Egil Hansen

I have been baffled by this every since switching to Vista last month. Sometimes I would only be able to get around 5 MB/sec transfer rates from my local server, while at other times it would max out around 10-12 MB/sec, which is as expected on a 100 Mbit network.

It turns out to be due to a bug in the new Multimedia Class Scheduler Service (MMSCC) included in Vista, that will help prioritize processing and network resources during media playback. As Mark Russinovich explains in his blog, the MMSCC will give media applications higher priority during playback, while at the same time throttle down network activity to ensure that streaming audio and video get through without glitches.

The problem seems to come from the hardcoded limit that is forced upon the network card, which would give a computer with a single network card a maximum throughput of about 15 MB/sec., which in itself is not that bad. The problem surfaces when you have more than one network card (like most laptops), then a bug in the MMSCC will throttle the network connections even more.

If you, like me, have multiple virtual network adapters from installing VMWare and various VPN software packages, you will have degradation out of proportions of what the MMSCC team intended for. Luckily, Microsoft has the networking and MMCSS team working on a fix for this. Meanwhile, remember to kill your online radio whenever you want to transfer data over the network at a reasonable speed.

This entry was posted on Wednesday, December 26th, 2007 at 14:31 and is filed under Windows. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.