A gateway is a network hardware device (or network node) that connects a remote network to a host network. The gateway is the entry and exit point—meaning all data must pass through and communicate with the gateway in order to use routing paths. Computers and routers are the most common gateways.
There are two types of gateways: unidirectional and bidirectional. Loyola University Chicago’s T4 Tutorial site defines these two gateway types as follows:
The unidirectional gateway allows alerts to send in only one direction. The changes occurring in the source ObjectServer are copied in the destination ObjectServer or application, but when changes are made in the destination ObjectServer or application, these changes are not copied in source ObjectServer. Unidirectional can be treated as archiving tools.
Bidirectional gateway provides permission to send an alert from the source ObjectServer to the target or exact destination ObjectServer or application and also provides a reply to the source ObjectServer.
In a bidirectional gateway configuration, the changes formed in the content of a source ObjectServer are copied in a destination ObjectServer or application, and the destination ObjectServer or application copies its alerts in the source ObjectServer. Bidirectional gateways can be treated as synchronization tools.