Re: Re: [ns] Problem about the implemention of mac802_11

[Yun Li <liy_china@yahoo.com>]

    You are right!It's my mistake.

THANKS EVERYBODY FOU YOUR DISCUSSING TO THIS PROBLEM.
--- ��Ӿ <cargirl@263.net> wrote:
> I have just examined the code of mac_802_11.cc and
> find that
> the implementation of ns is somewhat reasonable. I
> have mistaken
> that there are a backoff process after difs.
> Besides, In IEEE802.11
> standard 9.2,it says that "The CSMA/CA protocol is
> designed to 
> reduce the collision probably ... Just after the
> medium becomes
>  idle following a busy medium...This is the
> situation that 
> necessitates a random backoff procedure ...". When
> the medium is
> idle for some time, it's not necessary to backoff. 
> 
> >A simple example is the "void send(Packet * p,
> Handler
> > *h)" function in Mac-802_11.cc. In this
> >function,there 
> >are some statements like:
> >"
> >if(mhBackoff_.busy()==0) {
> >    if(is_idle()) {
> >       if(mhDefer_.busy()==0)
> >                mhDefer_.start(difs_);
> >     }
> >else {
> >     mhBackoff_.start(cw_.is_idle());
> >     }
> >}
> >"
> >    From these statements,we can conclude that when
> 
> >the media is busy, backoff a random time;else,
> defer
> > difs_ time and send the packet. But the Mac802.11
> > standard requires that even if the media is
> idle,the
> > mac sender must backoff a random time. THIS IS THE
> > FIRST CONFLICT that i can see.
> >   The second,we can't find where the physical
> layer's
> >CCA/CA function  which the standard requires was
> >implemented in ns-2.
> >
> > --- Jun Zhao <JZhao_NS@hotmail.com> wrote:
> >> Can you give us more detailed info? 
> >> ----- Original Message ----- 
> >> From: "Yun Li" <liy_china@yahoo.com>
> >> To: <ns-users@ISI.EDU>
> >> Cc: <ns-users@ISI.EDU>
> >> Sent: Tuesday, August 28, 2001 11:25 AM
> >> Subject: [ns] Problem about the implemention of
> >> mac802_11
> >> 
> >> 
> >> > Dear ns-users:
> >> > 
> >> > I have looked into the ns-2.1b8 resources code,
> >> > mAC-802_11.h and Mac-802_11.cc that implement
> the
> >> > MAC802.11 standard. I find that the
> implemention
> >> > doesn't follow the IEEE MAC802.11 standard.
> What's
> >> > your
> >> > opinion about this and am I right?
> >> >         Any idea will be appreciated!
> >> > 
> >> >
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> >
> >
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>                     ��
> ��
> 
>             ��Ӿ
>             cargirl@263.net
> 


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