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Re: [ns] Problem about the implemention of mac802_11
Hi,
From the 802.11 std. of 1999, it seems that we can not say Yes or No to a
station which has a pending PDU.
1) From chapt. 9.2.5.1:
"In general, a STA may transmit a pending MPDU when it is operating under
the DCF access method, either
in the absence of a PC, or in the CP of the PCF access method, when the STA
determines that the medium is
idle for greater than or equal to a DIFS period, or an EIFS period if the
immediately preceding medium-busy
event was caused by detection of a frame that was not received at this STA
with a correct MAC FCS value.
...
"
2) From chapt. 9.2.5.2
"A backoff procedure shall be performed immediately after the end of every
transmission with the More Fragments
bit set to 0 of an MPDU of type Data, Management, or Control with subtype
PS-Poll, even if no additional
transmissions are currently queued.
...
"
As noted above, one station may transmit when the medium is idle, but
unlikely to have chance capture the channel.
BTW: who can provide more docs about the 802.11 implementation in NS?
----- Original Message -----
From: "Yun Li" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Tuesday, August 28, 2001 2:46 PM
Subject: Re: [ns] Problem about the implemention of mac802_11
> 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 <[email protected]> wrote:
> > Can you give us more detailed info?
> > ----- Original Message -----
> > From: "Yun Li" <[email protected]>
> > To: <[email protected]>
> > Cc: <[email protected]>
> > 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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>