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[STDS-802-11-TGAQ] Transmission of Multicast-Group Addressed Frames with no Listeners

Regarding the conversation in the teleconference of 22 April we had about the transmission of multicast-group packets when there are no listeners for that multicast service associated to the AP, I quote the third paragraph of section 9.2.8 of IEEE 802.11-2012:

If the Address 1 field of an MPDU carrying an A-MSDU does not match any address (i.e., individual or group address) at a receiving STA, then the entire A-MSDU is discarded. 

and the last paragraph of section 9.3.6:

A STA shall discard an MPDU with a group address in the Address 1 field if the value in the Address 1 field does not match any value in the dot11GroupAddressesTable and does not match the Broadcast address value. 

I believe that there are other entries in IEEE 802.11-2012 that relate to this issue, but these are the ones that I found. Keep in mind that each of these quotes are in subsections that are specific to particular scenarios, so they may not be a complete description of multicast transmission rules.

Note also the distinction between a broadcast address versus a multicast-group address, as described in section
  1. b)  Group address. A multidestination address, which may be in use by one or more STAs on a given network. The two kinds of group addresses are as follows:

    1. 1)  Multicast-group address. An address associated by higher level convention with a group of logically related STAs.

    2. 2)  Broadcast address. A distinguished, predefined group address that always denotes the set of all STAs on a given LAN. All ones are interpreted to be the broadcast address. This group is predefined for each communication medium to consist of all STAs actively connected to that medium; it is used to broadcast to all the active STAs on that medium. 

So, if there are no client STAs associated with the AP that have requested to join that multicast service, the AP will not transmit the multicast-group data frame. This impacts the proposed solution discussed in the teleconference.

Again, since I can't attend the May interim, I'm trying to manipulate this discussion onto the e-mail reflector so that I can participate. ;-) More to the point, if we can clear up these issues before the May interim session, that should help make the discussion in the session more productive. (However, I will miss this more productive discussion...).

Mahalo.  -- Ed Reuss

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