This parameter specifies the Maximum Transmission Unit (MTU) for a network interface. By optimizing the MTU setting you can gain substantial network performance increases, especially when using dial-up modem connections.

MTU stands for Maximum Transmission Unit and in basic terms, it defines the maximum size of a packet that can be transferred in one frame over a network.
Open your registry and find the key below.

Create a new DWORD value, or modify the existing value, called "MTU" and set it to equal the required MTU size in decimal.

Recommended Values

576 - Dial-up Connections
1492 - PPPoE Broadband Connections
1500 - Ethernet, DSL and Cable Broadband Connections
Restart Windows for the change to take effect.

Note: For Windows NT 4 the key is [HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\ Tcpip\Parameters]

Note: IP datagrams may span multiple packets. Values larger than the default for the underlying network will result in the transport using the network default MTU. Values smaller than 68 will result in the tranport using an MTU of 68.