client tracking

Hi everybody!!
I have a question concerning client tracking.
I have seen posted those that have used client tracking and those that have not used client tracking.
In my assignment it says:
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The user must be able to book one or more seats on a chosen flight. If the flight cannot provide those seats, the user must be informed. It is not necessary to provide for live updates on multiple clients when new bookings are made at other clients.
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If you don�t use client tracking how can you make it possible to inform the right client about the status of booking..