Microsoft has acknowledged another embarrassing flaw in Windows Vista that slows network traffic when you're playing music or other multimedia. Various bloggers had already noticed the strange issue before Microsoft technical fellow Mark Russinovich finally admitted it in a post on his Microsoft Technet blog.

The problem isn't just limited to playback through Windows Vista, it also affects other applications such as iTunes.

Russinovich explained the cause of the problem in his post. "Many people have correctly surmised that the degradation in network performance during multimedia playback is directly connected with mechanisms employed by the Multimedia Class Scheduler Service (MMCSS), a feature new to Windows Vista.

"This throttling of network traffic is mainly apparent on networks with infrastructure allowing gigabit throughput and is experienced by a user receiving, as opposed to sending, data."

Gigabit connections slower

Essentially, the problem is that the faster the network you're pushing data through, the higher the number of system interruptions. Vista is designed to give the highest priority to media playback so that even when your PC is terribly busy, you don't experience any glitches. However, perversely, this has now slowed network traffic too much on Gigabit Ethernet systems.

Russinovich found network transfer rates of less than a third when he was playing media. The issue is more noticeable on Gigabit connections, though it still can be noticed on slower Ethernet connections.

A fix is currently being scheduled. It will also sort out a related bug that affects multiple network connections.