The embodiments herein relate to a method in a network node (110) for handling TCP traffic in a packet switched network (100). The network node (110) receives TCP traffic from a mobile node (101). The TCP traffic comprises an original window size. The network node (110) replaces the original window size with an optimized window size when the network node (110) comprises information about dropped TCP traffic and when the original window size is larger than the optimized window size. The network node (110) sends the TCP traffic comprising the optimized window size to a correspondent node (105) in the packet switched network (100) indicating an amount of TCP traffic receivable by the mobile node (101).