LCM multicast not working on all wifi networks

[Albert Thomas]

Hi,

I am completely new to LCM and Linux. However, I made LCM work between two laptops connected with my home wifi ( One laptop sending a message and the other laptop receiving it). However, I am trying to do the same process in my department's wifi. But not successful so far. 

I am getting a feel that the error is something pretty simple one. But not able to figure out. Is it because the department-router might be blocking the UDP multicast messages? 

Any suggestions will be of great help. 

Thanks,

Albert

[Jonathan Bendes]

Hey Albert,

I assume you've checked to make sure you're broadcasting with ttl=1 (which is probably how you got your in-home setup working). You can try upping the ttl, though this is very rarely the right thing to do. More likely than not, your department is blocking multicast traffic.

You can try running lcm's TCPService and broadcasting through that to see if your network will let the traffic through.

Best,
Jonathan

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[Albert Thomas]

Hi Jonathan,

Thanks a lot for the quick reply.I tried upping ttl and it dint worked. I think department is blocking the multicast. I will have to contact with the IT systems for solving this. When I checked with a different router ( With no internet) things works fine.

My ultimate aim is to pass messages remotely over computers distributed across different networks using LCM ( One computer sending a message and another computer in a different network listens to it). I think upping ttl is one step for this. But I assume the message needs to be passed through multiple routers. Is there any documentation that can help me in reaching to that point. I searched in the LCM site and I am able to find only basic steps for initializing and building a simple program.
If anyone can reply me with some information, it would be awesome! Thank you very much!

Thanks,
Albert Thomas

[Collin Johnson]

Hi Albert,

If you're trying to jump networks with LCM, especially over Wifi, your
best bet is to use the lcm-tunnel available in libbot
(https://github.com/RobotLocomotion/libbot).

In general, LCM isn't designed to work over Wifi. I was recently
playing with an 802.11-ac router sitting 0.5m from a laptop and
experienced significant message drop, regardless of the message size.
When using lcm-tunnel, I didn't have any messages drop.

Hope that helps.

-Collin

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[Albert Thomas]

Thanks Collin. I would explore this.

Thanks,

Albert

[Pradeep]

Hi 

I am working on a LCM Java application, where I need to run the server on the development board and the client on a windows laptop. Can you please let me know the procedure on how to get these two to work? When I am executing both of them on the same machine, it works fine. But when I run them on two separate machines, I do not get any response. I tried to add the IP address to the routing table in my windows machine(route -p add command), but it didn't work. I've set TTL value to 1. The development board is running Linux. I've connected Ethernet cable to the to the board and am the windows laptop is using the department's WiFi. I'm able to ping both of them.

Thanks & Regards,

Pradeep

On Wednesday, December 16, 2015 at 8:58:06 AM UTC-5, Collin Johnson wrote: