what does "proc cmu-trace" do in my tcl file

Hi every body

please I would like to know what does this function exactely


proc cmu-trace { ttype atype node } {
    global ns_ tracefd

    if { $tracefd == "" } {
        return ""
    }
    set T [new CMUTrace/$ttype $atype]
    $T target [$ns_ set nullAgent_]
    $T attach $tracefd
        $T set src_ [$node id]

        $T node $node

    return $T
}


thanks you