Re: [ns] mac-802.11.cc -- possible incorrect handling of RTS/CTS's?

["Neeraj Poojary" <legolas_3@hotmail.com>]

you've identified the answer to your own question. if the node is not the 
intended recipient of the CTS, it will not process the CTS. but it will 
update its network allocation vector (NAV) based on the duration advertised 
by the CTS. the "dh_duration" tells the node that overhears the CTS how long 
the subsequent DATA/ACK sequence is going to last and it defers its own 
transmissions accordingly. see set_nav() and its usage.

-neeraj

>From: Jake Whitehill <whitehil@CS.Stanford.EDU>
>To: ns-users@ISI.EDU
>Subject: [ns] mac-802.11.cc -- possible incorrect handling of RTS/CTS's?
>Date: Wed, 18 Oct 2000 20:06:19 -0700 (PDT)
>
>Hi there,
>
>I read in Peterson & Davie's (Comp. Networks 2nd ed, p. 138) that,
>according to 802.11, "any node that sees the CTS frame knows that it is
>close to the receiver, and therefore cannot transmit for the period of
>time it takes to send a frame of the specified length."
>
>However, in mac-802.11.cc of "ns", as far as I understand the following
>lines of code, all nodes except for the explicit target of the RTS or CTS
>completely *ignore* RTS or CTS packets, which would contradict Peterson &
>Davie:
>
>void
>Mac802_11::recv_timer()
>{
>         ...
>         hdr_mac802_11 *mh = HDR_MAC802_11(pktRx_);
>         ...
>
>         /*  <---------- could this following section explain my question?
>          * IEEE 802.11 specs, section 9.2.5.6
>          *      - update the NAV (Network Allocation Vector)
>          */
>         if(dst != (u_int32_t)index_) {
>                 set_nav(mh->dh_duration);
>         }
>
>	...
>
>	/*
>          * Address Filtering
>          */
>         if(dst != (u_int32_t)index_ && dst != MAC_BROADCAST) {
>                 /*
>                  *  We don't want to log this event, so we just free
>                  *  the packet instead of calling the drop routine.
>                  */
>                 discard(pktRx_, "---");
>                 goto done;
>         }
>
>	...
>
>                 switch(subtype) {
>
>                 case MAC_Subtype_RTS:
>                         recvRTS(pktRx_);
>                         break;
>
>                 case MAC_Subtype_CTS:
>                         recvCTS(pktRx_);
>			break;
>
>So, as far as I see it, only if the destination of *any* packet, RTS/CTS
>or not, is "this" node, will an RTS or CTS or anything else be
>processed. I also marked the section which I think might be relevant and
>which might answer my question, but I don't know enough about it.
>
>Does anybody know where I'm wrong or where "ns" is, or even if Peterson &
>Davie are correct about 802.11???
>
>Thanks,
>Jake
>

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