The megtest and traffic protocols print some general information to the display while the simulator is running. The simulated time elapsed is shown, along with messages from individual hosts about their states and error conditions. At the completion of a run, summary information is printed about the megtest transfer or traffic conversations.
The most interesting and important output generated by a simulation, however, takes the form of trace files. The protocols and routers included with the simulator have had trace statements inserted at places in the code where significant events occur; each trace statement writes a few bytes to a trace file, indicating the event and recording relevant state. See the ``Data Trace Library'' section of the x-kernel Programmer's Manual for information on the this tracing facility [NSR96]. Also, see the code for the TCP Vegas protocol in /xkernel/simulator/protocols/vtcp for an example of how to augment a protocol with trace statements. The file
README.trace in this directory lists all of the protocol's trace statements, and explains where each occurs and what information it saves. For an example of how to add trace statements to a driver protocol, see /xkernel/simulator/sim/ethd.
Two graphical display tools have been developed to convert the trace files generated by a simulation into readable PostScript graphs. They are ptcp and extrace, and both can be found in
/xkernel/bin/solaris-sparc, /xkernel/bin/sunos-sparc or
/xkernel/bin/osf1-alpha, depending on the system you are using. The ptcp tool generates TCP-specific graphs, displaying such information as the size of the send window and the time when a packet was retransmitted. Graphs produced by extrace show changes in queue sizes on the routers. For an explanation of how to interpret the output from these two tools, see Section 7 and Section 8.