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Vista Network Degradation Bug Linked to Streaming

A recent set of message board and blog posts has left Microsoft scrambling to modify a hard-coded Vista "fix" that causes any Vista system playing video or music to drop its network transfer rate to a level of 5-10% of transfer capacity.

In late June, a message board user named dloneranger posted information at 2CPU.com about a consistently slow data transfer rate on his Vista machine. Apparently the machine was set up to dual boot from both XP and Vista, so he could compare transfer capacities of the two systems. Those comparisons showed that XP transferred data across his Gigabit Ethernet card at approximately 50% of transfer capacity, while Vista limited transfer to 5% of capacity.

Like all true geeks, dloneranger was doing serious troubleshooting and listening to music while he did so.

"I followed all the advice," posted dloneranger, "disabling autotuning, setting all the different LAN driver settings, played with the TCP window size . . . none of it made a bit of difference, I was still stuck on 5% usage."

Then, he continued, at some point he stopped playing music. When he quit Windows Media Player, the data transfer shot back up to almost 50%, which is equivalent to XP's typical throughput.

The posting didn’t get widespread notice, as many commenters suggested a problem with dloneranger’s machine, but it was picked up in a more thorough test by Adrian Kingsley-Hughes, whose "Gear for Geeks" blog appears on ZDNet.com. In an August 21 posting titled "Playing Music Severely Degrades Network Transfer Performance in Vista," Kingsley-Hughes tips his hat to dloneranger and then lays out a detailed set of parameters—and resulting screenshots.

"With Windows Media Player 11 running," said Kingsley-Hughes, "and playing a Vista-supplied sample audio file (Symphony No. 3 in E-flat major, Op. 55, ‘Eroica’ - Scherzo- Allegro vivace) here’s what I saw: I’m getting half the performance that I was before without the music playing. As a consequence the file took twice as long to transfer."

Kingsley-Hughes found that the issue wasn’t limited to playing music with Windows Media Player. In fact, his later tests showed that just opening iTunes or Real Player or Windows Media Player caused an instantaneous drop in transfer speeds.

"Video also has the same effect," he said, demonstrating the similar impact that "playing random video files using Windows Media Center, Hauppauge Win TV and Nero ShowTime has on network performance. Any sound emitted by your system while transferring data seems to have . . . the effect of flatlining network transfers briefly."

Kingsley-Hughes then compared the results of the same tests in XP, showing that playing videos or sounds had no effect on XP data transfer rates. He concluded by saying: "Until this bug is fixed I’m switching off sounds on Vista and keeping all other noise to a minimum."

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