SAP Gateway 

The SAP Gateway forms the bridge between an SAP system and an external system, enabling data to be exchanged between the systems. All Remote Function Calls (RFCs) must be executed through a SAP Gateway (with CPI-C protocol).

Amadeus
When SAP Travel Planning is connected to the Amadeus Global Travel Distribution reservation system, at least one SAP Gateway must be involved in the configuration due to the fact that an external application on an NT server (the Amadeus Gateway) is integrated in the system infrastructure.

For stability and security reasons, SAP recommends that you set up a local SAP Gateway. If a problem should occur with the SAP Gateway when using a local SAP Gateway, you only need to restart the local SAP Gateway; the Amadeus Gateway and API server are not affected by the problem.

If you do not want to use a local SAP Gateway, set up the SAP Gateway on the application server on which SAP Travel Planning is installed.

Galileo
When SAP Travel Planning is connected to the Galileo reservation system, at least one SAP Gateway must be involved in the configuration due to the fact that an external application on a server (the Galileo Gateway) is integrated in the system infrastructure.
This should be a local SAP Gateway for the above reasons.

For general information on setting up an SAP Gateway, see the SAP Library under Basis Components ® Basis Services / Communication Interfaces ® SAP Communication: Configuration ® SAP Gateway.