Windows Vista/7 – solution for multimedia (Flash!) throttles your network: NetworkThrottlingIndex
Posted by jpluimers on 2010/02/09
When you play multimedia on Windows Vista, Windows 7 or Windows Server 2008, your network performance is throttled.
This behaviour was not present in Windows XP, but was introduced in Windows Vista and still present in Windows 7 and in Windows Server 2008.
From Vista SP1 on (including Windows 7 and Windows Server 2008), this behaviour is configurable in the registry by changing a registry value.
The Microsoft knowledge base explains this is the NetworkThrottlingIndex value, but falsely indicates at the bottom it is for Windows Vista SP1 only (it actually works since Vista SP1, so this includes both Windows 7 and Windows Server 2008).
The throttling by default is 10, meaning 10 network packets per millisecond (10000 per second), which counts for about 15 megabytes per second.
This is more than one 100 megabit network connection can deliver, but a lot less than one gigabit connection can deliver.
And it gets worse:
When you have more than one network card in your machine, the throttling gets tougher!
There is a bug in the throttling mechanism, which magnifies the throttling when you have more than one network card in your computer.
Mark Russinovich – techical fellow at Microsoft – explains about this bug in on his blog.
So, when you have LAN, Wireless, and two VM NICs, then the throtteling is 4000 packets per second, or roughly 6 megabytes per second.
You will easily experience that on a 100 megabit network.
I got into this because I have been involved in a large multi-media project that runs on XP Embedded.
They might want to go to a newever version of Windows Embedded that is based on Vista / Windows 7 (in that link, the title says 7, but the link Vista).
Going that route solves a bug: .NET WPF Video on XP sometimes looses vertical sync, this is fixed in Vista (and won’t be fixed in XP).
Doing some preliminary research to see if the move is feasible at all, I came along a blog post by Robert Love (long time Delphi friend, and very keen on keeping in touch with technology) telling that Vista performance in this matter is much much worse than any Linux distribution.
/me is not happy about this
Further reading:
- Rave Moyers: Windows 7 Ping Spikes [FIX] – Steam Users\\\’ Forums.
- Robert Love: Those Dang DPCs Clogging the MMCSS
- Mark Russinovich: Vista Multimedia Playback and Network Throughput
The Wiert Corner - irregular stream of stuff 
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