[icecast] weird differences between stats (xml vs. admin interface)

Thomas B. Rücker, DM8TBR dm8tbr at afthd.tu-darmstadt.de
Sat Aug 9 10:28:14 UTC 2003

While maintaining the Relay-Server for Radio Subether [1] the official Chaos Communication Camp [2] Radio Station I noticed some weird behaviour.

We don’t have QoS for the Relay-Path, so the Relay started pretty soon to be 
unstable. Especially the higher bandwidth streams are very often unavailable. To monitor this behaviour I was constantly reloading the "List MountPoints" page AND the normal status.xsl/stats.xml [3] page. Soon I noticed a big discrepancy between both readouts. The admin-readout was way higher than the status.xsl-readout. 

This was reproducible under following circumstances:
1. stable relay
2. increasing number of listeners (~70 on both readouts)
3. relay gets unstable
4. status.xsl shows that all mountpoints are unavailable / random mountpoints get into available status (1-3 listeners) on repeated page-reloads & admin-interface shows all/most mountpoints as available with much higher listener count.

While checking the availability of each stream with Winamp I developed an theory:
When listening to a stream on the relay it starts to rebuffer pretty often or even takes really long to rebuffer. So maybe the code generating the stats.xml file dumps all listeners of the stats on an "disconnected from source event" although they seem to stay connected. This is also what is shown by the listclients.xsl in the admin interface - many listeners have high "connected for" counts although the stats.xml had shown this mountpoint several times as unavailable.

Has anyone else noticed such behaviour? Is it a bug or a feature? ;)


[1] Radio Subether: http://www.subether.de
[2] Chaos Communication Camp: http://www.ccc.de/camp/
[3] status page: http://alft.afthd.tu-darmstadt.de:8000/status.xsl
    will be available until 10.08.03

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