[Battlemesh] Broadcast lost because of hidden station

[Paul Fuxjaeger]

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