Last year, we started hearing about poor Windows 95 Internet connection speeds due to default registry settings. The fix was to change those settings, although the changes needed varied per system. A few programs came along that assisted the Win95 user with optimizing those settings: TweakDUN and MTUSpeed.
Supposedly, NT didn't suffer this MTU problem: it was already properly optimized. Then last month, the author of MTUSpeed introduced a version for NT, and the question was reawakened: does NT automatically configure itself properly for the best Internet connection speeds.
There are three sources (web sites) I mainly used for this research:
- Win95 MaxMTU Fix (The TweakDUN page cited above), for a good description of the problem on Windows 95;
- Introduction to Internet Protocols, for some confirmation of the the first source; and
- Microsoft's TPC/IP Transport Entries, a Resource Kit document describing relevant NT Registry entries
My conclusion, simply, is that NT is self-configuring regarding the MTU settings, and while there might be a few tweaks related to TCP/IP from which some users might benefit, they aren't necessary, and probably wouldn't show much in the way of noticeable speed improvement.
TCP/IP Transfer Terms
A packet is a unit of data of size MTU (see next term) that your modem sends/receives over the Internet. A packet is also known as a "datagram" or a "frame".
MTU (Maximum Transmission Unit) consists of a packet "header" and its data, in units of octets, or 8 bits (which is a byte, which is one character). That is, you'd say the default Win95 MTU is 1500 octets. Furthermore, the part of the MTU which is the data only is MSS, or Maximum Segment Size.
TcpWindowSize (aka RWIN, Receive WINdow; aka DefaultRcvWindow) is a value that determines the number of packets your connection can handle without adknowledgement. It is usually a whole number multiple of MSS, like 4 X MSS, or 4 packets. If it were set wrong, you'd see framing errors (in the Dial-Up Networking Monitor). This value is dynamic in NT: it changes as need be (eg, poor line quality).
TTL is Time to Live: the maximum number of "hops" it can take to get to the page you're requesting. Default for Windows 95 and NT is 32. Doubling this value might be prudent.
Note: you can see for yourself how many "hops" it takes to get to a particular server using the tracert.exe command line applet (SYSTEM32 directory). Type tracert at the command line for usage.
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