ROPE Language Reference - "$tcp_window".

The TCP/IP protocol window value for the packet being inspected.

RFC_793 describes this field like this..

Window:  16 bits

  The number of data octets beginning with the one indicated in the
  acknowledgment field which the sender of this segment is willing to
  accept.

This is a read-only register.

This field is only relevant for TCP/IP packets, and will contain the value 0 for others types.

See Also