Tool for analyzing ROS network traffic?

edit

We have a robot with 3 onboard computers with an internal LAN. One of the onboard computers creates an adhoc wifi network and forwards packets to the others. We control the robot via a laptop connected over wifi. We are managing to bring down our wifi connection pretty regularly, so I'm trying to figure out which nodes/topics need to be throttled or moved to a different machine.

Is there a nifty ROS tool that shows bandwidth usage without affecting the network traffic, or is my best bet using wireshark?

EDIT:

"rostopic bw" doesn't quite do what I'm looking for, as it creates a new connection to the publisher and then monitors the bandwidth on that connection, which is actually dependent on what else is running. For example, starting up a second "rostopic bw /my_camera/image_raw" significantly slows down the first one.

So, I can use it in isolation to figure out what topics are likely to be an issue, but I'd like to be able to observe the whole system as it runs and dies, w/o affecting it. (Or at least the part that's transferring data to/from a given computer)

I'm not even sure that I'm asking the right question ... perhaps a better one would be "What's the best way to debug/understand network traffic in a system running ROS?" I'm envisioning some tool that's a mashup of rxgraph, rostopic and ???. If I'm approaching this all wrong, please let me know :)

EDIT 2:

I took a look at linux_networking, and it looks like it has tools to determine properties of a network and to emulate various network properties, but I didn't see anything that quite fits what I think I need.

So, I'm trying to use wireshark (running on the laptop) to monitor packets going over the wifi connection to the robot. I can successfully capture the packets and view their contents. However, I'm stuck on how to determine which packets correspond to which nodes and topics.

I've seen documentation about the connection header [1] and TCPROS [2], but I'm not sure how this translates into the raw data that I can view in wireshark.

Can anybody point me to information about how to set up appropriate filters?

[1] http://mirror.umd.edu/roswiki/ROS(2f)Connection(20)Header.html

[2] http://mirror.umd.edu/roswiki/ROS(2f)TCPROS.html