Subject: [manet] Sensitiveness in MANET node

From: Claudio Lavecchia <[email-masked]>
Date: Thu, 21 Apr 2005 11:43:30 +0200

Hello everyone,

I have a question regarding the setup of a 802.11 MANET.
I am setting up a MANET using an iPaq and a laptop as nodes. On iPaq 
(a.k.a LAB1)I use Familiar Linux (version 0.7.2) as an OS. I use Dell 
Truemobile 1150 WLAN adapters (Orinoco driver version 0.11b) set in ad 
hoc mode.

I configure the eth0 interface on my iPaq LAB1 with a script (wifi.sh) 
that contains the following lines.

~ # more ./wifi.sh
ifconfig eth0 down
ifconfig eth0 up
ifconfig eth0 inet $1
iwconfig eth0 mode Ad-Hoc
iwconfig eth0 channel 10
iwconfig eth0 essid mobman

In this script I statically assign an IP address to the node, then set 
the node in ad-hoc mode, set the channel and give it an ESSID
Straight after executing this script, iwconfig gives the following results:

~ # iwconfig eth0
eth0      IEEE 802.11-DS  ESSID:"mobman"  Nickname:"HERMES I"
          Mode:Ad-Hoc  Frequency:2.462GHz  Cell: 00:09:5B:FD:F3:20 
          Bit Rate:5.5Mb/s   Tx-Power=15 dBm   Sensitivity:1/242700000 
          Retry limit:4   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:26
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

This outcome is really odd for (at least) the following reasons:

1) Frequency does not correspond to channel 10
2) Despite the fact that there is already another node  (a Linux laptop 
equipped with the same Dell Truemobile 1150 WLAN adapter that I will 
call LAB2) online belonging to the same IBSS (=having the same ESSID and 
set in channel 10), the iPaq does not associate with this latter device 
but with "Cell: 00:09:5B:FD:F3:20".
3) "Sensitivity" value seems to be low.

At the beginning I did not figure out what this MAC address was. Then 
using a Wireless Network utility on a third PC ( a.k.a. LAB3) I found 
out that "Cell: 00:09:5B:FD:F3:20" corresponds to the MAC address of is 
an AP located in a besides building. This MAC address does not always 
appear in the wireless network utility on LAB3 but even when it does 
not, it seems somehow to perturbate the configuration of LAB1. I guess 
that this MAC appears on LAB3 only when the received signal is stronger 
than a given threshold.

My questions are:
1) Could this LAB1 strange behavior depend on the value of the 
"Sensitivity" parameter? This value seems to be extremely low, does this 
indicate that my LAB1 is very prone to be perturbated by surrounding 
devices?
2) If the sensitivity is the cause of my problem, how can I set it 
differently? I did not succeed in changing it using iwconfig. What are 
reasonable values?
3) What are the scripts to modify to make it so that my iPaq tunes to 
the right network every time I put the WLAN adapter in the PCMCIA slot? 
I heard that if I do so, the WLAN adapter will sty tuned to the selected 
network forever. Is this true?

Thx for any hint/suggestion/help

Claudio

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