[ns] How to add a queue?

[Wu Wei <wuwei@sdp.ee.tsinghua.edu.cn>]

I am a new comer of ns,recently I tried to add a new queue type in ns.I
emulate the implementation
of droptail queue,add my .cc,.h file in ns-2.1b6/ dir,add the obj in
Makefile and add the default value
in ns-default.tcl,but when I tested it,it complains no
"unblock_on_resume_" valiable,which is declared
in queue.h and I inherited from it. I asked the question in this mail
list several days ago. Today I change
my file name to droptail(.cc,.h) and change the ns-default.tcl, and
compile it. I test it and it works.
I think the only diff is the file name( change my new queue type file
name to droptail), I wonder whether
some other things should be done when adding new queue type.droptail do
somewhere so it works,I don't so
I meet error.Any hint would be fine,thanks in advance!