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

[��Ӿ <cargirl@263.net>]

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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