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[ns] reason of collision in 802.11?

To: [email protected]
Subject: [ns] reason of collision in 802.11?
From: Alan Wang <[email protected]>
Date: Mon, 2 Jul 2001 11:13:39 -0400 (EDT)
cc: [email protected], [email protected]
Sender: [email protected]

Hi,

I have some difficulty analysing the reason of collison in an 
802.11 trace file. I'm using ns-2.1b8.

Following is a part of the trace file. The network topology is string:
0->2->3->1. The distance betweeen nodes is 250m. No node moves. 0 sends
packets of 1500-byte to 1 through a FTP connection. All the other
simulation parameters use default values.

My question is: Collision happens at line(20). But what's the reason
of this collision? Which two packets collide? What's the packet sent at
line(17) and received at line(19) with a duration time of '1a1e' ? Is it 
a RTS/CTS? Why the duration time is so long? Thanks for your help!
________________________________________________________________________
(1)s -t 10.191273798 -Hs 2 -Hd -2 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 34e -Md 0 -Ms 2 -Mt 0 
// 2->0: RTS is sent
(2)r -t 10.191450632 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 34e -Md 0 -Ms 2 -Mt 0 
// 2->0: RTS is received
(3)s -t 10.191460632 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 2ac -Md 2 -Ms 0 -Mt 0 
// 0->2: CTS is sent
(4)r -t 10.191613465 -Hs 2 -Hd -2 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 2ac -Md 2 -Ms 0 -Mt 0  
//0->2: CTS is received
(5)s -t 10.191663465 -Hs 2 -Hd 0 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma a2 -Md 0 -Ms 2 -Mt 800 -Is 1.0 -Id 0.0 -It
ack -Il 128 -If 2 -Ii 11 -Iv 32 -Pn tcp -Ps 2 -Pa 0 -Pf 2 -Po 0
//2->0:TCP ACK(DATA) is sent
(6)r -t 10.192176298 -Hs 0 -Hd 0 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma a2 -Md 0 -Ms 2 -Mt 800 -Is 1.0 -Id 0.0 -It
ack -Il 76 -If 2 -Ii 11 -Iv 32 -Pn tcp -Ps 2 -Pa 0 -Pf 3 -Po 0 
//2->0: TCP ACK(DATA) is received
(7)s -t 10.192186298 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 0 -Md 2 -Ms 0 -Mt 0 
//0->2: link layer ack is sent
(8)r -t 10.192201298 -Hs 0 -Hd 0 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl RTR -Nw --- -Ma a2 -Md 0 -Ms 2 -Mt 800 -Is 1.0 -Id 0.0 -It
ack -Il 76 -If 2 -Ii 11 -Iv 32 -Pn tcp -Ps 2 -Pa 0 -Pf 3 -Po 0 
(9)r -t 10.192201298 -Hs 0 -Hd 0 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl AGT -Nw --- -Ma a2 -Md 0 -Ms 2 -Mt 800 -Is 1.0 -Id 0.0 -It
ack -Il 76 -If 2 -Ii 11 -Iv 32 -Pn tcp -Ps 2 -Pa 0 -Pf 3 -Po 0 
(10)s -t 10.192201298 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl AGT -Nw --- -Ma 0 -Md 0 -Ms 0 -Mt 0 -Is 0.0 -Id 1.0 -It tcp
-Il 1500 -If 2 -Ii 14 -Iv 32 -Pn tcp -Ps 5 -Pa 0 -Pf 0 -Po 0 
