UPI: Anatomy of a Payment Transaction

(timeseriesofindia.com)

59 points | by prtk25 5 hours ago

5 comments

  • elendilm 1 hour ago
    I have the utmost respect to people who makes UPI work. Made even the old people in the nation completely go digital for payments - a feat unparalleled in the world.
  • GZGavinZhao 56 minutes ago
    How is this different from Alipay/WeChat Pay in China? Handling transactions of this volume is an amazing technological feat, kudos to the team! However, I don't think this mobile QR code paying system is anything novel. Alipay rose to popularity much earlier (I can't recall exact when, but it was already super popular in ~2010, and definitely ubiquitous by 2015).
    • zaptheimpaler 3 minutes ago
      UPI is more like a routing/reconciliation layer like VISA that can work across any bank/wallet, and that core is run by a non-profit government org. It doesn't take custody of the funds and doesn't centralize the information into a private corporation. The fee is also minimal and flat-rate with no profit incentive, instead of paying a percentage of the entire countries transaction volume to some private company. I would guess that adds up to a huge amount of money saved overall.
    • bri3d 21 minutes ago
      It’s a completely different backend model; as far as I know alipay works just like PayPal where transactions are fully “internal” - the buyer pays Ant Group and the seller cashes out at a later date.

      UPI is a real inter-organization payment system more akin to credit card processing, where fund requests flow from the payer, through a payer processor, through a merchant processor, and finally to their end destination, and the actual reconciliation happens through a bank transfer system. It’s a much less centralized system.

    • repeekad 43 minutes ago
      Much of the world doesn’t like having a single entity own and control the process end to end, it’s more efficient but there’s only one point of trust. Multiple institutions that have to check each other means you don’t have to trust a single entity with everything.
  • pzmarzly 3 hours ago
    22B transactions a year mean an average of ~700 QPS for the NPCI switch. Of course the traffic is not uniform, it probably peaks at many times that number, but that still doesn't sound that bad - for comparison, a quick Google tells me Nasdaq TotalView ITCH feed peaks at 100k+ QPS at market open.
    • vinay_ys 1 hour ago
      The right comparison for Nasdaq's order processing volume or messaging volume would be India's National Stock Exchange (NSE). It does more executed orders per day than nasdaq.

      I worked on scaling UPI a few years ago. Real-time Payments is vastly more complex as it is much more distributed - each transaction involves the two banks holding funds, two end-user apps (and their banks), and the network (npci) – for the payment to complete end to end, multiple message exchanges need to happen between these parties while the user at both ends are waiting. So, if you measure the scale in messages/sec it would 10-25x higher.

      Real-time payment rails that works 24/7 365 days a year from any bank to any bank (domestic, no exceptions) for free is truly a game-changer. Compare that to US payment rails which is slow and expensive. Apart from UPI, India has 3 more payment rails – NEFT (similar to ACH – batch settlement), IMPS (similar to UPI, instantaneous - but different user experience), RTGS (real-time, intermediated by the central bank RBI, but only for high-value transactions) – all are 24/7/365 and free. Then, there's credit card rails – apart from Visa and Mastercard, India also has RuPay which has much lower interchange rate.

      • dj0k3r 1 minute ago
        None of them are free, most banks now charge nominally (look at NEFT and IMPS charges). UPI itself is paid off by taxpayers.

        Also RTGS is the only ISO 20022 complaint payment rail (back when it wasn't globally very common) - something that needs to be appreciated more.

        People need to realise what NPCI offers is vastly different from what RBI offers. In my opinion what NPCI is offering will end up negatively impacting the general population in the long run.

    • repeek 3 hours ago
      22B in the month of June 2026, so 264B extrapolated annually.
    • arter45 1 hour ago
      A great lesson for system design job interviews - if this is a popular payment system in a country with 1.5 billion people, your theoretical system you're designing for a small company cargo culting Google interviews will not likely support millions or even tens of thousands of average TPS.
  • jesuswasjew 3 hours ago
    Centralized, kyced, private money transaction network. Is this something good?
    • tancop 11 minutes ago
      way better than privately owned banks doing the same while extracting profits from users. better than todays crypto with terrible ux where its easy to lose all your money. more practical than cash (but that should still be an option).

      worse than a system thats convenient and decentralized and anonymous at the same time, but we dont have one yet. maybe in 5 years when ethereum figures out native account abstraction, seamless scaling and monero level privacy.

    • pixelatedindex 1 hour ago
      It’s extremely good, at least in terms of user experience and how practical it is. Adoption is massive and at small chai shops it makes transactions a breeze, allowing businesses to serve more volume. The downside is making it incredibly frustrating for foreigners to pay using this as it’s tied to your government ID that your bank has authorized.
    • haskman 2 hours ago
      Yes it is. It's not trying to be new money, it's your money that already works.
    • ChrisMarshallNY 1 hour ago
      I have heard nothing but good about it, from my Indian friends. They rave about it.
    • toomuchtodo 1 hour ago
      Yes, it is peak developed world financial infrastructure, ran as a utility under government direction.
    • fragmede 2 hours ago
      How is it KYCd yet also private?
      • globemaster99 1 hour ago
        It's the intention and use case. The government want to reduce the fund leakages and reduce corruption, directly transfer the money to citizens, reduce transaction costs. Hence it works.

        The government does not track all the transactions. You need a police FIR, to review these transactions.

        In short, Indian government does not track or they don't have the scaling to track. But they can do it, if there is any criminal complaint.