Hi all,<br><br>I am trying to solve a big WLAN roaming problem which the N800 experiences and I think it is of<br>interest to many as good WLAN responsiveness for the N800(and successors) is the key<br>for smooth user experience, so please chime in with your experiences, ideas how to solve<br>
those problems etc.<br><br>Some background:<br><br>As WLAN access points we use 2 Buffalo Technology WHR-HP-AG108<br><a href="http://www.buffalo-technology.com/products/wireless/wireless-ag-mimo-performance/wireless-ag-mimo-performance-broadband-router-and-access-point-with-high-gain-antenna/">http://www.buffalo-technology.com/products/wireless/wireless-ag-mimo-performance/wireless-ag-mimo-performance-broadband-router-and-access-point-with-high-gain-antenna/</a><br>
using only the 802.11g radio (802.11a is disabled)<br><br>We are trying to use the N800 with OS2008 for a data entry application which runs on<br>a linux server. Basically in order to keep things simple we run the maemo vncclient<br>
on the N800 and the linux server simply provides a 800x480 VNC screen where<br>the app runs in. It works fine and the speed is more than adequate BUT<br>since the area the data entry operators work in cannot be covered by a WLAN single access point<br>
we set up 2 APs on different frequences (for example 1 and 11).<br><br>The problem we have is that even though within the working area you always get a strong signal<br>from at least 1 AP the N800 sometimes behaves very erratic.<br>
For example when moving from AP1 to AP2<br>It seems like the N800 tried to stay associated as long as possible with AP1 even though<br>AP2 is much stronger and AP1 can barely exchange any data at all with the N800 as it<br>
is at the border of the coverage area.<br>VNC will become very slow and impossible to work with. Sometimes it takes 1-2 minutes<br>for the nokia to realize that it should roam, totally unacceptable for smooth operation.<br>
<br>I disable wlan power saving (in the maemo control panel)<br>in order to avoid problems when the n800 wakes up from standy,<br>keep in mind the operators move alot on the area and often they will not touch the<br>n800 for several minutes.<br>
I even ping the IPs of the n800 from the linux server in order to make sure that they don't sleep.<br><br>Sometimes it even happens that the operator when roaming and wanting to use the N800<br>the VNC session got stuck and nothing works, so he has to power cycle it.<br>
<br>VNC uses a single TCP socket to exchange data between server and client.<br>The question is could it be that the socket remains stuck due to the roaming and is not able<br>to recover ? I could try to add an external watchdog which keeps a socket open with the server<br>
and in case that this happens restart the vnc client, but I am not sure if this will work.<br><br>Keep in mind that using a Windows laptop and the same vnc client code in the same area<br>where the N800 are employed works perfectly,<br>
so the network coverage, bandwidth and server speed is excellent.<br><br>I tried to install wireless-tools and play with both<br>iwconfig sens (sensivity) parameter<br><a href="http://maemo.org/development/documentation/man_pages/iwconfig.html">http://maemo.org/development/documentation/man_pages/iwconfig.html</a><br>
<br>and with<br>iwpriv parameters:<br><a href="http://maemo.org/development/documentation/man_pages/iwpriv.html">http://maemo.org/development/documentation/man_pages/iwpriv.html</a><br><br>testing the follwing commands:<br>
set_scanthres (scan threshold) and set_scanint (scan interval)<br><br>iwconfig sens seems to have no effect at all<br><br>iwpriv set_scanthres as well does not seem to produce any improvement <br>(tried with values ranging from -100 to 0)<br>
<br>set_scanint seems to make some difference but it does not solve the problem.<br>the default value is 60000 which means as far as I understand that the wlan card in the N800<br>tries to scan for new APs each 60 secs.<br>
I tried to lower this value to 25000 , it sometimes leads to faster roaming but since<br>the scanning takes about 1 sec it is very disturbing that during that time you cannot<br>transmit any data (because the radio tries all frequencies from 1 to 11) and the VNC GUI<br>
thus freezes.<br>Is it possible to specify which frequencies the N800 should scan when roaming ?<br>i think this is a very important feature as it can speed up roaming speed considerably.<br>There are only 3 non overlapping frequencies anyway (1,6,11) and usually 2 frequencies<br>
are enough so if the n800 had a setting scanfrequencies=1,11 we could scan much more<br>frequently without disrupting the data flow for a long time.<br>if the seleciton of scan frequencies is not implemented in maemo yet please do it ASAP<br>
as it make it more smooth to use of the N800 in larger WLANs.<br><br>Any other wlan software parameters that I perhaps missed which could improve the situation.<br><br>So any idea how to make sure that the N800 roams smoothly ?<br>
<br>What are your experiences ? I can change the access point model without problem if you<br>tell me what access points provide good roaming performance in conjunction with the N800.<br>Any access points brands,models which gave you good experience while roaming ?<br>
<br>years ago I used a HP IPAQ and regular 802.11g access points (DI serie) and the roaming<br>was excellent, so I can hardly believe that Nokia did not do its homework and did not<br>think about this problem.<br>After all the N800 is an internet tablet and good and smooth WLAN connectivity is the key <br>
selling point for smooth internet experience.<br><br>Imagine if an N800 user roams through an university campus and wants to listen<br>web radio or stream a video from the web. If the N800 behaves like in my case<br>(which is a simple network with 2 APs) the radio and the vide owill constantly freeze<br>
leaving the user pissed off. The same happens if the user wants to use<br>some VOIP client like skype, SIP clients etc.<br>I know that for pure web page viewing roaming speed is not that important but<br>the N800 is a multimedia tablet and smooth multimedia performance is a must.<br>
<br>I hope the N800 hardware is not flawed and that a fix can be found,<br>thanks everyone in advance for your advices and help !<br><br>I think this kind of roaming performance tuning is important to many others too<br>and I hope that they can profit from the discussion that will come out too.<br>
<br>best regards,<br>Benno<br><br>