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How to Know That You Have Healthy TCP Sessions ?

Learn the 5 Criteria That Determine Whether You Have Healthy TCP Sessions

As a rule of thumb, healthy TCP sessions are identified and referenced by the following 5 Key Performance Indicators (KPIs) and their thresholds:

  • # SYN’s – refers to session starts; these should be twice the number of sessions. This is because of the 3-way handshake SYN | SYN-ACK | ACK (ACK equals Acknowledgment indicating “no errors – please continue”).
  • # RST’s – refers to session restarts; these should be close to zero, indicating a low number of session resets. Depending on the TCP stack, it could also be an indicator of the number of session endings; similar to using a FIN-ACK. In particular, Microsoft applications running over SSL are well-known for this (mis-)behavior.
  • # DupAck’s – refers to packets that are delayed or dropped; these should be close to zero indicating a low number of delayed/lost packets.
  • # 0-Win’s – refers to a high system utilization; the value is expected to be close to zero indicating that the hosts involved are in good shape for processing incoming packets.