A Sliding Window is a variable receive buffer capacity that is advertised in the 16 bit Window packet section of the TCP Header. This is how a transmitting device advertises the current receive buffer capacity to the sender. The 174CEV30010 and 174CEV30020 Modbus to Ethernet bridges support a sliding window. For example, if the CEV buffer starts out at 512 bytes capacity and there is an outstanding Modbus message size of 14 bytes, the advertised window will be 498 bytes in the response. Note that most PLC services support a fixed receive buffer window size.