Multi Hop Messaging

[TG]

Hi Stoker,

I am able to form the ad-hoc network with 3 Nexus 7 devices using Manet Manager.

Let say devices A, B, C. All have different IP addresses.
I am able to send messages among them when they all can see each other. But lets say A and C cannot see each other and B can see both A, B. I am trying to send messages to from A to C by typing in the IP address of C, but C is not receiving.
C's IP address is shown under the 2 Hop Interface Address under Neighbors in Routing Info. I am not sure what I am doing wrong here. Any suggestion of reliable steps to follow?

I tried to look into the source code to know how the message service works. I can see the Datagram packet is received by MessageListener thread in MessageService class, but I didn't understand how the multi hop works. There is nothing like packet rebroadcasting to destination.

Could you please kindly point me in the right direction to understand how the multi hop works.

Thanks,
TG

[stoker]

tcpdump is included with the MANET Manage install in /data/data/org.span/bin. Try running it on B to monitor the network when you send a packet from A to C. The packet should be received and relayed by B. Then run it on C and see if C gets the message.

Multi-hop is handled by OLSR: https://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol

- stoker

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[TG]

Hi Stoker,

I highly appreciate the quick response.
I didn't try running the tcpdump. Will try and get back if required.

In case of multi hop, I want to customize the message by including the intermediate node IP's to track the path(i.e., as per the previous example, I want to display C received message from A through B). So I am looking around where I need to make changes in the Manet Manager source code.

And one more question is, in the routing info sometimes there will a node shown under Neighbors but there will be nothing shown under the Routes table. Why is that? When I send message by typing in the address, message shown under neighbor at that time it is not delivered to the destination.

Thanks,
TG

[stoker]

Hi TG,

In order to track the routing path of the message you'll need to modify olsrd:

https://github.com/ProjectSPAN/android-manet-olsrd

I copied that code from here: http://www.olsr.org/?q=download

You should contact the OLSR folks for more info on that: http://www.olsr.org/?q=mailing-lists

There may already be an OLSR plugin that does what you want.

My guess is that you might have a node show up in the Neighbors table if you can hear his HELLO broadcasts, but he might not be able to hear yours. That's the difference between an asymmetric link and a symmetric link. You need a symmetric link to communicate with someone.

  

- stoker

[TG]

Hi Stoker,

Thanks for the references.

One more question... Why do we need SSID to form adhoc network?
There is no access point right ?

If some user want to join network we are expecting that user to know the SSID. As we are turning the WIFI off, user cannot discover the available networks also.


Regards,
TG

[stoker]

Hi TG,

There is no access point, but devices in the mesh will filter out (drop) messages that are tagged with a different SSID.

Yes, other users will need to know the SSID of the mesh before joining it. By default, all devices in a SPAN mesh attempt to join the default "Android Adhoc". 

When the device is in ad-hoc mode you can't scan for networks. If you turn off ad-hoc mode and put the device back in managed mode, you might be able to see some ad-hoc networks through the network preferences of the Settings app. In my experience, older Android devices do not list ad-hoc networks when performing a scan. Newer devices might. 

Even if you could scan and see an ad-hoc network, you will still need to assign yourself a static IP address before joining it. That might result in a conflict if other people are using the same IP address. Thus, at this time you need to do a little pre-configuration with the SSID and IP address before joining the mesh. I've don't a little research into link local addressing for dynamically assigning IP addresses, but not much.

- stoker