50.1.8 Variable Tracing

To visualize state variables associated with a protocol agent, we use feature trace events. Currently we allow a feature to display a simple variable, i.e., a variable with a single value. Notice that the value is simple treated as a string (without white space). Every feature is required to be associated with an agent. Then, it can be added or modified at any time after its agent is created. The trace line to create a feature is:
f -t time -s src -a agentname -T type -n varname -v value -o prev value
Flag <type> is

v

for a simple variable

l

for a list

s

for a stopped timer

u

for an up-counting timer

d

for a down-counting timer.

However, only v is implemented in ns. Flag -v <value> gives the new value of the variable. Variable values are simple ASCII strings obeying the TCL string quoting conventions. List values obey the TCL list conventions. Timer values are ASCII numeric. Flag -o <prev value> gives the previous value of the variable. This is used in backward animation. Here is an example of a simple feature event:
f -t 0.00000000000000000 -s 1 -n C1_ -a srm(1) -v 2.25000 -T v

Features may be deleted using:
f -t time -a agent name -n var name -o prev value -X