Pulseaudio ate my wifi

I’ve just spent a rather frustrating morning attempting to debug major performance problems with my home wireless network; one of my machines couldn’t associate with the AP at all anymore, and the laptop (which was upstairs in the home office, for a change) was getting horrific, sub-dialup speeds.

I did lots of moving of Linksys APs and tweaking of “txpower” settings, without much in the way of results. Cue tearing hair out etc.

Eventually, I logged into the OpenWRT AP over SSH, ran iftop to see what clients were using the wifi, and saw that right at the top, chewing up all the available bandwidth, was a multicast group called The culprit! There was nothing wrong with the wifi setup after all — the problem was massive bandwidth consumption, crowding out all other traffic.

You see, “pulseaudio”, the new Linux sound server, has a very nifty feature — streaming of music to any number of listeners, over RTP. This is great. What’s not so great is that this seems to have magically turned itself on, and was broadcasting UDP traffic over multicast on my wifi network, which didn’t have enough bandwidth to host it.

Here’s how to turn this off without killing “pulseaudio”. Start “paman”, the PulseAudio Manager, and open the “Devices” tab:

(click on the image to view separately, if it’s partly obscured.)

Select the “RTP Monitor Stream” in the “Sources” list, and open “Properties”:

Hit the “Kill” button, and your network is back to normal. Phew.

Another (quicker) way to do this, is using the command-line “pacmd” tool:

echo kill-source-output 0 | pacmd

It’s a mystery where this is coming from, btw. Here’s what “paman” says it came from:

But I don’t seem to have an active ‘module-rtp-send’ line in my configuration:

: jm 98...; grep module-rtp-send /etc/pulse/* /home/jm/.pulse*
/etc/pulse/default.pa:#load-module module-rtp-send source=rtp.monitor

Curious. And irritating.

Update: it turns out there’s another source of configuration — GConf. “paprefs” can be used to examine that, and that’s where the setting had been set, undoubtedly by me hacking about at some stage. :(

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  1. Nix
    Posted March 21, 2008 at 14:51 | Permalink

    If you have `load-module module-gconf’ in your configuration, that module will remember what other modules are running and their configuration, and reload them when it starts. That might be what’s biting you.

  2. Posted March 21, 2008 at 15:14 | Permalink

    nix: that’s it, alright! A comment also notes that the GConf-stored settings can be configured using “paprefs”, and sure enough, I have “Enable Multicast/RTP sender” ticked. Mystery solved.

    Of course, I must have done that, too, so it’s been my own bloody fault all along ;)

  3. Mark Preston
    Posted March 22, 2008 at 17:17 | Permalink

    Please move the right hand frame or column off the screenprints/shots or somehow, allow me to be able to read/print the pictures. Some (a lot) of the pictures are covered up by the Links and Archive list.

  4. reine dedeurwaerder
    Posted March 22, 2008 at 17:47 | Permalink

    As Mark Prestonsaid!, Reine

  5. Posted March 23, 2008 at 20:56 | Permalink

    guys — you can now click on the images to view them alone, without any obscuring sidebars etc.

  6. Geoff Whaite
    Posted March 24, 2008 at 00:11 | Permalink

    There seems to be a meme going about that you shouldn’t use table elements to layout your web page, that you should use div elements and css instead. The rationale behind this is to separate the content from the presentation so you can change one without affecting the other. However, in practice, it seems that this separation is rarely achieved and often the resulting layout is inconsistent, it may work on a particular browser with a particular font but on a different browser or change the font and things start overlapping and become obscured. Whenever I see a web page with obvious layout problems I view the source code and search for table elements and most often I am not not surprised that I don’t find them. This is a great idea in theory but in practice doesn’t always work, such as happens here (wouldn’t it be nice to be able to view the image and read the text relating to the image at the same time without having to open the image in a separate page and switch between them).

  7. reine dedeurwaerder
    Posted March 24, 2008 at 07:37 | Permalink

    i know, i know, it’s radical, but why not code for firefox, opera, flock etc, and FORGET microsomethingexploiter?. Naw, if “they” can’t get firefox “they” don’t deserve your site, and maybee even the net!!!. Reine.

  8. David Cawley
    Posted March 25, 2008 at 17:33 | Permalink

    I hadn’t seen the iftop tool before. Nice!

  9. Posted March 25, 2008 at 17:41 | Permalink

    hi David —

    yeah, iftop is really cool, especially on a gateway router. great piece of software…

  10. Posted August 11, 2008 at 15:30 | Permalink

    Though jnettop has started to grow on me after using iftop for ages. jnettop among its features supports IPv6 that iftop doesn’t do …. yet