Question about the trace file format

[Anotai Srikitja <anotai@lis.pitt.edu>]

>From NS document (Nov. 6,1997), the trace file format will indicate the 
operation status such as '+' for enque, '-' for deque and 'd' for drop.
Using the trace-all feature, it shows the 'r' status. Does anyone know 
what it means ?  
I happened to assume that 'r' is the event when a packet already sent 
through a link. So, now I am trying to use the trace-back command to 
collect the statistics such as average number of packets in the system and 
end-to-end packet delay time. The problem is trace-back doesn't capture 
'r' status trace (even it shown in trace-all file). 
Does anyone know if this is a limitation of ns tracing mechanism ? 
The network in my simulation is quite large. So, if you have any easier 
way to collect these statistics (avg. number in system and 
end-to-end pkt. delay) , please help me out. 
Thank you in advance for your corresponding.

--Anotai