[ns] Monitoring a queue in wireless scenario

[Bhanoji Kandalam]

I am trying to monitor queue using monitor-queue, by using the following
piece of code

set queue_mon [$ns monitor-queue $node_(0) $node_(1) [open queue1.tr w] 0.1]

and then I want to access the packets that are currently there in the queue

set packets [$queue_mon set pkts_] #will packets variable hold the current
number of #packets by using above statement?

When I do this it gives me following error
can't read "link_(0:1)": no such variable
    while executing
"$link_([$n1 id]:[$n2 id]) init-monitor $self $qtrace $sampleInterval"
    (procedure "_o3" line 3)
    (Simulator monitor-queue line 3)
    invoked from within
"$ns monitor-queue $node_(0) $node_(1) [open queue1.tr w] 0.1"
    invoked from within
"set queue_mon [$ns monitor-queue $node_(0) $node_(1) [open queue1.tr w]
0.1]"


Some body please help me in this regard