bandwidth in ad hoc between 3 laptops

July 20, 2011 at 07:27:10
Specs: Windows 7, 2 GB
Hi all,

I have three laptops (running ubuntu with different kernel versions) with wireless adapter Intel Corporation PRO/Wireless 3945 ABG.

Laptop A ----- Laptop B ----- Laptop C

I created an adhoc connection in laptop A with:
Essid: 'ad_hoc'
IP address: 10.42.43.1
Subnet: 255.255.255.0
Gateway: 0.0.0.0

Now the laptops B and C can see the wireless connection 'ad_hoc' and I can connect to them after setting IP 10.42.43.1 and 10.42.43.2 respectively. So, I created the adhoc connection between 3 laptops. Now, I wanted to check the bandwidth between the different paths.

The tool iperf was what I used for TCP bandwidth calculation. The bandwidth between A and B was around 4.5 Mbps , between A and C was around 4.0 Mbps but the bandwidth between B and C (B being server) was 677 kbps whereas C being server was 3.99.

I don't understand how can the bandwidth drop so high when B was made the server. The system adapters are identical. Does it have any explanation?

MAx


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#1
July 20, 2011 at 07:41:49
Yeah I have an explanation, you're using more than two computers in ad-hoc mode. I don't know what you're expecting from a mickeymouse setup like that but you're obviously expecting too much

If you want a more reliable setup, with better bandwidth, I recommend you spend the $50 (USD) and buy a wireless capabale SOHO Router. Setup a WPA Encrypted wirless network and join your laptops to it. Even if the interfaces on the laptops are G only, you could get up to 54 Mbps. If they're N and you buy an N router, you could get 100 Mbps.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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#2
July 20, 2011 at 08:59:10
Its ok there is this massive bandwidth drop cause there are 3 machines in adhoc. But it should be similar bandwidth the both ways for identical system.
A to B bandwidth 4Mbps
B to A bandwidth 677 Mbps.

How can this be true for identical configuration? I am using this mickey mouse setup to use some never used network cards rather than piling new ones ;)


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#3
July 20, 2011 at 10:08:58
4 Mbps is not even 1/4 of the rated bandwidth of a G interface (54 Mbps). You should be able to achieve 54 Mbps between two laptops in ad-hoc mode. If it were me, I'd test.

First, connect A and B (only) in ad-hoc.......what's the bandwidth.

Then connect A and C (only) and test

Then B and C.

Bandwidth should be consistent in all 3 cases. If it's not, then you may have some issues with the interface(s) and the above testing would help you isolate which interface is the problem (ie: the problem will follow the bad interface)

I am using this mickey mouse setup to use some never used network cards rather than piling new ones

Again, as per my initial response, I repeat, "Buy a wireless capable SOHO Router and create a WLAN on it and join your clients to it"

This allows you to create an actual WLAN (as vs. the ad-hoc mickeymouse solution) and then connect the laptops to it individually.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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