26.1 Trace Support

The trace support in OTcl consists of a number of specialized classes visible in OTcl but implemented in C++, combined with a set of Tcl helper procedures and classes defined in the ns library.

All following OTcl classes are supported by underlying C++ classes defined in ~ns/trace.cc. Objects of the following types are inserted directly in-line in the network topology:

Trace/Hop	trace a ``hop'' (XXX what does this mean exactly; it is not really used XXX)
Trace/Enque	a packet arrival (usually at a queue)
Trace/Deque	a packet departure (usually at a queue)
Trace/Drop	packet drop (packet delivered to drop-target)
Trace/Recv	packet receive event at the destination node of a link
SnoopQueue/In	on input, collect a time/size sample (pass packet on)
SnoopQueue/Out	on output, collect a time/size sample (pass packet on)
SnoopQueue/Drop	on drop, collect a time/size sample (pass packet on)
SnoopQueue/EDrop	on an "early" drop, collect a time/size sample (pass packet on)

Objects of the following types are added in the simulation and a referenced by the objects listed above. They are used to aggregate statistics collected by the SnoopQueue objects:

QueueMonitor	receive and aggregate collected samples from snoopers
QueueMonitor/ED	queue-monitor capable of distinguishing between ``early'' and standard packet drops
QueueMonitor/ED/Flowmon	per-flow statistics monitor (manager)
QueueMonitor/ED/Flow	per-flow statistics container
QueueMonitor/Compat	a replacement for a standard QueueMonitor when ns v1 compatibility is in use