Payment Switch

A payment switch is a piece of payment infrastructure that receives transaction messages from one party, decides where each message needs to go, forwards it to the right destination and sends the answer back, usually within a second or two. Switches connect ATMs, card terminals, e-commerce systems, banks and mobile apps, so that a customer of one bank can use another bank's ATM or pay a merchant whose account is somewhere else. The term covers both the software that does the routing and the organisations that run shared switches for a whole country.

Switches sit in the middle of payment flows. An acquirer's or bank's own switch connects its devices and channels to outside networks, while a national or regional switch connects many banks to each other, making systems interoperable. A switch is related to, but narrower than, a payment network or card scheme, which also sets rules and brands; and it differs from a payment gateway, which connects online merchants to processors rather than banks to banks.

Think of an old telephone exchange. A caller picks up the phone and asks for a number; the operator looks at it, plugs the call into the right line and connects the two people. The operator does not take part in the conversation, but without them nobody could reach anyone outside their own street.

A payment switch is the operator for money messages. When you use a card at another bank's cash machine, the machine does not know your bank. It sends a request to the switch, which reads the card number, sees which bank issued it, passes the request on, waits for a yes or no, and sends the answer back so the machine can give you cash.

1. Receive. The switch accepts a message from an ATM, point-of-sale terminal, acquirer host or app, often in the ISO 8583 card message format or, for newer account-to-account systems, in ISO 20022 messages.
2. Validate and translate. It checks the format, may verify or translate the encrypted PIN using hardware security modules, and converts between message dialects used by different banks.
3. Route. It looks up the destination, for cards usually by the BIN at the start of the card number, and applies payment routing rules, including fallback when a destination is unavailable.
4. Respond and log. It returns the issuer's approval or decline, handles time-outs and reversals, and records the transaction for clearing, fee calculation and settlement reconciliation.

Most switches only carry messages and calculate who owes whom. The actual movement of funds usually happens later through deferred net settlement across accounts at the central bank or a settlement bank, although real-time systems may settle continuously or through prefunded positions.

Many countries have a shared switch owned by banks or the central bank. Examples include:

• Pakistan. 1LINK, owned by a consortium of 11 banks, runs the main interbank switch and shared ATM network, operates the PayPak domestic card scheme and provides interbank funds transfers; it has been licensed by the State Bank of Pakistan as a payment system operator since 2015.
• India. The National Financial Switch, launched in 2004 and run by the National Payments Corporation of India since 2009, links the country's ATMs; NPCI also operates the Unified Payments Interface and the RuPay card scheme.
• United States. Debit networks such as STAR, NYCE and Pulse act as switches for PIN debit and ATM transactions, competing with Visa and Mastercard for debit routing.
• Other markets. Domestic switches such as Interswitch in Nigeria and mada in Saudi Arabia play a similar role for cards and ATMs.

A national switch keeps domestic transactions inside the country, can lower costs compared with routing through international schemes, and gives regulators visibility over payment flows. Switches are often the base on which instant-payment systems are built.

Banks, processors and fintechs also run their own switches, either built in-house or bought from vendors, to connect their channels to networks and their core banking system. Modern designs emphasise high availability (switches are expected to run around the clock), horizontal scaling, real-time fraud scoring, and smart payment routing that chooses between networks on cost and approval rates. Because a failed switch can stop card and ATM payments across a country, operators of national switches are usually overseen by the central bank as systemically important infrastructure, and must meet strict security standards such as the PCI DSS where card data is handled.

The terms overlap in everyday use. A payment processor handles transactions on behalf of acquirers or issuers and often contains a switch inside it. A gateway is the front door for online merchants. A switch is the routing core that connects participants, whether inside one company or between institutions. In some markets the same company provides all three, which is why the words are sometimes used interchangeably.

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