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Aug 252007

I’ve been running some tests on Vista networking tweaks and I would appreciate any input you might have, especially in the testing department. Below are the tweaks and test scenarios. I will report my impressions in a few days so as not to influence any would-be testers. If you provide feedback please include what type of connection (cable, dsl, etc.) you have, what type of network card (10/100, giga, etc.) and what type of downloading you do (standard from browser, torrent, download manager, etc).

Testing recommendation: You’ll need to test the following scenarios:
First, find a download that is + 100MB, bookmark it.
1 – Default, AutoTuning enabled. download file, write down results. Next browse the web (fast? slow?).
2 – Disable Auto-Tuning, clear cache, reboot retry same download and write down results. Next browse the web (fast? slow?).
3 – Enable Auto-Tuning and CTCP, clear cache, reboot retry same download and write down results. Next browse the web (fast? slow?).

*These are run from the command prompt. Start > Run (or press the Windows+R keys)> type cmd, hit Enter > copy/paste command, hit Enter.

Disable Vista Auto-Tuning
netsh int tcp set global autotuninglevel=disable
netsh int tcp set global autotuninglevel=normal

Notes – There are any number of variables that can have an effect on your network speed. Some (usually older) network equipment can’t do Window Tuning. Some download methods / programs (torrent etc.) may also have issues with Windows Tuning.
More info: Windows Core Networking – Receive Window Auto-Tuning on Vista , MS KB929868, Neoblog – Vista + Network = Slow

Enable Compound TCP ( CTCP)
This is disabled by default in Vista. You need to have Auto-Tuning enabled for this to work.
netsh interface tcp set global congestionprovider=ctcp
netsh interface tcp set global congestionprovider=none
Notes: VERY, VERY careful with this one folks, see page linked below, understand it or leave it alone. “large bandwidth-delay product” usually means there is a very busy (congested) network or a connection that has a long trip to make (like satellite).
From Microsoft:

For TCP connections with a large TCP Receive Window size and a large bandwidth-delay product (the bandwidth multiplied by the latency of the connection), Compound TCP (CTCP) in the Next-Generation TCP/IP stack aggressively increases the amount of data sent at one time by monitoring the bandwidth-delay product, delay variations, and packet losses. CTCP also ensures that its behavior does not negatively impact other TCP connections. In testing performed internally at Microsoft, large file backup times were reduced by almost half for a 1 Gigabit-per-second connection with a 50-millisecond round-trip time. Connections with a larger bandwidth-delay product can have even better performance. TCP Receive Window Auto-Tuning optimizes receiver-side throughput and CTCP optimizes sender-side throughput. By working together, they can increase link utilization and produce substantial performance gains for large bandwidth-delay connections.

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