Reference Manual

NAME

setw - set the base value of window size advertisement in outgoing TCP ACK segments.
SYNOPSIS
setw ifn [value]

 

...
DESCRIPTION
When invoked with only the ifn argument, setw prints the current setting of the base value used to override window size advertisements in outgoing TCP ACK segments on the specified interface. The current scaling factor is also printed.

Argument ifn can be specified as p to denote the Primary Interface or as s to denote the Secondary Interface.

Argument value specifies the maximum value used to override the window advertisement on the specified interface. NAT32 calculates a scaling factor from network activity levels on private interfaces. The actual advertisement is value/scale or value if scale is 0. The advertised window will never be adjusted to be less than MTU-40 bytes. If the original window advertisement is already less than the value NAT32 has calculated, the outgoing advertisement is not modified.

If value = 0 the mechanism is turned off.

Value must be less than 65536 and should be greater than about three times the MTU.

NOTES
When traffic arrives over a slow interface such as a Dial-Up Networking connection, the following problem occurs:
The local machine sets the TCP Window Size in ACK segments to typically 16,384 or more, causing the remote machine to send up to 16,384 bytes of data. That data saturates the slow link, leaving no bandwidth available for other traffic. Users experience delays while the transfer is in progress.
The setw command allows NAT32 to dynamically reduce the advertised receive window size to a lower value during periods of heavy traffic, thereby reducing delays for other machines using the connection.
SEE ALSO
mtu, netcfg, setp, sets