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Card networks

Card networks—frequently referred to as card schemes or payment brands (predominantly Visa, Mastercard, American Express, and Discover)—provide the global switching infrastructure, message formats, and legal rulebooks that enable interbank electronic payments.

Crucially, card networks are neither deposit-taking commercial banks nor lending institutions. They do not hold merchant accounts, extend consumer credit lines, or make real-time authorization decisions. Instead, card networks define the technical protocols that govern transactions, switch messages securely between member institutions, establish pricing schedules, and calculate multilateral net settlement obligations at the end of each banking day.

The four-party model versus the three-party model​

Modern payment processing relies on the four-party model (also known as an open-loop scheme). In this architecture, issuing banks and acquiring banks do not maintain direct bilateral contractual relationships with each other; instead, both institutions hold memberships in the card network.

Because all participants adhere to standardized network protocols, a credit card issued by a regional credit union in Australia functions instantly and predictably at a grocery store terminal in Canada. The four participating parties are:

  1. The cardholder
  2. The issuing bank
  3. The merchant
  4. The acquiring bank

In contrast, closed-loop systems (historically epitomized by American Express and Discover) operate on a three-party model. In a pure three-party architecture, a single entity acts simultaneously as both the card issuer and the merchant acquirer. Because one institution manages both ends of the transaction, three-party networks do not require an interbank interchange schedule. In recent years, however, both American Express and Discover have partnered with third-party bank issuers and merchant aggregators, blurring the historical boundary between open and closed schemes.

Core network functions​

Card networks perform seven primary roles across global commerce:

  • High-speed transaction switching: The network routes real-time authorization requests from acquiring processors to appropriate issuing banks, returning approvals or declines in several hundred milliseconds.
  • Publishing and enforcing scheme rules: Networks author the comprehensive scheme rules that govern chargeback timeframes, presentment standards, valid authorization windows, and technical data integrity requirements.
  • Maintaining the interchange schedule: The network publishes the comprehensive interchange schedule that categorizes transactions by card type, channel (card-present vs card-not-present), and merchant category, determining the fee paid to the issuer on each sale. The network sets these rates but does not retain them.
  • Assessing network fees: The network charges its own operational fees—known as assessments—on aggregate gross processing volume and transaction counts, generating its primary operating revenue.
  • Multilateral net settlement calculation: Networks reconcile daily interbank transactions, calculating the exact net balances member banks owe one another rather than settling transactions individually.
  • Formal dispute arbitration: When an issuer and an acquirer cannot resolve a contested chargeback through standard representment cycles, the card scheme provides formal arbitration, issuing a binding legal judgment and imposing significant administrative penalties on the losing institution.
  • Stand-in processing (STIP): When an issuing bank experiences a data center failure, scheduled maintenance, or network timeout, the network can provide stand-in processing, approving or declining authorization requests on the issuer's behalf within strictly pre-configured parameters.

Operational boundaries and escalation channels​

While card networks define the rules governing payment processing, individual merchants do not maintain direct contracts with the networks. If settled funds are delayed, if rolling reserves are imposed, or if merchant fees fluctuate, contacting a card network directly is futile. Commercial terms, fee markups, and funding schedules are established exclusively through the merchant's contract with its acquiring bank or payment service provider.

Terms introduced​

  • Four-party model: issuer, acquirer, network, and merchant, with the two banks connected only through the network.
  • Three-party model: a closed loop where one company both issues the card and acquires the merchant.
  • Scheme rules: the network's published rulebook, which sets deadlines, dispute rights, and evidence standards.
  • Interchange schedule: the network's published table assigning each transaction category its interchange rate.
  • Stand-in processing: the network approving on the issuer's behalf when the issuer is unreachable.