RTS Collision

Hello all,

The last week I am trying to figure out how the 802.11 should
operate in the following scenario. Any help much appreciated.

Consider the scenario of 4 nodes 0-3

0<->1<->2<->3

Where each node has transmission range to reach only one of its
neighbours. At time t1 a unicast frame is transmitted by node 3 with
destination node, 2. And another unicast frame from node 1->2. At the
unicast case the standard specifies that a full RTS/CTS handshaking
must be done. Then both nodes 1 and 3 should start transmitting the
RTS frame. And then this packet collides. But nodes 0 and 1 does not
know about the collision and node 0 should send back its CTS. Then
when node 1 receives the CTS should start the data frame tx.

Actually I have simulate this in NS2 but it gives me unreasonable
results.

As you can see the CTS frameis droped at node 2 due to collision. but
why node1 re-Tx RTS?

Please help on that one.

Cheers,
Christos


s 11.778628029 _1_ MAC --- 0 RTS 44 [325e 0 1 0]
s 11.778628062 _3_ MAC --- 0 RTS 44 [325e 2 3 0]
r 11.778980695 _0_ MAC --- 0 RTS 44 [325e 0 1 0]//0 has received RTS


D 11.778980895 _2_ MAC COL 0 RTS 44 [325e 2 3 0]
s 11.778990695 _0_ MAC --- 0 CTS 38 [3124 1 0 0]//0 has sent CTS

r 11.779295362 _1_ MAC --- 0 CTS 38 [3124 1 0 0]// 1has received CTS
but retransmitting RTS again

s 11.779695695 _1_ MAC --- 0 RTS 44 [325e 0 1 0]
D 11.780048362 _0_ MAC BSY 0 RTS 44 [325e 0 1 0]
s 11.780983329 _3_ MAC --- 0 RTS 44 [325e 2 3 0]
r 11.781336162 _2_ MAC --- 0 RTS 44 [325e 2 3 0]
s 11.782363329 _3_ MAC --- 0 RTS 44 [325e 2 3 0]
r 11.782716162 _2_ MAC --- 0 RTS 44 [325e 2 3 0]
s 11.784170962 _1_ MAC --- 0 RTS 44 [325e 0 1 0]
D 11.784523629 _0_ MAC BSY 0 RTS 44 [325e 0 1 0]//Why is 0 dropping
RTS sent by 1?

s 11.785270962 _1_ MAC --- 0 RTS 44 [325e 0 1 0]
D 11.785623629 _0_ MAC BSY 0 RTS 44 [325e 0 1 0]
s 11.787838595 _3_ MAC --- 0 RTS 44 [325e 2 3 0]
r 11.788191429 _2_ MAC --- 0 RTS 44 [325e 2 3 0]
s 11.795246229 _1_ MAC --- 0 RTS 44 [325e 0 1 0]
r 11.795598895 _0_ MAC --- 0 RTS 44 [325e 0 1 0]
s 11.795608895 _0_ MAC --- 0 CTS 38 [3124 1 0 0]
r 11.795913562 _1_ MAC --- 0 CTS 38 [3124 1 0 0]
s 11.795923562 _1_ MAC --- 876 cbr 1532 [13a 0 1 800] ------- [1:0 0:0
32 0] [436] 0 0
r 11.808180229 _0_ MAC --- 876 cbr 1480 [13a 0 1 800] ------- [1:0 0:0
32 0] [436] 1 0
s 11.808190229 _0_ MAC --- 0 ACK 38 [0 1 0 0]
r 11.808494895 _1_ MAC --- 0 ACK 38 [0 1 0 0]