[ns] IFQ and 802.11 mac sublayer woes - lost packets.

[Daniel Russo <drusso@utdallas.edu>]

I'm seeing some really weird stuff going on between the IFQ and the 
802.1 MAC sublayer when running some wireless adhoc simulations.I have a 
feeling its becuase of high collision and contention rates, but thats 
only a guess.
Sometimes when a link is not present and i try to send a packet accross 
it, i see it fail. i.e. the MAC layer passes it back to me and I drop it 
with CBK flag. e.g:

[drusso@dslsrvr1 <mailto:drusso@dslsrvr1> <mailto:drusso@dslsrvr1> 
<mailto:drusso@dslsrvr1> test-sims]$ grep " 14216 " ssls-packet.tr
s 598.549243107 _0_ AGT  --- 14216 cbr 512 [0 0 0 0] ------- [0:2 16:1 
32 0] [23] 0 255
r 598.549243107 _0_ RTR  --- 14216 cbr 512 [0 0 0 0] ------- [0:2 16:1 
32 0] [23] 0 255
s 598.549243107 _0_ RTR  --- 14216 cbr 532 [0 0 0 0] ------- [0:2 16:1 
31 7] [23] 0 255
s 598.549707434 _0_ MAC  --- 14216 cbr 584 [a2 7 0 800] ------- [0:2 
16:1 31 7] [23] 0 255
r 598.552044098 _7_ MAC  --- 14216 cbr 532 [a2 7 0 800] ------- [0:2 
16:1 31 7] [23] 1 255
r 598.552069098 _7_ RTR  --- 14216 cbr 532 [a2 7 0 800] ------- [0:2 
16:1 31 7] [23] 1 255
f 598.552069098 _7_ RTR  --- 14216 cbr 532 [a2 7 0 800] ------- [0:2 
16:1 30 14] [23] 1 255
D 598.552069098 _7_ RTR  CBK 14216 cbr 532 [a2 7 7 800] ------- [0:2 
16:1 30 14] [23] 1 255

Othertimes when a link isnt present and i try to send a packet accross 
it, it just dissapears. e.g: Packet 14304 is never referenced again the 
trace file.

[drusso@dslsrvr1 <mailto:drusso@dslsrvr1> <mailto:drusso@dslsrvr1> 
<mailto:drusso@dslsrvr1> test-sims]$ grep " 14304 " ssls-packet.tr
s 604.921851420 _13_ AGT  --- 14304 cbr 512 [0 0 0 0] ------- [13:1 8:0 
32 0] [1] 0 255
r 604.921851420 _13_ RTR  --- 14304 cbr 512 [0 0 0 0] ------- [13:1 8:0 
32 0] [1] 0 255
s 604.921851420 _13_ RTR  --- 14304 cbr 532 [0 0 0 0] ------- [13:1 8:0 
31 15] [1] 0 255
s 604.922315758 _13_ MAC  --- 14304 cbr 584 [a2 f d 800] ------- [13:1 
8:0 31 15] [1] 0 255
r 604.924652427 _15_ MAC  --- 14304 cbr 532 [a2 f d 800] ------- [13:1 
8:0 31 15] [1] 1 255
r 604.924677427 _15_ RTR  --- 14304 cbr 532 [a2 f d 800] ------- [13:1 
8:0 31 15] [1] 1 255
f 604.924677427 _15_ RTR  --- 14304 cbr 532 [a2 f d 800] ------- [13:1 
8:0 30 6] [1] 1 255

Othertimes when a link isnt present and i try to send a packet accross 
it,I see huge delays in the middle of routing, this example shows over 
167 seconds of delay when passing a packet between node 3 and 14. e.g:

[drusso@dslsrvr1 <mailto:drusso@dslsrvr1> <mailto:drusso@dslsrvr1> 
<mailto:drusso@dslsrvr1> test-sims]$ grep " 12751 " ssls-packet.tr
s 500.000000000 _2_ AGT  --- 12751 cbr 512 [0 0 0 0] ------- [2:2 15:0 
32 0] [0] 0 255
r 500.000000000 _2_ RTR  --- 12751 cbr 512 [0 0 0 0] ------- [2:2 15:0 
32 0] [0] 0 255
s 500.000000000 _2_ RTR  --- 12751 cbr 532 [0 0 0 0] ------- [2:2 15:0 
31 3] [0] 0 255
s 500.001618336 _2_ MAC  --- 12751 cbr 584 [a2 3 2 800] ------- [2:2 
15:0 31 3] [0] 0 255
r 500.003954672 _3_ MAC  --- 12751 cbr 532 [a2 3 2 800] ------- [2:2 
15:0 31 3] [0] 1 255
r 500.003979672 _3_ RTR  --- 12751 cbr 532 [a2 3 2 800] ------- [2:2 
15:0 31 3] [0] 1 255
f 500.003979672 _3_ RTR  --- 12751 cbr 532 [a2 3 2 800] ------- [2:2 
15:0 30 14] [0] 1 255
s 667.877524639 _3_ MAC  --- 12751 cbr 584 [a2 e 3 800] ------- [2:2 
15:0 30 14] [0] 1 255
r 667.879861129 _14_ MAC  --- 12751 cbr 532 [a2 e 3 800] ------- [2:2 
15:0 30 14] [0] 2 255
r 667.879886129 _14_ RTR  --- 12751 cbr 532 [a2 e 3 800] ------- [2:2 
15:0 30 14] [0] 2 255
f 667.879886129 _14_ RTR  --- 12751 cbr 532 [a2 e 3 800] ------- [2:2 
15:0 29 4] [0] 2 255
s 667.933868272 _14_ MAC  --- 12751 cbr 584 [a2 4 e 800] ------- [2:2 
15:0 29 4] [0] 2 255
r 667.936204582 _4_ MAC  --- 12751 cbr 532 [a2 4 e 800] ------- [2:2 
15:0 29 4] [0] 3 255
r 667.936229582 _4_ RTR  --- 12751 cbr 532 [a2 4 e 800] ------- [2:2 
15:0 29 4] [0] 3 255
f 667.936229582 _4_ RTR  --- 12751 cbr 532 [a2 4 e 800] ------- [2:2 
15:0 28 15] [0] 3 255
s 667.948459891 _4_ MAC  --- 12751 cbr 584 [a2 f 4 800] ------- [2:2 
15:0 28 15] [0] 3 255
r 667.950796636 _15_ MAC  --- 12751 cbr 532 [a2 f 4 800] ------- [2:2 
15:0 28 15] [0] 4 255
r 667.950821636 _15_ AGT  --- 12751 cbr 532 [a2 f 4 800] ------- [2:2 
15:0 28 15] [0] 4 255

has anyone see this behavior before. I'm using ns-2.1b6 on linux.
thanks,
daniel