Re: [SPAM] Madwifi v0.9.4 latest release: Frames transmitted out of sequence

Hi Dennis & Wayne,

Thanks for your response.

In my application I receive UDP/IPV4 packets from a wired interface. I have
no control on this protocol.

My application has a peek of the data in frame, collects some statistics and
just forwards the frame over the wireless interface using dev_queue_xmit.
One of the nodes is configured as AP & the other as Station. There is a
sequence number associated with the payload. That is how I know that the
packets are out of order when I receive them at the far end.

I have Linux version 2.6.18 running on MIPS platform with AR5414A chipset
based mini-PCI.

When I started work on this application, I had examined the packet sequence
from the wired i/f. They seemed to be in order. I will verify this once
again. 

My question now is are there any circumstances under which madwifi or
dev_queue_xmit can reorder packets ?

Regards

R.Mohan



-----Original Message-----
From: Wayne Johnson [mailto:[email protected]] 
Sent: Wednesday, December 15, 2010 11:52 PM
To: Dennis Borgmann; MOHAN.R.
Cc: [email protected]
Subject: RE: [Madwifi-users] [SPAM] Madwifi v0.9.4 latest release: Frames
transmitted out of sequence



> -----Original Message-----
> From: Dennis Borgmann [mailto:[email protected]]
> Sent: Wednesday, December 15, 2010 5:39 AM
> To: MOHAN.R.
> Cc: [email protected]
> Subject: Re: [Madwifi-users] [SPAM] Madwifi v0.9.4 latest release:
> Frames transmitted out of sequence
> 
> Hi Mohan!
> 
> Maybe this is not an issue of madwifi, but an issue of you IP
protocol?
> Are you using UDP? If so, try TCP since it guarantees the sequence of
> packet transmission.
> 
> HTH,
> Dennis Borgmann

I don't think your statement is necessarily correct. With TCP, data
leaving the transport layer and entering the application layer is
guaranteed to be in order but packets can still arrive on the network
layer out of order. 

It has been some time since I have done a lot of TCP/IP work but it is
my understanding the out of order typically not a problem unless there
is routing going on. 

> 
> MOHAN.R. schrieb:
> > Dear All,
> >
> >
> >
> > Occasionally I find that frames are being transmitted out of
sequence
> by
> > both AP as well as Station.
> >
> >
> >
> > This is not desirable for my application.
> >
> >
> >
> > Can anyone tell me why this happens and how to ensure that frames
are
> > always sent in sequence.
> >

Without making quite a few assumptions it's not possible to even
understand what you are asking here. A lot more detail is required. How
are you sending the packets? How are you determining they are out of
order? What hardware and software are you using on both ends? What are
you trying to do? 

I don't want you to take this the wrong way, I am still trying to be
helpful. Even though engineers are known for their literary skills ;-),
answering questions still takes quite a bit of effort. I have found that
most people try hard to be helpful when they can see that you are trying
hard to figure it out. Most likely you are working very hard to figure
out your problem but your email does not convey that and will probably
be ignored by the people who (unlike me) can be most helpful.

Wayne



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