"XO-1 classrooms" don't reliably connect to many/most Wifi AP's

[Adam Holt]

*[Terry Gillett summarizes his weeks of testing, **with this very revealing
report below.  That's tgillett at gmail.com <tgillett at gmail.com> of the
Village Telco project: can we/Nepal/Lesotho/others help him add the key
takeaways to http://wiki.laptop.org/go/Wifi_Connectivity
<http://wiki.laptop.org/go/Wifi_Connectivity> so the "almost 2 million
XO-1s worldwide" can benefit?  Spoiler Alert: XO-1 deployments must
carefully buy the correct Wifi Access Point, EG "Linksys WRT54GL" or
"Billion 7404VGP" appear to solve most all problems.  Likewise we've had a
lot of success in Haiti with the TP-Link TL-MR3020.]*


SUMMARY

The core problem is that XO-1 laptops will not reliably connect to a range
of wifi Access Points (AP).  By comparison, XO-1.5 and later laptops will
successfully connect to the same APs.

The behaviour of a group of XO-1s is different from that when they are
tested individually.  A single XO-1 may connect quite reliably, but when
used in a group of ten or more, many individual XO-1s will fail to connect
to the AP.

Note that this issue is just about connecting to the AP, it is not about
whether the AP can sustain a large number of connections or handle the
associated data throughput requirements.

A number of routers configured as APs have been tested to establish a
baseline.

The test process used requires 10 XO-1 laptops and is as follows:

1. Set up the AP on an unoccupied wifi channel, at least two and preferably
three channels away from unoccupied channels.
2. Connect each XO-1 individually to the AP and check that it is operating
correctly and has adequate signal strength.
3. Power off all the XOs
4. Start up one XO and allow it to connect successfully.
5. Start up the other none XOs
6. When the last XO has completed its boot up sequence, check the
connection status of each XO.

The result of a connection test for each XO is one of the following:
1. Successful automatic connection
2. No connection, but AP icon shows in Network Neighbourhood (NN) window
3. The AP icon does not appear.

Typically there will be a mix of XOs in each of the three states.
A Pass requires that all ten XO-1s are successfully connected at the end of
the test without manual intervention.

The proportion of XOs in each state will typically vary from 20 to 80% in a
Failed test.
The proportion of successful connections seems to vary by router type, but
changes in repeated tests.
Individual XOs will typically be in different states in repeated tests.

A range of routers has been tested with this procedure and the results
appear in the table below.

The only two routers that passed the test were the Billion and the Linksys.
Interestingly both these routers date from the same vintage as the XO-1.

Note that testing with less than five XO-1s results in a much greater
likelihood of a Pass result, and if the same AP is tested with ten XO-1s it
will likely fail.

A Pass result with ten XO-1s is considered (at this point) to be a
reasonable indication of likely success in a real world deployment with
greater numbers of XOs.

The working hypothesis is that modern APs have implemented the wifi specs
and/or default configurations in a way that has resulted in an
interoperability problem with the wifi implementation in the XO-1.


ROUTER TEST RESULTS

Billion 7404VGP        (old, Star Int, proprietary OS)          Pass
Linksys WRT54GL     (old, Broadcom, DD-WRT)             Pass

Netgear FWG114P     (old, proprietary OS)                       Fail
TP Link WR710n          (new, proprietary OS)                     Fail

TP Link WR703            (Atheros AR9331, OpenWrt)         Fail

TP Link WR842             (Atheros AR9287, OpenWrt)         Fail
TP Link MR3020           (Atheros AR9330, OpenWrt)         Fail
TP Link WDR4300        (Atheros AR9341, OpenWrt)         Fail
VT  MP01                       (Atheros AR23xx, OpenWrt)          Fail
VT  MP02                       (Atheros AR9331, OpenWrt)         Fail

--
Unsung Heroes of OLPC, interviewed live @ http://unleashkids.org !
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