[Server-devel] [laptop.org #8321] Questions about XO mesh networking

Bryan Berry bryan.berry at gmail.com
Fri Mar 28 00:55:28 EDT 2008


I am cc'ing Martin Langhoff, John Watlington who are in charge of the
School Server at OLPC

> 1.  ideally the school server (running XS) will have 3 active antenna
> each running on a diff channel (1,3,6) and XOs will connect to one of
> these.

>2. Or should we replace the WRT54G with
> another AP/Router in the short term?

I would replace the WRT54G. I hate them. I have had 3 fail on me in the
last year. I would get 3 other wireless routers. I like DLink


My understanding is that in a dense deployment such as yours you should
use a regular wireless router and not the active antennas, for the short
and the long term. Wad and Michailis, pls correct me if I am wrong.

>3. Running ejabberd on a central server means that collaboration
> features will work while the XOs are connected to an AP (or school
> server with active antenna)? The only change we need to make on the XOs
> is to support this, is to change the jabber server using
> sugar-control-panel?

Correct

>4. Can we expect to get around 50 XOs per channel?


Don't know, sounds good to me. We are planning 60 XO's per channel w/ a Deliberant Radio + Omni 12 dbi antenna
(Dev can provide more details)

Wad, Michailis can you advise?


> 6. Are the specs here for the hardware of a server here still current :
> http://wiki.laptop.org/go/XSX_Server_Implementation

I don't know about this. We are using different specs in Nepal

1.8 GHz Intel Core duo
1 GB of RAM
120 GB Hard drive

We have a souped up XS because we intend to use Moodle and Mediawiki
extensively. 

>Currently the only hardware we
> have to run XS would be one of the XOs or an old IBM/Panasonic laptop
> (PIII800)

This might work for basic networking services but not any content
management stuff. It might also get bogged down when running Squid.


You should join server-devel mailing list to keep on top of XS testing
and development.  http://lists.laptop.org/listinfo/server-devel

Good luck!

