For authorisation types of transactions, the External Host Interface (EHI) can operate in one of four modes:

• Gateway Processing: Mode 1 - the External Host maintains card balances and participates in transaction authorisation by approving or declining the transaction.
• Cooperative Processing: Mode 2 - Thredd maintains balances and performs all types of the authorisation, but the External Host can overrule in some circumstances.
• Full Service Processing: Mode 3 - read-only data feed from the Thredd system to the Client's system.
• Gateway Processing with STIP: Mode 4 - External Host maintains Balance (with Thredd stand-in).

For more information, see the External Host Interface Guide.