[Battlemesh] Broadcast lost because of hidden station

Henning Rogge hrogge at gmail.com
Sat Apr 26 12:07:05 CEST 2014


but I would expect that at least "one in five" broadcasts would make
it through, because unicasts get up to 4 retransmissions.

Henning Rogge

On Fri, Apr 25, 2014 at 11:16 AM, Paul Fuxjaeger <fuxjaeger at ftw.at> wrote:
> On 24.04.14 14:04, Henning Rogge wrote:
>> Hi,
>> we found a curious effect this week on our Ubiquity M5 bullets.
>> Because of a hidden station, a node wasn't able to receive any
>> multicast frames of a neighbor (sent with 6 MBit/s), but it was still
>> able to send unicasts over the link to the neighbor!
>> Any idea why multicast is more easy to block by the hidden station
>> transmission than unicast?
> my guess:
> in case of unicast the L2 error protection (ACKing and
> fast-retransmission-when-ACK-timeout) does what it is supposed to do and
> largely improves error statistic seen at upper layers in the presence of
> lowSNR and/or bursty interference (at the cost of additional airtime
> being consumed). Whereas for multicasts the above mentioned mechanism
> cannot be used since it does not make sense for multipoint reception.
> trigger some unicasts from the node that can't reach the neighbor via
> multicasts and check the retry stats on the TX side shortly afterwards.
> -paul
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