Bryan
OLE Nepal
Kathmandu

On Fri, 2008-03-28 at 14:24 +1100, matt wolstencroft wrote:
> Hi,
> Many thanks for all your responses. Before I answer your queries, I just
> want to clarify a few points :
> 
> 1. I have taken another look at the server docs and my understanding is
> that  ideally the school server (running XS) will have 3 active antenna
> each running on a diff channel (1,3,6) and XOs will connect to one of
> these. Other wireless equipment would connect to a sep standard wireless
> AP connected to the server. The server is then connected to the WAN
> modem and acts as router, firewall and DHCP for the 3 networks. Is this
> a correct summary of the ideal situation?
> 
> 2. Without any active antenna, would a short term solution be to use a
> standard AP and connect it to our WRT54G (with wireless disabled on
> this)? Once we have a stable XS server we can remove the WRT54G and
> connect the AP to the server? Or should we replace the WRT54G with
> another AP/Router in the short term?
> 
> 3. Running ejabberd on a central server means that collaboration
> features will work while the XOs are connected to an AP (or school
> server with active antenna)? The only change we need to make on the XOs
> is to support this, is to change the jabber server using
> sugar-control-panel?
> 
> 4. Can we expect to get around 50 XOs per channel?
> 
> 5. Would you recommend the use of an XO as school server and if so how
> many clients would you say it would support? 
> 
> 6. Are the specs here for the hardware of a server here still current :
> http://wiki.laptop.org/go/XSX_Server_Implementation
> 
> In response to your queries :
> 
> > Do you have a server (e.g. school server) in place?
> 
> We do not currently have a school server in place. As an interim we have
> been using an XO with lighttpd and an rsyncd running. This was just a
> quick way to allow us to distribute files to the XOs and backup up the
> olpc home directories prior to updating the laptops. The long term plan
> is to have a server in place running XS. Currently the only hardware we
> have to run XS would be one of the XOs or an old IBM/Panasonic laptop
> (PIII800)
> 
> > Minimum requirements? 
> 
> - network needs to support existing IBM/panasonic laptops used by
> teachers and students (for certain apps that are not currently running
> on the XOs e.g. dyned). These have pcmcia orinoco 802.11b silver cards
> - students need internet connectivity
> - XO backups
> - proxy with filtering capability
> - DHCP
> - DNS
> - firewall/router
> - ability to power external antenna for remote sites
> 
> > Time frames?
> 
> The deadline given to me by the school administrator for having basic
> network services provided and an outline for a long term solution is the
> 11th April. It would be good to have a working wireless network as soon
> as possible though, however I am not sure when funds will be available
> for new equipment.
> 
> Thanks again for your invaluable help,
> 
> Regards
> Matt
> 
> On Thu, 27 Mar 2008 08:06:20 -0400, "Greg Smith (gregmsmi)"
> <gregmsmi at cisco.com> said:
> > Hi Matt, (Bryan or Sulochan, please see questions for you below),
> > 
> > Sorry we didn't get you an answer before this but thanks for reaching
> > out and following up! 
> > 
> > Do you have a server (e.g. school server) in place?
> > 
> > We probably do not have a tested and approved wireless AP with router,
> > firewall and DHCP. The original idea was that  routing, firewall and
> > DHCP are done on the server.
> > 
> > That said we may be able to find someone to help test and qualify an AP
> > with your requirements.
> > 
> > You may want to focus on connectivity and defer mesh support until
> > later. I know that mesh is a core application but there are some open
> > issues with it right now.
> > 
> > What is your time frame? 
> > 
> > If you come up with a list of absolutely must have minimum things you
> > need done and a date, that helps focus everyone on getting you launched.
> > Then we can add the next level of applications in a second pass.
> > 
> > If we don't nail your answer by tomorrow AM US ET, I'll bring it up on
> > the server and development lists to see if I can get more input.
> > 
> > Bryan and Sulochan,
> > 
> > I know its crunch time in the Himalayas but some input ASAP would be
> > greatly appreciated for this roll out in Cambodia.
> > 
> > What access point did you deploy? Do you have a suggestion for one that
> > has a built in router?
> > 
> > Are you going ahead with the mesh turned on or should we defer that?
> > 
> > BTW congratulations on your success and thanks for all your great blogs,
> > e-mail lists, forums and feedback (http://www.olenepal.org/)! It really
> > helps other sites and helps focus development on real user needs. The
> > fun part is just beginning :-)
> > 
> > Thanks,
> > 
> > Greg S
> > 
> > 
> > -----Original Message-----
> > From: matt wolstencroft [mailto:mwolstencroft at fastmail.com.au] 
> > Sent: Thursday, March 27, 2008 4:58 AM
> > To: Greg Smith (gregmsmi)
> > Subject: Fwd: Re: [laptop.org #8321] Questions about XO mesh networking
> > 
> > Hi,
> > I have been trying to find out from help at laptop.org what wireless router
> > will be compatible with our 200 XOs after we found out that the WRT54Gv7
> > has problems due to WDS. So far I have had no response and my colleague
> > Phillip gave me your email in the hope that you might be able to help. I
> > have included the email history below to give you some context.
> > 
> > Could you recommend a wireless AP with router, 2 antennas (pref rev
> > tnc), compatible with 802.11g & 802.11b, stateful firewall, DHCP, 4
> > 10/100 LAN ports and costing around $100? The main criteria is that it
> > does not have any problems with XO mesh networks.
> > 
> > Any assistance would be greatly appreciated.
> > 
> > Thanks, Matt
> > 
> > 
> > --
> > Matt Wolstencroft
> >   mwolstencroft at fastmail.com.au
> > 
> > --
> > http://www.fastmail.fm - One of many happy users:
> >   http://www.fastmail.fm/docs/quotes.html
> > 
> > ----- Original message -----
> > From: "matt wolstencroft" <mwolstencroft at fastmail.com.au>
> > To: help at laptop.org
> > Date: Mon, 24 Mar 2008 20:19:49 +1100
> > Subject: Re: [laptop.org #8321] Questions about XO mesh networking
> > 
> > Hi,
