Technical architecture

Figure 1 shows the technical architecture for an open loop payment and its interaction with Google Pay:

Figure 1. Data flow between Google Pay, the TSP, and the transit agency.

The following are definitions for each part of the technical architecture.

Mobile Device with Google Pay

Mobile devices powered by Android OS allow users to securely add their cards to Google Pay. Google Pay facilitates the process of tokenization, which is when payment networks tokenize the card and add a device-specific token on the mobile device. For more information about tokenization, see How payments work.

Google Pay is compatible with the majority of modern Android devices across multiple manufacturers and form factors. For minimum requirements, see Prerequisites.

Transit Reader

Transit readers are typically card readers at a transit station or bus entry point. The transit readers and terminals receive a payment credential from Google Pay in the same way that they receive a payment credential from a physical, contactless credit or debit card. To accept contactless payments, the transit reader must be compliant with EMV protocol. For more information, see Basic functionality requirements.

In order for the readers to become compliant and support mobile EMV payments, they might need software upgrades. For more information about the Google requirements for EMV tags, see Basic functionality requirements.

For readers that are offline or without a reliable high-speed internet connection, the transit operations are required to enable offline device authentication (ODA). For minimum requirements, see Prerequisites.

Transit Server
The backend server. Transit operators or their systems integrators typically operate it. Card readers often connect to the server on an intermittent basis and batch transactions together. Servers receive batch processing requests and pass requests on to the transit operator’s payment processor.
Payment Processor
The payment processor is the firm that handles transactions. It de-tokenizes the tokenized payment credentials and completes the transaction with the issuing bank. For more information about payment processing, see How payments work.
Token Service Provider (TSP)
The TSP for payment networks provides services to tokenize and de-tokenize credit and debit cards. Processors leverage TSPs to retrieve payment credentials based on the tokens the Google Pay app sends to them.
Google Server
The server provides a link between Google's partners and the user's Android-powered mobile device. The TSP sends transaction notifications, such as authorization and settlement notifications, to the Google servers. The Google servers use this information to show notifications and transaction receipts to the user.