If you have noticed many TCP Retransmission, Out Of Order or Duplicate Acknowledge packets while running a TCP/IP application based on MQX RTCS then you may be interested in this article. After some investigation it comes to be that the default value of global variable _TCP_rto_min may cause this congestion depending on your application. Finally this problem was solved by setting a new value to this variable after calling function RTCS_create(). This article explains what is behind this behavior and how _TCP_rto_min affects the performance in an application using RTCS.