Transparent Handoff

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Breno Jacinto

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Jun 23, 2014, 3:58:32 PM6/23/14
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Hello friends,

     I'm into the following experiment. We're willing to test the ability for BATMAN/MPs o handling transparent handovers/handoff. Our scenario is illustrated in the attached file. 

    We're assuming that:

1 - Given that BATMAN is a layer-2 protocol, re-routing should happen automatically at this layer and no IP address changes are necessary

2 - Transport protocols must keep the same IP address of the node in order to preserve the connection that could be happening

3 - Somehow we must force the IP address to stay the same using DHCP and/or static address. Wondering the best usability to be achieve here. 

     Our experiment is simple. Given a large file Node A is downloading and moving, how can we keep that download from timing out while the node is roaming? Has anyone been into this? 

cheers, 



---> Breno Jacinto
---> Instituto Federal de Educação, Ciência e Tecnologia de Alagoas (IFAL)
-----> http://www.ifal.edu.br
---> Life is Choice. You can choose to be a victim, or anything else you want to be. (Sócrates - Peaceful Warrior) <--
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T Gillett

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Jun 23, 2014, 5:26:20 PM6/23/14
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Hi Breno

Handoff between mesh nodes certainly works for SIP phone calls without dropping the call, so it should work for a file transfer.

This assumes that the mobile device is attached to a mesh node AP via a normal wifi connection and doesn't have to change its IP address along the way. 

I think that having to change the IP address would be problematic.

It also assumes that the mobile device has a sensible algorithm for selecting and connecting to the 'best' AP. Newer devices seem to be OK in this respect.

Also of course there has to be overlap of coverage from the mesh nodes - if there is a gap eg in stair wells between floors, then you will lose the connection for some period of time.

Is there any reason why the mobile device would not be able to acquire an IP address and keep it as it attaches to different nodes?

How many DHCP servers are you running in the network?

Regards
Terry 


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Breno Jacinto

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Jun 23, 2014, 9:55:34 PM6/23/14
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Hi Terry,

    I guess you figured out a key point for this experiment. I was using the default configuration and using one DHCP for each AP. So every time the device roamed it would get another IP address. So I guess one part of the solution would be to use a single DHCP server and through its caching it usually preserves the same IP for that device's MAC (I'm guessing here, but I believe it's possible to force this kind of behavior)

    If this gap you mentioned exists, that's one the reasons we're doing this experiment. I'm trying to find out the level of reliability (from a user experience standpoint) of a Mesh network in an indoor environment at first. But the next step is to bring this experiment to an outdoor environment. We intend to test several times of hardware and configurations - default antennas, external antennas, etc. That way we can provide enough data to bring more money to research Mesh networking and exploit its use in several scenarios. 

    So the other question remains: is this gap long enough to make a TCP connection timeout, for example? That should be hard to know without experimentation. 

cheers,

---> Breno Jacinto
---> Instituto Federal de Educação, Ciência e Tecnologia de Alagoas (IFAL)
-----> http://www.ifal.edu.br
---> Life is Choice. You can choose to be a victim, or anything else you want to be. (Sócrates - Peaceful Warrior) <--


T Gillett

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Jun 23, 2014, 10:33:36 PM6/23/14
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Hi Breno

The default SECN config has no DHCP server running on the node for just this reason.

In setting up the network a key design point is working out how the IP address assignment should work.

This is largely nothing to do with the mesh per se.

The mesh will act as a distributed switch. So a gap in coverage is like unplugging from one port of a switch and plugging in to another.

What happens is essentially determined by the tolerance of the end point application for breaks in the link.

For IP address assignment you might like to consider static or reserved addresses for speed of connection.

Also if you use the DHCP server in one or more SECN nodes, they are based on the dnsmasq package which is very flexible and well documented.

If you use more than one, eg for redundancy, look at the "authoritative" setting which is available in the SECN web interface.

More advanced settings might require editing the config file.

Regards
Terry

Carlos Rey-Moreno

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Jun 24, 2014, 1:12:03 AM6/24/14
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Hi Breno and Terry, very interesting discussion. I would like to know more about the results you obtain. I think I have read about something related to Handoffs in the batman-adv mailing list. Maybe you can get other angles and experiences from there.

Best, 

carlos



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Breno Jacinto

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Jun 26, 2014, 6:24:43 PM6/26/14
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Hi Terry and Carlos,

   Thanks for the answers. I'm digging into the problem more deeply and as soon as I get results I'll post them here. 

best regards,

---> Breno Jacinto
---> Instituto Federal de Educação, Ciência e Tecnologia de Alagoas (IFAL)
-----> http://www.ifal.edu.br
---> Life is Choice. You can choose to be a victim, or anything else you want to be. (Sócrates - Peaceful Warrior) <--


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