f ). Without the !r option, delays are absolute. Since each data-gram is independently delayed, datagrams may be sent out in a different order than they arrived.See further discussion under TECHNICAL DETAILS below.!snumber!senumberThe separation of datagrams in milliseconds (default is 100; see also !f ). If e is specied, thedelay is an exponential random variable with mean number . Otherwise, it is a constant.!x percent The percentage of datagrams that should be dropped (default is 10%).INTERACTIVE MODEAfter being started, the troll normally runs in an interactive mode, and will prompt for commands with themessagetroll>A command may be abbreviated to any unambiguous prex of the name specied here.capcity numberSets the capacity of the network, in datagrams. If this capacity is exceeded, newly arrivingdatagrams will be discarded immediately.drop percent Sets the percentage of datagrams that will be dropped (i.e., will not be forwarded).CS438 1TROLL(1) Revised April 19, 1993 TROLL(1)maxlifetime numberSpecies a maximum datagram lifetime, in milliseconds. Just before sending a datagram,the troll checks whether it has been holding on to it for too long, and if so, drops it ratherthan forwarding it. If this parameter is set to zero (the default), no maximum lifetime isenforced.Note that the troll can buffer only a limited number of datagrams, as specied by the capac-ity parameter; if a datagram arrives and the capacity is exceeded, the datagram is dropped.Datagrams dropped as specied by the drop parameter do not consume any resources, butdatagrams that exceed the maxlifetime parameter occupy space until they are discared onoutput. Setting delay or duplicate to a sufciently high value may result datagrams beingdropped even if the drop and maxlifetime parameters are zero.delay millisecondsdelay exponential meandelay le lenameThese commands control the delay distribution. Depending on the setting of the reorderoption, the delay parameter controls the delay of datagrams or separation between them.The rst form sets delay to a specic value. The second sets it to an exponentially distrib-uted random variable with the indicated mean. (Other distributions may be provided byfuture releases of the troll). The third form sets it to a random variable with a distributionindicated by the histogram contained in the named le. The rst line of the le should con-tain an integer indicating the precision, in milliseconds. The remainder of the le shouldhave hav e one line for each possible delay value (in multiples of the precision). The lengthof each line (not including the newline character at its end) controls the relative frequencyof corresponding delays. (The actual contents of the lines are ignored). For example, if lecontains 100 <two empty lines> xx xxxxxx xxx x x then 2/13 of the datagrams will bedelayed 200ms, 6/13 will be delayed 300ms, 3/13 400ms, 1/13 500ms, 1/13 600ms, and nodatagrams will be delayed less than 200 or more than 600 milliseconds. As a special case, ale with only one non-empty line after the rst will generate a deterministic distribution (alldatagrams delayed the same amount of time).Warning: Although delays are specied in milliseconds, the Unix timing facilities are usu-ally less precise, so delays may actually be longer than specied.reorder Toggles the reorder option (initially on unless cleared by the !r command-line option). Ifreorder is off, the delay distribution is used to compute the delay between datagrams. Ifreorder is on, the delay distribution is used to compute the total delay for each datagram(or duplicate). If the reorder option is on and delay is not a constant, datagrams may notbe forwarded in the same order they were received.garble percentSets the percent of forwarded datagrams that will be garbled (i.e., have one or more bitschanged).duplicate percentSets the percent of forwarded datagrams that will be duplicated (i.e., transmitted more thanonce); of those, percent will be duplicated again, etc. Each duplicate of a particular data-gram is independently delayed and garbled.source lenameReads “interactive” commands from. lename.The remaining commands do not take any argument.parameters Prints the current values of the reliability parameters.statistics Prints statistics about the number of datagrams dropped, garbled, duplicated, etc. Thesestatistics are also printed on
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