IDS or Intrusion Detection Systems is the final line of technology to create a shield around your organization. IDS attempts to uncover individuals trying to break through the firewall by evaluating anomalies within a data flow.
IPS is the active part of IDS, or IDPS (Intrusion Detection and Prevention System). IPS systems attempt to stop the intrusion via blocking the TCP/UDP flows. This type of active blocking process delivers an interesting problem – if the flow is expected but the IPS blocks it, business operation can be affected. The solution has to be monitored carefully for false positive operation.