The host-based model requires that the registration platform’s web server collect the card information (CARD), dollar amount (AMT), assign a unique reference number (REF) and then send the request message to the gateway. After a few seconds the response message is returned. The entire transaction is completed in one request/response call so no information is held by the gateway from one request to the next.
It is also used for refunds or subsequent charges using a token originally obtained during a web-redirect payment.