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Re: [ns] reason of collision in 802.11?

Subject: Re: [ns] reason of collision in 802.11?
From: Felix Ko <[email protected]>
Date: Tue, 03 Jul 2001 17:40:03 +0200
CC: [email protected]
References: <[email protected]>
Sender: [email protected]
Hi Alan,

I just have a suggestion:

A packet can be *received* successfully (with the
parameters of mac-802.11 set to their default values) 
within a range of 250m. But it's signal power is above
the carrier-sense threshold within a range of about 550m
around the sender. This means a packet transmitted by
node 0 (line 17!) could collide with a packet received
at node 3 which is 500m away.

My guess is that the MAC-broadcast packet in line 17
(maybe the RTS for the next TCP segment?) collides
with the RTS sent from node 1 to 3...

But this is just a guess...

Hope this helps

Bye
Felix

Alan Wang wrote:
> 
> 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
References:
- [ns] reason of collision in 802.11?
  - From: Alan Wang <[email protected]>
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