On events TX and TXEXC ?

Hongwei Zhang zhangho at cis.ohio-state.edu
Fri Jul 16 18:09:29 EDT 2004


Greetings,

I am a graduate student doing research in wireless networking, I am now 
implementing a routing as well as reliable transport protocol for 
multi-hop communication in sensor network back-bones (using IEEE802.11 
card as the radio). To reduce control overhead, I would like to use the 
feedback from MAC layer to decide whether a packet is successfully 
received by the intended receiver or not (via the ACK from the receiver) 
at each routing hop.

After looking through the file "hostap_hw.c" and the "PRISM Driver 
Programmers Manual", I found that the events TX and TXEXC are used to 
signal the status of packet delivery. Yet I am not sure about some 
detailed semantics of TX and TXEXC, as well as the implementation of the 
hostap driver. So here are my questions:

    * Would TX be signaled only if the ACK is received by the sender?
    * Would TX and TXEXC be signaled for broadcast packets, considering
      the fact that there is no ACK for broadcasting?
    * In hostap_hw.c, function prism2_tx_ev(...) does not generate any
      event as prism2_txexc(...) does. I wonder if I could use
      wireless_send_event(...) to send an event to the user-space for
      TX? Would this cause any problem in practice?
    * Is there a way to associate, in an user-space program, a TX or a
      TXEXC event with the corresponding packet? (I am sending a short
      UDP message via wlan0, so that there is no message segmentation
      and each message is carried in one MAC packet.)

Any suggestions and help regarding the above issues would be greatly 
appreciated. (I am quite new to the network stack implentation of Linux, 
so the above questions may look irrational, in which case please forgive 
my ignorance.)

Thanks a lot for your time and have a good weekend (despite my long 
email :-) ),

Hongwei

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