Draytek Vigor2820 Series User Manual page 91

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. However, Queue timeout is
configured for TCP protocol only; session timeout is configured
for the data flow which matched with the firewall rule.
Vigor2820 Series User's Guide 83