> > Thanks for the quick response. I have a few more questions :
> > 
> > 1. Will automatic MPP be turned on in future builds?
> > 
> > 2. According to the OpenWrt website, the WRT54Gv7 cannot run the openwrt
> > firmware. I just want to clarify that in this case we will have to
> > replace the router?
> > 
> > 3. The DLink equipment is just an AP. Could you recommend any wireless
> > routers? Or is there a more up to date list than this :
> > http://wiki.laptop.org/go/Wireless_Access_Point_Compatibility?
> > 
> > Thanks very much for your help,
> > Regards,
> > Matt
> > 
> > On Sun, 23 Mar 2008 20:01:45 -0400, Support at rt.laptop.org said:
> > > On Sat Mar 22 01:44:19 2008, mwolstencroft at fastmail.com.au wrote:
> > > > Hi,
> > > > I have just started working at Reaksmy school in Cambodia with 200 
> > > > XOs (build 656). Access to the Internet is via a satellite which is 
> > > > connected to a linksys WRT54G v7 with the  latest firmware
> > (v7.00.4).
> > > > The wireless configuration of the router is as follows :
> > > >  
> > > > Channel : 11
> > > > Encryption : none
> > > > Wireless SSID broadcast : enabled
> > > > 
> > > > Documentation I have read suggests that the mesh networking should 
> > > > work in the following manner:
> > > > 
> > > > - majority of XOs in the mesh act as mesh points : "uses its WiFi 
> > > > interface to both access the network itself and to relay traffic 
> > > > from other mesh points"
> > > > - certain XOs will act as mesh portals (MPP): "connected to an 
> > > > external network, and that forward traffic in and out of the mesh"
> > > > - an XO will associate itself with a mesh based on the following :
> > 
> > > >    1. The laptop will issue a DHCP request, followed by a RREQ for a
> > > >    Mesh Portal anycast address and wait for RREP replies, on all
> > three
> > > >    channels being proposed for OLPC meshes (1, 6, and 11) before
> > making
> > > >    any decisions.
> > > >    2. If any channel provides a lower hop count to a Mesh Portal, it
> > is
> > > >    selected unless its signal strength is significantly lower.
> > > >    3. If all channels provide the same hop count to a Mesh Portal,
> > > >    random selection is used.
> > > > 
> > > > I have a few questions regarding the mesh networking and the 
> > > > configuration of the WRT54G:
> > > > 
> > > > 1. Is automatic MPP turned off in build 656 and is it enabled as
> > per:
> > > >
> > "http://wiki.laptop.org/go/Test_Config_Notes#Turn_on_MPP_Capability"?
> > > It is turned off now and in all current builds.
> > > 
> > > > 2. What are the determining factors that affect which XOs become 
> > > > mesh portals?
> > > Every laptop that can see a AP can become a MPP if that functionality 
> > > is enabled.
> > > 
> > > > 3. We have been seeing intermittent dropouts of connection to the AP
> > 
> > > > forboth XOs and normal laptops. Are there any known problems with 
> > > > the WRT54G and the XOs?
> > > From Michail Bletsas, in charge of connectivity:
> > > "Using WDS frames for the mesh traffic turns out that it creates 
> > > serious  interoperability problems with WDS-capable access points that
> > 
> > > implement  Dynamic establishment of links with other WDS peers (like 
> > > the ubiquitous  Linksys WRT54 router/AP). We found that out during 
> > > field testing and it  took several months to identify all the failure
> > modes."
> > > 
> > > So the answer to whether you should/can use WRT54Gx APs is "only if 
> > > you  can upgrade them to an OpenWRT variant". "A good starting point 
> > > should be the DLINK DWL-2100AP which uses an Atheros  Chipset."
> > > 
> > > 
> > > > 
> > > > 4. Is there any recommended/tested firmware for the WRT54G v7? Is 
> > > > openwrt tested/supported?
> > > 
> > > It has been tested by users, but no offical testing has been
> > undergone.
> > > Users report that OpenWRT does not have the problems of the original 
> > > firmware.
> > > > 5. If we were to replace the WRT54G is there a list of preferred 
> > > > wireless equipment for OLPC systems?
> > > 
> > > See answer to #3.
> > > 
> > > > 6. Some documentation I have seen suggests that wireless APs should 
> > > > be configured to use channel 1,6 or 11. Is this still the case?
> > > 
> > > 
> > > 
> > > > 7. If the steps listed above are correct then we should see XOs 
> > > > forming and connecting to mesh networks on channel 1,6,11 however 
> > > > they always seem to form a mesh on channel 1. Is this correct?
> > > 
> > > XO's search all 3 mesh channels, looking for a school server running 
> > > on that mesh channel. When they don't see a school server on any of 
> > > the three channels, they connect to a serverless mesh on channel 1.
> > > 
> > > > 8. Can XOs connected to different mesh networks currently see each 
> > > > other?
> > > 
> > > No.  Each mesh channel is a totally independent network running at a 
> > > different frequency. However, if there is a school server with 
> > > multiple antennas, it can route packets between the networks.  
> > > Therefore, if there is a school server with 3 mesh antennae, XO's can 
> > > use all 3 channels, and all see each other.
> > > 
> > > 
> > > > 
> > > > 9. Our XOs can see the AP in the neighborhood view and when they 
> > > > connect to it, they become disconnected from the mesh network. Is 
> > > > this correct behavior?
> > > 
> > > Yes.  When MPP mode is disabled, an XO will only connect to either an 
> > > Access Point or a mesh
> > >                channel, but not both.
> > > > Any assistance would be greatly appreciated. Thanks in advance,
> > > > 
> > > > Matt Wolstencroft
> > > 
> > > The above answeres were provided by Ben Schwartz (author of the 
> > > Distance activity), and the quotes were from Michail Bletsas.
> > > 
> > > Keep in mind I am not an OLPC employee, I am a support volunteer. if 
> > > this does not answer your questions try countries at laptop.org, as it is
> > 
> > > answered by OLPC staff.
> > > --
> > > Thanks,
> > > FFM
> > > OLPC Support Volunteer
> > --
> > Matt Wolstencroft
> >   mwolstencroft at fastmail.com.au
> > 
> > --
> > http://www.fastmail.fm - One of many happy users:
> >   http://www.fastmail.fm/docs/quotes.html
> > 
> -- 
> Matt Wolstencroft
>   mwolstencroft at fastmail.com.au
> 



More information about the Server-devel mailing list