[OLPC-AU] Adhoc wireless sharing help

[James Cameron]

G'day Jonathan,

You did not mention the software version you are using, so I'm presuming
you are using the current release 10.1.2 also known as build os852.

1.

The most likely cause of the symptom you describe is laptops going into
idle suspend.  There is a known problem where this will prevent the
neighbourhood view from being updated as activities are shared (#10363).

You can workaround this by turning off Automatic Power Management in My
Settings -> Power.  A future release (10.1.3 due in December) may
suppress idle suspend when an activity is shared from a laptop, but not
prevent it on the other laptops in a group.

2.

The second most likely cause is noisy radio environment (#10397).

Each ad-hoc group has within it one laptop that is the timing master for
the group.  The role moves from laptop to laptop dynamically, under
control of the firmware in the wireless card.  The purpose of the timing
master is to ensure that the other laptops in the group only transmit
when no other laptop in the group is transmitting.

When there is another ad-hoc group nearby, with it's own timing master,
there is very little coordination, and so the transmissions can occur at
the same time, resulting in several laptops not receiving them.

Further, the transmission of "new shared activity" is done as a
"multicast" packet using the slowest data rate, and is done only every
three minutes after the first transmission!  Three minutes is an
eternity in class time.  So if the first packet is lost, it can take a
long time before the second packet is heard.

You can workaround this by (a) restricting the number of nearby ad-hoc
networks, by increasing the distance between groups, (b) ensuring all
laptops in the same room join the same ad-hoc network, (c) using an
access point for the timing master, or (d) stopping the shared activity,
starting a new activity, and sharing it once more.

3.

The third most likely cause is that not all laptops "saw" each other in
the neighbourhood view before the activity was shared.

You can workaround this by checking that all laptops can see each other
in that view before sharing an activity.  The cause of not seeing one
another relates to #2 above.

References:

http://dev.laptop.org/ticket/10363
http://dev.laptop.org/ticket/10397

-- 
James Cameron
http://quozl.linux.org.au/