Integrating Terminal Application into a Payment Ecosystem

If you are implementing your own terminal application or planning to integrate terminal applications into your payments ecosystem, you have to choose potential ways of interaction with payment terminals.

In our previous article we discussed the pros and cons of several payment terminal solution implementation options. Now we are going to analyze several approaches to integration of payment terminal applications into your payment ecosystem.

In essence, you can choose from among the two conceptually different approaches: standalone terminal use and integrated terminal use. The first approach allows the terminal to function on its own. The second approach envisions control of the terminal by point-of-sale (POS) application.

Standalone terminal use

You can often witness a classical example of standalone terminal use in many convenience stores. In such a store, after all the items you’ve picked are rung up at the POS, the cashier keys in the amount into the terminal and hands it over to you to complete the payment. In this case, the POS application has no interaction with the terminal.

When the terminal functions independently, in order to process a payment, you only have to input the payment amount. After that, the payment is made, while POS application, through which the sale was made, is not even “aware” of that.

As more and more commercial and open-source POS systems become available for various segments of businesses, the demand for standalone terminal offerings is gradually declining, because more and more businesses desire to have an integrated approach.

Integrated solution for terminal application

To integrate a POS system with a terminal, you have to connect the terminal to the workstation (on which the POS system is installed). Traditionally, POS was connected to the terminal through a serial port (presently – through a USB port). There are several ways of structuring interaction between POS and the terminal.

Fully integrated versus semi-integrated approaches

When it comes to integrated terminal solutions, there are two terms, that are commonly used to define the communication paradigm between POS and a terminal: semi-integrated and fully integrated.

Traditionally, all of the applications were fully integrated. In a fully integrated approach a terminal is used as a reader, obtaining card information, which is then consumed by the POS system, formatted into appropriate message, and sent to the gateway for processing. In a semi-integrated approach, the terminal is used as a standalone processing unit, which collects payment information, formats the appropriate message, and sends it to the gateway or processor for authorization.

Regardless of the communication approach used, there are several ways, in which the actual integration can be done.

Integration through an SDK

Traditionally, the terminal was managed through low-level libraries, allowing communication with serial/USB ports. In case of Windows these were the DLL libraries, provided by the manufacturer of the terminal (as we’ve mentioned in the previous article).

The advantage of the approach is that it is the most popular and widely spread one, as respective SDKs are available, and generic drivers such as uPOS, JavaPOS, etc, are available and supported by the existing POS systems.

Some payment solution providers see the advantage in the fact that most of the terminal behavior-controlling logic is located outside of the terminal, i.e. on the POS end, and, thus, in order to change the application’s “behavior”, no updates within the terminal are required. Consequently, you can reduce dependence on terminal management system (which is primarily used for remote terminal application updates).

The disadvantage of the approach is that it is not always suitable for web applications, which are not allowed to access to the low-level services of an operating system. While such applications can fall back on usage of ActiveX controls or Java Applets, these approaches present various security and deployment challenges.

Integration through a REST API

An alternative approach is to connect to the terminal through a REST API.

The advantage of the approach is that you do not have to deal with native code. Any application, capable of making web-service calls, can communicate with the terminal and control it.

The disadvantage of the approach is that all the logic driving the terminal’s behavior is, usually, deployed within the terminal as the terminal application. In this case, any enhancements of the application require updates within the terminal. Consequently, it is difficult to maintain such a configuration without involving a terminal management system of some sort.

Non-integrated approach

In some cases, the POS system does not need to control the terminal’s behavior at every step of the process. In such cases, POS developers prefer not to do integration with the terminal of any kind. However, you might still need the terminal to receive the information on the amount to be collected, while your POS system has to get the information about payments going through terminal.

In such cases you can utilize the so-called non-integrated approach.

When the POS system needs to process a transaction, it sends it to the gateway (without payment information included). Once a key on a terminal is pressed, the terminal connects to the gateway and checks if there are any pending transactions to be processed. It “sees” the transaction, that the POS sent previously, collects the payment information from the cardholder, and sends it to the gateway for processing. Once the gateway authorizes the transaction, it issues a call to the POS system, informing it that the original sale request has been fulfilled and the payment has been successfully made.

Naturally, the solution is available only for systems with a centralized processing server, such as web-based systems.

The advantage of this approach is that web-based systems can use the terminal without actually integrating with it.


Now that you have better understanding of payment terminal integration issues, you can decide, what terminal strategy is best for your business.