TRACING OUTPUT

[harlisya@erg.abdn.ac.uk (Harlisya Harun)]

Hi,
I've tried to understand the trace output from the out.tr files (by running one of the duplex-link tcl scripts).  I read the NS notes and Documentation to help me in understanding what is going on....but, still not really clear.  It is really hard to picture out what is going on????? 

+ 0 0 1 tcp 1000 ------- 1 0.0 1.0 0 0
- 0 0 1 tcp 1000 ------- 1 0.0 1.0 0 0
r 0.0153333 0 1 tcp 1000 ------- 1 0.0 1.0 0 0
+ 0.0255467 0 1 tcp 1000 ------- 1 0.0 1.0 1 2
- 0.0255467 0 1 tcp 1000 ------- 1 0.0 1.0 1 2
+ 0.0255467 0 1 tcp 1000 ------- 1 0.0 1.0 2 3
- 0.03088 0 1 tcp 1000 ------- 1 0.0 1.0 2 3
r 0.04088 0 1 tcp 1000 ------- 1 0.0 1.0 1 2
r 0.0462133 0 1 tcp 1000 ------- 1 0.0 1.0 2 3
+ 0.0510933 0 1 tcp 1000 ------- 1 0.0 1.0 3 6
- 0.0510933 0 1 tcp 1000 ------- 1 0.0 1.0 3 6
(....to few lines more.....)
r 1.00931 0 1 tcp 1000 ------- 1 0.0 1.0 179 340
- 1.00997 0 1 tcp 1000 ------- 1 0.0 1.0 182 346
r 1.01464 0 1 tcp 1000 ------- 1 0.0 1.0 180 342
- 1.01531 0 1 tcp 1000 ------- 1 0.0 1.0 183 348
+ 1.01533 0 1 ack 40 ------- 2 0.1 1.1 0 380
(....until at the end of file....)

Well, what i've understood is '+' represent arrival (enque operation), '-' means departure (deque operation), and 'r' is a received event.  At first, when I look at the output, I thought that r is the same as ACK, for one rtt...But, when I figure out column 8 and 9, which indicate the packet's source and destination node address, it is not an ACK (an ack should be in reverse)  .Furthermore, when I trace another few lines, there is an "ACK"...I just wondering, why it took quite some time to produce an ACK?  In this case, it took 1.01533 simulation time.  If in real experiment, an ACK is important for 'self-clocking', what I meant is that, every packet sent must have an ACK, or if not, retransmission occurs.  I am a bit confuse here!!!!

What is '+', '-' and 'r' really imply for????  I can not imagine at all what's happening...I tried to figure out from the FIGURE in page 41 in NS Notes and Documentation, but still in the dark.  The FIGURE looks like this:


	    
head -->O-->enqT_ --> queue_ --> deqT_ --> link_ --> ttl_ -->
			\
			 drophead_ --> drp_T


Could anyone please explain to me....Your cooperation is highly appreciated.

Thank you.

harlisya