[ns] 802.11 Carrier sense

[shshah@cairo.cs.uiuc.edu]

On Tue, 16 Apr 2002, Sorav Bansal wrote:

> 
> 
> The call to is_idle in the function check_pktRTS() is the call to is_idle
> before an RTS is to be dispatched.

Thanks. I'm unable to generate a scenario, however, in which the 'if (!  
is_idle())' check turns out to be true. The channel always seems to be 
idle and the condition always seems to be false, however high a rate I 
send at.

Thus, if I set the backoff interval differently (not using inc_cw() as is 
done in check_pktRTS(), but using a function of my own), this code is not 
executed at all since the if (! is_idle()) is always false. Hence, my 
purpose is still not served. Can you give me any input on this?

Thanks and regards,
Samarth.

> 
> --sorav
> 
> 
> 
>                                                                                                 
>                     shshah@cairo.c                                                              
>                     s.uiuc.edu           To:     Sorav Bansal/India/Contr/IBM@IBMIN             
>                                          cc:     ns-users@ISI.EDU, <ns-users-admin@ISI.EDU>     
>                     04/15/02 09:33       Subject:     Re: [ns] 802.11 Carrier sense             
>                     PM                                                                          
>                     Please respond                                                              
>                     to shshah                                                                   
>                                                                                                 
>                                                                                                 
> 
> 
> 
> On Mon, 15 Apr 2002, Sorav Bansal wrote:
> 
> >
> >
> > Hi,
> >     The function is_idle() in mac-802_11.cc checks if the medium is idle
> or
> > not (carrier sensing).
> 
> Yes, I am aware of this, but I would like to know which particular call to
> is_idle() is the *first* carrier sense before the *first* RTS is sent.
> is_idle() is checked multiple times in mac-802_11.cc, I am only interested
> in the particular above case. Could you give me this info? Thanks in
> advance.
> 
> Regards,
> Samarth.
> 
> The medium is not idle if a packet is being
> > received. And all packets with signal strength above the carrier sense
> > threshold are received by the MAC layer (except that the error field is
> set
> > to 1 for packet below the receiving threshold). Hope that answers your
> > query.
> > --sorav
> >
> >
> >
> >
> 
> >                     shshah@cairo.c
> 
> >                     s.uiuc.edu           To:     ns-users@ISI.EDU
> 
> >                     Sent by:             cc:
> 
> >                     ns-users-admin       Subject:     [ns] 802.11 Carrier
> sense
> >                     @ISI.EDU
> 
> >
> 
> >
> 
> >                     04/15/02 01:12
> 
> >                     PM
> 
> >                     Please respond
> 
> >                     to shshah
> 
> >
> 
> >
> 
> >
> >
> >
> >
> > Hi,
> >
> > I'm unable to discern exactly when (i.e. where in the 802.11 code) the
> > first carrier sense before the first RTS for a packet occurs. If the
> > carrier is found busy at this carrier sense, I would like to be able to
> > modify the backoff interval after the deferral that follows the busy
> > carrier sense. Rather than have the station backoff cw_ slot times, I'd
> > like to have it backoff some other number of slot times.
> >
> > I do not wish to modify the backoff procedure that is followed after a
> > collision, however. I want the cw_ doubling, backoff = cw_ number of
> > slots, etc. to remain as is, in the case of collision.
> >
> > Could anyone kindly provide me some guidance? Thanks in advance.
> >
> > Regards,
> > Samarth.
> >
> >
> >
> >
> >
> >
> >
> >
> 
> 
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>