Draytek Vigor2912 Series User Manual page 175

Window size – It determines the size of TCP protocol
(0~65535). The more the value is, the better the
performance will be. However, if the network is not stable,
small value will be proper.
Session timeout – Setting timeout for sessions can make
the best utilization of network resources.
After finishing all the settings here, please click OK to save the configuration.
165 Vigor2912 Series User's Guide