This is the maximum TCP/IP buffer length to use for RX and TX buffers.
Prior to version 4, the default is 33,554,432 bytes if not defined. This has no bearing on the size of the RPC packets transmitted and should be left to default settings.
From version 4 onwards, the default is 262144. This defines the maximum amount of data from the socket connection that Windows will use. If VTScada does not drain the buffers, further transmissions from the remote end of the socket connection will cease until it is drained. This also defines the TCP "window size" that VTScada uses.
There is an important relationship between this value and RPCMaxPacketSize. RPCManager reads the packet header from the socket and then waits for sufficient data to become available before reading it. This is intentional and reduces the amount of buffer that VTScada must allocate and the amount of script code processing that needs to be done until the entire packet has been received. This effectively reduces the "attack surface" of RPCManager by limiting the amount of data that can be maliciously pushed into a socket connection.
Therefore, for version 4 onwards, the transmitting machine's RPCBufferLength MUST be greater than RPCMaxPacketSize by at least 10%. Otherwise, you will end up with a zero-length TCP window and lose your connection.
The default values will work for LANs and WANs.