(11)r -t 10.192201298 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl RTR -Nw --- -Ma 0 -Md 0 -Ms 0 -Mt 0 -Is 0.0 -Id 1.0 -It tcp
-Il 1500 -If 2 -Ii 14 -Iv 32 -Pn tcp -Ps 5 -Pa 0 -Pf 0 -Po 0 
(12)s -t 10.192201298 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl AGT -Nw --- -Ma 0 -Md 0 -Ms 0 -Mt 0 -Is 0.0 -Id 1.0 -It tcp
-Il 1500 -If 2 -Ii 15 -Iv 32 -Pn tcp -Ps 6 -Pa 0 -Pf 0 -Po 0 
(13)r -t 10.192201298 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl RTR -Nw --- -Ma 0 -Md 0 -Ms 0 -Mt 0 -Is 0.0 -Id 1.0 -It tcp
-Il 1500 -If 2 -Ii 15 -Iv 32 -Pn tcp -Ps 6 -Pa 0 -Pf 0 -Po 0 
(14)s -t 10.192201298 -Hs 0 -Hd 2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl RTR -Nw --- -Ma 0 -Md 0 -Ms 0 -Mt 0 -Is 0.0 -Id 1.0 -It tcp
-Il 1536 -If 2 -Ii 14 -Iv 32 -Pn tcp -Ps 5 -Pa 0 -Pf 0 -Po 0 
(15)s -t 10.192201298 -Hs 0 -Hd 2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl RTR -Nw --- -Ma 0 -Md 0 -Ms 0 -Mt 0 -Is 0.0 -Id 1.0 -It tcp
-Il 1536 -If 2 -Ii 15 -Iv 32 -Pn tcp -Ps 6 -Pa 0 -Pf 0 -Po 0 
(16)r -t 10.192339132 -Hs 2 -Hd -2 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00
-Ne -1.000000 -Nl MAC -Nw --- -Ma 0 -Md 2 -Ms 0 -Mt 0 
//0->2: link layer ack is received
(17)s -t 10.192408298 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 1a1e -Md 2 -Ms 0 -Mt 0
//***What's this packet?*** 
(18)s -t 10.192555132 -Hs 1 -Hd -2 -Ni 1 -Nx
800.00 -Ny 200.00 -Nz 0.00
-Ne -1.000000 -Nl MAC -Nw --- -Ma 34e -Md 3 -Ms 1 -Mt 0 
//1->3: RTS is sent
(19)r -t 10.192585132 -Hs 2 -Hd -2 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00
-Ne -1.000000 -Nl MAC -Nw --- -Ma 1a1e -Md 2 -Ms 0 -Mt 0 
//***what's this packet?***
(20)d -t 10.192731965 -Hs 3 -Hd -2 -Ni 3 -Nx 550.00 -Ny 200.00 -Nz 0.00
-Ne -1.000000 -Nl MAC -Nw COL -Ma 34e -Md 3 -Ms 1 -Mt 0 
//why collision here?
(21)s -t 10.193550798 -Hs 2 -Hd -2 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00
-Ne -1.000000 -Nl MAC -Nw --- -Ma 34e -Md 0 -Ms 2 -Mt 0 
//2->0: RTS is sent
(22)r -t 10.193727632 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 34e -Md 0 -Ms 2 -Mt 0 
//2->0: RTS is received
(23)s -t 10.193737632 -Hs 0 -Hd -2 -Ni 0 -Nx 50.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma 2ac -Md 2 -Ms 0 -Mt 0 
//0->2: CTS is sent
(24)r -t 10.193890465 -Hs 2 -Hd -2 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00
-Ne -1.000000 -Nl MAC -Nw --- -Ma 2ac -Md 2 -Ms 0 -Mt 0 
//0->2: CTS is received
(25)s -t 10.193940465 -Hs 2 -Hd 0 -Ni 2 -Nx 300.00 -Ny 200.00 -Nz 0.00 -Ne
-1.000000 -Nl MAC -Nw --- -Ma a2 -Md 0 -Ms 2 -Mt 800 -Is 1.0 -Id 0.0 -It
ack -Il 128 -If 2 -Ii 12 -Iv 32 -Pn tcp -Ps 3 -Pa 0 -Pf 2 -Po 0 
//2->0: TCP ACK(DATA) is sent
.....
___________________________________________________________________________


Alan

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