Re: [ns] 802.11 versus extending range in ad-hoc networks

[Anders Lindgren <dugdale@sm.luth.se>]

Hi,

It almost sounds like it could have something to do with the propagation
delay. When you go to 1500 m, you get a one way propagation delay of 5 us
(speed of light 3*10^8 m/s), thus an RTT of 10 us. By default, a SIFS is
10 us. Because of this, all your RTS frames will "time out" before you get
the CTS back, so you won't be able to send any data.

I'm not 100% sure, but this is probably the cause of your
problems. So... I suppose one way of increasing the range to more than
1500 m would be by tweaking with the SIFS and related stuff, but I'm not
really sure it would be good to do that... Might mess up something else...

/Anders

On Tue, 2 Jan 2001, Leonardo da Silva Mattos wrote:

> Hi all,
> 
> I am trying to use ranges larger than 250m in ad-hoc networks, but still
> using 802.11 as the MAC layer.
> I realized that by changing RXThresh_ to a specific value in my TCl script I
> can get different ranges. Also, by changing the RANGE variable in setdest.cc
> I can generate movement files aware of the new range.
> I used Wei's threshold.cc to find the appropriate value for RXThresh for the
> range I wanted in my tworayground propagation model.
> 
> However, looking at the trace file for a simple example, where 2 nodes that
> don't move try to communicate with each other, I concluded that somehow the
> MAC802.11 layer is dropping all my packets, when I exceed 1500m. I mean,
> 1499.99m seeems to be the maximum range I can use.
> The main reason for the dropping (observed in the trace files with mactrace
> ON) seems to be STA, which stands for DROP_MAC_INVALID_STATE.
> 
> Well, I would like to simulate ranges greater than 1500m . So,if anybody
> knows how to overcome this problem, I will highly appreciate. I must say
> that it looks like I have to change some default parameters in the
> mac-802_11.cc or .h , but I don't know which ones.
> 
> Thanks,
> Leo from Naval Postgraduate School
>