[ros-users] Wifi communication getting slow

[Cedric Pradalier]

Hello,

Regarding testing wifi performance, using iperf could also be a good solution.

Regarding the initial increasing delay problem, I've noticed something
similar when using callbacks taking a long time to execute, maybe
because they were communicating with some HW or doing some complex
computation.

In this case, I was getting message build-up even with when the
subscriber used a queue size of one. It seems that the teleop message
where small enough to accumulate in the TCP kernel or HW buffer and
not being discarded while the callback was running. This can be easily
identified by looking at the message timestamp. In our case, the
message age was increasing (obviously, you can only evaluate that on
machines with synchronised clocks).

My solution was to run the complex code in its own thread, and
implement myself the message discarding code in the callback with
something like "if (!HW thread available) return;".

If you're affected by a similar problem, reducing the sending
frequency of your teleop node could solve it.

HTH

On Tue, Jan 4, 2011 at 5:40 PM, Dan Lazewatsky <dlaz at cse.wustl.edu> wrote:
> Hi Steven -
> I've noticed similar problems on a few of our robots, mainly when using
> image_transport to send video over wifi. To figure out if wifi is the
> problem, there are two things I've found helpful: before starting any of the
> code running, from your workstation, ping the robot and see if the ping time
> increases. The other thing you can try is watching iwconfig on the robot to
> see if the link quality deteriorates over time.
> Unfortunately, I never really figured out what was going on. Replacing the
> wifi cards in the affected computers seemed to solve the problem.
> -Dan
>
> On Tue, Jan 4, 2011 at 9:15 AM, Steven Bellens
> <steven.bellens at mech.kuleuven.be> wrote:
>>
>> Hi,
>>
>> when using ROS to command a mobile base, I'm running a hokuyo_node and
>> an orocos component node on the mobile base. On my workstation I have
>> the navigation stack running, which gets laserscan data from the
>> hokuyo node and sends velocity commands to the orocos component. I
>> only switched to use the wireless network recently and noticed that,
>> after running the app for some minutes, it looks like some delay
>> starts to build up: when I drive the robot with the teleop_keyboard,
>> after 2 minutes, it starts reacting very slow on my input commands.
>> What's the best way to determine if the Wifi is indeed the problem
>> and, if so, can I run this more optimally with ROS considering this
>> restriction?
>>
>> regards,
>>
>> Steven
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>
>
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-- 
Cedric Pradalier