31.1.1 Multicast Behavior Monitor Configuration

ns supports a multicast monitor module that can trace user-defined packet activity. The module counts the number of packets in transit periodically and prints the results to specified files. []attach enables a monitor module to print output to a file. []trace-topo insets monitor modules into all links. []filter allows accounting on specified packet header, field in the header), and value for the field). Calling []filter repeatedly will result in an AND effect on the filtering condition. []print-trace notifies the monitor module to begin dumping data. ptype() is a global arrary that takes a packet type name (as seen in []trace-all output) and maps it into the corresponding value. A simple configuration to filter cbr packets on a particular group is:

        set mcastmonitor [new McastMonitor]
        set chan [open cbr.tr w] # open trace file;
        $mmonitor attach $chan1  # attach trace file to McastMoniotor object;
        $mcastmonitor set period_ 0.02         # default 0.03 (sec);
        $mmonitor trace-topo   # trace entire topology;
        $mmonitor filter Common ptype_ $ptype(cbr) # filter on ptype_ in Common header;
        $mmonitor filter IP dst_ $group # AND filter on dst_ address in IP header;
        $mmonitor print-trace  # begin dumping periodic traces to specified files;

The following sample output illustrates the output file format (time, count):

0.16 0
0.17999999999999999 0
0.19999999999999998 0
0.21999999999999997 6
0.23999999999999996 11
0.25999999999999995 12
0.27999999999999997 12