चलती है (ग्वालियर-भोपाल वाया गुना बीना ICE) उड़ती है धूल जलते है दुश्मन खिलते है फूल - Adi Singh

There is a major difference between Railway booking and other systems like air travel and Bus. In case of rail booking there is no concept of blocking a seat for a particular session. i.e. no block and book. Booking is one step process.
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There are logistical challenges in implementing the block and book scheme on internet medium, i.e. users will select a seat and will not make payment till say next 10 minutes, so available number of seats will keep on fluctuating, ex: it will show 30 AVBL, but suddenly as...
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users select seats it will block them and show 0 AVBL , then as few of them don't make payment in stipulated time then those are released and again 10 AVBL and so on.
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Railway booking is always in high demand hence it is next to impossible to implement such scheme.
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Directly connected terminal applications like at PRS have the facility of holding requested number of seats for max 20 seconds only.