TX error due to colision or erroneous TX

[David Gibson]

On Tue, Feb 26, 2002 at 07:09:00PM -0500, Amit Jain wrote:
> 
> Just to check whats happening, I configured my laptop to run in Ad-hoc
> mode with just it as the node in the network. And I ran 'ping' to some
> hosts and obviously the ping reprted  "Destination unreachable" since the
> network has only one node.

Specifically "destination unreachable" means that your machine
received no reply to its ARP query.

> But the surprising thing is that card raised the interrupts corresponding
> to HERMES_EV_TX and not HERMES_EV_TXEXC. ??
> 
> Since there are no other stations in the n/w, it is impossible for my
> laptop to recevie an ACK for the transmitted packet. So if TX is
> based on 802.11 ACK protocl, then in this cse function handler
> corresponding to EV_TXC  should have been called. I do not understand why
> I am getting "Successful transmission signal" as indicated by EV_TX.
> (in 802.11 succesfull packet trnasmission means that the packet was
> trnamitted correctly and subsequent ACK received correctly)

I think this must be because the ARP is failing.  ARP requests are
broadcast packets, and for obvious reasons these wouldn't be ACKed.

> Kindly help, as my whole experimentation are based on this event handling.
> 
> I did this experiment in my apartment (rather than lab) so I was quite
> sure thre no effects due to other wireless stations. Below is the
> information regarding system paramaters.
> 
> iwconfig output:
> 	eth1: IEEE 802.11-DS ESSID:"JAS Network" Nockname:"sagar"
> 	      Frequency:2.457 Ghz  Sensitivity:1/3   Mode:Ad-Hoc
>               Acces Point : 02:02:2D:4a:33:23
> 	      Bit Rate:2Mb/s RTS thr:off  Fragment thr: off
>               Encryption Key:off
>               Power Management:off
>               LInk Quality:0 Signal:0 Noise Level:0
> 	      Rx invalid nwid:0 invalid crypt:0 invalid misc:0
> 
> Also, there was some strnage thing happening. when I was sding the pa kes
> thru eth1 my loopback interface also showed increment in TX and RX ??
> 
> 
> 
> On Thu, 21 Feb 2002, David Gibson wrote:
> 
> > On Wed, Feb 20, 2002 at 04:47:17AM -0500, Amit Jain wrote:
> > >
> > > Thanks for your reply.
> > >
> > > Can you provide one more clarification.
> > >
> > > Since 802.11 protocol requires ACK for every TX packet that means card
> > > waits for the ACK. So, does this mean that interrupt TX_EXC is based on a
> > > timeout (smaller and different from tx_timeout, which detects h/w lockups
> > > or missing interrupts)
> >
> > Yes.

-- 
David Gibson			| For every complex problem there is a
david at gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.  -- H.L. Mencken
http://www.ozlabs.org/people/dgibson