The MTU (Maximum Transmission Unit) sets the size of packets transmitted/expected. The internet standard is 576. But Microsoft has set the default for Win95 to 1500, the LAN standard. There are also a few related settings that should be adjusted. For example, the Receive Window (RWIN), which dictates how many packets are to be handled simultaneously. Once again. Microsoft's default is set to a figure more appropriate to a LAN.
Setting the MTU can greatly enhance DUN performace—its almost like upgrading your modem. To adjust these settings you must edit the registry and add a few strings to override the defaults. Note please that these adjustments are for a PPP connection.
Start the Registry Editor (REGEDIT) in the Windows 95 directory.
In the tree on the left, find the key HKEY_LOCAL_MACHINE, and expand it. Then expand the following subkeys: System, CurrentControlSet, Services, Class, NetTrans.
Once NetTrans is expanded you will see a number of numbered entries (eg. 0000, 0001, 0002). Double click each of these in turn, and on the right the contents will appear. Find the key(s) containing the string and value: DriverDesc=TCP/IP.
On a blank area of the right panel right click, and from the resulting context menus choose "New", then "String". Name this string MaxMTU. Then right click on MaxMTU and choose "Modify". Enter 576 as the value. The new string you have created should now appear on the right as MaxMTU=576. This figure includes room for header information, ans Windows will automaticly set the working figure to MaxMTU minus 40.
Return to the tree on the left. You can close the Class subkey if you like, but leave the rest expanded. Expand the subkeys VxD, MSTCP. Now open MSTCP in the left panel.
In the right panel add the string DefaultRcvWindow, and assign the value 2144. This value is equal to 4 X (MTU-40), or 4 packets (default is 8192). The string and value "DefaultRcvWindow=2144" should appear on the right.
Optionally, you may want to make a final adjustment in this key. The TTL—Time To Live—dictates how long a packet will given to be received before being rerequested/retransmitted. Default is 32ms, but is inappropriate for today's busy internet. So add the string DefaultTTL, and assign the value 64 to it. This will give all packets twice as long before your machine gives them up for lost. Thus the string and value "DefaultTTL=64" should now appear on the right.
Now close REGEDIT, and reboot for the setting to take effect.
After rebooting connect to your ISP, and watch your apparent throughput increase dramatically as you make much more efficient use of your bandwidth.