Subject: [manet] Medium Capture in Ad hoc

From: "Ehsan Hamadani" <[email-masked]>
Date: Mon, 14 Mar 2005 13:17:21 -0000

Hi all,
 
I have a trivial question regarding the way different flows try to
access the medium. In my simulation, I have defined a cross topology
where one flow is constantly running and the second flow starts and
finished while the first one is still running. The result that I am
seeing is that when the second flow starts, the fist flow stops
completely (for about 30 seconds). Then the second flow release the
medium after this time and flow one restart its transmission for a while
(10 seconds) and this swapping is continued till flow two finishes its
data or TCP connection for flow one is aborted. So, two flows never can
send continuously.
 
Well, though I think this is a direct result of 802.11 exponential
backoff, I am wondering whether some of you have experienced (or
probably have a solution for) this medium capture or not?  
 
Thanks
 
Ehsan
 
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---

From: Brown Tim <[email-masked]>
Date: Mon, 14 Mar 2005 08:46:15 -0700 (MST)

We have an outdoor test bed and observed exactly this kind of behavior
when we had competing flows. We believe it is a combination of 802.11
and TCP. We tried many variations with a similar
result. To name a few:
Symmetric flows: Node A sends through several hops to Node B, while Node B
sends to Node A.

Non-symmetric flows: Node A sends through B and C to Node D. Node C sends
to B.

Partial Overlap: Node A sends through B to Node C. Node D sends through C
to B.

Common end node: Node A sends through B to Node C. Node E sends through D
to Node C.

In any case, in all these cases one flow often would cause the other
flow to stall until it finished. There was no obvious pattern. The flow
that stalled would sometimes be the first or the second or they would find
some mutual rate where they would both simultaneously exhange data.
	Regards,
		Tim

> probably have a solution for) this medium capture or not?

Timothy X Brown
Interdisciplinary Telecommunications
Electrical and Computer Engineering
ECOT 256 Campus Box 530
University of Colorado
Boulder, CO 80309
Tel: (303) 492-1630
Fax: (303) 492-1112
http://ece.colorado.edu/~timxb

---

From: Claudio Lavecchia <[email-masked]>
Date: Tue, 15 Mar 2005 11:36:01 +0100

Hello Ehsan,

A hint to understand the factors that drive the medium capture can be 
found in "Unfairness and capture behaviour in 802.11 adhoc networks" 
(http://intl.ieeexplore.ieee.org/xpl/abs_free.jsp?arNumber=853084).

Ciao

Claudio

Ehsan Hamadani wrote:

> medium after this time and flow one restart its transmission for a 
> while (10 seconds) and this swapping is continued till flow two 
> finishes its data or TCP connection for flow one is aborted. So, two 
> flows never can send continuously.
>
>  
>
>------------------------------------------------------------------------
>

---

From: "John Stine" <[email-masked]>
Date: Tue, 15 Mar 2005 08:27:32 -0500

For those of you who are at IEEE WCNC and are interested in this capture
problem and how it might be overcome, I encourage you to come to session
PHY28: Ad Hoc Networks I tomorrow morning.  I will be presenting a paper
titled

Exploiting processing gain in wireless ad hoc networks using synchronous
collision resolution medium access control schemes.

In this presentation I describe how the channelization problem and the near
far problem can be resolved in ad hoc networks as well as plant the idea
that this access protocol can support one node transmitting different
packets to different destinations simultaneously just as a CDMA base
station.  All of this is accomplished while still having a contention based
MAC in a mobile environment.

John

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Claudio Lavecchia
Sent: Tuesday, March 15, 2005 5:36 AM
To: Ehsan Hamadani
Cc: [email-masked]
Subject: Re: [manet] Medium Capture in Ad hoc

Hello Ehsan,

Ciao

Claudio

---

From: yingpei zeng <[email-masked]>
Date: Wed, 16 Mar 2005 00:45:33 +0800 (CST)

Hi,I am not an expert about this,But This result is really surprising.for the 802.11a  almost has been a  mature MAC standard protocol, have you try MACAW? it's said to be more care about fairness
 
YingPei Zeng

Ehsan Hamadani <[email-masked]> wrote:

Hi all,

I have a trivial question regarding the way different flows try to access the medium. In my simulation, I have defined a cross topology where one flow is constantly running and the second flow starts and finished while the first one is still running. The result that I am seeing is that when the second flow starts, the fist flow stops completely (for about 30 seconds). Then the second flow release the medium after this time and flow one restart its transmission for a while (10 seconds) and this swapping is continued till flow two finishes its data or TCP connection for flow one is aborted. So, two flows never can send continuously.

Well, though I think this is a direct result of 802.11 exponential backoff, I am wondering whether some of you have experienced (or probably have a solution for) this medium capture or not?  

Thanks

Ehsan

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